An Occultation of Saturn
Published on Dec 6, 2006 at 8:22 am.
2 Comments.
Filed under amateur astronomy, observing.
The Moon moves around the sky, taking about a month to complete one circuit. Along the way, it passes by various other objects. When the Moon passes something, we call that a conjunction. But, occasionally, in its motion the Moon passes right in front of another body. This we call an occultation. This weekend, the Moon will occult Saturn, for some people. Now, most people won’t get an opportunity to see this. You have to be in just the right place. If you are too far south or west, then the Moon will look like it is passing north of Saturn, and you’ll see a conjuction instead of an occultation. This will be what most of us in North America see — a conjunction a little before dawn on December 10. Now, you might ask why some see a conjunction and some an occultation. That has to do with the angle that we are looking from. The Moon is not terribly far away (as celestial objects go), so looking at it from different locations on Earth give a slightly different perspective. If you hold your hand out in front of you and close one eye, it seems to be in front of certain objects. Then, if you look with your other eye, your hand appears to be in front of different objects. We call this parallax. So, some people will see an occultation, and some a conjunction. And, of course, the Moon has to be up when you are looking! Great Brittain will see the Moon just covering Saturn right as it sets, so there won’t be much to see for most of the islands. In most of Europe, the Moon will have just set as it covers Saturn. Iceland and Greenland have the best views, in that the entire event, both the dissappearance and the reappearance. The southern edge of the Moon will pass over Saturn. In northern Greenland, the view will be perfect. The Sun won’t be up. But, there’s a problem with seeing the event in Iceland. It will be twilight. That means that Saturn will disappear behind the bright side of the Moon (hard to see with the naked eye), and reappear on the dark side just about sunrise. You’ll need a telescope to really appreciate the view. Normally, this is something that you can see with the naked eye. But, the problem will be that the sky likely will be a bit bright to see Saturn with the naked eye. Bermuda will be right on the edge of where you can see the occultation, and the edge of the Moon will just cover Saturn, but the event will occur during the daylight. But, it can still be seen if you use a telescope. 
Now, a lot of people don’t realize that you can observe planets in the daylight. But, you can! You just have to know where to look. Often finding a planet in the daylight can be a bit tricky, but not in this case, because a big bright and obvious Moon will be there to guide you!
So, what will you see? Here are some photos taken by an amateur astronomer (Ginger’s Postcards from Earth and Beyond) that show an occultation of Saturn a few years ago. This one was during the night. I’ve seen one at night and one in the daytime before. It looks similar in the daytime, except that Saturn appears rather washed out. A yellow or light red filter often helps with that (a hint for observers in Bermuda).
But, as I said, only some people will get a chance to see even that. Most of us will miss it altogether. The Moon will simply appear to pass by Saturn early in the morning, a bit before dawn. The farther south that you are, the bigger the miss will be. And for everyone who doesn’t get up before dawn to watch the event, you’ll be able to see Saturn late at night (say 11 pm or midnight) in the eastern sky on the night of December 9 with the Moon a little above it. But, when you look at the same time on the night of December 10, the Moon will be below Saturn. Still, that is a good way to see the motion of the Moon. Below are simulations of what you’ll see from Miami at about 11:30pm on December 9 and December 10.
And here in the DFW area, we will see the Moon pass right near Saturn about 4:30 in the morning.  This is a conjunction. Over the course of the night, the Moon will be getting closer to Saturn, and then start to pull away just before dawn. The next night, it will be a hand’s width away from Saturn.
So, go look at Saturn and the Moon, and enjoy!
-Astroprof
(Images Courtesy of Ginger’s Postcards from Earth and Beyond)
(Skyviews generated using Starry Night Pro)
A Ler…-- Rastos de Luz on December 6, 2006 at 11:35 am: 1
[…] “An Occultation of Saturn“, no Astroprof’s Page; […]
Astroprof’s Page » A planetary grouping on December 9, 2006 at 12:36 pm: 2
[…] So, what did I forget to tell you? Well, tomorrow morning, there is something else to see (maybe) besides the Saturn conjunction/occultation. Sunday morning, there will be a very close grouping of planets. Jupiter, Mercury, and Mars will all be very close together. In fact, they will be so close together that you might be able to get them all in the field of view of a telescope at low power. You could hold your hand out at arm’s length and cover all three with your thumb. Such close groupings happen every now and then. There was a grouping, not as close, just a few years ago, and I remember going out to photograph such a close grouping with a friend about 15 or 16 years ago (we didn’t get the photos bacause her camera was jammed with sand from a trip to the beach a while earlier). This particular grouping is a bit closer than most. Depending upon how you categorize such groupings, it is the closest in about 80 years. But, there are several ways to categorize these things, and using other methods, it is only the closest in about 25 years. But, that doesn’t really matter. All three planets will fit into a circle of 1° diameter. (Note: for my readers in Australia, New Zealand, Japan, and other places on the other side of the International Date Line, this will be Monday morning, December 11.) So, if you want to see this close grouping, what do you do? Well, I’ve got bad news for you. It will likely be quite difficult to see. All three of these planets are quite far away, on the other side of the Solar System. In fact, they are nearly directly opposite the Sun from us, so they will appear very near the Sun in the Sky. You’ll see them only a half hour before sunrise, as civil twilight is getting the sky bright, particularly in the souteast where the planets will be. In fact, at that time, if you hold your hand at arm’s length with your fist clenched and held horizontal, the planets will only be the heigth of your fist above the horizon. That means that any clouds or haze on the horizon is likely to obstruct your view. Likewise for any hills, buildings, trees, bushes, or about anthing else. And then, the sky itself will be getting bright, washing out the planets. If you do have a clear horizon, you should be able to see Jupiter easily enough. Mercury will be the next easiest to see, just up and perhaps a little to the left of Jupiter (depending where upon Earth you are looking from). Mars will be the tough one. It will be about 1/10 as bright as Mercury and a bit to the right of the Jupiter and Mercury pair. Binoculars might help. However, if you use any optical aid, such as binoculars or telescopes, be VERY careful and mindful of what you are doing. The Sun will rise in almost that same area just a few minutes later, and you DO NOT want to accidently catch the Sun with your binoculars or telescope. […]