There's more than 100 moons in our Solar System and you can actually see many of them with binoculars... if you know where to look.
At this point in time, 146 moons have been confirmed in our solar system. An additional 28 are still under review. There sizes vary but a few are easily visible to the amateur astronomer. In fact, many of the moons that can be seen don't require sophisticated nor expensive equipment. A few can actually be viewed with binoculars if you know what to look for and where to look.
Earth is unique in the sense that it has only one moon. Venus and Mercury have none while Mars has two. The big story beyond our moon are the moons of Jupiter and Saturn. Both have numerous moons as well as Neptune and Uranus although the moons of Uranus and Neptune are invisible except to the largest, professional scopes.
Jupiter has 65-67 moons including some of the largest and most dynamic moons in our solar system. Ganymede tops the size list with Callisto a close second. In fact both Ganymede and Callisto are larger than the planet Mercury. Two more moons of Jupiter including Europa and Io are a bit smaller than Mercury but also display dramatic characteristics. All 4 of these moons are visible and usually appear like stars in close proximity to the planet.
Another factor affecting visibility is surface colour. Europa is a great example. It's surface is essentially ice and the white colour of Europa increases its magnitude. Unfortunately, Io and Europa orbit relatively close to Jupiter so their occurrence as visible objects is reduced. On the other hand, Ganymede and Callisto have more distant orbits and are easier to spot with regularity.
You should also note that what may appear to be a moon passing in front of its home planet is often the moon's shadow. This image from NASA shows the shadow of Europa as the small, black spot on the lower left of Jupiter.
When a moon itself passes in front of the planet its brightness usually causes it to become washed out against the planets surface and difficult to see.
Saturn has 62 moons. The largest moon of Saturn is appropriately named Titan, and the next four easiest inner moons to find are Rhea, Tethys, Dione, and Enceladus. Much like Europa, Enceladus is also believed to be a moon covered in ice which has given it a bright magnitude relative to its size.
Curiously, the larger moons of Jupiter and Saturn's moon, Titan can be viewed with binoculars or the simplest telescope. If you want to view some of the smaller moons such as Saturn's Rhea, Tehthys and Dione (all 10th magnitude), or Enceladus (12th magnitude) you'll need a 15 to 20 centimeter or 6 to 8-inch scope. A very dark sky with little light pollution and a new moon also help to see the smaller moons.
In spite of the relatively close proximity of Mars to the Earth, its two moons: Phobos and Deimos are difficult to see without a very large telescope. In fact, this is the actual scope used to discover these two moons for the first time by Asaph Hall at the U.S. Naval Observatory in 1877.
Beyond our own moon and the moons of Jupiter and Saturn, it's very difficult for even the most accomplished amateur astronomer to view many of the other moons in our solar system. This is due to both their relatively small size and/or distance. Neptune's moon Triton is a good example. Even though it's roughly the same size as Europa, it's distance from Earth makes it virtually invisible even with professional scopes.
Regardless, the moons of Jupiter and Saturn offer plenty to see and can be a great reason for a planned night out during a new moon.
Maybe you’d like to try this article on the possibility of life on Europa?
Find more on: Observing the Night Sky
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