On the morning of February 18th, 2020, observers in most of North America will be able to see the waning crescent Moon pass in front of (occult) the planet Mars. The photo at the right, taken by Andrew Chaikin during the 2003 lunar occultation of Mars, is more dramatic than this event will appear through a telescope. In the 2003 occultation, Mars was just 0.48 astronomical units (AU) from the Earth, while this time Mars will be at distance of 1.81 AU, 3.8 times farther away and correspondingly smaller and dimmer. Still, Mars will shine at magnitude 1.2, one of the brightest “stars” in the sky, and its reddish hue will stand out against the colourless Moon.
This map shows the visibility of the occultation. The occultation will be visible in the area delimited by the cyan shape at the top and the multicoloured curve at the bottom. The event will thus be visible in most of North America (except for Alaska and the far north of Canada), Central America, and the Caribbean. In the area of the loop at the top left, covering part of the American northwest and western Canada, the Moon will rise with the occultation already in progress, but observers will be able to see Mars emerge from behind the Moon’s dark limb at its conclusion.
Because the Moon is relatively close to the Earth, there is substantial parallax affecting its apparent position in sky depending upon an observer’s location on the Earth. Predictions for the occultation for 753 sites within the region of visibility are available from the International Occultation Timing Association Web site. For each site, the time, and the altitude of the Sun and Moon are given for both disappearance and reappearance. If the altitude of the Sun is negative, the event occurs before sunrise at that location. Times are given in Universal Time (as appears in the header line of this site)—convert to your local time zone to plan observations. The duration of the occultation depends upon your latitude; in most locations in the U.S. it will be around an hour and a half. There is, of course, nothing to see while Mars is behind the Moon. Observers on Mars would see the Moon transit part of the disc of the Earth.
For observers in the West, the disappearance (visible in some locations) and emergence will occur before dawn and can be observed with nothing fancier than the Mark I eyeball. Further east, the occultation will take place in twilight or daytime skies. While the Moon will, of course, be easily visible, to see Mars in daylight you’ll need a modest telescope, but since Mars will be so close to the Moon, there’s no difficulty finding it.
Here is the emergence of Mars from the occultation of 2008-05-10, photographed from New Delhi, India. In that occultation, the emergence was from behind the illuminated limb of the Moon, while this time it will reappear behind the dark limb.
If you want to try photographing the occultation, the most spectacular photos are taken with the longest focal length that can be arranged (or with a camera attached to a telescope) that show the planet just before or after passing behind the Moon. Observers in locations where the sky will be dark can video the event with any camera which allows zooming in so the Moon’s disc is clearly visible. For video, remember to turn off auto-focus and manually focus at infinity: otherwise the camera is likely to “hunt” in focus, producing embarrassing and nausea-inducing blurring in the video.