Come Monday night (Jan. 30), the central and northern United States and southern Canada will be able to watch as a waxing gibbous moon will slide closely below the planet Mars.
But across parts of southern California, the Southern Rockies and the Southwest Desert, as well as much of Texas and Oklahoma and down into the Deep South including Southern Georgia and Florida, the moon will cross in front of Mars, causing an occultation or eclipse of the planet. It can also be seen throughout all of Mexico, Cuba and much of Central America.
This event occurs nearly eight weeks after the moon occulted Mars across much of North America (with the exception of parts of the Southeast U.S. and the Atlantic Seaboard). On that occasion, the moon was fully illuminated while Mars was at opposition to the sun and shone at a dazzling magnitude of nearly -2.
For this upcoming game of hide-and-seek, however, the moon will be not quite so bright (74% illuminated) and neither will Mars. Having retreated 29.63 million miles (47.68 million km) farther away from Earth since its December lunar encounter, Mars now appears less than one-quarter as bright.
Nonetheless, shining at a magnitude of -0.3, it still ranks as a brilliant object. Among the stars, only Sirius and Canopus shine brighter and to even casual observers, yellow-orange Mars will likely call attention to itself to even casual viewers looking up toward the moon on this particular night.
For most parts of country, the occultation, or closest approach of the moon relative to Mars, will occur high in the sky, though in the Northeast U.S. and Atlantic Canada, closest approach between the moon and Mars will come after local midnight (early Tuesday morning, Jan. 31) with both objects hovering only about a quarter of a way up above the west-northwest horizon. From Puerto Rico and the Caribbean, the moon and Mars will hovering low above the west-northwest horizon.
What will make this a far more striking and appealing occultation compared to the one that occurred in early December is the fact that unlike last time when Mars disappeared and reappeared from behind the moon's fully illuminated brightly-lit rim, this time — as the moon approaches from the west — Mars will appear to vanish behind the moon's dark limb. Reappearance will take place from behind the bright limb.
In addition, those who are set up along the graze line — which is actually a path, measuring roughly 13 miles (21 km) in width — Mars will appear to be only partially covered by the moon. In examining the map of the contiguous U.S. (see .jpg file), that section of the graze path outlined in green will see Mars graze the illuminated portion of the moon's disk, while along the section outlined in black, Mars will graze past the dark/unilluminated portion of the moon's disk. Those within the graze path will see, for several minutes or more, the fascinating sight of Mars interacting with the rugged lunar terrain, partly disappearing, then reappearing behind lunar mountains and valleys.
Notable cities located within or very near to the graze path include Fresno, CA, Kanab, UT, Oklahoma City, OK, and Brunswick, GA.
Below is a timetable listing 12 selected cities that will see Mars disappearing and then reappearing from behind the moon.
The table gives civil times of Mars' disappearance and reappearance (disappearance and reappearance times are for Mars' center). For times listed with an asterisk (*) the calendar date is Jan. 31.
Table was adapted from data provided by the International Occultation Timing Association (IOTA).
Unlike a star — which appears as a speck of light even through a large telescope — and seems to instantaneously disappear and reappears from behind the disk of the moon, Mars appears as a disk measuring nearly 11 arc seconds across. So, unlike a star, the red planet will appear to gradually disappear from or reappear into view. About 30 seconds will elapse for the disk of Mars to completely disappear where the occultation is nearly central and lasts for close to an hour and a half, such as at Mexico City, Mexico. The disk of Mars will take longer to completely disappear and reappear farther north where the planet goes behind the moon more obliquely. For Greenwood, Mississippi, where the occultation will last only 17 minutes, it will take two minutes for the moon to fully cover, then uncover Mars.
At any location, the duration of reappearance is about the same as of disappearance.
For others ... a near miss
For the rest of North America, this will be an exceedingly close approach of the moon to Mars (called an appulse). The moon, moving around the Earth in an easterly direction at roughly its own diameter each hour will seem to creep slowly toward and ultimately pass just below the ochre planet. Even though the central and northern US and southern Canada will miss out on an occultation, Mars will prominently stand out, as it slowly appears to glide above the moon. For places like Huntsville, Tulsa and Atlanta, Mars will come to within just 1 arc minute of the moon's limb; they'll almost seem to touch each other. To the naked eye, Mars will look like an amber jewel on the upper edge of the moon.
After closest approach, the moon will move slowly away from Mars through the balance of the overnight hours of January 30-31. Table 2 provides the specific details for 15 selected cities in the US and Canada.
The table below gives civil times (all a.m.) of Mars's closest approach to the edge of the moon's lower limb. Separation between Mars and the moon's lower edge is given in terms of minutes of arc (the apparent width of the Moon on January 30-31 is 30 arc minutes).
For times listed with an asterisk (*) the calendar date is Jan. 31.
|10 arc min
|2 arc min
|9 arc min
|Salt Lake City
|3 arc min
|3 arc min
|1 arc min
|13 arc min
|3 arc min
|1 arc min
|7 arc min
|13 arc min
|12 arc min
|10 arc min
|7 arc min
|1 arc min
Example: From Kansas City, closest approach is 11:38 p.m. Central Standard Time, the separation is listed at 3 arc minutes or fractionally roughly 1/10 of the moon's width will separate Mars from the moon's upper edge.
Calculated exclusively for SPACE.com by Joe Rao.
If you want to get a front-row look at the lunar occultation of Mars, our guides for the best telescopes and best binoculars are a great place to find the gear you need. If you're looking to take some photos of the event, see our best cameras for astrophotography and best lenses for astrophotography.
Editor's Note: If you get a great photo of the lunar occultation of Mars and would like to share it with Space.com's readers, send your photo(s), comments, and your name and location to firstname.lastname@example.org.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.
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Joe Rao is Space.com's skywatching columnist, as well as a veteran meteorologist and eclipse chaser who also serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Joe is an 8-time Emmy-nominated meteorologist who served the Putnam Valley region of New York for over 21 years. You can find him on Twitter and YouTube tracking lunar and solar eclipses, meteor showers and more. To find out Joe's latest project, visit him on Twitter.