The moon's terminator line divides day and night on the moon. As we see it from Earth, it marks the line of lunar sunsets or sunrises. Read more.
The post The moon's terminator line divides night and day first appeared on EarthSky.
The moon's terminator is the dividing line marking the edge between day and night on the moon. It's sometimes called the twilight zone, because it marks where the sun is either rising or setting, putting the moon's landscape there in a twilight state. Want to see lunar features more clearly through binoculars or a small telescope? Look along the terminator line. That's where the contrast between light and shadow reveals the moon's topography in stark relief. Mountains tower over the lunar regolith – the loose dust, broken rocks and other materials covering most of the moon's surface – while craters sink away from their rocky ledges. Now on sale! The 2023 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year. Treat yourself! The terminator line in motion The terminator isn't fixed on the moon, of course. It creeps across the moon's surface, with the change in its location noticeable in just hours to those peering through telescopes. A day on the moon lasts 29.5 Earth-days. The moon's terminator moves a bit slower than 10 miles per hour (16 kph) across the moon's surface. That pace seems almost glacial when you consider that, for those at the equator on Earth, our world's terminator flashes across its surface at about 1,000 mph (1,600 kph). If you set your treadmill at a 10-mile-per-hour (16 kph) pace to reflect the speed of the moon's terminator, you could jog (or, more likely, run) and see if you'd be able to keep up with the sweep of nightfall across the moon. You'd have to run at a pace that equals about a 6-minute and 15-second mile. (For reference, if you…