November
2018
Updated: 13 November 2018
Welcome to the night skies of Spring, featuring Mars, Saturn, Sagittarius, Aquila, Lyra and Cygnus
Note: Some parts of this webpage may be formatted incorrectly by older browsers.
The Alluna RC-20 Ritchey Chrétien telescope was installed in March, 2016.
The 20-inch telescope is able to locate and track any sky object (including Earth satellites and the International Space Station) with software called TheSkyX Professional, into which is embedded a unique T-Point model developed for our site with our equipment over the past year.
Explanatory Notes:
Rise and set times are given for the theoretical horizon, which is a flat horizon all the
way round the compass, with no mountains, hills, trees or buildings to obscure the view. Observers will have to make allowance for their own actual horizon.
Transient phenomena are provided for the current month and the next. Geocentric phenomena are calculated as if the Earth were fixed in space
as the ancient Greeks believed. This viewpoint is useful, as otherwise rising and setting times would be meaningless. In the list of geocentric events, the nearer object is
given first.
When a planet is referred to as ‘stationary’, it means that its movement across the stellar background appears to have ceased, not that
the planet itself has stopped. With inferior planets (those inside the Earth’s orbit, Mercury and Venus), this is caused by the planet heading either directly
towards or directly away from the Earth. With superior planets (Mars out to Pluto), this phenomenon is caused by the planet either beginning or ending its
retrograde loop due to the Earth’s overtaking it.
Apogee and perigee: Maximum and minimum distances of the Moon or artificial satellite from the Earth.
Aphelion and perihelion: Maximum and minimum distances of a planet, asteroid or comet from the Sun.
The zenith is the point in the sky directly overhead
from the observer. The
meridian is a semicircle starting from a point on the horizon that is exactly
due north from the observer, and arching up into the sky to the zenith and
continuing down to a point on the horizon that is exactly due south. On the way
down it passes through the South Celestial Pole which is 26.6 degrees above the
horizon at Nambour. The elevation of the South Celestial Pole is exactly the
same as the observer's latitude, e.g. from Cairns it is 16.9 degrees above the
horizon, and from Melbourne it is 37.8 degrees. The Earth's axis points to this
point in the sky in the southern hemisphere, and to an equivalent point in the
northern hemisphere, near the star Polaris, which from Australia is always below
the northern horizon.
All astronomical objects rise until they reach the meridian, then they begin to
set. The act of crossing or 'transitting' the meridian is called 'culmination'.
Objects closer to the South Celestial Pole than its altitude above the southern
horizon do not rise or set, but are always above the horizon, constantly
circling once each sidereal day. They are called 'circumpolar'. A handspan at arm's length with fingers spread covers an angle of approximately 18 - 20 degrees.
mv = visual magnitude or brightness. Magnitude 1 stars are very bright, magnitude 2 less so, and
magnitude 6 stars are so faint that the unaided eye can only just detect them under good, dark conditions. Binoculars will allow us to see down to magnitude
8, and the Observatory telescope can reach visual magnitude 17 or 22 photographically. The world's biggest telescopes have detected stars and galaxies as faint as
magnitude 30. The sixteen very brightest stars are assigned magnitudes of 0 or even -1. The brightest star, Sirius, has a magnitude of -1.44. Jupiter can reach -2.4, and
Venus can be more than 6 times brighter at magnitude -4.7, bright enough to cast shadows. The Full Moon can reach magnitude -12 and the
overhead Sun is magnitude -26.5. Each
magnitude step is 2.51 times brighter or fainter than the next one, i.e. a magnitude 3.0 star is 2.51 times brighter than a magnitude 4.0. Magnitude 1.0
stars are exactly 100 times brighter than magnitude 6.0 (5 steps each of 2.51 times, 2.51x2.51x2.51x2.51x2.51 = 2.515 = 100).
The Four Minute Rule:
How long does it take the Earth to complete one rotation? No, it's not 24 hours - that is the time taken for the Sun to cross the meridian on successive days. This 24 hours is a little longer than one complete rotation, as the curve in the Earth's orbit means that it needs to turn a fraction more (~1 degree of angle) in order for the Sun to cross the meridian again. It is called a 'solar day'. The stars, clusters, nebulae and galaxies are so distant that most appear to have fixed positions in the night sky on a human time-scale, and for a star to return to the same point in the sky relative to a fixed observer takes 23 hours 56 minutes 4.0916 seconds. This is the time taken for the Earth to complete exactly one rotation, and is called a 'sidereal day'.
As our clocks and lives are organised to run on solar days of 24 hours, and the stars circulate in 23 hours 56 minutes approximately, there is a four minute difference between the movement of the Sun and the movement of the stars. This causes the following phenomena:
1. The Sun slowly moves in the sky relative to the stars by four minutes of time or one degree of angle per day. Over the course of a year it moves ~4 minutes X 365 days = 24 hours, and ~1 degree X 365 = 360 degrees or a complete circle. Together, both these facts mean that after the course of a year the Sun returns to exactly the same position relative to the stars, ready for the whole process to begin again.
2. For a given clock time, say 8:00 pm, the stars on consecutive evenings are ~4 minutes or ~1 degree further on than they were the previous night. This means that the stars, as well as their nightly movement caused by the Earth's rotation, also drift further west for a given time as the weeks pass. The stars of autumn, such as Orion are lost below the western horizon by mid-June, and new constellations, such as Sagittarius, have appeared in the east. The stars change with the seasons, and after a year, they are all back where they started, thanks to the Earth's having completed a revolution of the Sun and returned to its theoretical starting point.
We can therefore say that the star patterns we see in the sky at 11:00 pm tonight will be identical to those we see at 10:32 pm this day next week (4 minutes X 7 = 28 minutes earlier), and will be identical to those of 9:00 pm this date next month or 7:00 pm the month after. All the above also includes the Moon and planets, but their movements are made more complicated, for as well as the Four Minute Drift with the stars, they also drift at different rates against the starry background, the closest ones drifting the fastest (such as the Moon or Venus), and the most distant ones (such as Saturn or Neptune) moving the slowest.
Solar System
Sun:
The Sun begins the month in the constellation of Libra, the Scales. It leaves Libra and enters a claw of Scorpius on November 24. It leaves the claw and enters the non-zodiacal constellation of Ophiuchus, the Serpent Bearer, on November 30.
Moon Phases: Lunations (Brown series): #1185, 1186, 1187
First Quarter:
Full Moon:
Lunar Orbital Elements:
December 12: Moon at apogee (405 181 km) at
22:02 hrs, diameter = 29.5'
Moon at 8 days after New, as on November 17.
The photograph above shows the
Moon when approximately eight days after New, just after First Quarter. A detailed map of the Moon's near side is available here. A rotatable view of the Moon, with ability to zoom in close to the surface
(including the far side), and giving detailed
information on each feature, may be downloaded here.
Click
here for a photographic animation showing the lunar phases. It also shows the Moon's wobble or libration, and how its apparent size changes as it moves from perigee to apogee each month. It takes a little while to load, but once running is very cool ! All these downloads are freeware, although the authors do accept donations if the user feels inclined to support their work.
Lunar Feature for this Month
:Each month we describe a lunar crater, cluster of craters, valley, mountain range or other object, chosen at random, but one with interesting attributes. A recent photograph from our Alluna RC20 telescope will illustrate the object. As all large lunar objects are named, the origin of the name will be given if it is important. This month we will look at a pair of craters named after the two strong men of legend, Hercules and Atlas.
This image of the craters Hercules (71 km diameter) and Atlas (90
km diameter) was taken at 5:36 pm on 15 September 2018. This image of Hercules and Atlas shows the craters greatly foreshortened due to perspective, but they are both more-or-less circular. The floor of
Hercules is lava filled and flat except for some low hills and tiny craterlets, but it is distinguished by the presence of a 13 km crater known as G, which
dominates the southern half. Atlas contains one mountain, some hills and many clefts. There are two ash volcanoes on its rugged floor.
The walls of Hercules and Atlas have both suffered large landslips, which have
resulted in complex terraces
Hercules and Atlas
Hercules is a legendary hero and god, and is the Roman equivalent of the Greek Heracles, who was the son of the leader of the gods Zeus and a mortal woman, Alcmene, in classic mythology. He is famous for his great strength and many adventures, twelve of which are known as the "Labours of Hercules".
Atlas, in Greek mythology, was a Titan condemned to hold up the sky for eternity. He has become identified with the Atlas Mountains in north-west Africa. He was the son of the Titan Iapetus and the Oceanid Klymene. He had many children, mostly daughters, called the Hyades, the Pleiades and the Hesperides. Another daughter was the nymph Calypso. He was reputed to stand at the western end of the Earth. "Atlantic Ocean" means "Sea of Atlas", while " Atlantis" means "Island of Atlas". In the 16th century, books of maps began to appear. Gerardus Mercator published one in 1580, and it featured on the title page an engraving of the Titan Atlas holding up the world on his shoulders. This idea was adopted by other map publishers, and soon the books of maps became known as atlases.
The photograph of Hercules and Atlas covers the area inside the rectangle above.
Click
Geocentric Events:
It should be remembered that close approaches of Moon, planets and stars are only perspective effects as seen from the Earth - that is why they are called
'geocentric or Earth-centred phenomena'. The Moon, planets and stars do not really approach and dance around each other as it appears to us from the vantage
point of our speeding planet.
November 6: Moon 9º north of Venus at 19:41 hrs
November 7: Mercury at greatest elongation east (23º 09') at 00:56 hrs (diameter = 6.6")
November 9: Moon 4.3º north of Jupiter at 04:02 hrs
November 12: Moon 2.1º north of Saturn at 01:42 hrs
November 12: Moon has a grazing occultation of the star Pi Sagittarii (mv= 2.88) between 23:44 and 23:52 hrs
November 13: Moon 1.5º north of Pluto at 03:40 hrs
November 16: Moon 1.1º north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 02:52 hrs
November 16: Limb of Moon 35 arcsminutes south of Mars at 13:19 hrs
November 16: Venus at western stationary point at 20:25 hrs (diameter = 51.3")
November 17: Mercury at eastern stationary point at 11:24 hrs (diameter = 8.4")
November 17: Moon 2.4º south of Neptune at 17:21 hrs
November 21: Moon 4.1º south of Uranus at 08:51 hrs
November 24: Moon 2.1º north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 08:21 hrs
November 25: Limb of Moon 1 arcminute south of the star Zeta Tauri (mv= 2.97) at 09:35 hrs
November 25: Neptune at eastern stationary point at 08:38 hrs (diameter = 2.3")
November 26: Limb of Moon 7 arcminutes south of the star Mu Geminorum (mv= 2.87) at 02:01 hrs
November 26: Jupiter in conjunction with the Sun at 16:27 hrs (diameter = 31.0")
November 27: Mercury in inferior conjunction at 19:07 hrs (diameter = 9.9")
November 28: Mercury 25 arcminutes north of Jupiter at 08:03 hrs
December 3: Mars at eastern quadrature at 09:34 hrs (diameter = 9.1")
December 4: Moon 3.9º north of Venus at 06:25 hrs
December 6: Moon 2.3º north of Mercury at 06:44 hrs
December 6: Neptune at eastern quadrature at 08:19 hrs (diameter = 2.2")
December 7: Moon 4º north of Jupiter at 00:24 hrs
December 7: Mercury at western stationary point at 07:18 hrs (diameter = 8.e")
December 8: Mars 2.2 arcseconds north of Neptune at 00:14 hrs
December 9: Moon 1.2º north of Saturn at 16:09 hrs
December 10: Moon occults the star Pi Sagittarii (mv= 2.88) between 04:51 and 5:36 hrs
December 10: Moon 33 arcminutes north of Pluto at 12:48 hrs
December 13: Moon 17 arcminutes north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 08:26 hrs
December 14: Jupiter 54 arcminutes south of the star Psi Ophiuchi, mv= 4.48) at 00:29 hrs
December 15: Moon 2.2º south of Neptune at 03:07 hrs
December 15: Moon 3.2º south of Mars at 10:35 hrs
December 16: Mercury at Greatest Elongation West (21º 09') at 01:08 hrs (diameter = 6.6")
December 17: Mercury 1.1º north of the star Graffias (Beta1 Scorpii, mv= 2.56) at 00:51 hrs
December 18: Moon 4.5º south of Uranus at 15:32 hrs
December 21: Moon 1.8º north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 16:02 hrs
December 22: Mercury 50 arcminutes north of Jupiter at 03:56 hrs
December 22: Limb of Moon 2 arcminutes south of the star Zeta Tauri (mv= 2.97) at 16:54 hrs
December 23: Moon 1º south of the star Mu Geminorum (mv= 2.87) at 11:46 hrs
December 23: Jupiter 13 arcnibures north of the star Omega Ophiuchi (mv= 4.45) at 13:50 hrs
December 23: Venus 2.9º north of the star Zuben Elgenubi (Alpha Librae, mv= 2.75) at 17:52 hrs
December 27: Venus at perihelion at 04:07 hrs (diameter = 28.0")
The Planets for this month:
Mercury: Mercury passed through superior conjunction on September 21 and is now in the western twilight sky. It shines nearly as bright as Sirius, but is only visible when it is at a large angular distance from the glare of the Sun. As Mercury lies well inside the Earth's orbit and close to the Sun, it can never move more than 27.8º from the Sun. During October, Mercury was close to the western horizon during twilight, but it will be further from the Sun and easier to find in the first three weeks of November. The thin crescent Moon will be between Mercury and Jupiter on November 9. Mercury will be best seen when it is approaching its maximum angular distance from the Sun in the first three weeks of November. Its maximum angular distance from the Sun (greatest elongation east) will occur on November 7, when it will reach 23.1º.
Mercury will pass through inferior conjunction (between the Earth and the Sun) on November 27 and will disappear from our western twilight sky. It will reappear in our eastern pre-dawn sky in early December, reaching maximum elongation west on December 16.
Venus:
This, the brightest planet, passed through inferior conjunction (between the Earth and the Sun) on October 27, and has now disappeared from the western twilight sky and reappeared in the eastern pre-dawn sky where it will be joined by Mercury at the end of this month. This month it is very prominent in the early mornings as a so-called 'morning star', and it will remain a pre-dawn object until next August.(The coloured fringes to the first and third images below are due to refractive effects in our own atmosphere, and are not intrinsic to Venus. The planet was closer to the horizon when these images were taken than it was for the second photograph, which was taken when Venus was at its greatest elongation from the Sun).
February 2018 August 2018 October 2018
Click here for a photographic animation showing the Venusian phases. Venus is always far brighter than anything else in the sky except for the Sun and Moon. For most of 2017, Venus appeared as a 'Morning Star' in the pre-dawn sky, where it stayed for about nine months. Venus passed between us and the Sun (inferior conjunction) on October 27 last, and is now in the morning sky as a 'Morning Star'. It will return to the evening sky to be an 'Evening Star' once again on August 14 next year, although it won't be away from the Sun's glare to be easily visible until next October.
Because Venus is visible as the 'Evening Star' and as the 'Morning Star', astronomers of ancient times believed that it was two different objects. They called it Hesperus when it appeared in the evening sky and Phosphorus when it was seen before dawn. They also realised that these objects moved with respect to the so-called 'fixed stars' and so were not really stars themselves, but planets (from the Greek word for 'wanderers'). When it was finally realised that the two objects were one and the same, the two names were dropped and the Greeks applied a new name Aphrodite (Goddess of Love) to the planet, to counter Ares (God of War). We use the Roman versions of these names, Venus and Mars, for these two planets.
Venus at 6.55 pm on September 7, 2018. The phase is 36 % and the angular diameter is 32 arcseconds.
This is the year of Mars:
The red planet is still well positioned for viewing, but the Earth has now left it far behind, and Mars is now much reduced in size, being only 12 arcseconds in diameter on November 1. By November 30 its diameter will have fallen to 9 arcseconds, and all month it will have a phase of 86%. On November 1 at 7 pm (end of twilight), Mars will be about 10º or half-a-handspan north-west of the zenith, in the constellation Capricornus. By November 30 at 7:30 pm (end of twilight), Mars will be about 30º or nearly two handspans north-west of the zenith, in the constellation Aquarius. On November 16, the waxing gibbous Moon (just a little past First Quarter) will be close by Mars in the early evening sky.
In this image, the south polar cap of Mars is easily seen. Above it is a dark triangular
area known as Syrtis Major. Dark Sinus Sabaeus runs off to the left, just south of the equator. Between the south polar cap and the equator is a large deser
t
called Hellas. The desert to upper left is known as Aeria, and that to the north-east of Syrtis Major is called Isidis Regio. Photograph taken in 1971.
Brilliant
Mars at left, shining at magnitude 0.9, passes in front of the dark molecular clouds in Sagittarius on October 15, 2014. At the top margin is the white fourth magnitude
star 44 Ophiuchi. Its type is A3 IV:m. Below it and to the left is another star, less bright and orange in colour. This is the sixth magnitude star SAO 185374,
and its type is K0 III. To the right (north) of this star is a dark molecular cloud named B74. A line of more dark clouds wends its way down through the image
to a small, extremely dense cloud, B68, just right of centre at the bottom margin. In the lower right-hand corner is a long dark cloud shaped like a figure
5. This is the Snake Nebula, B72. Above the Snake is a larger cloud, B77. These dark clouds were discovered by Edward Emerson Barnard at Mount Wilson in 1905.
He catalogued 370 of them, hence the initial 'B'. The bright centre of our Galaxy is behind these dark clouds, and is hidden from view. If the clouds were
not there, the galactic centre would be so bright that it would turn night into day.
Mars, called the red planet but usually coloured orange, has now taken on a yellowish
tint and has brightened by 0.4 magnitude, making it twice as bright as previous predictions for the July 27 opposition. These phenomena have been caused by a great dust storm
which has completely encircled the planet, obscuring the surface features so that they are only seen
faintly through the thick curtain of dust. Although planetary photographers are
mostly disappointed, many observers are interested to see that the yellow colour and increased brightness mean that a weather event on a distant planet can actually be detected
with the unaided eye - a very unusual thing in itself. The three pictures above were taken on the evening of July 24, at 9:05, 9:51 and 11:34 pm. Although the fine details that are usually seen on Mars are hidden by the dust storm,
some of the larger features can be discerned, revealing how much Mars rotates in two and a half hours. Mars' sidereal rotation period (the time taken for one complete
rotation or 'Martian day') is 24 hours 37 minutes 22 seconds - a little longer than an Earth day. The dust storm began in the Hellas Desert on May 31, and after two months
it still enshrouded the planet. In August it began to clear.
Central meridian: 295º.
The two pictures immediately above were taken on the evening of September 7, at 6:25 and 8:06 pm. The dust storm is finally abating, and some of the surface features are
becoming visible once again. This pair of images also demonstrates the rotation of Mars in 1 hour 41 minutes (equal to 24.6 degrees of longitude), but this time the view is
of the opposite side of the planet to the set of three above. As we are now leaving Mars behind, the images are appreciably smaller (the
angular diameter of the red planet has fallen to 20 arcseconds). Well past opposition, Mars on September 7 exhibited a phase effect of 92.65 %.
Mars
photographed from Starfield Observatory, Nambour on June 29 and July 9, 2016, showing two different
sides of the planet. The north polar cap is prominent.
Mars near opposition, July 24, 2018
Central meridian: 180º.
Jupiter:
On November 1, this gas giant planet is only visible in the sky for an hour after sunset, low in the west. It is in the centre of the constellation Libra, the Scales. It spends the first three weeks of November near the eastern boundary between Libra and Scorpius, and will cross into Scorpius on November 21. It is too close to the Sun to be observed safely, and will pass on the far side of the Sun on November 26. At that time it will be less than half a degree from the actual edge of the Sun's disc. Observers will not be able to view Jupiter again until next year.
Jupiter as photographed from Nambour on the evening of April 25, 2017. The images were taken, from left to right, at 9:10, 9:23, 9:49, 10:06 and 10:37 pm. The rapid rotation of this giant planet in a little under 10 hours is clearly seen. In the southern hemisphere, the Great Red Spot (bigger than the Earth) is prominent, sitting within a 'bay' in the South Tropical Belt. South of it is one of the numerous White Spots. All of these are features in the cloud tops of Jupiter's atmosphere
.
Jupiter as it appeared at 7:29 pm on July 2, 2017. The Great Red Spot is in a similar position near Jupiter's eastern limb (edge) as in the fifth picture in the series above.
It will be seen that in the past two months the position of the Spot has drifted
when compared with the festoons in the Equatorial Belt, so must rotate around the planet at a slower rate. In fact, the Belt enclosing the Great Red Spot rotates around the
planet in 9 hours 55 minutes, and the Equatorial Belt takes five minutes less. This high rate of rotation has made the planet quite oblate. The prominent 'bay'
around the Red Spot in the five earlier images appears to be disappearing, and a darker streak along the northern edge of the South Tropical Belt is moving
south. Two new white spots have developed in the South Temperate Belt, west of the Red Spot. The five upper images were taken near opposition, when the Sun was
directly behind the Earth and illuminating all of Jupiter's disc evenly. The July 2 image was taken just four days before Eastern Quadrature, when the angle
from the Sun to Jupiter and back to the Earth was at its maximum size. This angle means that we see a tiny amount of Jupiter's dark side, the shadow being
visible around the limb of the planet on the left-hand side, whereas the right-hand limb is clear and sharp. Three of Jupiter's Galilean satellites are visible, Ganymede to
the left and Europa to the right. The satellite Io can be detected in a transit of Jupiter, sitting in front of the North Tropical Belt, just to the left of its centre.
Jupiter at opposition, May 9, 2018
Jupiter reached opposition on May 9, 2018 at 10:21 hrs, and the above photographs were taken that evening, some ten to twelve hours later. The first image above was
taken at 9:03 pm, when the Great Red Spot was approaching Jupiter's central meridian and the satellite Europa was preparing to transit Jupiter's disc.
Europa's transit began at 9:22 pm, one minute after its shadow had touched Jupiter's cloud tops. The second photograph was taken three minutes later at 9:25
pm, with the Great Red Spot very close to Jupiter's central meridian.
The third photograph was taken at 10:20 pm, when Europa was approaching Jupiter's central meridian. Its dark shadow is behind it, slightly below, on the clouds of the North Temperate Belt. The shadow is partially eclipsed by Europa itself. The fourth photograph at 10:34 pm shows Europa and its shadow well past the central meridian. Europa is the smallest of the Galilean satellites, and has a diameter of 3120 kilometres. It is ice-covered, which accounts for its brightness and whitish colour. Jupiter's elevation above the horizon for the four photographs in order was 50º, 55º, 66º and 71º. As the evening progressed, the air temperature dropped a little and the planet gained altitude. The 'seeing' improved slightly, from Antoniadi IV to Antoniadi III. At the time of the photographs, Europa's angular diameter was 1.57 arcseconds. Part of the final photograph is enlarged below.
Jupiter at 11:34 pm on May 18, nine days later. Changes in the rotating cloud patterns are apparent, as some cloud bands rotate faster than others and
interact. Compare with the first photograph in the line of four taken on May 9. The Great Red Spot is ploughing a furrow through the clouds of the South
Tropical Belt, and is pushing up a turbulent bow wave.
Saturn:
Uranus:
Neptune:
The icy blue planet reached opposition on September 8, so
will be best observable this month before midnight. In mid-November it is about
a handspan north of the zenith as darkness falls.
The waxing gibbous Moon will be in the vicinity of Neptune on November 17.
Neptune, photographed from Nambour on October 31, 2008
Pluto:
The movement of the dwarf planet Pluto in two days, between 13 and 15 September, 2008. Pluto is the one object that has moved.
Width of field: 200 arcseconds
This is a stack of four images, showing the movement of Pluto over the period October 22 to 25, 2014. Pluto's image for each date appears as a star-like point at the upper right corner of the numerals. The four are equidistant points on an almost-straight line. Four eleventh magnitude field stars are identified. A is GSC 6292:20, mv = 11.6. B is GSC 6288:1587, mv = 11.9. C is GSC 6292:171, mv = 11.2.
D is GSC 6292:36, mv = 11.5. (GSC = Guide Star Catalogue). The position of Pluto on October 24 (centre of image) was at Right Ascension = 18 hours 48 minutes 13 seconds, Declination = -20º 39' 11". The planet moved 2' 51" with respect to the stellar background during the three days between the first and last images, or 57 arcseconds per day, or 1 arcsecond every 25¼ minutes.
S Taurids
November 3 and 4
Waning crescent Moon, 21% sunlit ZHR = 15
Radiant: Near the Pleiades star cluster. Associated with Comet
Encke
N Taurids
November 13 and 14
Waxing crescent Moon, 30% sunlit ZHR = 15
Radiant: Near the Pleiades star cluster. Associated with
Comet Encke
Leonids
November 18 and 19
Waxing gibbous Moon, 72% sunlit ZHR =
12
Radiant: Near the third magnitude star Adhafera, in the Lion's mane.
Associated with Comet Tempel-Tuttle
Use this
Meteoroids are small rocky or metallic bodies in the Solar System, left over from the creation of the planets. Some are produced
by impacts of asteroids with the Moon, Mars or other solid Solar System bodies,
others from the disintegration of periodic comets, where material is spread
around the comet's orbit, usually in clumps. Their sizes range from about a metre to a grain of sand. If they are
smaller than a sand grain they are called 'micrometeoroids' or 'space dust'. The Earth encounters thousands every day. They enter our atmosphere at a
speed averaging 20 kilometres per second or 72000 kilometres per hour. Friction with our atmosphere burns them up immediately at an average
height of 70 to 90 kilometres, producing a streak of light called a 'meteor' if they occur at night. Sometimes a faint trail of smoke persists for a
minute or two. The resulting dust and ash floats down to the Earth's surface and settles on the ground. Much of our topsoil contains this
material,
Although most meteoroids are found in swarms associated with debris from comets, there are numerous 'loners', meteoroids travelling on solitary
paths through space. When these enter our atmosphere, unannounced and at any time, they are known as 'sporadics'. On
average clear and dark evenings, an observer can expect to see about ten meteors
per hour. In the past, large meteorites (possibly comet nuclei or small asteroids) collided with the Earth and produced huge craters which still exist
today. These craters are called 'astroblemes'. Two famous ones in Australia are Wolfe Creek Crater
in the Kimberley District and Gosse's Bluff near Alice Springs. The Moon and Mercury are covered with such astroblemes, and craters are also found on Venus, Mars,
planetary satellites, minor planets, asteroids and even comets.
Comets:
Green comets in the news
Comet C/2018 V1 Machholz-Fujikawa-Iwamoto
ZHR = zenithal hourly rate (number of meteors expected to be observed at the zenith in one hour). The
maximum phase of meteor showers usually occurs between 3 am and sunrise. The reason most meteors are observed in the pre-dawn hours is because at that time
we are on the front of the Earth as it rushes through space at 107 000 kilometres per hour (30 kilometres per second). We are meeting the meteors head-on, and the speed at
which they enter our atmosphere is the sum of their own speed plus ours. In the evenings, we are on the rear side of the Earth, and many meteors we see at that
time are actually having to catch us up. This means that the speed at which they enter our atmosphere is less than in the morning hours, and they burn up less
brilliantly.
Comet 46P/Wirtanen
In December, Comet 46P/Wirtanen will sweep past Earth, making one of
the ten closest approaches of a comet to our planet since 1960. If forecasters are correct, Comet Wirtanen could become visible to the naked eye for
weeks next month. The small but unusually active comet will come closest to Earth just four days after its closest approach to the Sun, and it will be "up"
all night long, making this an exceptional flyby. Visit
Spaceweather
for more information.
Comet PANSTARRS (C/2017 S3)
A comet that may become visible to the naked eye exploded in brightness, suddenly increasing its luminosity 16-fold on July 1. Whatever happened on Comet PANSTARRS (C/2017 S3) has given it an expanding green atmosphere almost twice the size of the planet Jupiter. Visit the July 4 edition of Spaceweather and subsequent news releases for pictures and more information about this comet.
Comet 21P/Giacobini-Zinner
On September 10, another green comet will make its closest approach to Earth in 72 years. This small but active comet is named Comet 21P/Giacobini-Zinner. The 'P' indicates that it is a periodic comet in an elliptical orbit around the Sun, and returning regularly for us to see. After it passes Earth, it will swing around the Sun and head out towards the furthest point in its orbit, just beyond Jupiter. After 36 years it will head back towards the Sun.
This month it will shine at magnitude 7 so it will be easy to see in small telescopes and binoculars, but not with the unaided eye. It will only be observable in the hour or so before dawn begins to light the sky, low to the north-east horizon. On September 10 it will be gliding through the stars of the constellation Auriga about 58 million kilometres from our planet. In the week ahead, it will cross into Gemini and on September 15 it will pass right across the rich star cluster M35, providing a spectacular photo-opportunity for amateur astronomers. Visit the September 9 edition of Spaceweather for details and observing tips.
Comet Lulin
This comet, (C/2007 N3), discovered in 2007 at Lulin Observatory by a collaborative team of Taiwanese and Chinese astronomers, is now in the outer Solar System, and has faded below magnitude 15.
Comet Lulin at 11:25 pm on February 28, 2009, in Leo. The brightest star is Nu Leonis, magnitude 5.26.
The
LINEARNearly all of these programs are based in the northern hemisphere, leaving gaps in the coverage of the southern sky. These gaps are the areas of sky where amateur astronomers look for comets from their backyard observatories.
To find out more about current comets, including finder charts showing exact positions and magnitudes, click
here. To see pictures of these comets, click here.
The 3.9 metre Anglo-Australian Telescope (AAT) at the Australian Astronomical Observatory near Coonabarabran, NSW.
Deep Space
Sky Charts and Maps available on-line:
There are some useful representations of the sky available here. The sky charts linked
below show the sky as it appears to the unaided eye. Stars rise four minutes earlier each night, so at the end of a week the stars have gained about half an
hour. After a month they have gained two hours. In other words, the stars that were positioned in the sky at 8 pm at the beginning of a month will have the
same positions at 6 pm by the end of that month. After 12 months the stars have gained 12 x 2 hours = 24 hours = 1 day, so after a year the stars have returned
to their original positions for the chosen time. This accounts for the slow changing of the starry sky as the seasons progress.
The following interactive sky charts are courtesy of Sky and Telescope magazine. They can simulate a view of the sky from any location on Earth at any time of day or night between the years 1600 and 2400. You can also print an all-sky map. A Java-enabled web browser is required. You will need to specify the location, date and time before the charts are generated. The accuracy of the charts will depend on your computer’s clock being set to the correct time and date.
To produce a real-time sky chart (i.e. a chart showing the sky at the instant the chart is generated), enter the name of your nearest city and the country. You will also need to enter the approximate latitude and longitude of your observing site. For the Sunshine Coast, these are:
latitude: 26.6o South longitude: 153o East
Then enter your time, by scrolling down through the list of cities to "Brisbane: UT + 10 hours". Enter this one if you are located near this city, as Nambour is. The code means that Brisbane is ten hours ahead of Universal Time (UT), which is related to Greenwich Mean Time (GMT), the time observed at longitude 0o, which passes through London, England. Click here to generate these charts.
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Similar real-time charts can also be generated from another source, by following this second link:
The first, circular chart will show the full hemisphere of sky overhead. The zenith is at the centre of the circle, and the cardinal points are shown around the circumference, which marks the horizon. The chart also shows the positions of the Moon and planets at that time. As the chart is rather cluttered, click on a part of it to show that section of the sky in greater detail. Also, click on Update to make the screen concurrent with the ever-moving sky.
The stars and constellations around the horizon to an elevation of about 40o can be examined by clicking on
The view can be panned around the horizon, 45 degrees at a time. Scrolling down the screen will reveal tables showing setup and customising options, and an Ephemeris showing the positions of the Sun, Moon and planets, and whether they are visible at the time or not. These charts and data are from YourSky, produced by John Walker.
The charts above and the descriptions below assume that the observer has a good observing site with a low, flat horizon that is not too much obscured by buildings or trees. Detection of fainter sky objects is greatly assisted if the observer can avoid bright lights, or, ideally, travel to a dark sky site. On the Sunshine Coast, one merely has to travel a few kilometres west of the coastal strip to enjoy magnificent sky views. On the Blackall Range, simply avoid streetlights. Allow your eyes about 15 minutes to become dark-adapted, a little longer if you have been watching television. Small binoculars can provide some amazing views, and with a small telescope, the sky’s the limit.
In November, the Eta Carinae Nebula can only be viewed low in the south-south-east, in the hours after midnight, above the Southern Cross.
The Stars and Constellations for this month:
These descriptions of the night sky are for 10 pm on November 1 and 8 pm on November 30. Broadly speaking, the following description starts low in the south-west and follows the horizon to the right, heading round to the east, then south, then overhead.
The stars of Sagittarius are setting low in the west-south-west, with Saturn very close to the horizon. Just above them, the faint stars of Capricornus will soon be gone, too. In the first week of November, the planet Mars will be close to the two stars Nashira and Deneb Algedi, a pair of third magnitude stars that mark the tail of the Sea-Goat. Above Capricornus is another rather faint constellation, Aquarius, the Water Bearer. There are no stars brighter than third magnitude in this constellation, but it does contain many interesting objects, including a group of four stars known as the 'Water Jar'. Also, this year faint Neptune may be found in its centre, about a handspan east of the star Deneb Algedi. Mars will pass into Aquarius on November 11 and into Pisces on December 21. The constellation of Pisces, the Fishes crosses the meridian at 9 pm in mid-November, followed by Aries and then Taurus.
The centre of the Lagoon Nebula
The first magnitude star Altair (Alpha Aquilae) can be seen approaching the horizon a little north of west. Altair is the brightest star in the constellation Aquila, the Eagle. It has a fainter star above and another below, making a vertical line of three, quite close together. These stars, from top to bottom, are Alshain, Altair and Tarazed, and they indicate the Eagle's body. A handspan east of the bright, first magnitude Altair is a faint but easily recognised diamond-shaped group of stars, Delphinus the Dolphin. The Great Square of Pegasus is beginning to tilt over towards the north-west, and Andromeda and Triangulum are above the northern horizon.
The names of the four stars marking the corners of the Square (starting at the top-left one and moving in a clockwise direction around the Square) are Markab, Algenib, Alpheratz and Scheat. Although these four stars are known as the Great Square of Pegasus, only three are actually in the constellation of Pegasus, the Winged Horse. In point of fact, Alpheratz is the brightest star of the constellation Andromeda, the Chained Maiden. This is the best time of year to observe two close spiral galaxies, for they are due north and at their highest elevation. M31 (in Andromeda) and M33 (in Triangulum) are members of the Local Group of galaxies (our Milky Way is a third member), and can be easily seen with good binoculars. They are the nearest galaxies that can be observed from the large observatories in the Northern Hemisphere.
Andromeda trails down from Alpheratz to below the north-eastern horizon. To its right is the zodiacal constellation of Aries, now well up in the
north-east. The brightest star in Aries is a second magnitude orange star called Hamal. Between Aries and Aquarius is a faint constellation, Pisces, the
Fishes. A well-known asterism in Pisces is the Circlet, a faint circle of seven fourth and fifth magnitude stars. About one and a third handspans east of the
Circlet may be found the planet Uranus, but it is not visible without at least a pair of binoculars.
Taurus, with its two star clusters the Pleiades and the Hyades, is well above the north-eastern horizon, below Aries. The Pleiades is a small group like a question mark, and is often called the Seven Sisters, although excellent eyes are needed to detect the seventh star without optical aid. The group is also known as ‘Santa’s Sleigh’, as it appears around Christmas time. All the stars in this cluster are hot and blue. They are also the same age, as they formed as a group out of a gas cloud or nebula. There are actually more than 250 stars in the Pleiades. The Japanese name for this cluster is 'Subaru', and the cars of that make have a representation of the cluster as their badge.
The Hyades cluster appears larger, with the appearance of a capital A or inverted V. At the foot of its right leg is a bright orange star called Aldebaran (Alpha Tauri). The V shape looked to the ancients like the face of a bull, with Aldebaran as his angry orange eye. Being in the southern hemisphere, we see it upside down. The Pleiades form the bull’s shoulder.
The Pleiades is the small cluster at centre left, while the Hyades is the much larger grouping at centre right.
Wisps of gas can be seen around the brighter stars in the Pleiades cluster.
Orion the Hunter is rising in the east, and to its right is his Great Dog (Canis Major), marked by the brilliant white star Sirius (the Dog Star), quite close to the horizon. Sirius is the brightest star in the night sky, because it is one of our closest neighbours, only 8.6 light-years away. The second-brightest star in the night sky is Canopus, which is two handspans to the right of Sirius, high in the south-east. It is bright, not because it is close, (as it is at a distance of 312 light-years, 36 times further away than Sirius), but because it is in fact a supergiant star. About one handspan south-east of the zenith is a bright first-magnitude white star, Achernar (Alpha Eridani). Achernar, the ninth brightest star, is at one end of a very long, faint constellation, Eridanus, the River. It winds all the way from Achernar to Cursa (Beta Eridani), a 2.9 magnitude star just above Rigel, the brightest star in Orion (see below).
Achernar is midway between two other bright stars, Canopus and Fomalhaut. The latter is a handspan south-west of the zenith. Slightly north of the zenith is a
mv 2.2 star. This is Beta Ceti, the brightest ordinary star in the constellation Cetus, the Whale. Its common name is Diphda,
and it has a yellowish-orange colour. By rights, the star Menkar or Alpha Ceti should be brighter, but Menkar is
actually more than half a magnitude fainter than Diphda. Menkar may be seen high in the north-east, halfway between
Diphda and Aldebaran.
Above Diphda is Fomalhaut, a bright, white first magnitude star in the faint constellation Piscis Austrinus, the Southern Fish. Fomalhaut is almost directly overhead at 8 pm on November 1. South-west of Fomalhaut is a large, upside-down flattened triangle of stars, Grus, the Crane. North of Achernar, the faint constellation of Phoenix may be seen. Its brightest star is Ankaa, a mv 2.39 star which is halfway between Fomalhaut and Achernar.
Cetus is a large constellation, and to the unaided eye it appears unremarkable. But it does contain a most interesting star, which was discovered before the telescope was invented. It is named Mira, the Wonderful (see below). Between Cetus and Pegasus is the zodiacal constellation of Pisces, the Fishes. Pisces is found just above Aries. Moving westwards from Cetus we see the zodiacal constellations of Aquarius, then Capricornus.
Rising in the south-east are the stars of the constellation Carina, and the False Cross. The true Southern Cross (Crux) is below the southern horizon, but will rise soon after midnight. Above the horizon due south, is the small constellation of Musca, the Fly. Musca is a circumpolar constellation, i.e. it is always in our sky, being too close to the South Celestial Pole to set. Alpha Centauri is close to the horizon nearby.
The zodiacal constellations visible tonight, starting from the south-western horizon and heading overhead to the north-east horizon, are Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, and Taurus.
If you would like to become familiar with the constellations, we suggest that you access one of the world's best collections of constellation pictures by clicking
here . To see some of the best astrophotographs taken with the giant Anglo-Australian Telescope, click
The 3.9 metre Anglo-Australian Telescope near Coonabarabran, NSW
The amazing thing about the star Mira or Omicron Ceti is that it varies dramatically in brightness, rising to magnitude 2 (brighter than any other star in Cetus), and then dropping to magnitude 10 (requiring a telescope to detect it), over a period of 332 days.
This drop of eight magnitudes means that its brightness diminishes over a period of five and a half months to one six-hundredth of what it had been, and then over the next five and a half months it regains its original brightness. The seventeenth century Polish astronomer Johannes Hevelius named it Mira, meaning 'The Wonderful' or 'The Miraculous One'.
We now know that many stars vary in brightness, even our Sun doing so to a small degree, with a period of 11 years. One type of star varies, not because it is actually becoming less bright in itself, but because another, fainter star moves around it in an orbit roughly in line with the Earth, and obscures it on each pass. This type of star is called an eclipsing variable and they are very common.
The star Mira though, varies its light output because of processes in its interior. It is what is known as a pulsating variable. Stars of the Mira type are giant pulsating red stars that vary between 2.5 and 11 magnitudes in brightness. They have long, regular periods of pulsation which lie in the range from 80 to 1000 days.
Mira near minimum, 26 September 2008 Mira near maximum, 22 December 2008
Astronomers using a NASA space telescope, the Galaxy Evolution Explorer, have spotted an amazingly long comet-like tail behind
Mira as the star streaks through space. Galaxy Evolution Explorer - "GALEX"
for short - scanned the well-known star during its ongoing survey of the entire
sky in ultraviolet light. Astronomers then noticed what looked like a comet with
a gargantuan tail. In fact, material blowing off Mira is forming a wake 13
light-years long, or about 20,000 times the average distance of Pluto from the
sun. Nothing like this has ever been seen before around a star.
Double and multiple stars
Estimates vary that between 15% and 50% of stars are single bodies like our Sun, although the latest view
is that less than 25% of stars are solitary. At least 30% of stars and possibly as much as 60% of stars are in double systems, where the two stars are
gravitationally linked and orbit their mutual centre of gravity. Such double stars are called binaries. The remaining 20%+ of stars are in multiple
systems of three stars or more. Binaries and multiple stars are formed when a condensing Bok globule or protostar splits into two or more parts.
Binary stars may have similar components (Alpha Centauri A and B are both stars like our Sun), or they may be completely dissimilar, as with
Albireo (Beta Cygni, where a bright golden giant star is paired with a smaller bluish main sequence star).
The binary stars Rigil Kentaurus (Foot of the Centaur, or Alpha Centauri) at left, and Beta Cygni (Albireo), at right.
Rigel (Beta Orionis, left) is a binary star which is the seventh brightest star in the night sky. Rigel A is a large white supergiant which is 500 times brighter than its small companion, Rigel B, Yet Rigel B is itself composed or a very close pair of Sun-type stars that orbit each other in less than 10 days. Each of the two stars comprising Rigel B is brighter in absolute terms than Sirius (see above). The Rigel B pair orbit Rigel A at the immense distance of 2200 Astronomical Units, equal to 12 light-days. (An Astronomical Unit or AU is the distance from the Earth to the Sun.) In the centre of the Great Nebula in Orion (M42) is a multiple star known as the Trapezium (right). This star system has four bright white stars, two of which are binary stars with fainter red companions, giving a total of six. The hazy background is caused by the cloud of fluorescing hydrogen comprising the nebula.
Acrux, the brightest star in the Southern Cross, is also known as Alpha Crucis. It is a close binary, circled by a third dwarf companion.
Alpha Centauri (also known as Rigil Kentaurus, Rigil Kent or Toliman) is a binary easily seen with the smallest telescope. The components are both solar-type main sequence stars, one of type G and the other, slightly cooler and fainter, of type K. Through a small telescope this star system looks like a pair of distant but bright car headlights. Alpha Centauri A and B take 80 years to complete an orbit, but a tiny third component, the 11th magnitude red dwarf Proxima takes about 1 million years to orbit the other two. It is about one tenth of a light year from the bright pair and a little closer to us, hence its name. This makes it our nearest interstellar neighbour, with a distance of 4.3 light years. Red dwarfs are by far the most common type of star, but, being so small and faint, none is visible to the unaided eye. Because they use up so little of their energy, they are also the longest-lived of stars. The bigger a star is, the shorter its life.
Close-up of the star field around Proxima Centauri
Knowing the orbital period of the two brightest stars A and B, we can apply Kepler’s Third Law to find the distance they are apart. This tells us that Alpha Centauri A and B are about 2700 million kilometres apart or about 2.5 light hours. This makes them a little less than the distance apart of the Sun and Uranus (the orbital period of Uranus is 84 years, that of Alpha Centauri A and B is 80 years.)
Albireo (Beta Cygni) is sometimes described poetically as a large topaz with a small blue sapphire. It is one of the sky’s most beautiful objects. The stars are of classes G and B, making a wonderful colour contrast. It lies at a distance of 410 light years, 95 times further away than Alpha Centauri.
Binary stars may be widely spaced, as the two examples just mentioned, or so close that a small telescope is struggling to separate them (Acrux, Castor, Antares, Sirius). Even closer double stars cannot be split by even large telescope, buts the spectroscope can disclose their true nature by revealing clues in the absorption lines in their spectra. These examples are called spectroscopic binaries. In a binary system, closer stars will have shorter periods for the stars to complete an orbit. Eta Cassiopeiae takes 480 years for the stars to circle each other. The binary with the shortest period is AM Canum Venaticorum, which takes only 17½ minutes.
Sometimes one star in a binary system will pass in front of the other one, partially blocking off its light. The total light output of the pair will be seen to vary, as regular as clockwork. These are called eclipsing binaries, and are a type of variable star, although the stars themselves usually do not vary.
Why are some constellations bright, while others are faint ?
If we look at ninety degrees to the plane, either straight up and out of the galaxy or straight down, we are looking through comparatively few stars and gas clouds and so can see out into deep space. These are the directions of the north and south galactic poles, and because we have a clear view in these directions to distant galaxies, these parts of the sky are called the intergalactic windows. The southern window is in the constellation Sculptor, not far from the star Fomalhaut. This window is well-placed for viewing this month, and many distant galaxies can be observed in this area of the sky. The northern window is between the constellations Virgo and Coma Berenices, roughly between the stars Denebola and Arcturus. It is below the horizon in the evenings this month.
Some of the fainter and apparently insignificant constellations are found around these windows, and their lack of bright stars, clusters and gas clouds presents us with the opportunity to look across the millions of light years of space to thousands of distant galaxies.
The Milky Way
A glowing band of light crossing the sky is especially noticeable during the winter months, but it
is far less noticeable this month, virtually skirting the horizon at 9 pm. This glow is the light of millions of faint stars combined with that coming from glowing gas
clouds called nebulae. It is concentrated along the plane of our galaxy, and at the beginning of November it can be seen at 7:30 pm running from
south-south-west to north-north-west, reaching a maximum elevation above the horizon of about two handspans, due west. Constellations in the Milky Way
at this time tonight will run from Centaurus through Scorpius, Sagittarius and Aquila to Cygnus.
The plane of our galaxy from
Scutum (at left) through Sagittarius and Scorpius (centre) to Centaurus and Crux
(right). The Eta Carinae nebula is at the right margin, below centre.
The Coalsack is clearly visible, and the dark dust lanes can be seen. Taken with an
ultra-wide-angle lens.
It is rewarding to scan along this band with a pair of binoculars, looking for star clusters and emission nebulae. Dust lanes along the plane of the Milky Way appear to split it in two in some parts of the sky. One of these lanes can be easily seen, starting near Alpha Centauri and heading towards Antares.
The centre of our galaxy. The constellations partly visible here are Sagittarius (left), Ophiuchus (above centre) and Scorpius (at right). The planet Jupiter is the bright object below centre left. This is a normal unaided-eye view.
Finding the South Celestial Pole
The South Celestial Pole is that point in the southern sky around which the stars rotate in a clockwise direction. The Earth's axis is aimed exactly at this point. For an equatorially-mounted telescope, the polar axis of the mounting also needs to be aligned exactly to this point in the sky for accurate tracking to take place.
To find this point, first locate the Southern Cross. Project a line from the orange star at the top of the Cross (Gacrux) to the star at its base (Acrux) and continue straight on towards the south (to the left) for another four Cross lengths. This will locate the approximate spot. There is no bright star to mark the Pole, whereas in the northern hemisphere they have Polaris (the Pole Star) to mark fairly closely the North Celestial Pole.
Another way to locate the South Celestial Pole is to draw an imaginary straight line joining Beta Centauri in the south-west to Achernar in the south-east. Bisect this imaginary line to locate the pole. Neither method is much use on November evenings as the Cross is below our southern horizon until after midnight.
Interesting photographs of this area can be taken by using a camera on time exposure. Set the camera on a tripod pointing due south, and open the shutter for thirty minutes or more. The stars will seem to move during the exposure, being recorded on the film as short arcs of a circle. The arcs will be different colours, as the stars are. All the arcs will have a common centre of curvature, which is the south celestial pole.
A wide-angle view of trails around the South Celestial Pole, with Scorpius and Sagittarius at left, Crux and Centaurus at top, and Carina and False Cross at right.
Star trails between the South Celestial Pole and the southern horizon. All stars that do not pass below the horizon are circumpolar.
Star clusters
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The two clusters in Taurus, the Pleiades and the Hyades, are known as Open Clusters or Galactic Clusters. The name 'open cluster' refers to the fact that the stars in the cluster are grouped together, but not as tightly as in globular clusters (see below). The stars appear to be loosely arranged, and this is partly due to the fact that the cluster is relatively close to us, i.e. within our galaxy, hence the alternate name, 'galactic cluster'. These clusters are generally formed from the condensation of gas in a nebula into stars, and some are relatively young.
The photograph below shows a typical open cluster,
M7. It lies in the constellation Scorpius, just above the scorpion's sting. It lies in the direction of our galaxy's centre. The cluster itself is the group of white stars in the centre of the field. Its distance is about 380 parsecs or 1240 light years.
Galactic Cluster M7 in Scorpius, known as Ptolemy's cluster
Outside the plane of our galaxy, there is a halo of Globular Clusters. These are very old, dense clusters, containing perhaps several hundred thousand stars, in some cases . These stars are closer to each other than is usual, and because of its great distance from us, a globular cluster gives the impression of a solid mass of faint stars. Many other galaxies also have a halo of globular clusters circling around them.
The largest and brightest globular cluster in the sky is NGC 5139 , also known as Omega Centauri. It has a slightly oval shape. It is an outstanding winter object, but this month it is below the horizon for most of the night. Shining at fourth magnitude, it is faintly visible to the unaided eye, but is easily seen with binoculars, like a light in a fog. A telescope of 20 cm aperture or better will reveal its true nature, with hundreds of faint stars giving the impression of diamond dust on a black satin background. It lies at a distance of 5 kiloparsecs, or 16 300 light years.
Although Omega Centauri is poorly placed for viewing this month, there is another remarkable globular, second only to Omega, which is in a good position. Close to the SMC (see below), binoculars can detect a fuzzy star. A telescope will reveal this faint glow as a magnificent globular cluster, lying at a distance of 5.8 kiloparsecs. Its light has taken almost 19 000 years to reach us. This is
NGC 104, commonly known as 47 Tucanae. Some regard this cluster as being more spectacular than Omega Centauri, as it is more compact, and the faint stars twinkling in its core are very beautiful. This month, Omega Centauri is not at a good position for viewing, but 47 Tucanae is well placed before midnight.
The globular cluster 47 Tucanae
Observers aiming their telescopes towards the SMC generally also look at the nearby 47 Tucanae, but there is another globular cluster nearby which is also worth a visit. This is NGC 362, which is less than half as bright as the other globular, but this is because it is more than twice as far away. Its distance is 12.6 kiloparsecs or 41 000 light years, so it is about one-fifth of the way from our galaxy to the SMC. Both NGC 104 and NGC 362 are always above the horizon for all parts of Australia south of the Tropic of Capricorn.
* M7:
This number means that
Ptolemy's Cluster in Scorpius is No. 7 in a list of 103
astronomical objects compiled and published in 1784 by Charles Messier.
Charles was interested in the discovery of new comets, and his aim was to
provide a list for observers of fuzzy nebulae and clusters which could easily be
reported as comets by mistake. Messier's search for comets is now just a
footnote to history, but his list of 103 objects is well known to all
astronomers today, and has even been extended to 110 objects. ** NGC 5139: This
number means that Omega Centauri is No. 5139 in the New General Catalogue of
Non-stellar Astronomical Objects. This catalogue was first published in 1888
by J. L. E. Dreyer under the auspices of the Royal Astronomical Society, as his New
General Catalogue of Nebulae and Clusters of Stars. As larger telescopes
built early in the 20th century discovered fainter objects in space, and also
dark, obscuring nebulae and dust clouds, the NGC was supplemented with the
addition of the Index Catalogue (IC). Many non-stellar objects in the sky
have therefore NGC numbers or IC numbers. For example, the famous Horsehead
Nebula in Orion is catalogued as IC 434. The NGC was revised in 1973, and lists
7840 objects. The recent explosion of discovery in
astronomy has meant that more and more catalogues are being produced, but they
tend to specialise in particular types of objects, rather than being
all-encompassing, as the NGC / IC try to be. Some examples are the Planetary
Nebulae Catalogue (PK) which lists 1455 nebulae, the Washington Catalogue
of Double Stars (WDS) which lists 12 000 binaries, the General Catalogue
of Variable Stars (GCVS) which lists 28 000 variables, and the Principal
Galaxy Catalogue (PGC) which lists 73 000 galaxies. The largest modern
catalogue is the Hubble Guide Star Catalogue (GSC) which was assembled to
support the Hubble Space Telescope's need for guide stars when photographing sky
objects. The GSC contains nearly 19 million stars brighter than magnitude 15.
Two close galaxies
Above the south-south-eastern horizon, two faint smudges of light may be seen. These are the two
Clouds of
Magellan, known to astronomers as the LMC (Large Magellanic Cloud)
and the SMC (Small Magellanic Cloud). The LMC is below the SMC,
and is noticeably larger. They lie at distances of 190 000 light years for the
LMC, and 200 000 light years for the SMC. They are about 60 000 light years
apart. These dwarf galaxies circle our own much larger galaxy, the Milky Way.
The LMC is slightly closer, but this does not account for its larger appearance.
It really is larger than the SMC, and has developed as an under-sized barred
spiral galaxy.
The Large
Magellanic Cloud - the bright knot of gas to left of centre is the famous
Tarantula Nebula
These two Clouds are the closest galaxies to our own, but lie too far south to be seen by the large telescopes in Hawaii, California and Arizona. They are 15 times closer than the famous Andromeda and Triangulum galaxies in the northern half of the sky, and so can be observed in much clearer detail. Our great observatories in Australia, both radio and optical, have for many years been engaged in important research involving these, our nearest inter-galactic neighbours.
The LMC is less than a handspan above the horizon, and the SMC is a little more than a handspan above and slightly to the right of the LMC.
The Andromeda Galaxy and the President of the United States
In 1901, U.S.A. President William McKinley was assassinated and his Vice-President,
Theodore Roosevelt, took his place. Theodore became a popular President, and was elected in his own right in 1904 for a second term. He was known as Teddy Roosevelt, and the Teddy Bear is named after him. As President he was a dynamic, vigorous and energetic man, very keen on preserving the wonders of nature through the creation of national parks, forests, and natural monuments such as Rainbow Bridge.Teddy made the acquaintance of noted American naturalist, scientist, explorer and author
William Beebe who shared his love of nature. They became friends and would meet regularly for dinner and an evening's conversation, sometimes with friends of similar interests. Both men had strong egos, but recognised the dangers of pride in themselves and in their accomplishments.It is said that after dinner, Roosevelt, Beebe and their friends would step outside for cigars and lengthy discussions about world affairs. At the conclusion, they would look up at the starry sky. Roosevelt or Beebe would point out a small, faint smudge of light close to the Great Square of Pegasus and they would both recite, almost as a litany, something similar to the following:
"That is the Spiral Galaxy in Andromeda. It is as large as our Milky Way. It is one of a hundred million galaxies. It consists of one hundred million suns, many larger than our sun." The President would then turn to the others. "Now I think we are small enough," he would say. "Let's go to bed."
Whereas from the latitude of Washington D.C. the Andromeda Galaxy is visible for most of the year, f
rom Australia it is so far north (41 degrees north Declination) that it is only visible in the evenings during spring and early summer. For us, this magnificent galaxy is due north at 8:50 pm in mid-November, about one handspan above the horizon.
The Great Galaxy in Andromeda, M31, photographed at Starfield Observatory with an off-the-shelf digital camera on 16 November 2007.
Astronomy Picture of the Day:
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