Excellent ejecta
We select six of the best lunar ray systems you can observe with either binoculars or a small telescope
S COPERNICUS
Copernicus is a magnificent crater that has an extensive ray system surrounding it that’s every bit as impressive as its terraced walls and towering central peak mountains. The crater’s bright ejecta blanket can be perceived with the naked eye when the Moon is full or in a late gibbous phase, but to explore the intriguing wavy nature of the rays you’ll need a small telescope of 4-6 inches (100mm–150mm) in aperture.
TYCHO ▶
The crater Tycho possesses, undoubtedly, the most spectacular ray ejecta system on the Moon. Some rays from Tycho stretch most of the way across the lunar disc and dominate the rugged southern highlands, where Tycho sits. Binoculars will show the ray system and the bright ejecta blanket surrounding Tycho when sunlight is shining from a high angle onto the crater and its surroundings.
S KEPLER
A short hop from Copernicus is the similarly impressive crater Kepler. Though Kepler itself is smaller than Copernicus it nonetheless has a fine ray system that is a delight to explore with a large telescope using a medium magnification eyepiece. There’s an interesting mix of forms visible within the rays, from some that shoot out radially in a fairly straight fashion, to others that have a slightly meandering appearance.
▶ with an aperture of around 60mm is perfectly suited to providing wide views of the streaked landscape around Copernicus, Kepler and Tycho.
You can even use a small telescope to look for the brighter ejecta regions when they are shrouded in lunar night. When the Moon is a thin crescent the light scattered off Earth illuminates the nightside of the lunar disc with ‘Earthshine’. At these times, even though they are in darkness, the rays and ejecta blankets of craters like Aristarchus and Tycho still stand out clearly, lit only by our planet’s glow.
Stunning ray systems
If you have access to a larger telescope, say 8–10 inches (200–250mm) in aperture, you’ll be able to UHVROYH QHU GHWDLOV LQ WKH UD\ V\VWHPV RQ QLJKWV of good seeing. A larger aperture instrument will also open up the smaller ray systems, such as the striking double streaks from the crater Messier and the fantastically shaped ejecta from the crater Proclus, which is likely to be the result of a shallowangle impact. There are also a number of craters
T PROCLUS
The 27km-wide crater Proclus lies in the cratered and hilly terrain that sits between the eastern shore of Mare Tranquillitatis and the curved western shore of Mare Crisium. The crater has one of the more unusual ray ejecta systems on the Moon – appearing somewhat like a handheld fan. The striking shape of the ejecta is visible in 10x50 binoculars and also makes it an interesting target for high-resolution imaging.
ARISTARCHUS ▶
Set within the vast Oceanus Procellarum, the crater Aristarchus cannot be missed around the time of full Moon as its dazzling inner walls are spectacularly bright and stand out conspicuously against the surrounding basalt plains. The crater also has an interesting ray system that spreads out in a filamented fan shape broadly towards the southeast. It makes for a fascinating target to explore with a telescope – either visually or with an imaging setup.
S MESSIER
When the Sun is high over the Mare Fecunditatis, a small telescope will reveal an intriguing ray system emanating from the twin craters of Messier and Messier A. The system’s most prominent rays appear as two slightly diverging lines pointing towards the western edge of Mare Fecunditatis, and they stand out quite clearly against the darker lunar sea. The bright rays appear to stretch at least 160km, and may be even longer.
that have more modest ray systems around them, which are not quite as bright and showy as the most famous examples but are nonetheless fun to image or view at the eyepiece. Examples include those around the craters Aristillus, Langrenus, Anaxagoras and Petavius B.
Sketching with pencils or pastels can also be a great way to record views of lunar ray systems at the eyepiece. And that’s indicative of what we love so much about these captivating features: there are many different ways to enjoy and explore them – binoculars, large scope, camera sensor or eyeball. Why not take one of our top picks and get started investigating them for yourself this month.