The Moon is the easiest thing to observe with a telescope in the night sky. It’s visible anywhere, even through thin clouds, smoke, light pollution, and haze. You can find 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 cultural significance, but it’s also the closest planetary body within our reach. It has been visited by humans during the Apollo missions from 1968 to 1972, and NASA and the Chinese Space Agency are both planning lunar landings and permanent bases as part of the Artemis and ILRS programs in the second half of the 2020s.
The Moon’s surface is a fascinating landscape with over ten thousand named features, including around 9137 craters. These craters range in size and complexity, with some showcasing central peaks, terraced walls, and ray systems extending outward from the impact site. The formation of these craters provides a historical record of the impacts the Moon has experienced over billions of years. The named features also include mountains, valleys, and large, flat plains called maria. The absence of a significant atmosphere means that these features remain well preserved, allowing astronomers to study geological processes and the history of the solar system in great detail.
This article will go into some terms, things you can see on the Moon with your telescope, what you expect to see with your telescope, and even how to watch lunar eclipses. You can observe all of the details on the Moon we describe with a telescope no greater than 4” in aperture, though pretty much any telescope with decent optics and a sturdy mount will do.
We highly recommend obtaining a digital or printed Moon map to aid in your observations of the Moon. Due to the differing and confusing terminology for lunar east and west, combined with the sheer complexity of providing consistent navigation instructions, we aren’t going to be providing location information on lunar features.
Important Terms for Observing the Moon
When can I see the Moon with My Telescope?
The Moon takes about 27 days to circle the Earth (its orbital period), but due to the Earth’s travel around the Sun, the cycle takes 29.5 days to repeat (the synodic period).
The Moon can be spotted as a very thin crescent within 15 hours on either side of a new Moon by experienced observers. But when it is this thin, it is almost always 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 observe the Moon for around 24 days or so out of the month easily.
The Moon looks best through a telescope when it is between a thin waxing 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, and thus 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 with 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.
What Size Telescope Do I need to see the Moon?
Binoculars will show you the largest craters on the Moon, as will 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 by those numbers, no ground-based telescope has sufficient resolution to reveal the Apollo lunar landing sites – the abandoned Lunar Module descent stages and rovers are only about the size of an ordinary automobile. 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 the most common feature on the Moon by far, and you can always see some of interest. Some – particularly younger – craters like Tycho, Copernicus, and Aristarchus, 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, while the craters Messier and Messier A 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.
Mare Crisium is a prominent lunar mare that stands out due to its isolation from other similar features. It is visible just days after the new Moon with the naked eye as a near-circular “spot”, has a nearly circular shape, and spans about 555 kilometers in diameter. Through a telescope, Mare Crisium offers a smooth and dark surface, contrasting sharply with the surrounding highlands. The region contains various ridges, rilles, and craters that provide intriguing details for telescopic exploration.
The small craters of Armstrong, Aldrin, & Collins appear near the Apollo 11 landing site, around 50 kilometers away from where Armstrong and Aldrin touched down in 1969.
Schiller is an unusual, elongated crater on the Moon’s surface. Measuring approximately 180 kilometers in length but only 70 kilometers wide, its peculiar shape has led to many theories regarding its formation. Through a telescope, Schiller’s oblong appearance, central ridges, and complex surrounding area make it an intriguing target for lunar observation. Its unique appearance sets it apart from the more common circular craters and adds to the diversity of features that make the Moon a continually engaging object to explore.
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.
Montes Apenninus, also referred to as the Appennines, is one of the most striking mountain ranges on the Moon. Extending over 600 kilometers, these mountains rise to heights of up to 5 kilometers. Through a telescope, Montes Apenninus appears as a jagged and imposing chain of peaks, particularly striking near the terminator, where shadows are elongated. The range is best observed during the first quarter phase of the moon, when it is prominently highlighted.
The tallest lunar mountains are similar to many on Earth, with Mons Huygens at 18,000 ft or 5.5 km, 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.
Lunar domes are intriguing geological features on the Moon’s surface that have fascinated astronomers for centuries. These domes are thought to be extinct, partially buried shield volcanoes and are characterized by their gentle slopes and wide bases. They typically rise between 100 and 120 meters above the lunar surface and can span up to 20 kilometers in diameter. Observing lunar domes is a rewarding experience for amateur astronomers with moderate-sized telescopes. The best time to observe these domes is when the Sun’s light is striking the lunar surface at a shallow angle, as is the case along the terminator during the lunar sunrise or sunset. The low angle of illumination casts long shadows, emphasizing the contours of the domes and making them more visible. These features offer vital clues to the Moon’s volcanic history and the geophysical processes that have shaped our natural satellite.
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 Lunar X and Lunar V are fascinating clair-obscur effects that appear on the Moon under specific lighting conditions. The Lunar X is an X-shaped feature created by the interplay of sunlight and shadows on the rims and walls of various craters. Similarly, the Lunar V is a V-shaped pattern. Both appear at the same time and are visible prominently for several hours around the first quarter (or half-illuminated) Moon.
The far side of the Moon can be observed during favorable librations, with the most prominent technically far side feature being 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 its central peak are quite conspicuous to the north.
Observing Lunar Eclipses with a telescope
Total solar eclipses is 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 being a lunar eclipse.
Lunar eclipses occur when the Moon passes into the Earth’s shadow, which only happens occasionally as the Moon’s orbit is inclined by a few degrees. During a total lunar eclipse, the Moon initially dims from entering the Earth’s penumbra, where the Earth obscures a portion of the sun as seen from the lunar 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 with telescope, unlike solar eclipses, which require safe filtered eclipse glasses and solar filters. 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 Conjunctions & 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 detail that is too small or too highly angled to directly resolve 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 all seven of the visible planets in our Solar System as well as appearing in conjunction with them – that is, close by—often enough so that they fit in the same low-power field of view with a telescope or binoculars.
Lunar occultations of stars and planets cannot happen everywhere on Earth at once on account of the Moon appearing in a slightly different part of the sky depending on where you are – an effect known as parallax. This is because the distance between different points on the globe can make up a sizable portion of the distance between us and the Moon – a few percent, yes, but enough to displace it by a few degrees, or several times its apparent width in the sky. Thus, people outside the occultation path will see the planet merely in extremely close conjunction of the planet with the Moon.
