Skip to content

Real astronomy and dated history, with sources. Documented traditions and folklore. Modern lunar astrology · symbolic, not predictive.

Fact #155 Observing

Observers who care about lunar shadows do not talk about phases. They use colongitude — the longitude of the sunrise line on the Moon — because that is what decides how a crater will look tonight.

It runs from 0 degrees at first quarter through 90 at full and round again, advancing about half a degree an hour. Two different lunations at the same colongitude show you the same landscape lit the same way, which is what makes lunar sketching and photography repeatable at all.

Source: Rukl, Atlas of the Moon; BAA Lunar Section · checked Sep 2026

Tonight's phase needs JavaScript. The phase, the rise and set times and the calendar are all worked out on your device. There is no server doing it for you, which is also why the site has no account. The facts themselves are plain pages and read fine without it — start at Explore.

Observers who care about lunar shadows do not talk about phases. They use colongitude — the longitude of the sunrise line on the Moon — because that is what decides how a crater will look tonight.

Settings

Gear that makes it better

Where these numbers come from

Observers who care about lunar shadows do not talk about phases. They use colongitude — the longitude of the sunrise line on the Moon — because that is what decides how a crater will look tonight.

More on observing