Looking Up: A closer look at Jupiter

The brilliant white "star” rising in the east these September evenings is the great planet Jupiter. A small telescope is all you need to begin to see the dynamic, changing face of this world, which is 318 times the mass of Earth.

Jupiter is believed to be a great mass of gas, possibly with a relatively small, solid core. This is a strange planet to our senses; in effect, it is more atmosphere than planet. In this way, Jupiter more resembles a star that is not shining on its own, a gaseous world reflecting sunlight.

For its great mass, Jupiter is moving very fast. It is spinning once around every nine hours and 50 minutes. This quick rotation causes the planet to noticeably bulge at the equator, somewhat flattening itself at the poles.

How big is Jupiter? Its so big, Earth could be one of its moons. Jupiter is 87,000 miles wide at the equator; the Earth is 7,918 miles.

A small telescope magnifying about 60x to 100x is enough to reveal the slight flattening on top and bottom. You should also be able to see a dark band across the mid-northern section or latitudes.

Note: You might notice that the dark band is in the LOWER half of Jupiter, though I just said its in the northern half of Jupiter. Telescopes do funny things. Unlike binoculars, which corrects the orientation for daytime use, an astronomical telescope inverts everything so that south is UP (and north is DOWN)! This takes some getting used to.

Last year, there were two dark bands across Jupiter, one on either side of its equator. One of the bands has mysteriously disappeared. It may have become temporarily hidden by higher clouds. It has faded away in the past and returned.

A larger telescope, under very good seeing conditions, would allow you to observe a large number of distinct and faint bands, as well as a variety of spots and wisps.

Jupiter’s clouds are ever-changing. There are fantastic cyclones which cause materials of various colors from deep within the interior, to flow on top. High winds affect the  edges of the bands, churn and fling material, and allow spots to come and go. Jupiter’s most well-known spot, known as the Great Red Spot, is a tremendous oval-shaped hurricane that has lasted over 300 years. It appears orange-tan in hue in larger telescopes and in photos.

The Great Red Spot is  visible in a small telescope, though you have to catch it when it is on the side facing us. Because the planet spins once in nearly 10 hours, you can actually notice the progress of the spin if you keep track of the Great Red Spot through the night.

Jupiter has a faint system of rings, similar to Saturn but much less visible. The four moons discovered by Galileo in 1610 are now known to be among a family of at least 60 satellites.

Any telescope will show you the four “Galilean” moons. Their names are Callisto, Ganeymede, Callisto and Io. They appear roughly in a line, seen in different places night to night as they shift in their orbits. Some nights you will see two or three; the others are either crossing the face of Jupiter or hidden behind the planet or in its shadow. It is a challenge to see one of the moons transiting across Jupiter, but what is easy is its inky black shadow, cast on the bright planet.

Seeing detail on Jupiter or any of the planets is a challenge for any telescope observer. The size of the telescope and magnification used will mean little if the Earth’s atmosphere is particularly turbulent. As you keep watching, you may be rewarded by moments of fine seeing, where more details will be resolved. It is better if you aim your telescope at Jupiter when it is high up in  the sky. When you look at anything low to the horizon, you see looking through a great deal more bulk of air. Good quality optics, good alignment and a sturdy mount also will aid you.

Above all, patience and practice will show you much more than those who demand the quick and immediate. Even a short glance, however, should be enough to keep you coming back!

First-quarter moon is Sept. 15.

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Keep looking up!