The Moon is the easiest thing to observe in the night sky. It’s visible anywhere, even through thin clouds, smoke, light pollution, and haze. You can find it and look at it in broad daylight safely; aiming at it is trivial even if your telescope lacks a finder or steady mount, and even the smallest and lowest-quality instruments can show you lots of detail. The Moon is not only responsible for the tides, the stability of the Earth’s axis and rotation, and its cultural significance, but it’s also the closest planetary body within our reach, having been visited by humans during the Apollo missions from 1968 to 1972, and with NASA and the Chinese Space Agency both planning lunar landings and permanent bases as part of the Artemis and ILRS programs in the second half of the 2020s.
This article will explain some terminology, what you can see on the moon, what to expect when observing the moon with a telescope, and even how to watch lunar eclipses. You can observe all of the details on the Moon we describe with a telescope no larger than 4 inches in aperture, though pretty much any telescope with decent optics and a sturdy mount will do.
We highly recommend obtaining a digital or print Moon map to aid in your observations of the Moon. We aren’t going to be providing location information on lunar features because of the differing and confusing terminology for lunar east and west, combined with the sheer complexity of providing consistent navigation instructions.
Important Terms for Observing the Moon
When can I see the Moon?
The Moon takes about 27 days to circle the Earth, but due to the Earth’s travel around the Sun, the cycle takes 29.5 days to repeat. This is the basis for a month, which is derived from the word “moon” (originally “moonth”). The Moon can be spotted as a very thin crescent within 15 hours on either side of a new Moon by experienced observers, but it is too low on the horizon in the absence of the sun, which it is much too close to, to observe well or safely with a telescope. You can easily observe the moon for about 26 days out of the month.
The Moon looks best when it is between a thin crescent and a waxing gibbous a couple of days out from the full Moon. During this time, shadows are more elongated, and thus there is more of a sensation of depth. A full Moon is the worst time to observe it with a telescope. During a full Moon, the Sun is shining obliquely, so there is no relief or shadows to be seen on any surface detail, and the Moon is also obnoxiously bright through a telescope (as well as washing out anything else of interest in the sky besides the planets).
When the Moon is seen as a thin crescent with the naked eye, you might be able to distinguish the unlit side from the background sky with the naked eye. This is because the Moon’s “dark” side is lit up by light reflected off the Earth, just like the Moon lights up our planet at night, though a few times brighter on account of the Earth’s greater size and reflectivity. This phenomenon is known as “Earthshine” and can be seen through a telescope or binoculars during all phases except when the Moon is full.
How Good of a Telescope Do I need to see the Moon?
Binoculars will show you the largest craters on the Moon, as can any telescope. Telescopes of 3-4” or larger aperture will reveal smaller craterlets, fine detail on mountains, rilles, and ridges, and other details down to just 3 miles (~5 km) in size when atmospheric seeing conditions permit. Larger telescopes are limited by the Earth’s atmosphere most of the time, but in theory, your resolution goes up with a linear increase in aperture. So a 12” telescope can show details around 1 mile across, and a monster 24” instrument might have a resolution of 0.5 miles. Linear features like rilles and ridges may only be a few tens of meters wide, but they can still be seen if their length on one axis is longer than the telescope’s resolution limit. This is because of some strange things about how light works and how it bends.
As you might’ve guessed from those numbers, no ground-based telescope has sufficient resolution to reveal the Apollo lunar landing site. The Lunar Module descent stages and rovers that were left behind are about the size of a regular car. In the future, if Artemis astronauts were to build large-scale structures like solar power farms or radio dishes, those might be visible as very reflective, albeit tiny spots near the lunar South Pole.
Magnification can essentially be thrown at the Moon in unlimited amounts, though exceeding 50x or 60x magnification per inch of aperture with your telescope is going to result in a dim, blurry, and hard-to-focus view, and atmospheric seeing conditions will often limit you to lower powers than what your telescope can handle anyway. Making sure your telescope is collimated and cooled down to ambient temperature is also important for achieving a sharp view.
Observing Lunar Surface Features with Telescope
Impact craters are by far the most common feature on the Moon, and you can always see some of interest. Some craters, particularly younger ones, like Tycho and Copernicus, have bright rays of scattered material from the impact, which make them even vaguely distinguishable to the unaided eye. Others, like Petavius or Poseidonius, have rilles within them as a result of volcanic activity beneath the craters after they formed. Crater chains or catenae such as Abulfeda occur when the ejected material from another impact scatters and rains down in a line. The craters Messier and Messier A, on the other hand, seem to be from an impact that hit the Moon at a shallow angle and skipped off the surface like a stone on a pond before crashing down again downrange.
Some craters formed before the lunar maria and were filled in by lava flows, such as Plato, which has a few tiny craterlets within. Sinus Iridum – the “bay of rainbows” – is a crater that had half its walls destroyed by lava flows and was filled in, looking like a prominent brow on the north side of the Moon when it is a waxing gibbous. Similar “horseshoe bays” exist around the Moon, and some have proposed that places on Earth like Hudson Bay in Canada – or at least part of it – are similar geological features originating from impacts and then filled in.
The small craters Armstrong, Aldrin & Collins appear near the Apollo 11 landing site around 50 kilometers away from where Armstrong and Aldrin touched down in 1969.
The overlapping craters of Theophilus, Cyrillus and Catharina make a prominent “L” shaped appearance on the waxing crescent Moon. In addition to overlapping craters, craters or “craterlets” within larger craters can be observed, the most famous of these being Clavius, a monster crater measuring 150 miles (232 km) wide and deep enough to fit most of the Rocky Mountains inside. Clavius has dozens of craterlets which make for a great resolution test for either your telescope or local seeing conditions. The crater Cassini shows two funny-looking round craters within its raised rim, appearing like a face with unequal eyes.
Volcanic craters, known to some as calderas, also exist on the Moon. Hyginus is the largest volcanic caldera on the Moon and shows a triangle of rilles radiating outward. The canceled Apollo 19 or 20 mission would’ve visited Hyginus.
Mountain chains are common on the Moon, and many are named after terrestrial mountain ranges like the Alps, Caucasus, and Appennines. The tallest lunar mountains are similar to many on Earth, with Mons Huygens at 18,000 feet (5.5 kilometers) tall, rivaling some of the tallest of our own planet’s summits—though you’d be able to see a lot more from the top owing to the Moon’s lack of an atmosphere and smaller diameter. The Alpine Valley shows prominent graben.
Many ridges and rilles exist on the Moon. The Lamont region is thought to be a huge impact crater that was buried under lava flows. Rupes Recta, or the “straight wall,” is nearly invisible when illuminated from overhead but casts a huge and prominent shadow when lit from the side, appearing like a cavalry sword with a handle.
The far side of the Moon can be observed during favorable librations. The most prominent technically far side feature is the crater Goddard, which straddles the cartographic near and far sides at about 90 degrees east longitude on the Moon (appearing west to us, of course). The lunar south pole also tilts by different amounts during librations, with the exact south pole lying within the near-invisible Shackleton crater. Malapert Massif, a fairly prominent mountain near the south pole, can be seen fairly easily during favorable librations and is one of the likely candidates for the Artemis 3 lunar landing, the first lunar landing since Apollo 17 in 1972 which NASA and SpaceX plan to conduct in 2025 or 2026. If you’re having trouble finding Malapert Massif, nearby crater Moretus and is central peak are quite conspicuous to the north.
Observing Lunar Eclipses
Total solar eclipses are already covered in our separate article and are as much a phenomenon involving the Sun as the Moon. However, they are only one of the two types of eclipses; the other is a lunar eclipse.
Lunar eclipses happen when the Moon moves into the shadow of the Earth. This happens very rarely because the Moon’s orbit is tilted by a few degrees. During a total lunar eclipse, the Moon starts to get darker as it moves into the Earth’s penumbra. This is where the Earth blocks out part of the sun as seen from the Moon’s surface. The Moon then begins to enter the umbra, as the east-facing side gradually appears to have a “bite” taken out of it. Eventually, the whole disk is obscured by the Earth’s shadow. However, our planet’s atmosphere acts like a lens or prism and bends a tiny bit of sunlight around it, illuminating the Moon with dusky refracted sunlight at a fraction of its normal intensity. The scattered light is reddish or orange like a sunset due to the refraction by the Earth’s atmosphere. This gives rise to the pop culture “blood moon” we think of when we picture a lunar eclipse.
Depending on weather conditions such as clouds, smoke, and dust near the day-night line on the Earth at the time of the eclipse, the Moon can vary from a bright orange to a nearly invisible gray-brown color. This is evaluated on a scale called the Danjon scale, with 0 indicating a near-invisible brownish eclipsed Moon and 4 indicating an orange-copper eclipse with a bluish-white rim of light around the Moon’s edges. Most eclipses are reddish and fall in the middle range.
Partial lunar eclipses occur when the Moon does not entirely enter the umbra – a recent partial eclipse in 2021 had only a tiny sliver outside the umbra and thus appeared practically total to the eye. Penumbral lunar eclipses can also occur where the Moon either only enters part of the penumbra and barely dims, or the Moon enters the penumbra but little to none enters the umbra.
Lunar eclipses are perfectly safe to observe, unlike solar eclipses, which require safe filtered eclipse glasses and solar filters for telescopes. You can use a telescope to watch a lunar eclipse, but the most enjoyable views are really just with binoculars or the unaided eye. Lunar eclipses are incredibly slow, with totality lasting between 30-90 minutes, the umbral phase lasting 30-60 minutes on each side, and the penumbral phase stretching another 30-60 minutes, so they can be up to a 6-hour event in total. Lunar eclipses can be viewed from anywhere on Earth that the Moon is visible, unlike a solar eclipse.
Observing Lunar Occultations
The Moon frequently occults, or passes in front of, stars. This can be extremely interesting when the star just brushes the edge of the Moon’s north or south pole, and dips periodically behind mountains, crater rims, and other features. This can be used to evaluate details that are too small or too highly angled to be directly resolved from the Earth. The timing of how long a star takes to disappear behind the Moon can also be used to measure the physical diameter of stars, despite the fact that few can be directly resolved with even the most powerful telescopes. For instance, a star with an angular diameter of 0.001 arc seconds (which would require a telescope over 100 meters across to resolve directly) takes a whopping 1/50 of a second to disappear entirely behind the Moon, which can actually be measured even with analog film. Likewise, extremely close double stars that cannot be split normally can be resolved during an occultation when one star is occulted slightly earlier than the other. For casual observers, seeing a star disappear behind the Moon and reappear later in the night gives a real-time demonstration of just how fast the Moon moves in its orbit and across the sky.
More rarely, the Moon occults planets. This usually doesn’t happen everywhere on Earth on account of the Moon appearing in a slightly different part of the sky depending on where you are; people outside the occultation path will see the planet merely in extremely close conjunction with the Moon.