Asteroids: Picture Gallery

Ceres Vesta Juno

The asteroids are a very large group of small mainly rocky objects orbiting in several bands between Mars and Jupiter. They are generally thought to be debris left over from the formation of the solar system which was unable to coalesce into a "proper" planet due to the disrupting influence of the gravitation of the giant planet Jupiter. Only a few asteroids are of any size, with just one of 600mls diameter and three more at about 300mls. In fact, these four together constitute over half the mass of the entire asteroid belt!

Being small and relatively far away, the asteroids are rather dim and thus quite hard to image. Just one, Vesta, is (theoretically!) a naked-eye object but it would need crystal clear skies, a very dark night and excellent eyesight to see it in practice. It, and the other three of the "big four" (Ceres, Pallas & Juno), can be seen in binoculars though.

Ceres

Discovered on New Year's Day 1801, Ceres is (at a diameter of 590mls) by far the largest of the asteroids, containing about 32% of the total mass of the belt. It is almost certainly the only one to have a spherical shape and this has led to it being officially designated a dwarf planet. As mentioned above, it never reaches naked-eye visibility but in February and March 2009 it was unusually bright due to its opposition distance (closest approach to the earth) being the smallest since 1857! This was because opposition was only a couple of weeks after its closest approach to the sun and just two months after the earth's farthest distance from the sun i.e. very near to the time when the distance between Earth and Ceres would be minimised. Despite this, as with any target that does not show a disc it was still necessary to photograph the correct point of light! Fortunately, on this occasion Ceres crossed a distinctive group of stars at opposition, making it easy to find and its motion particularly clear.

The group of stars in question is the isosceles triangle in the centre of this image, a section of sky 10deg wide and 7¹/2deg high sitting on the back of the constellation of Leo, the Lion. There aren't any named stars here, however, so all I can say is that the one at the tip of the triangle (the brightest one in the frame) is known as 54 Leonis. But where is Ceres? Click on the image and all will be revealed! Or, if your eyesight is in need of a check-up, right click for a close-up view. (In each case, click again to go back to just the stars).

The images were taken on 28th Feb. and 1st, 5th & 6th March (it was cloudy from 2nd to 4th March!) and show two main things of note. Firstly, Ceres moves from "left to right" instead of the more usual motion from right to left (i.e. west to east). Secondly, even with just the four positions shown, I think it is clear that the track taken by Ceres is curved - slightly downwards in fact. The first observation confirms that it was at or near opposition at the time - see my page on opposition loops here for an explanation of this behaviour. Opposition was actually at 1:34pm on 25th February. The second suggests that, for the curved nature of Ceres' path through the sky to be so easily noticeable, its opposition loop was markedly oval/circular rather than zig-zag. This is indeed true: at nearest approach it was only 7¹/2wks before the most northerly point in its orbit and it has an orbital inclination of 10.59deg (compared to 1.85deg for Mars), two factors which the Opposition Loops page tells us will give a large visible loop. The lower image confirms this - it is a plot made with the SkyMap program of the position of Ceres against the stars of Leo over a period of eight months, starting at 1st November 2008 at mid-right. A red blob marks the start of each successive month and the green blob shows the point of closest approach. The stars forming the triangle mentioned above are easily seen in the mid-upper section close to the mark for 1st March. The situation in 2000 was slightly better from the "large loop" point of view, as Ceres was then just 6¹/2wks after its most northerly point: it was fractionally further away from the earth though.

The interesting opposition loops traversed by Ceres encouraged me to undertake a detailed exploration of various aspects of the dwarf planet's orbit, including periodicities in the dates of its oppositions and the influence of the nearby giant planet Jupiter. As ever in these pages, I realise this level of detail may not be of general interest so I have placed the information on a separate page: click here to explore what turned out to be a most intriguing topic!

Vesta

Vesta may be called the second "biggest" asteroid, being at 330mls in diameter only slightly smaller than Pallas but much heavier. It is estimated to contain 9% of the total mass of the asteroid belt. It is the brightest asteroid, reaching magnitude 5.1 at opposition. It still looks just like a star though so, as with other such targets, a good way to get a convincing image is when it comes close to an outer planet. This does not happen all that often so I was pleased to discover that Vesta would get within ¹/3 degree of Jupiter late in August 2007. The downside was that Jupiter would be quite low in the sky so weather conditions would be critical! A fairly grim August finally relented on the 25th, so I was able to get some shots that evening in an almost perfectly clear sky - two even had Vesta on them: yippee! The story of the next three nights was cloud, cloud and more cloud but a brief clearance on the 29th gave a further opportunity to capture some images. The evening of closest approach was showery but as the month ended the skies again cleared for an extended period on the 31st allowing me to capture the best shots so far! The first couple of days of September were cloudy and grey so by the time I was able to see the stars again on the 3rd Vesta had moved quite a long way from Jupiter - in fact it was no longer in the same camera frame as my reference star so I decided to call a halt after that. It goes without saying that the next few nights were clear as crystal - that's the English weather for you!! However, I had managed to get four good observations and thus establish Vesta's track so, considering the conditions, I was quite pleased with my first "asteroid hunt".

The images were taken with a Minolta Dimage A200 digital camera mounted on a tripod, using a 200mm lens with a x4 digital zoom. Exposure was generally the maximum the camera would allow - 4secs at f3.5, 800ASA equivalent. The "noise" in the background is precisely that - electronic noise generated by the camera when viewing a dark field at the very high sensitivity implied by the 800ASA setting. Reducing the ASA would improve this problem but at the risk of probably not capturing Vesta!

This picture is the sum of two images taken on 25th August, contrast adjusted and converted to black-and-white but not otherwise enhanced. The large over-exposed blob to the left is of course Jupiter (plus some of its moons), and the bright spot lower down is the star Omega Ophiuchi. Vesta is the much fainter spot to top right - the separation to Jupiter on this date was 1¹/4 deg. By the 29th Vesta had moved considerably closer to Jupiter (look to its "1 o'clock" position). The separation was now just ¹/2 deg. Less obviously perhaps, Jupiter had also moved: compare its distance from the star in this image to that in the one on the left. This picture is the sum of six images, processed as before and balanced to be the same brightness as the previous one. Note that the orientation is slightly different as the images were taken an hour earlier.

Two days later Vesta had "overtaken" Jupiter: it is now at top left - the separation is just under ¹/2 deg, only slightly more than at closest approach the day before. This picture is a stack of four images, but in fact that night the sky was so clear that Vesta was visible on several single images. To make the point about the good "seeing", this is a completely unprocessed single image taken on the 31st: it has simply been converted to black-and-white. While Vesta is clearly visible at top left it is much fainter than in the other images, showing how stacking and image processing can improve matters.

By 3rd September Vesta had moved so far that I've had to increase the width of the picture to show everything! In fact, capturing all three objects was a bit of a problem as the separation was greater than the field of view of the camera. I thus reduced the digital multiplier to x2 to compensate: the picture is at the same scale as the others though. As ever, it's a stack - of four images this time.

This image is a composite of the four above, each having been rotated to align correctly with one other: Jupiter and Vesta are labelled with the dates they were in a given position. The movement of Jupiter is now much more obvious, as is the fact that the paths of the two are not parallel - this is, in part, a consequence of the inclination of Vesta's orbit to the plane of the solar system (7 degrees).

This movie shows Vesta and Jupiter moving across the sky relative to the fixed star. The pale area across the fourth image is actually a slight cloud band which I didn't notice when taking the pictures! Just to dispel any lingering doubts that all I've been showing you is carefully selected camera noise (!), here's a long exposure shot [15sec] with the images of Vesta, Jupiter (plus moons) and Omega Ophiuchi extended into trails. See - it really is there!

And finally - a pretty shot! A "wide angle" view of the situation on 4th September, showing (clockwise from the tree at bottom left) a pair of magnitude 7.6 stars, Vesta [magnitude 7.3], magnitude 6.3 star, Omega Ophiuchi [magnitude 4.4] with Jupiter in the centre. To find out about the magnitude scale, click here.

Juno

Although it was the third asteroid to be discovered (in 1801), with a mean diameter of 145mls Juno is only the tenth largest. The reason it was discovered so early seems to be because its surface is unusually reflective and so it is brighter than its size alone would indicate. On the other hand, its orbit is very eccentric (even more so than Pluto) and so its observed brightness varies considerably. During oppositions when it is at its closest to the sun it can reach magnitude 7.5 but is usually only at 8.7 - barely visible in binoculars.

One such favourable opposition was in 2009 so this seemed an ideal time to capture an image. Opposition was on 21st September but I had my first try during a spell of fine weather in late August as Juno was then close to a distinctive group of stars which would make identification easier: see left. Click on the image to reveal Juno as it moves across the starfield from 20th to 23rd August (click again to go back to just the stars). My astronomy program gave Juno as mag. 8.3 during this period, almost exactly the same as the faint stars to top left and much dimmer than the four near the bottom, which are about 2 magnitudes brighter.

I next picked up Juno on 12th & 18th September, just before opposition (lots of cloudy nights in between!). In this composite image it is firstly at the apex of the thin triangle of faint stars near top middle and then it's the lower of the two faint stars near middle right. Click on the image to label Juno with the dates (click again to remove the dates). Note the yellow and blue colour of two stars in the cluster just left of centre. These colours are real, not artefacts of the camera, and could be clearly seen in binoculars. The colour of a star indicates its temperature - yellow stars are cool and blue stars are hot.

I was somewhat luckier with the weather close to opposition. This composite shows Juno on 18th (same position as above), 20th, 22nd, 25th & 26th September. Again, a click will show the dates. It was given as mag. 7.6 at this time and the image agrees with this as it is just fractionally brighter than the stars it is next to on the 25th & 26th (mag. 7.9). Note that this image and the top one cannot be compared for brightness as the top one had to be more heavily enhanced to show the fainter Juno - the extra "noise" comes from this processing. The scale of all three images is the same though, showing that, taking into account the differing numbers of days between the positions, Juno's movement across the sky was constant through opposition (on 21st September).

When checking on Juno's position with my astronomy programs I noticed that the major planet Uranus was not far from Juno. This "wide-angle" shot shows them both. If I tell you that it was taken on 20th September you can probably find Juno easily enough, and Uranus is in the top right corner. Click when you think you've found them. As a guide to scale, the separation between the two is 5deg (10times the apparent diameter of the moon): not really close enough to be called a conjunction. By comparison, the movement of Juno from 18th to 26th was just over 2deg.

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This picture is the sum of two images taken on 25th August, contrast adjusted and converted to black-and-white but not otherwise enhanced. The large over-exposed blob to the left is of course Jupiter (plus some of its moons), and the bright spot lower down is the star Omega Ophiuchi. Vesta is the much fainter spot to top right - the separation to Jupiter on this date was 1¹/4 deg.	By the 29th Vesta had moved considerably closer to Jupiter (look to its "1 o'clock" position). The separation was now just ¹/2 deg. Less obviously perhaps, Jupiter had also moved: compare its distance from the star in this image to that in the one on the left. This picture is the sum of six images, processed as before and balanced to be the same brightness as the previous one. Note that the orientation is slightly different as the images were taken an hour earlier.


Two days later Vesta had "overtaken" Jupiter: it is now at top left - the separation is just under ¹/2 deg, only slightly more than at closest approach the day before. This picture is a stack of four images, but in fact that night the sky was so clear that Vesta was visible on several single images.	To make the point about the good "seeing", this is a completely unprocessed single image taken on the 31st: it has simply been converted to black-and-white. While Vesta is clearly visible at top left it is much fainter than in the other images, showing how stacking and image processing can improve matters.


By 3rd September Vesta had moved so far that I've had to increase the width of the picture to show everything! In fact, capturing all three objects was a bit of a problem as the separation was greater than the field of view of the camera. I thus reduced the digital multiplier to x2 to compensate: the picture is at the same scale as the others though. As ever, it's a stack - of four images this time.


This image is a composite of the four above, each having been rotated to align correctly with one other: Jupiter and Vesta are labelled with the dates they were in a given position. The movement of Jupiter is now much more obvious, as is the fact that the paths of the two are not parallel - this is, in part, a consequence of the inclination of Vesta's orbit to the plane of the solar system (7 degrees).


This movie shows Vesta and Jupiter moving across the sky relative to the fixed star. The pale area across the fourth image is actually a slight cloud band which I didn't notice when taking the pictures!	Just to dispel any lingering doubts that all I've been showing you is carefully selected camera noise (!), here's a long exposure shot [15sec] with the images of Vesta, Jupiter (plus moons) and Omega Ophiuchi extended into trails. See - it really is there!

	And finally - a pretty shot! A "wide angle" view of the situation on 4th September, showing (clockwise from the tree at bottom left) a pair of magnitude 7.6 stars, Vesta [magnitude 7.3], magnitude 6.3 star, Omega Ophiuchi [magnitude 4.4] with Jupiter in the centre. To find out about the magnitude scale, click here.

	One such favourable opposition was in 2009 so this seemed an ideal time to capture an image. Opposition was on 21st September but I had my first try during a spell of fine weather in late August as Juno was then close to a distinctive group of stars which would make identification easier: see left. Click on the image to reveal Juno as it moves across the starfield from 20th to 23rd August (click again to go back to just the stars). My astronomy program gave Juno as mag. 8.3 during this period, almost exactly the same as the faint stars to top left and much dimmer than the four near the bottom, which are about 2 magnitudes brighter.
	I next picked up Juno on 12th & 18th September, just before opposition (lots of cloudy nights in between!). In this composite image it is firstly at the apex of the thin triangle of faint stars near top middle and then it's the lower of the two faint stars near middle right. Click on the image to label Juno with the dates (click again to remove the dates). Note the yellow and blue colour of two stars in the cluster just left of centre. These colours are real, not artefacts of the camera, and could be clearly seen in binoculars. The colour of a star indicates its temperature - yellow stars are cool and blue stars are hot.
I was somewhat luckier with the weather close to opposition. This composite shows Juno on 18th (same position as above), 20th, 22nd, 25th & 26th September. Again, a click will show the dates. It was given as mag. 7.6 at this time and the image agrees with this as it is just fractionally brighter than the stars it is next to on the 25th & 26th (mag. 7.9). Note that this image and the top one cannot be compared for brightness as the top one had to be more heavily enhanced to show the fainter Juno - the extra "noise" comes from this processing. The scale of all three images is the same though, showing that, taking into account the differing numbers of days between the positions, Juno's movement across the sky was constant through opposition (on 21st September).
	When checking on Juno's position with my astronomy programs I noticed that the major planet Uranus was not far from Juno. This "wide-angle" shot shows them both. If I tell you that it was taken on 20th September you can probably find Juno easily enough, and Uranus is in the top right corner. Click when you think you've found them. As a guide to scale, the separation between the two is 5deg (10times the apparent diameter of the moon): not really close enough to be called a conjunction. By comparison, the movement of Juno from 18th to 26th was just over 2deg.