Transit of Earth from Mars

During a transit, Earth would be visible from Mars as a small black disc moving across the face of the Sun.

[citation needed] Transits of Earth from Mars usually occur in pairs, with one following the other after 79 years; rarely, there are three in the series.

During the 1879 event, this permitted Charles Augustus Young to attempt a careful measurement of the oblateness (polar compression) of Mars.

Much more recently, better measurements of the oblateness of Mars have been made by using radar from the Earth.

This short story was first published in the January 1971 issue of Playboy magazine.