The Moon and Antares
Published on Jun 6, 2009 at 1:41 pm.
2 Comments.
Filed under observing, skywatching.
As the Moon goes around the Earth, it naturally passes in front of various stars now and then. The heavens are full of stars, so this is a pretty normal occurrence. When my students are doing their moon observations through the telescope, I often look to see if a star is near the limb (the astronomical term for the visible edge) of the Moon. I have the students watch to see if the Moon is getting closer or farther from the star over the course of the lab. Once in a while, we get lucky. As we are watching the Moon passes in front of the star. This is called an occultation. Most of the stars that are occulted, as I said, are pretty dim. Once in a while, though, a really bright star is occulted. That is happening tonight. The Moon will pass in front of the star Antares (the brightest star in the constellation Scorpius). Antares is a rather distinctive star. It is one of the stars that has a noticeable color. It appears orange or reddish. In fact the name Antares means Rival of Mars. The star Antares is about the color and brightness that Mars typically appears in the sky.
Antares is a quite bright star, easily visible with the naked eye. Normally, that makes an occultation very easy. However, the Moon will be very nearly full, and that will complicate the matter. I’d suggest using a pair of binoculars if you want to observe the event. If you want to observe the event, you ought to look up when it will happen for your particular location. That will vary a little from place to place. The International Occutation Timing Association has a web page dedicated to this particular occultation, and it has the needed information. One word of caution, though, about using that web site. The times given are Universal Time. That is NOT the time that your clock reads. You will need to find out how far your local time varies from Universal Time, which is the local mean time at the Prime Meridian (often called Zulu Time or Greenwich Mean Time). For here in Fort Worth, the dissapearance will occur at 01:53 UT. That is 8:53PM Central Daylight Time (what the clock reads). This will be a very difficult event to observe. You will need to be in exactly the right spot, because the Moon will be only about 7 degrees above the horizon. That is quite low, so you must find a spot where you can see the eastern horizon and catch the Moon before the event happens. It will have just risen about half an hour before it passes in front of Antares. The star, itself, will rise immediately after the Moon. In binoculars, you would see something like the following image right before the occultation.
The entire event will occur during twilight, so you might have trouble seeing Antares without binoculars. For observers farther east, this will be much easier to see. Florida and the entire east cost of the US should have a wonderful view. Unfortunately, observers in Europe are not properly placed to observe the occultation, though they will see the Moon passing very close to Antares. Observers in the western United States miss out because the Moon will not have risen at that time. Part of Canada (south of Hudson Bay) see the occultation. The rest of Canada misses the event, though. They will see the Moon pass right by Antares, in an event known as a conjunction. Central America gets to see the entire event, though, as does the northern part of South America. Most of South America sees a conjunction on the opposite side of the Moon from what Canada sees. Observers in the Carribean probably get the best view.
But, the Moon keeps moving, and it eventually moves out from in front of Antares. This will occur after the end of twilight here, as seen in the following image.
Here in the Fort Worth area, the reappearance will happen about 03:08 UT (that is about 10:08 CDT). At this time, the Moon will be 19 degrees above the horizon, much easier to observe. Still, I think that binoculars will help the observing because Antares will be appearing on the more lit side of the Moon (remember, it is just before full).
I always like observing occultation events. It is dynamic, and you actually get a chance to observe that things are moving in the sky. If you get a chance, go out and look for the event (especially if you are in Central America, northern South America, or eastern North America).
-Astroprof
Images created using Stellarium software
The Moon occults Antares tonight! | Bad Astronomy | Discover Magazine on June 6, 2009 at 6:14 pm: 1
[…] it a shot! Binoculars are probably best for this, but if you have a small telescope that works too. Astroprof and AstroGuyz have more info, […]
Amy on September 23, 2009 at 6:52 pm: 2
Sounds really cool, I’m sorry I’m hearing about this so late. I would have loved to have seen it!