Observing
The Moon works in any telescope, from any city, on any night it is up. Getting the most from it is a matter of when to look, where on its face to look, and how much light to let through.
The line between day and night on the Moon is where shadows are longest. Craters, mountains and valleys stand out in relief there and nowhere else. It moves night by night, so the same feature changes as the Sun rises over it.
A full Moon is the worst time to look: the Sun is straight overhead and shadows vanish. A crescent to gibbous Moon shows the most.
A bright Moon dazzles the eye and ruins dark adaptation. Celestron’s variable Moon filter adjusts from 1 to 40% transmission; Vixen’s ND4 filter passes a fixed quarter of the light without tint.
On most nights 100x to 150x is the useful range. A long-focus telescope such as the NexStar 4SE, at 1325 mm, gives 220x with a 6 mm eyepiece like the Omni 6 mm; on 650 mm, a 2x Barlow does the same job.
A phone held to the eyepiece with an adapter photographs the Moon well. It is the easiest astrophotography there is.
It is found without a finder and stands any magnification the sky allows.
The only target that works with a queue of people behind the eyepiece.
The same crater changes entirely from one evening to the next. That is the interest.
| The moment | What is shown | What limits |
|---|---|---|
| Crescent | Relief | Nothing |
| Quarter | The terminator | The sky |
| Gibbous | Broad areas | Brightness |
| Full | Contrasts | The glare |
An instrument used only on the Moon is used at high magnification, and that reveals every fault of collimation and of steadiness. That is not a problem with the Moon, it is a test.
This site publishes stated specifications; the Sun stays outside its scope.
Variable 1–40% transmission · two polarizing elements · 1.25 in Celestron eyepiece thread
Celestron's Variable Moon Filter: a two-element polarizing filter for 1.25-inch eyepieces whose transmission adjusts from 1 to 40 percent by rotating its lower ring.
Best for: The Moon across its whole cycle, where a fixed filter is right at only one phase
≈ $43
ND4 neutral density (about 25% transmission) · 1.25 in (31.7 mm) eyepiece mount · 19 mm effective diameter · 10 g
Vixen's 1.25-inch Moon filter: a neutral density filter equivalent to ND4, which passes about a quarter of the light, with a 19 mm effective diameter, for eyepieces of 31.7 mm.
Best for: A 1.25 in eyepiece case where a neutral, known dimming factor matters
≈ $58
102 mm (4 in) Maksutov-Cassegrain · 1325 mm at f/13 · GoTo fork with built-in wedge · 21 lb with tripod
Celestron's NexStar 4SE: a 4-inch Maksutov-Cassegrain with StarBright XLT coatings on a computerized single-arm GoTo mount whose tripod has a built-in wedge, 21 lb with tripod.
Best for: A first computerized telescope for the Moon and planets that can also take short-exposure photos
≈ $649
6 mm (0.24 in) Plössl · 50° apparent field · four elements · blackened lens edges · anodized aluminum
Celestron's Omni 6 mm: a four-element Plössl with a 50-degree field, multi-layer coatings, blackened lens edges, an anodized aluminum barrel with a filter thread and a fold-down rubber eyecup.
Best for: Planetary detail on a medium-focal-length telescope, from a maker with a US warranty
≈ $32
2x Barlow · 1.25 in · fully multi-coated with blackened edges · keeps eye relief · 2-year US warranty
Celestron's Omni 2x: a 1.25-inch Barlow with fully multi-coated optics and blackened lens edges, which doubles each eyepiece's power while keeping its eye relief.
Best for: A first Barlow for an existing 1.25-inch eyepiece set
≈ $35
Away from full. Between a thin crescent and first quarter, and again after last quarter, the shadows along the terminator show craters and mountains in relief.
Not for safety, but for comfort. A gibbous or full Moon is dazzling; a filter lets detail show and protects night vision.
Start around 50x for the whole disk, then 100x to 150x on a feature. The atmosphere, not the telescope, usually sets the limit.
For observing: The Moon across its whole cycle, where a fixed filter is right at only one phase
Where it is strong: Transmission adjustable from 1 to 40%
Where it is weak: Two elements are thicker than a single filter
For observing: A 1.25 in eyepiece case where a neutral, known dimming factor matters
Where it is strong: Dimming factor published: ND4, about 25%
Where it is weak: About $58 for a fixed Moon filter
For observing: A first computerized telescope for the Moon and planets that can also take short-exposure photos
Where it is strong: Built-in wedge for polar alignment, which reduces field rotation in exposures
Where it is weak: 4 inches of aperture limits faint deep-sky objects
For observing: Planetary detail on a medium-focal-length telescope, from a maker with a US warranty
Where it is strong: Blackened lens edges and multi-layer coatings, stated
Where it is weak: Short eye relief, as with any 6 mm Plössl
For observing: A first Barlow for an existing 1.25-inch eyepiece set
Where it is strong: Fully multi-coated with blackened lens edges, at $35
Where it is weak: Element count not published
$16 – $35
9 models
$37 – $100
9 models
$100 – $1 699
9 models
Model against model, where the comparison is already published.
The models above are taken from the catalog of this site. Specifications are the ones the maker publishes and the ones on the Amazon page; prices are the Keepa reading for the date shown, and both change. Ranking uses declared specifications, the weight of stated strengths against stated limits, and price. Nothing here has been pointed at the sky by us, and the page makes no such claim.
Last checked on
Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.
