Lunar Occultation Of Saturn,
22 May 2007
Introduction to lunar occultations.
On 22 May 2007, the Moon occulted Saturn. The occultation was the second of the planet during the year, the earlier one having occurred on 02 March. The occurrence of two such rare events within a period of only two and a half months stimulated more than usual interest, and several members of OASI attempted observations of the May event as below.
Predicted circumstances for Orwell Park Observatory were as follows (event times refer to the centre of the planetary disk):
||-1.9° lat, 6.7° lon
|PA of lunar axis
||19:10:13 UT, PA 141°, CA 57° from S cusp on dark limb
||20:18:07 UT, PA 284°, CA 86° from S cusp on bright limb
Table 1. Predicted circumstances of lunar occultation of Saturn.
Conditions were not ideal, as the disappearance event took place with the Sun above the horizon and the reappearance event took place during twilight.
Observing reports from members of OASI are below.
Martin Cook Observing From East Ipswich
After receiving a phone call from Alan Smith at 7.15pm asking why he could not see Saturn, I thought that I might have missed the occultation! However, quickly checking details on the ephemeris package Starry Night I found that the occultation did not start until approximately 19:10 UT. I set up my 25 cm F5.4 Dobsonian with an 18 mm eyepiece and found Saturn. Then I phoned Alan to inform him that he needed to look in the right place and buy a decent telescope!
There was slight high level cloud. The sky was very bright and Saturn very washed out which made timing very difficult. However, I persevered and recorded the following event times (UT):
||First noticed ring starting to disappear behind dark side of the Moon.
||Body of Saturn made first contact with lunar limb.
||Could not time the full disappearance of the ring as it appeared small and was lost in the bright sky. After disappearance the sky clouded and only started to clear again before re-appearance.
||In fact, it may have been 21:18:50 - it became too dark to read my watch accurately and I only just managed to get my telescope ready in time. First noticed Saturn's re-appearance. I watched the event but did not time it.
I took the following photograph from the eyepiece with an Olympus C765
digital camera. It shows Saturn (indicated) just after reappearance.
Alan Smith Observing From Grundisburgh
It's been a while since I had the covers off the telescope and I'm a bit out of practice! My recorded timings are as follows:
||First contact of outer ring with lunar limb.
||Final disappearance of rings behind lunar limb.
||No timings for occultation of the planetary globe.....
Equipment: 250 mm Newtonian, approx. 1000 mm focal length, 6 mm Orthoscopic eyepiece. Seeing very poor, contrast very low. Saturn swimming in and out of focus, but Cassini Division just visible. Details visible on the globe of Saturn and on the lunar surface.
Gerry Pilling Observing From Martlesham
I observed the occultation, but did not time it accurately.
I could not see Saturn in binoculars shortly before the disappearance event or earlier in the day and so got the telescope out. This was the first time for daylight observing with my kit.
After some time I found Saturn, at about five minutes before disappearance, using a 40 mm eyepiece. Mrs P found Saturn difficult to spot, but when she found it she said that it was pretty against the light sky. After Saturn emerged from behind the bright limb of the Moon, just over an hour later, she said that it was quite a "wow" against the lunar limb.
The Cassini Division in the rings and some planetary details were just visible. The seeing was reasonable at times, but the Moon appeared to be "boiling".
Then I observed Venus at half phase; both I and Mrs P noted the phase.
Then it clouded over. Phew just made it!
Equipment: 200 mm Fullerscope Newtonian, focal length 1225 mm, using 40 mm and then 12.5 mm eyepiece (magnifications 30x and 98x approx).
Paul Whiting Observing From Goostrey, near Jodrell Bank, Cheshire
Equipment: 18x50 binoculars.
Conditions: sky very bright, mainly clear but with some cirrus and many vapour trails.
The crescent lunar phase meant that problems due to glare from the Moon were reduced. However, ingress at 20:04 UT was very difficult to observe with the binoculars owing to the brightness of the sky (the Sun was still above the horizon). Reports from observers with larger telescopes indicated that the disappearance of Saturn appeared to be much quicker than anticipated, probably due to the ambient light making observation difficult.
Egress at 21:11 UT was much easier to observe as the Sun had set by this time. The re-appearance of the rings is always a magical sight and so it was on this occasion. Easily observed in the binoculars (with stabilisation mechanism) and a magnificent site in a 250 mm Dobsonian.
I also observed, in the twilight, Venus at half phase, Mercury and a nice display of Earth-shine on the dark side of the Moon.