Young Observers

Prime-time Planets

December 8: The Moon, Jupiter and Saturn are all lined up in a row, and on December 9, the three make a triangle in the sky. Astronomers call these events conjunctions

JUPITER : RULER OF THE ROMAN GODS.

Jupiter is hard to miss. Being the largest planet in our solar system, it is brighter than everything around it in the sky. Because Jupiter is closer to Earth, it is considerably brighter than Saturn. Jupiter is 605 million kilometres from Earth and Saturn is twice as far away as Jupiter is. Saturn appears 10 degrees (a fist-width at arm's length) to its upper right. Notice the Pleiades close by above Saturn. By midnight the whole group shines high in the south, and by dawn it's very low in the west.

The four largest moons of Jupiter are called the Galilean moons. They are: Io, Europa, Ganymede and Callisto. They orbit in the same plane and are all visible in a small telescope.

Jupiter's most familiar feature is swirling mass of clouds called the Great Red Spot, it is like a great hurricane caused by tremendous winds that develop above the rapidly spinning planet. Jupiter spins around once in 10 hours while Earth spins around once in 24 hours. Winds blow counterclockwise around this disturbance at about 250 miles per hour. Hurricanes on Earth rarely generate winds over 180 miles an hour. The Red Spot is twice the size of Earth and has been raging for at least 300 years. It is one of several storms on Jupiter and it can be seen in larger telescopes.

Jupiter was believed by Mesopotamians to be a wandering star placed in the heavens by a god to watch over the night sky. In 1610, Galileo Galilei used a 20x telescope to observe the "stars" around Jupiter. Over several nights he observed these "stars," but each night they were in different positions, leading to his conclusion that they were moons orbiting the giant planet.

In 1994, astronomers around the world watched as the fragments of comet Shoemaker-Levy 9 struck Jupiter -- an event that had been forecast. This image shows a bright cloud more than 8,600 miles in diameter caused by the impact.

One more thing: You could stuff 1,300 Earths into Jupiter. That is if you could, of course.

SATURN: ROMAN GOD OF AGRICULTURE

Saturn has 18 known satellites, made mostly of ice and rock. The largest, Titan, which is larger than the planet Mercury, has a thick atmosphere that obscures its surface. Though researchers aren't sure how many moons Saturn has, the total is likely at least 20, and may be much higher.

The mile-thick rings are made of countless orbiting ice particles, from less than an inch to several feet in size. Up close, it's clear that Saturn has more rings than we can count. Though you can't see all of them from Earth, you can still spot them with a small backyard telescope.

When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing -- a symbol with one large circle and two smaller "ears" on each side.  Debate raged for more than 40 years about this strange shaped object until Christiaan Huygens proposed that they were rings. Giovanni Domenico Cassini later discovered a gap between the rings, which gained his name, and that is also the name of a space satellite on it’s way to Saturn now.

Viewing tips for the planets.

A lot of detail of Jupiter and its moons and Saturn and its rings can be seen in small backyard telescopes. Dark skies, away from streetlights are best for any astronomical observing, but this is not as important with planets. They are usually brighter than the stars. There are, however, some things you can do to improve your view no matter where you live.

Give your eyes 15 minutes to become used to the dark and use a flashlight with a red filter. Heat rising in front of the telescope can distort your view. Try to avoid pointing your scope over large parking lots, rooftops, and cars, which tend to give off heat at night. Wait until the planets are higher in the sky, as light from the planet passes through less of Earth's atmosphere, and the image is clearer.

This page last modified: December 16, 2000