Astronomer Jeffrey Bennett writes:
A really cool astronomical event is coming up on Wednesday night (Dec. 7): Mars will disappear behind the Moon. This event, called an “occultation,” is essentially the same as an eclipse, in which one object passes in front of another as seen from Earth. In this case, because Mars moves very slowly relative to the stars in our sky while the Moon moves at a rate of about half a degree per hour (that is, it moves by about its own angular diameter each hour relative to the stars), it is actually the Moon that will be passing in front of Mars.
This particular occultation will be especially cool because it is happening when Mars is at opposition (directly opposite the Sun in our sky) and the Moon is full, so both objects are at their brightest. (Most occultations do not occur with these special circumstances, so this is a lucky coincidence for this particular one.) Sky and Telescope put out a great summary of how to watch this event, from which I’ve extracted these key points:
- The occultation of Mars will be visible to anyone in the swath shown on the map below, which means most of the United States, Canada, and Europe. If you are outside this swath, you will still see Mars close to the Moon, but it won’t pass directly behind it. Be sure you watch on the correct night: It is the NIGHT of Wednesday, Dec. 7. This means after dark on Dec. 7 for those watching in North America, and pre-dawn on Dec. 8 for those in Europe.
- If you have clear skies, it will be very easy to spot the Moon and Mars throughout the night, since they’ll be close together and very bright. But to see Mars disappear behind the Moon (and reappear later), you’ll need to look at just the right times. The table below lists times for selected cities; for other locations, you can make an estimate based on the times for cities near you, or check this page from the International Occultation Timing Association with a much more complete listing (note that times on that page are UT [also called UTC or GMT], meaning time in Greenwich, England, so be sure to convert to local time). Again, note that these times are after dark on Wednesday (Dec. 7), which for Europe means the pre-dawn of Dec. 8.
| City | Disappearance | Reappearance |
| Los Angeles, CA | 6:30 p.m. PST | 7:30 p.m. PST |
| Seattle, WA | 6:52 p.m. PST | 7:51 p.m. PST |
| Vancouver, BC | 6:55 p.m. PST | 7:52 p.m. PST |
| Phoenix, AZ | 7:32 p.m. MST | 8:31 p.m. MST |
| Denver, CO | 7:45 p.m. MST | 8:48 p.m. MST |
| St. Louis, MO | 9:06 p.m. CST | 9:52 p.m. CST |
| Chicago, IL | 9:11 p.m. CST | 10:05 p.m. CST |
| Toronto, ON | 10:29 p.m. EST | 11:18 p.m. EST |
| London, UK | 4:58 a.m. GMT | 5:59 a.m. GMT |
| Stockholm, SE | 5:54 a.m. CET | 6:43 a.m. CET |
| Paris, FR | 6:04 a.m. CET | 7:02 a.m. CET |
| Madrid, ES | 6:21 a.m. CET | 7:07 a.m. CET |
- You don’t need any equipment to see this event, as it will be easily visible to the naked eye. However, you’ll be able to watch with more detail if you have a pair of binoculars or a telescope.
Additional note:
It’s a complete coincidence that just as Mars reaches its biggest, brightest and best for 26 months it will be occulted—eclipsed—by the full Moon.
Forbes.com