Actually, this is one of the first questions that most novice astronomy lovers have. Someone thinks that through a telescope you can see the American flag, planets the size of a soccer ball, colored nebulae, as in photographs from Hubble, etc. If you also think so, then I will immediately disappoint you - the flag is not visible, the planets with peas, galaxies and nebulae are gray colorless spots. The point is that a telescope is not just a funnel for entertainment and getting "happiness into the brain." This is a rather complex optical device, with the correct and thoughtful use of which you will get a lot of pleasant emotions and impressions from viewing space objects. So what is visible through a telescope?
One of the most important parameters of a telescope is the diameter of the objective (lens or mirror). As a rule, beginners buy inexpensive telescopes with a diameter of 70 to 130 mm - so to speak, for exploring the sky. Of course, the larger the telescope lens diameter, the brighter the image will be with the same magnification. For example, if we compare telescopes with a diameter of 100 and 200 mm, then at the same magnification (100x) the image brightness will differ by 4 times. The difference is especially noticeable when observing faint objects - galaxies, nebulae, star clusters. Nevertheless, it is not uncommon for beginners to immediately acquire a large telescope (250-300 mm), then being amazed at its weight and size. Remember: the best telescope is the one you see more often!
So what is visible through a telescope? First, the moon. Our space companion is of great interest to both beginners and advanced amateurs. Even a small telescope with a diameter of 60-70 mm will show lunar craters and seas. With a magnification of more than 100x, the moon will not fit into the field of view of the eyepiece at all, that is, only a piece will be visible. As the phases change, the appearance of the lunar landscapes will also change. If you look through a telescope at a young or old moon (narrow crescent), you can see the so-called ash light - a faint glow of the dark side of the moon caused by the reflection of the earth's light from the lunar surface.
Approximate view of the Moon through a telescope with 40x magnification and an eyepiece with a 40-degree field of view
An approximate view of the Moon through a telescope at high magnification
You can also see all the planets of the solar system through a telescope. In small telescopes, Mercury will look just like a star, and in telescopes with a diameter of 100 mm or more, you can see the phase of the planet - a tiny crescent. Alas, you can catch Mercury only at a certain time - the planet is not far from the Sun, which makes it difficult to observe
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Venus - aka the morning evening star - is the brightest object in the sky (after the sun and moon). The brightness of Venus is so high that it can be seen with the naked eye during the day (you just need to know where to look). Even with small telescopes, you can see the phase of the planet - it changes from a tiny circle to a large crescent like the moon. By the way, sometimes people, for the first time looking at Venus through a telescope, think that they are showing the moon.
Venus has a dense, opaque atmosphere, so you won't be able to see any details - just a white sickle.
Venus through an amateur telescope
Earth. Ironically, the telescope can also be used for ground-based observations. Quite often, people buy a telescope both as a space eye and a telescope. Not all types of telescopes are suitable for ground-based observations, namely lens and mirror-lens telescopes - they can provide a direct image, while in Newtonian mirror telescopes the image is inverted.
Mars. yes, the one that is visible every year on August 27 as two moons