Mercury and Venus, the two planets closer to the sun than Earth, are plainly visible to the naked eye. Venus, in fact, is by far the brightest object in the sky other than the sun and the moon, which of course occupy unique places in the hierarchy of observable astronomical objects.
Similarly, you do not need a telescope to see Mars, Jupiter or Saturn. You may need one to spot Uranus, and you certainly need one to appreciate any of its unusual features – a caveat that of course applies to everything in the night sky. And unless you are a character who appears in comic books, you absolutely need a telescope to see Pluto (no longer officially a planet but still a prominent member of the solar system) and Neptune.
You do, however, require a magnified view of these objects to see their finer features, and, in a beautiful twist provided by nature, each of the eight planets in the solar system, including Earth, can be easily distinguished from any of the others on the basis of a number of outstanding physical features.
Viewing the Planets Through a Telescope: Basic Tips
If you own or have access to even a small telescope, you will be able to see everything mentioned in this article. You can also try a Web search for "observatories near me" to find out if a local college or other institution is offering "star parties" or the like for members of the public, which many observatories do for free.
A small telescope measures 4 inches in diameter, and that should be adequate for the task. 6- to 10-inch telescopes are generally needed to meaningfully visualize objects beyond the solar system and a few interesting ones within it. Yours probably came with a variety of color filters, which can be useful for making certain colors of observed objects stand out more, something you can experiment with using trial and error.
Ideally, you will be able to find a spot as free of light pollution as possible, such as a clearing in the woods. Obviously you need to plan on a clear sky, or at least on the part of it you're most interested being clear. You should have an interactive sky chart at your disposal, such as the online star atlas listed in the Resources.
Galileo and the First Telescopes
There are almost as many people credited with making the first "real" telescope as there are stars in the evening sky. Generally, it is agreed that the first telescopes useful on an astronomical scale appeared in the Netherlands in 1608, when the Scientific Revolution and the Enlightenment had been underway for over a century.
Galileo Galilei, widely regarded as the scientist who ushered in modern astronomy, learned of the invention being boasted about elsewhere in Europe and immediately improved upon it with one of his own. Galileo's demonstration of his tool in Venice earned him a lifetime of acclaim and respect. He discovered that the moon is pockmarked with craters and mountains rather than "flat" deformations and that Jupiter has at least four moons.
While Galileo's enthusiastic publishing of his findings was a major part of the rapid expansion and dissemination of human scientific knowledge, his work also invited mortal consequences. In proposing that the Earth revolves around the sun rather than the other way around, Galileo contradicted some 15 centuries of religious dogma, which resulted in him spending his last years under house arrest (a number of his peers were put to death for heresy for making the same suggestion).
The Inner Planets
The four innermost planets, including the one you're camped on, are smaller, hotter and more metallic and rocky in composition than their four outermost counterparts.
Mercury is the smallest and closest planet to the sun. It orbits the sun every 88 days at a distance of about 39 million miles (for reference, the Earth is about 93 million miles from the sun). It is too small to retain much of an atmosphere, so despite its proximity to the sun, it is not the hottest planet.
Mercury through a telescope: Because it is closer to the sun than Earth, yellowish Mercury – even more easily mistaken for a star than the other four planets that are easily visible to the naked eye – appears at its brightest when it is west of the sun in the (eastern) morning sky or east of the sun in the (western) evening sky, depending on the relative positions of Mercury, the sun and Earth. You may notice that it has phases, like the moon.
Venus, which is the most Earth-like planet in terms of mass and also Earth's nearest neighbor, has a thick atmosphere that traps greenhouse gases and keeps the temperature at around 900 F, hot enough to melt lead and making exploration of its surface an enormous technical challenge. It is the brightest-looking planet from Earth owing to both its proximity and the nature of its atmosphere.
Venus through a telescope: Venus keeps its surface well hidden under its dense cloud cover, but you can probably spot dark variations throughout the generally light-colored atmosphere. The phases of Venus are clearly visible.
- Because Venus is so bright, certain astronomical configurations allow you to look at it with relative ease even when it is after dawn or before sunset.
Mars and the Asteroid Belt
Mars, historically, is probably the most famous planet no one has ever walked on. Notoriously serving as the centerpiece of countless early- to mid-20th-century science-fiction books, radio shows and films, it is red, cratered and cold, being 152 million miles from the sun and having a year 687 days long.
Mars though a telescope: The "Red Planet" immediately reveals why, with the advent of telescopes, it became the source of intense and very real speculation about whether life exists, or at some point has existed, on Mars; with this notion came bona fide (though unfounded) fears about possibly malevolent Martians paying Earth a visit.
Channels visible on its surface could plausibly have been the product of artificial rather than natural processes – a seemingly laughable and quaint conclusion now, perhaps, but not in the days when humankind knew comparatively little about planets up close.
- Mars has a fairly substantial atmosphere, and you may be able to see differences from Martian season to Martian season if you are persistent and keep a Mars journal for a couple of Earth years.
The asteroid belt: Asteroids are essentially large chunks of rock that orbit the sun between Mars and Jupiter. Most of these thousands of whizzing bodies are far too small to be seen with a typical telescope. But the larger ones, including Ceres, Pallas and Vesta, can sometimes be found by intrepid astronomy sleuths.
The Gas Giants
The four planets beyond the asteroid belt – Jupiter, Saturn, Uranus and Neptune – are similar in composition to each other and radically different from their relatively minuscule counterparts on the interior. Made mostly of hydrogen and helium and other frozen gases, each of these specimens provides a rich visual and learning opportunity for amateur astronomers.
Jupiter and Saturn in many ways represent the face of the solar system. Saturn has long been known for its iconic rings, which can be seen with a decent pair of binoculars, and Jupiter, in addition to bearing the notoriety that comes with being the biggest in any bunch, is also renowned for its "Great Red Spot," an apparently endless windstorm roiling away in the planet's southern hemisphere.
Jupiter and Saturn are the largest and second-largest of the planets, respectively, giving Earth observers ample surface space to examine despite their remoteness. They orbit the sun at distances of 491 million and 933 million miles respectively.
Jupiter through a telescope: One could spend years in intensive study of Jupiter without either finishing the job or getting bored, as new discoveries about it are being made all the time. Its two most compelling features are the aforementioned Great Red Spot and its many moons, with four of them – Ganymede, Europa, Io and Callisto – ranking among the largest in the solar system (Ganymede being the largest). Also note the bands circling the planet horizontally.
Saturn through a telescope: Saturn's rings as seen live through a telescope are enough to take the breath from most first-time observers, but they are sometimes more prominent than they are at other times. This is because they are sometimes almost edgewise with respect to Earth, while at other times, sizable portions of the upper or lower surfaces rings present themselves nicely; a dark space between the two largest, called the Cassini gap, becomes apparent under these circumstances.
Uranus and Neptune form a natural pair of sorts, being in consecutive order from the sun and being about the same size (Uranus is slightly bigger, but also slightly lighter because of its lesser density). Uranus is greenish-blue, while Neptune is a more distinct blue.
Uranus (1.85 billion miles from the sun) is an oddity in that its axis of rotation is tilted close to 90 degrees from the plane of its orbit around the sun. It can be seen as a faint star by keen-eyed people who know where to look, but only using a telescope does it appear as anything else. Uranus has faint rings, which because of the planet's extreme tilt appear to be oriented in an "up-down" direction instead of a side-to-side one.
Neptune (2.7 billion miles from the sun) is a fabulously windy locale, with gusts topping a remarkable 1,500 miles per hour. It also has the solar system's second-biggest moon in Triton. Sunlight takes four hours to reach the solar system's most distant planet.
Uranus through a telescope: Uranus was discovered – or to be more accurate, identified – in 1781, when William Herschel, who had been tracking the object's movements, realized that it was shifting too quickly against the background of stars to be anything other than a planet itself.
Uranus does not present a lot of variation when viewed through a typical telescope, but the fact that it is somewhat flattened due to its rapid rotation can be confirmed.
Neptune through a telescope: The allure of spotting Neptune isn't so much the details as it is being able to spot it at all. With Pluto demoted to the status of dwarf planet in 2006, Neptune is now the only planet that is not visible with the unaided eye. You may be able to make out Triton apart from the tiny blue disk of Neptune itself.
Beyond the Solar System
Earth and the solar system are part of the Milky Way Galaxy, the closest galactic neighbor of which is the slightly larger Andromeda Galaxy in the constellation Perseus. A look at the Andromeda Galaxy through an 8-inch telescope or 10-inch model allows for a peek at a truly massive entity and another spiral galaxy like the Milky Way; you may be able to make out its "arms" if conditions are ideal.
- If you have a good, steady telescope, Jupiter and Saturn offer the most impressive views. Even a small telescope (such as a 4-inch reflector) can show you Jupiter’s Great Red Spot or Saturn’s rings. You can also look for Jupiter’s four largest moons.
- Use a red-colored flashlight to consult your charts and to adjust the telescope. Red light will not hurt your night vision as much as white light.
- Uranus and Neptune, while observable with a telescope, are not visible to the naked eye. You will need accurate coordinates and a good knowledge of finding coordinates in the sky to locate these planets. However, even in a telescope, you should not expect to see much detail.
- Mercury and Venus always remain close to the Sun in the sky. Because of the brightness at dawn and dusk, telescopes may have only limited use in observing these planets.
About the Author
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs.com and the editor of "Run Strong," he has written for Runner's World, Men's Fitness, Competitor, and a variety of other publications. More about Kevin and links to his professional work can be found at www.kemibe.com.