The astronomy gift they can find in the night sky

Astronomers locate features on the Moon with selenographic coordinates, the lunar equivalent of latitude and longitude. Every ExplOrbit territory is recorded this way, in regions visible from Earth, such as the great dark seas of Mare Tranquillitatis, Mare Serenitatis and Mare Imbrium.

The dark maria are visible to the naked eye. A pair of 10x50 binoculars brings out crater rims and mountain ranges, and even a small telescope shows individual craters in sharp relief. The territory itself is far too small to resolve from about 239,000 miles away, as is anything a few acres across, but the region it sits in is unmistakable once you know where to look.

Experienced observers rarely wait for the full Moon. Around first quarter and last quarter the line between day and night, called the terminator, throws long shadows across craters and mountains, and the surface looks almost three dimensional. A full Moon is bright and beautiful, but flat.

Other moments worth planning for include earthshine, the faint glow on the dark part of a thin crescent that is sunlight reflected off Earth; lunar eclipses, when the full Moon turns copper red; and International Observe the Moon Night, an annual public event held each autumn when astronomy clubs around the world set up telescopes for anyone who wants a look.

The Moon is the only other world people have walked on, and it is the doorway to the rest of the solar system for most new astronomers. It also travels through the same band of sky as the planets, so it regularly passes close to Venus, Mars, Jupiter or Saturn in what astronomers call a conjunction. Those evenings are a lovely chance to point out a gifted territory and a planet in the same view.

For the planet lover who reads every mission update, the certificate is a small, personal connection to the one world beyond Earth that we have already visited, and are now preparing to visit again.