Observing the moon with an astronomical telescope

First of all, let’s talk about the requirements for the optical system; because the moon is a celestial body with an extended surface, the main purpose is to observe the details of the lunar surface. Therefore, the resolving power of astronomical telescopes must be strong.

The resolution and the effective aperture of the telescope have the following relationship: 6=140/D, D is the effective aperture, expressed in millimeters. To resolve details of 1 arcsecond on the lunar surface, the effective aperture of the telescope must be at least 140 mm. Of course, this is not just about pursuing a telescope with a large diameter and a large amount of light. The premise is that the telescope optical system is required to eliminate chromatic aberration, spherical aberration and coma. Generally speaking, the better objective lenses of refracting telescopes are composed of two lenses, with the purpose of eliminating these three differences. At the same time, the relative aperture of the refracting telescope is usually 1/15 to 1/20. They have long focal lengths and a large film scale (that is, the line size of celestial objects on the film). The relative aperture of reflecting telescopes is often 1/3.5 to 1/5, which is larger than that of refracting telescopes. Reflecting telescopes also produce greater instrumental scattered light than refracting telescopes. Therefore, generally speaking, refracting telescopes are more suitable for lunar observation than reflecting telescopes. Schmidt-Cassegrain and Maksutov-Cassegrain telescopes are also suitable for observing the moon. It is true that reflecting telescopes of good quality and with smaller fields of view can also observe the moon. The diameter of the objective lens of the refracting telescope should not be less than 5 cm, and the diameter of the objective lens of the reflecting telescope should not be less than 10 cm.

Secondly, the requirements for the mechanical system are preferably an equatorial device with tracking. Only in this way can the above-mentioned systematic observations be carried out. Third, the requirement for the eyepiece system is that a variety of eyepieces should be available. For visual observation, eyepieces with a crosshair device are ideal for positioning and drawing. It would be better if there is a moving wire micrometer.