The lunar surface at the eyepiece
Though some details might be subtler, the Moon is still a spectacular sight
▲ This is how large the Moon’s disc appears in the field of a 150mm scope, 15mm eyepiece and 2x Barlow lens
The Moon doesn’t really suffer too much from a visual observing ‘expectation gap’ like faint deep-sky objects do – it’s impressive even when seen through basic telescopes. But if astro images are your main reference points for what its surface features look like through a scope, do bear in mind that these usually show a level of fine detail that won’t be visible to the eye.
Amateur imagery of the Moon is often captured using high frame-rate cameras. These are used specifically to overcome one of the things that pretty much defines the lunar visual observing experience: the undulating of the atmosphere. The cameras capture thousands of frames, which are analysed so that the sharpest data can be extracted. Our eyes don’t have this luxury, of course, so at the eyepiece you’ll see the
Moon’s surface gently wobbling as its light is distorted – only in very brief moments will finer details become visible. Not only that, but camera data is typically heavily processed on top of this. This means that at the eyepiece, the views of craters and mountains and the like are often softer and more subtle than sharpened photos might suggest they would be. Through a small telescope at low magnification you’ll usually be able to see the whole, or at least much of, the lunar disc in the eyepiece. As you up the magnification you’ll be able to get a ‘closer-in’ view of features like craters, mountains and rilles; but be warned that doing this isn’t like zooming in on a phone screen, where the image largely retains the brightness and clarity of the wide view. Increasing a telescope’s magnification will make the overall view fainter, and if seeing conditions are poor you may not actually see that much more detail, as it’ll be overwhelmed by the blurring of the turbulent atmosphere.