Exploring the Planets With an Amateur Telescope

The worlds of the solar system explorable with small telescopes.
Planetary observing from the backyard opens up new worlds to explore through a small telescope. NASA

If you're a new telescope owner, the whole sky is your playground. But if you're a beginner, you may want to start by looking for planets. The brightest ones stand out in the night sky and are easy to spot through your scope. 

There's no "one size fits all" solution to planet-gazing. In general, small telescopes (three inches or smaller) with low magnification will not show as much detail as larger amateur telescopes at higher magnification. (Magnification is a term that means how many times larger a telescope will make an object look.)

Setting Up the Scope

Practice setting up the telescope before use.
Make sure the telescope is properly attached to its mount and that all the eyepieces and other attachments are handy. Andy Crawford/Getty Images

With a new telescope, it's always a very good idea to practice setting it up inside before taking it outdoors.

Many practiced amateur observers let their scopes get used to outside temperatures. This takes about 30 minutes. While the equipment is cooling down, observers gather their star charts, warm clothes, and other accessories.

Most telescopes come with eyepieces. It's always best to check the help guides to see which one is best for planetary viewing. In general, look for eyepieces with names like Plössl or Orthoscopic, in lengths of three to nine millimeters. Which one depends on the size and focal length of the telescope.

If this all seems confusing (and it is in the beginning), it's always a good idea to take the scope to a local astronomy club, camera store, or planetarium for advice from more experienced observers. There's a wealth of information available online, too.

It’s important to research which stars will be in the sky at any given time. Magazines such as Sky & Telescope and Astronomy publish charts each month on their websites showing what's visible, including the planets. Astronomy software packages, like Stellarium, have much of the same information. There are also smartphone apps such as StarMap that provide star charts at your fingertips.

Another thing to keep in mind is that we all view the planets through Earth's atmosphere, which can very often make the view through the eyepiece look less sharp.

Planetary Targets: The Moon

Viewing the moon in a telescope.
Near-full moon on November 14, 2016. The full moon gives a wide variety of features to explore with any size telescope or binoculars. Tom Ruen, Wikimedia Commons.

The easiest object in the sky to observe with a telescope is the Moon. It's usually up at night, but it's also in the sky during the day during part of the month. Nearly every telescope, from the smallest beginner equipment to the most expensive amateur one, will give a great view of the lunar surface. There are craters, mountains, valleys, and plains to check out.

Venus

Venus in one of its phases.
This simulated view (by the US Naval Observatory) showed what Venus's phase was in early 2017. The planet moves through a series of phases just as Earth's Moon does. US Naval Observatory

Venus is a cloud-covered planet, so there's not a lot of detail that can be seen. Still, it does go through phases, as the Moon does, and those are visible through a telescope. Venus looks like a bright, white object, and is sometimes called the "Morning Star" or "Evening Star," depending on when it's up. Usually, observers look for it after sunset or before sunrise.​​

Mars

Viewing the planet Mars through a 4" telescope.
Mars as seen through a four-inch telescope and simulated atmospheric "jitter". This is the best view an observer with a smaller telescope is likely to get of the Red Planet. Loch Ness Productions, used by permission.

Mars is a fascinating planet and many new telescope owners want to see details of its surface. The good news is that when it's available, it's easy to find. Small telescopes show its red color, its polar caps, and the dark regions on its surface. However, it takes stronger magnification to see anything more than bright and dark areas on the planet. People with larger telescopes and high magnification (say 100x to 250x) might be able to make out clouds in Mars. Still, it's worth the time to check out the red planet and see the same views that people like Percival Lowell and others first saw at the beginning of the 20th century. Then, marvel at the professional planetary images from such sources as Hubble Space Telescope and the Mars Curiosity rover.

Jupiter

Jupiter through a four-inch telescope.
A view of Jupiter and its four largest moons, belts, and zones through a four-inch telescope. Higher magnification will give more details. Loch Ness Productions, used by permission.

The massive planet Jupiter offers observers a chance to see its four largest moons (Io, Europa, Callisto, and Ganymede) fairly easily. Even the smallest telescopes (less than 6" aperture) can show the cloud belts and zones, particularly the dark ones. If small scope users are lucky (and seeing conditions here on Earth are good), the Great Red Spot might be visible, too. Folks with larger telescopes will definitely be able to see the belts and zones in greater detail, plus a better view of the Great Spot. For the widest view, though, put in a low-power eyepiece and marvel at those moons. For more details, magnify as much as possible to see the fine details.

Saturn

viewing saturn through a backyard telescope
Saturn and its rings at high magnification, along with its moons. Smaller telescopes can easily show the rings and the largest moon, Titan. Carolyn Collins Petersen

Like Jupiter, Saturn is a "must-see" for scope owners. Even in the smallest telescopes, people can usually make out the rings and they might be able to make out a glimmer of the cloud belts on the planet. However, to get a really detailed view, it's best to zoom in with a high-powered eyepiece on a medium to​ a large-size telescope. Then, the rings really come into sharp focus and those belts and zones come into better view.

Uranus and Neptune

Finding Uranus and Neptune to view through a small telescope.
A chart showing a typical location for Uranus. Both Uranus and Neptune will appear dot-like and bluish-green. Carolyn Collins Petersen

The two most distant gas giant planets, Uranus and Neptune, can be spotted through small telescopes, and some observers claim they've found them using high-powered binoculars. Uranus looks like a little blue-green disk-shaped point of light. Neptune is also bluish-green, and definitely a point of light. That's because they're so far away. Still, they're a great challenge and can be found using a good star chart and the right scope.

Challenges: The Larger Asteroids

Star charts help observers find asteroids and minor planets, too.
A typical scene in the free software Stellarium, showing the position of the minor planet Vesta, which lies in the Asteroid Belt. Amateur observers can use such charts to find the larger asteroids and minor planets. The software will show current conditions for an observer's location. Carolyn Collins Petersen

Those lucky enough to get good-sized amateur scopes can spend a lot of time searching out the larger asteroids and possibly the planet Pluto. It takes some doing, requiring a high-power setup and a good set of star charts with asteroid positions carefully marked. Also check astronomy-related magazine Web sites, such as Sky & Telescope Magazine and Astronomy Magazine. NASA's Jet Propulsion Laboratory has a handy widget for dedicated asteroid searchers that gives updates on asteroids to watch out for.

The Mercury Challenge

A sample star chart for finding Mercury.
Mercury can be observed safely just before sunrise or after sunset, when it is most distant from the Sun. It's a naked-eye object, but can also be observed (with great care) using a small telescope or binoculars. It will appear as a small point of light. Carolyn Collins Petersen

Planet Mercury, on the other hand, is a challenging object for another reason: it's so close to the Sun. Ordinarily, no one would want to point their scope toward the Sun and risk eye damage. And no one should unless they know exactly what they're doing. However, during part of its orbit, Mercury is far enough away from the Sun's glare that it can be safely observed through a telescope. Those times are called "greatest western elongation" and "greatest eastern elongation". Astronomy software can show exactly when to look. Mercury will appear as a dim, but distinct dot of light either right after sunset or before sunrise. Great care should be taken to protect the eyes!