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Planets and Comets



Transit of Mercury, 9 November 2006


Sunrise on November 9 occurred at 4.54 am. Soon after, starting at 5.19 am, Mercury was visible through the telescope as a black dot moving across the Sun’s disc. This transit of Mercury’ lasted until 10.12 am. These transits are quite rare, and the next one will occur on 9 May, 2016. Unfortunately, the next five transits of Mercury will not be visible from Australia, and we will have to wait for 46 years to see the next one from Nambour. The November 9 event occurred on a cloudy morning with some rain, but despite the weather, the following images were captured at Starfield Observatory:





Phases of Venus

                           April 2017                              June 2017                         December 2017                      





Mars near the 2016 opposition


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.


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.




Jupiter near opposition in 2017

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. 





Left: Saturn showing the Rings when edge-on.    Right: Over-exposed Saturn surrounded by its satellites Rhea, Enceladus, Dione, Tethys and Titan - February 23/24, 2009.

Saturn with its Rings wide open on June 29, 2016. The shadow of its globe can be seen on the far side of the Ring system. There are three main concentric rings: Ring A is the outermost, and is separated from the brighter Ring B by a dark gap known as the Cassini Division, which is 4800 kilometres wide, enough to drop Australia through. The innermost parts of Ring B are not as bright as its outermost parts. Inside Ring B is the faint Ring C, almost invisible but noticeable where it passes in front of the bright planet as a dusky band. Spacecraft visiting Saturn have shown that there are at least four more Rings, too faint and tenuous to be observable from Earth, and some Ringlets. Some of these extend from the inner edge of Ring C to Saturn's cloudtops. The Rings are not solid, but are made up of countless small particles, mainly water ice with some rocky material, all orbiting Saturn at different distances and speeds. The bulk of the particles range in size from dust grains to car-sized chunks.





Neptune, photographed from Nambour on October 31, 2008







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.




Comet 17P / Holmes,   October - December 2007


Comet 17P/Holmes is an extremely faint periodic comet that returns every 6.88 years without anyone taking much notice. Its arrival last year gained it world-wide attention, for it exploded on 24 October 2007. A vast sphere of dust and debris was ejected in an ever-growing cloud. Though the comet’s head is only some tens of kilometres across, the cloud rapidly reached the size of Jupiter by November 9 grew larger than the Sun. It has continued to enlarge until it exceeded two million kilometres in diameter.

Before the eruption, the comet could only be seen through large telescopes, but the explosion caused it to brighten a millionfold within 36 hours, making it an obvious naked-eye object. It is possible that there could be a second explosion, as occurred in 1892 and led to its discovery by Edwin Holmes.

Since the explosion was first detected, the comet expanded dramatically, to become the largest object in the solar system. It reached a size in the night sky a little larger than the diameter of the Moon.  How a small comet could produce such an enormous cloud has not yet been explained.

In mid-November 2007, Comet Holmes experienced a ‘disconnection event’ - its faint, beautiful blue ion tail became detached from its head. Comet tails can be disconnected by gusts of solar wind which trigger magnetic storms around the comet similar to the geomagnetic storms which cause aurorae on Earth. Such a storm and disconnection was observed earlier this year in the tail of Comet Encke.

Was it really the largest object in the Solar System? In diameter, yes, but of course the Sun is the most massive object by several orders of magnitude. Some comets produce tails many millions of kilometres long, so they would be longer, but not 'bigger'. Photographs taken from Starfield Observatory, Nambour appear below.


This image and those following are all taken with the same equipment and have the same plate scale, except when indicated otherwise. They therefore show how the ejecta cloud surrounding the nucleus has expanded from night to night. The sphere of ejecta surrounding the comet's nucleus is most clearly defined in the direction of the Sun, In the picture above this direction is towards the lower right. The magnitude 11.4 star GSC 3321:602 can be seen shining through the cloud at upper left. The diameter of the expanding cloud had reached 15 arcminutes and was still growing.

In the remaining images, the direction of the Sun is to the right. This image was taken ten nights later, on 13 November. The cloud of dust surrounding the nucleus is much larger - in fact the cloud itself was larger than the Sun and appeared in the sky about the same size as the Full Moon.



This image was taken three nights later, just after midnight on 17 November. The cloud of dust surrounding the nucleus continues to grow, and the comet is now the largest object in the Solar System.  It appeared to the unaided eye like a faint ghost of the Full Moon. The bright star at lower left is Mirfak, a yellow-white F5 star of magnitude 1.79.



This image was taken two nights later, on November 19. The coma of Comet Holmes appears to swallow the much more distant star Mirfak. At this stage the comet is fading, and becoming swamped by moonlight from the waxing gibbous Moon.



This image was taken ten nights later, on November 29. The cloud is still expanding, and has reached a diameter of 46 arcminutes (cf approximately 30 arcminutes for the Full Moon. A newly developing tail can be seen extending from the spherical cloud to the left-hand margin.



This image was taken at the prime focus of the RCOS reflector, and has a much larger plate scale than the other images above. It shows the interior of the ejecta cloud, which fills the frame and has now become the comet's coma. The nucleus or head is just right of centre, and the beginnings of the tail stream off to the left. Image acquired on December 3.




Comet 2006 P1 (McNaught),   January - February 2007


Comet McNaught provided a magnificent display in early 2007, the best since the 1910 apparition of Halley's Comet. At its brightest, the head outshone nearby Venus, and the tail developed great fan-shaped streamers of dust and gas that spread over a large span of the night sky. The following images were taken on January 20 and 21, when there was a break in persistent overcast weather.  Thanks to Nambour Plaza's Digital Dog for careful processing.


Comet McNaught faintly appears out of the twilight shortly after sunset. Photographed from the Maleny-Conondale Road on January 20.



As twilight fades, Comet McNaught becomes easily seen.



The comet becomes clearly visible as darkness falls.



The great tail does not become visible until twilight fades. Unfortunately this happens after the comet's head has passed below the horizon. Photographed from Starfield Observatory in Nambour on January 21. The house lights in the foreground are at Image Flat. The short curved lines in the sky are star trails caused by the Earth's rotation.


The full extent of the tail is revealed after darkness falls. A faint line of dots crossing the frame is the trail left by the strobe lights of the local rescue helicopter on its flight path to the Nambour Hospital.


There are over a dozen synchronic bands or streamers visible in the comet's tail in this photograph. The lights on the skyline are private homes built on Kureelpa Falls Road, on the edge of the Highworth Range escarpment. The Dulong Lookout is at the left margin. The brightest star trail at upper right was made by the first magnitude star Fomalhaut.  The bright star behind the comet's tail (above left centre of photograph) is the star Al Nair in the constellation Grus. Taken from Starfield Observatory with a standard lens which has a field width of 43 degrees.


By February 6 the synchronic bands have merged into a wide, triangular fan tail covering an angle of about 55 degrees. The star just below the comet's coma (the glowing gas and dust surrounding the nucleus) is SAO 247006, magnitude 7.47. The faintest stars on this image are of magnitude 13. None of these stars is visible to the unaided eye. Taken from Starfield Observatory - the field width is 4.5 degrees.



Comet 2007 N3 (Lulin),   February - March  2009


Comet Lulin was discovered in 2007 at Lulin Observatory by a collaborative team of Taiwanese and Chinese astronomers. It moved rapidly from Scorpius to Gemini, the head reaching a magnitude of 5. It had bright ion and dust tails, and an anti-tail. 


Comet Lulin at 11:30 pm on February 23, 2009, in Leo.



Comet Lulin at 11:25 pm on February 28, in Leo. The brightest star is Nu Leonis, magnitude 5.26.




The Moon                                        to:  The Stars


Below is a picture of the Moon's Mare Imbrium taken forty years ago on Kodachrome II colour slide film by the writer at the East Warwick Observatory, using a Celestron 14. Following this is a set of pictures taken with a digital video camera at Nambour in 2016 and 2017.


Mare Imbrium, with the large walled plain Plato (centre left, 100 km diameter) and the 130 km
long Alpine Valley (centre right).


The following are digital images taken with the Alluna RC-20 at Starfield Observatory. The video cameras used are a NexImage Solar System Imager and a ZWO ASI120MM-S. The video streams of 2000 - 2500 frames are processed using AutoStakkert and RegiStax 6 to produce still images. The most delicate detail visible in these images is the Alpine Valley rille which is only 600 metres across.

This area was photographed from Starfield Observatory, Nambour on October 10, 2017. East (where the
Sun is rising) is to the right, north is to the top. The area is dominated by the large walled plain Plato at upper left,
and the impact crater Cassini at lower right. Between the two is a rugged mountainous area called the Alps,
to the west of which is a large basin filled with solidified lava, called Mare Imbrium (the Sea of Rains).
 Most of the craters on the Moon larger than about 8 kilometres are named, usually after famous philosophers
or scientists. In addition, the lava plains, mountain ranges, peaks, shallow valleys (called 'rilles'), and other
 notable features have also received names, sometimes after places on the Earth. As there are no rivers,
 cities or countries on the Moon, these names help observers to find their way around. The second picture
above shows some examples.

Sunrise over the 166 km long Vallis Alpes (Alpine Valley). It has a maximum width of 10 km. A delicate rille runs
along the entire length. The rille has an average width of 600 metres and an average depth of 78 metres.

An enlargement of the main part of the Vallis Alpes, showing the sinuous rille.

The eastern end of Mare Imbrium (Sea of Rains). The crater at the centre of the top margin is Callippus.
The largest crater in the image, with two smaller craters inside it, is Cassini. Below Cassini and above
the bottom margin is Aristillus, a fine crater with a cluster of small mountains at its centre.
A tiny craterlet only 3 kilometres across is on the right margin about 30% of the way up from the bottom.
This is Linné, a very recent impact which is surrounded by a light-coloured halo of ejecta. The centre of the
 image is mostly filled with mountain massifs, which separate the Mare Imbrium in the west from the
 Mare Serenitatis (Sea of Serenity) in the east. This photograph was acquired and processed within five
minutes in the presence of participants in our first 2017 astronomy course.

This well-known trio dominates the south-eastern quadrant of Mare Imbrium. The craters are Archimedes (left),
Aristillus (top right) and Autolycus (lower right). The Fresnel Rilles and Hadley Rille are in the lower right-hand corner.
Some small craterlets dot the flat floor of Archimedes. The complex of mountains at upper left is called the Spitzbergen.
This image adjoins the one preceding.

This area shows Tranquility Base, site of the landing by Apollo 11's lunar module on July 21, 1969.
It was photographed from Starfield Observatory, Nambour on October 7, 2016. East (where the Sun is
rising) is to the right, north is to the top. The largest crater in the image above is in shadow near the centre of
 the left margin, and is called Delambre. The deformed crater in the bottom right corner is named Torricelli.
The landing site is shown by an asterisk  *. Three two and three kilometre-wide craters called Armstrong,
Collins and Aldrin (from right to left, the direction from which the lunar module was coming) are named.

This area was photographed from Starfield Observatory, Nambour on October 10, 2016. East (where
the Sun is rising) is to the right, north is to the top. Eratosthenes is the crater at top right, Copernicus
is at lower left. The debris field caused by rubble from the Copernicus impact is at centre,
where the ghost crater Stadius can be faintly seen.

Hadley Rille and its environs, where Apollo 15 landed. The Rille varies between 1 and 1.5 km in width,
and is 80 km long.  There are many more rilles to the north.

Comparing the image above with the NASA image below, from Nambour we see the area considerably
foreshortened as we are at 27º South while Hadley Rille is at latitude 26º North.

A photograph of Hadley Rille from an Apollo spacecraft, in orbit around the Moon, cropped to cover the
same area as the previous photograph taken from Nambour, for comparison purposes. The circle
shows the exact landing site. The camera is looking vertically down, so there is no foreshortening.
This was the first mission to include an LRV (lunar roving vehicle).


Theophilus (top), Cyrillus and Catharina (bottom) were photographed from Starfield Observatory, Nambour
on  October 7, 2016.  East (where the Sun is rising) is to the right, north is at the top.

Of these three craters, Theophilus (top) is obviously the newest, for it is more clearly defined and overlaps
Cyrillus. Catharina is the oldest of the three, appearing much more degraded and damaged by continual impacts
 by small meteorites over billions of years, All three craters were named by Giovanni Riccioli in the mid-17th century.
He was a Jesuit priest who knew his history of astronomy and astronomers very well, and used this knowledge
when applying names to the lunar features. The names were not chosen at random, and the three above were
named after people connected with the lost Great Library of Alexandria.

Catharina has a diameter of 100 kilometres and a depth of 3130 metres. It has been damaged by a later impact
on its northern wall, which has produced a 46 kilometre wide crater, Catharina P. The walls of Catharina are
 quite steep in places, but the rugged floor is reasonably flat with no large, central mountains. The floor does
 contain some small hills and fissures, and is disrupted in the south by a 16 kilometre crater called Catharina S.
 Nearby, on the southern wall of Catharina, there is a small, bright, bowl-shaped crater 7 kilometres across, Catharina F.

Petavius was photographed from Starfield Observatory, Nambour on July 9, 2016. East (where the Sun is rising)
 is to the top, north is to the left. As Petavius is near the south-east limb of the Moon, we see the crater at an angle,
 which foreshortens its circular shape into an ellipse. On the southern wall of Petavius (on the right in the picture
 above, is an 11 kilometre wide crater, Petavius C. A peculiar double ridge 150 kilometres long passes
through Petavius C and ends at the end of the Great Cleft.

Gassendi was photographed from Starfield Observatory, Nambour on August 14, 2016. South is to the left,
east is to the bottom. Gassendi is a moderately large crater, with a diameter of 114 km. It is completely
 circular, but due to its position towards the Moon's west-south-western limb, we see it considerably
foreshortened. It is quite ancient, and since it was formed by the impact of a large meteor or small asteroid
about 3.9 billion years ago, a large more recent impact has deformed its northern wall (on the right-hand side
 in the image above). This later crater is called Gassendi A, and is 33 kilometres across.  Almost adjoining it
on its north-western side is Gassendi B, which is 26 kilometres across. The floor of Gassendi is flat, with a
group of mountains in the centre that average 1200 metres high. To the south  is a large, flat lava plain called
Mare Humorum (the Sea of Humours). The Mare Humorum was caused by an asteroid striking the Moon in
the epoch after Gassendi was formed.

This huge impact blasted out a crater 391 kilometres across, fracturing  the Moon's crust in the area. These
fractures released pressure on the hot rocky layers below, which immediately liquified, allowing hot magma
to come to the surface as lava, which filled up the crater that  had been formed,  resulting in the large, level
 lava plain that was discovered and named the "Sea" of Humours by Giovanni Riccioli in the mid-17th century.

As the lava spread out from the impact crater, much of it reached the southern wall of Gassendi, sweeping
over it and bursting in to pool on the southern end of Gassendi's floor (to the left as seen in the image above).
We can see a gap in Gassendi's southern ramparts where the wall has been completely demolished, and
other parts of the southern wall have been smoothed over by the lava. As the lava cooled, ripples in it became
solid, and can be seen close to the south and south-east walls of Gassendi. The eastern, northern and
western walls, unaffected by the lava flow, are rugged.

The three largest craters above, which once were called ‘walled plains’, are near the centre of the Moon’s
Above centre is the large walled plain, Ptolemæus, which has a diameter of 145 km.  Its flat floor
is marked by numerous craterlets. South of Ptolemæus is another crater plain, Alphonsus, which is
121 km in diameter and has a central peak. To the right of these two large craters is a third, Albategnius,
139 km in diameter. This whole area of this image is damaged by material blasted across the surface
by a cataclysmic explosion called the Imbrium Event.  The damage appears as grooves crossing the
image from north-north-west to south-south-east.

Alphonsus was photographed from Starfield Observatory, Nambour on October 10, 2016. East (where
the Sun is rising) is to the right, north is at the top. Alphonsus is 121 kilometres in diameter and
has walls up to 2730 metres high. Some of the walls have terraces. The crater floor is fairly flat, but a central
 spine runs roughly from north to south. It connects with a fracture on the west margin of Ptolemaeus which
adjoins Alphonsus to the north. Alongside this spine, a large mountain peak is a few kilometres north-east
of the crater's centre. The mountain's base has been swamped by lava that has flooded the floor, so that only
 its peak stands above the surface. The floor is broken by numerous faults and rilles, some of which are
radial but some are roughly parallel to the walls.

In places on these faults and rilles, there are small craters with dark haloes around them. These are volcanic
 vents, obviously connected with the fault lines. Called ash volcanoes, they emit quantities of fine-grained
 dark-coloured ejecta which accumulates around the vent, sometimes filling in the closer parts of the fault
trough. There are nine ash vents visible in the above image. The crater is named Alphonsus after  
King Alfonso X  of Castille.

At centre is the 6 km wide crater Hyginus. Its northern wall is deformed by a 2 km wide smaller
crater. Passing through Hyginus is a notable valley or rille, rather disjointed in outline, appearing
in parts to be made up of chains of collapse craterlets. To its right is the long Ariadæus Rille. This area of
the Moon shows numerous clefts as well, extending south past the crater Triesnecker as seen below..

Triesnecker and its system of clefts.

The south-eastern quadrant of the Moon is covered with overlapping craters ranging in size from large to
tiny. There are no lava plains (known as "Maria" or "seas" in the area. The two largest craters in the image
above are Stöfler (left, deformed on its south-eastern rim by Faraday) and Maurolycus.

The Altai Mountains or Rupes Altai is a wall or fault scarp 495 km long, which runs from west of the crater
Catharina (see above) trending south-east to the 90 km crater Piccolomini (lower right corner of image).

Dominating this area is the magnificent crater Clavius, 233 km in diameter.  The walls rise in places
over 3.6 km above the floor. The slopes at lower right exhibit massive land slips. A remarkable series
of five craters begins on the southern wall (top) and trends in ever-decreasing size towards the north,
 then west  (right). The floor of Clavius is covered with numerous craterlets and other delicate features.

This area was photographed from Starfield Observatory, Nambour on May 6, 2017. East (where the Sun
 is rising) is to the right, north is to the top. The largest crater in the image above is Milichius, which is a
 minor crater only 14 kilometres in diameter. Milichius is surrounded by a great number of volcanoes, in
the form of low domes. These are of a roughly circular shape, and average only 200 to 300 metres high.
At the summit of each one is a volcanic crater, but all appear to be either dormant or extinct.

Once it was thought that all the craters on the Moon were volcanic  in origin, for that is how craters on the
 Earth are generally formed. Not until the beginning of the 19th century  did astronomers become aware
 of huge rocky masses flying through space that could impact the Moon,  the Earth and other planers.
These rocks, as big as a truck or as big as Tasmania, were called 'asteroids' (star-like) by William Herschel,
as in the telescope they are simply points of light, but they are now called SSSBs (Small Solar System
Bodies) a name they share with comets and meteors. 

More domes are found about 160 km south-east of Milichius in the area shown here, which adjoins the
one above it. The largest crater in this image is Hortensius, 15 km in diameter, and there is a fine cluster
of eleven domes, each with a volcanic vent at its summit, just north of Hortensius.

These domes are only observable when the angle of sunlight is very small, i.e. the Sun is just rising above
the Moon's horizon. This produces shadows which reveal the nature of the domes, which are generally
less than 400 metres in height. As the Sun rises over the Moon, the shadows diminish and soon disappear
entirely, the only remaining features to be observed being the tiny crater vents at the top of most of them.
These vents rarely exceed 1000 metres in diameter.






The Stars


Sirius (Alpha Canis Majoris) is the brightest star in the night sky. It has been known for centuries as the Dog Star. It is a very hot A0 type star, larger than our Sun. It is bright because it is one of our nearest neighbours, being only 8.6 light years away. The four spikes are caused by the secondary mirror supports in the telescope's top end. The faintest stars on this image are of magnitude 15. To reveal the companion Sirius B, which is currently 10.4 arcseconds from its brilliant primary, the photograph below was taken with a magnification of 375x, although the atmospheric seeing conditions in the current heatwave were more turbulent. The exposure was much shorter to reduce the overpowering glare from the primary star.

Sirius is a binary, or double star. Whereas Sirius A is a main sequence star like our Sun, only larger, hotter and brighter, its companion Sirius B is very tiny, a white dwarf star nearing the end of its life. Although small, Sirius B is very dense, having a mass about equal to the Sun's packed into a volume about the size of the Earth. In other words, a cubic centimetre of Sirius B would weigh over a tonne. Sirius B was once as bright as Sirius A, but reached the end of its lifespan on the main sequence much earlier, whereupon it swelled into a red giant. Its outer layers were blown away, revealing the incandescent core as a white dwarf. All thermonuclear reactions ended, and no fusion reactions have been taking place on Sirius B for many millions of years. Over time it will radiate its heat away into space, becoming a black dwarf, dead and cold. Sirius B is 63000 times fainter than Sirius A. Sirius B is seen at position angle 62º from Sirius A (roughly east-north-east, north is at the top), in the photograph above which was taken at Nambour on January 31, 2017.  That date is exactly 155 years after Alvan Graham Clark discovered Sirius B in 1862 with a brand new 18.5 inch (47 cm) telescope made by his father, which was the largest refractor existing at the time.



Rigel (Beta Orionis, left) is a binary star which is the seventh brightest star in the night sky.  It is huge when compared with Sirius. 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. 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.) 


Antares, a red supergiant star

The star which we call Antares is a binary system. It is dominated by the great red supergiant Antares A which, if it swapped places with our Sun, would enclose all the planets out to Jupiter inside itself. Antares A is accompanied by the much smaller Antares B at a distance of between 224 and 529 AU - the estimates vary. (One AU or Astronomical Unit is the distance of the Earth from the Sun, or about 150 million kilometres.) Antares B is a bluish-white companion, which, although it is dwarfed by its huge primary, is actually a main sequence star of type B2.5V, itself substantially larger and hotter than our Sun or Sirius.  Antares B is difficult to observe as it is less than three arcseconds from Antares A and is swamped in the glare of its brilliant neighbour. It can be seen in the picture above, at position angle 277 degrees (almost due west or to the left) of Antares A. Seeing at the time was about IV on the Antoniadi Scale, or in other words below fair. Image acquired at Starfield Observatory in Nambour on July 1, 2017.


The red supergiant star Betelgeuse (Alpha Orionis) is almost a twin of Antares, but has no companion.



Achernar is the ninth brightest star in the night sky. Its visual magnitude ( mv ) is  0.45, and it is a hot blue-white star of B3 spectral type. The width of the field is 24 arcminutes and the faintest stars are mv 15.  As it is in the extreme southern sky, it is the only first magnitude star unknown to the ancient Greeks.


Arcturus, an orange K2 giant star, magnitude -0.05.



Gamma Crucis is a red star at the top of the Southern Cross. It shines at magnitude 1.59, and is a giant star of type M4. The white star seen just to lower right of the main star is a sixth magnitude companion, in orbit around the system's barycentre.



The star Regor, properly called Gamma Velorum. There are at least four stars in the system. The brightest star in the image above, Gamma Velorum A, is itself a binary or double star composed of a blue supergiant and a massive Wolf-Rayet star. They are too close to be split optically, being closer than Mercury is to our Sun. Their double nature is only revealed by examination of their combined spectrum. The second component to its left, Gamma Velorum B, is also a spectroscopic binary, with a period of less than two days. The main star in this pair is a blue-white giant, and it is so close to its companion that the spectrum of the companion is swamped by the other. Wolf-Rayet stars have strong emission lines in their spectra and will end their lives with Type 1b supernova explosions. The one in Gamma Velorum A is one of the closest supernova candidates to the Sun.


The optical double star Mu Scorpii, halfway along the body of Scorpius, is a useful test of keen eyesight, being only 6 arcminutes apart. Though the two components look similar, it is only a chance alignment, not a true binary system. The stars are not related in any way. The upper  star of the two is an eclipsing binary 822 light years distant, while the lower star, a blue-white subgiant, is only 517 light years away.


 A typical nebula, where hydrogen gas is condensing into stars. The Great Nebula in Orion, M42, with its smaller companion at left, M43.



The central section of the Great Nebula in Orion.



The brightest spot in the centre of the nebula is illuminated by a famous multiple star system.



Embedded in the centre of the nebula is a multiple star known as the Trapezium.


The Trapezium is composed of 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.



The Trifid Nebula, M20, is a combination of blue reflection nebula, red emission nebula, and dark molecular clouds.



A planetary nebula, the 'Ghost of Jupiter', NGC 3242, formed when the central star exploded.



A galactic cluster in Scorpius, M7, also known as Ptolemy's Cluster.



The Ring Nebula, M57, a planetary nebula.



 The 'Wishing Well Cluster', NGC 3532.



The Eagle Nebula, M16, a star-forming area.



 This nebula has almost entirely contracted to form a cluster of new, hot, blue stars. Small amounts of wispy nebulosity remain around the brighter stars. This is the Pleiades star cluster, M45. Such clusters are called 'open clusters' or 'galactic clusters'.


 Star clouds in Sagittarius, with the dark Snake Nebula obscuring the stars behind. A satellite trail crosses the image.



The cluster IC 2602, known as the 'Southern Pleiades'.



The globular cluster Omega Centauri



The central core of Omega Centauri



There are over 120 globular clusters like this one, on the outer fringes of our galaxy. They contain hundreds of thousands of old stars. This example is named NGC104, but is popularly known as 47 Tucanae.


 The centre of our galaxy, the Milky Way, in the constellation Sagittarius.


 Proxima Centauri (circled) is an 11th magnitude red dwarf star 4.2 light years away. It is the
nearest star to the Sun. It orbits the bright binary star Alpha Centauri (at left).


Close-up of the star field around Proxima Centauri



The binary star at the centre of the Alpha Centauri triple system. Both stars are solar types.


The binary star Albireo (Beta Cygni), which is well known for its colour contrast.


The central part of the Eta Carinae nebula, showing dark lanes, molecular clouds, and glowing clouds of fluorescing hydrogen



The Keyhole, a dark cloud obscuring part of the Eta Carinae Nebula



The Homunculus, a tiny planetary nebula ejected by the eruptive variable star, Eta Carinae



 The Cat's Paw Nebula


 The star Zeta Scorpii and the open cluster Caldwell 76.


The Dumbbell Nebula, M27.



The Lagoon Nebula, M8, in Sagittarius, adjacent to Scorpius


The eastern half of the Lagoon Nebula, M8, showing dark Bok globules where protostars are forming



The centre of the Lagoon Nebula



Nebulosity in Scorpius.



The two bright stars at centre form the sting of the Scorpion's tail. Their names are Shaula and Lesath.

Shaula and Lesath are both hot, blue B type stars.


This cluster of new, hot B type stars surrounds the star Theta Carinae, and is sometimes called the
 'Southern Pleiades'.


 Halley's Comet, photographed as it passed in front of the stars of Scorpius in April, 1986.



The Great Spiral M33 in Triangulum.



The Great Galaxy in Andromeda, M31, photographed at Starfield Observatory with an off-the-shelf digital camera on 16 November 2007.


NGC 4945, an edge-on spiral galaxy in Centaurus.




The Quasi-Stellar Object 3C-273 is extremely remote.  It lies at a distance of 2440 million light years, over one sixth of the way to the edge of the universe. It is 1000 times further away than the Andromeda Galaxy shown above. 



NGC 5128 was once believed to be a dusty spiral galaxy in collision with an elliptical galaxy.


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