Based on my own experiences, this is how I would rank objects when seen through a telescope. While I have seen spectacular views of every object type depending on the conditions, this is a general ranking on a typical night, especially if you are under a sky hindered with light pollution. The following objects are listed from WORST to BEST, with a few exceptions in the lesser categories.
Asteroids and Minor Planets
They’re going to be grouped all the same. All of them are so far away and too small to be resolved into anything but star like points. People ask me to point to Pluto, and not only do I need a larger telescope, but I also need a detailed chart of the sector of the sky it is in, because it will look just like any other background star! You usually don’t see their movement unless you’re taking pictures days apart.
Galaxies are notoriously disappointing when seen through a telescope with the naked eye. Galaxies do not contrast very well from city skies, and they display very little structure and shape. Darker skies increase the contrast, but they often just look like irregularly shaped smudges. Usually it’s just their bright cores that are visible, and the spiral arms are either invisible or very unstructured. Larger telescopes can make them appear brighter and bring out a little more structure, but long exposure photography is the reason why we know what these objects actually are.
Exceptions: Andromeda Galaxy – brightest and closest galaxy to our own. Can be seen with the naked eye under dark skies. The core is bright enough to see under bright city skies.
Globular Star Clusters
Globular clusters look very pretty in long exposure pictures, and larger telescopes can definitely make the biggest and brightest of these clusters look similar to the pictures. But most of the time, especially through a smaller telescope, they look like dim fuzzy “snowballs” in the sky. Unless you have a large aperture telescope, don’t expect to see much when it comes to globular clusters.
Exceptions: Omega Centauri – brightest and largest globular cluster in the night sky. Visible to the naked eye under dark skies… if you are at a latitude further south. From more northern latitudes, M13 is a great choice, and with an 8″ telescope can easily resolve individual stars at higher magnifications.
We see all these bright and colorful pictures of nebulae and think that’s what we’ll see with the naked eye. Nope! To the naked eye, most nebulae appear dim and gray, because our eye does not resolve color that well in low light settings, and cannot absorb the light like a camera can.
Exceptions: Orion Nebula – this one is very bright, shows hints of green, and with the naked eye can be seen as a “fuzzy star” in the “sword” of Orion. Even under a city sky, the nebula can show structure if the sky conditions are good enough.
People often think that if we point a telescope at a star, we’ll see them as discs with spikes. But as big as they are, they’re way too far away for that. However, what you can see is a brighter point of light than you would see with the naked eye, and of course some of them show off their color very well. When the air is turbulent, bright white stars like Capella shine in different hues with every twinkle.
Of course, sometimes a comet does become a naked eye object bright enough to see from dark skies, and they do offer a rare treat if the head and tail is on full display. However, comets are ranked lower because most comets are too small and dim to be seen through a typical telescope, and are unimpressive when they’re below naked eye level brightness.
Exceptions: Great comets! The comets that are super big and bright are AMAZING! Too bad they’re super rare.
Mercury is elusive due to its proximity to the Sun. When it does get far enough away from the Sun’s glare, it’s not visible in the sky for very long. Because it is so far, it will always appear white, and even though it exhibits phases like Venus, you need to view at high power to see the phase.
This is entirely dependent on the filters you are using! With a white light filter, if there are sunspots visible on the photosphere, then they are nice features to look at. But if there are no sunspots, the Sun looks boring unless there is a transit or eclipse occurring. Different filters will give you different results. For example, a hydrogen alpha filter can show you flares and prominences emanating from the photosphere!
To those of us at Griffith Observatory, it’s almost like a running joke on how disappointing Mars can be. Because it appears really bright when it’s closer to Earth, people expect it to be as amazing as the planets I would deem best. First, it looks more like a bright salmon colored orb rather than the famed rusty red planet, and then its size and distance make it hard to resolve any features on the planet. Plus, when we’re dealing with bad seeing conditions, forget about it!
Exceptions: However, if it’s close enough (<40-50 million miles), if the seeing conditions are fine, and if there’s no sandstorm covering the planet, it’s nice to be able to see an ice cap or two, plus some dark brown albedo features.
Uranus and Neptune
Even though Uranus and Neptune require high magnification to see a bluish colored disc, to me it still looks more striking than the bright featureless butterscotch orb that Mars often looks like. Unless you’re viewing through a large and powerful telescope, you most likely won’t see any features, but the cyan color of Uranus and deep azure color of Neptune is just… cooler!
Venus appears white, and don’t expect any other color since the cloud tops are white! This planet can be observed during the day, and when it cycles through its phases just like the moon does, it’s fun to showcase it. I can’t tell you how many people confuse it for the Moon whenever it has a half moon or crescent moon appearance.
Double stars are often nice targets to find. Some of them appear far enough through a wider eyepiece, others need higher magnification to resolve the individual stars. Whether they are true binary systems, or visual binaries, many of them offer striking color contrasts in the sky, such as Albireo and Almach. Castor is a beautiful blue double, and Epsilon Eyrae is called the “double double” because you can see two double stars in the same view!
Open Star Clusters
Open Star Clusters can either be naked eye objects like the Pleiades, or fuzzy patches resolved through binoculars or telescopes like the Beehive Cluster and Double Cluster. Either way, they are very easy to see, and are quite beautiful through telescopes with the right magnification setting.
Jupiter is often a showstopper when it’s in the sky. At high magnification, you can not only see it as a cream colored disc, but can easily see the brown cloud bands, the great red spot, and the four Galilean moons orbiting the planet! Jupiter comes very close to looking just like the pictures when you get to see it with your own two eyes. Even if you can’t view at high magnification, it’s still nice to see a disc with its four moons.
Even if it’s the closest thing in the sky, the Moon offers amazing views through a telescope no matter which magnification you’re using! Wide views of the entire moon already showcase details you can’t see without equipment, and zoomed in views will make you feel like you’re walking on the surface of the Moon! Even if the Moon is not visible in the sky, people STILL ask “why isn’t this pointed at the Moon?!”
Without a doubt, Saturn is the best planet to view through a telescope! Saturn is just bright enough where the glare doesn’t block too many details, and it looks just like the pictures! With the right amount of magnification, you can see a yellow planet with white rings! Of course, when the rings are at that correct angle, they are quite spectacular at high magnification. Not only can you see the space between the rings and the planet, but you can also see a space ON the rings themselves known as the Cassini Division.