Occultation of Mars

Mars was approximately 10' in diameter when Florida amateur Rick Ramsdell recorded the occultation of the red planet by the Moon on May 16, 1971.

Courtesy Rick Ramsdell.

During the predawn hours of Thursday, July 17th, the waning gibbous Moon will cover Mars for skywatchers in southeastern Florida, the Caribbean, and parts of Central and South America. Because the planet’s disk will be 19.6" across, its disappearance on the Moon’s dark limb will take almost a minute (or even longer where the Moon’s limb approaches at a slant). The planet’s reappearance will also be gradual.

Especially interesting will be the dark-side, northern-limit partial occultation visible for several minutes around 4:30 a.m. Eastern Daylight Time from an approximately 30-mile-wide band extending from Ft. Myers and vicinity to the Vero Beach–Malabar coastline in Florida. A detailed map of this grazing-occultation zone can be found on the International Occultation Timing Association's Web site.

For those in Miami, Mars will be covered at 4:14 a.m. EDT and will reappear at 4:51 a.m. On Key West both events occur about 5 minutes earlier. Here are local disappearance and reappearance times for other selected locations:

  • San Juan, Puerto Rico, 4:06 and 5:33 a.m.;
  • San Jose, Costa Rica, 1:14, 2:41;
  • Panama City, Panama, 2:21, 3:55;
  • Quito, Ecuador, 2:06, 3:38;
  • Bogota, Colombia, 2:25, 3:57;
  • Lima, Peru, 2:14, 2:54.
    On IOTA's Web site is a world map showing where the Mars occultation will be visible.

    Elsewhere the Moon will pass stunningly close. The least separation (in arcminutes) between the Moon’s limb and the brilliant red planet is as follows on the morning of the 17th, using local civil times:

  • Boston, MA (4' at 5:01 a.m.);
  • Chicago, IL (10' at 3:34);
  • Columbus, OH (8' at 4:41);
  • Dallas, TX (10' at 3:04);
  • Denver, CO (15' at 1:57);
  • Edmonton, AB (20' at 2:03);
  • Houston, TX (8' at 3:03);
  • Jacksonville, FL (2' at 4:35);
  • Los Angeles, CA (15' at 12:22 a.m.);
  • Mexico City, Mexico (4' at 2:36);
  • Montreal, QC (6' at 4:59);
  • New Orleans, LA (6' at 3:16);
  • New York, NY (4' at 4:57);
  • St. Louis, MO (10' at 3:26);
  • Seattle, WA (20' at 12:42 a.m.);
  • Tampa, FL (1' at 4:31);
  • Toronto, ON (8' at 4:49);
  • Washington, DC (4' at 4:51).
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