Since the beginning of winter in December the bright planet Venus has been king of the western evening skies, slamming reflected sunlight our way. But there’s a new celestial sheriff coming to town in Pacific Northwest skies.
As Venus gradually slips out of the evening sky this summer, Jupiter, the true king of the planets, is on the rise in the east. Jupiter is by far the largest planet in our solar system, 88,000 miles in diameter. It’s so big that if it were a hollow sphere you could fit almost a thousand of our Earths inside Jupiter.
Venus is about the same size as our Earth, about 7,700 miles in diameter, but it’s much brighter than Jupiter because Jupiter is so much farther away. Tonight Venus is a little over 64 million miles away, but Jupiter is almost 400 million miles from our backyards.
Despite that distance, Jupiter and Earth are the closest they will get to each other this year. As you can see in the diagram, this month Earth is nearly directly in a line between the sun and Jupiter, something astronomers call opposition. This is a great time for Jupiter gazing, not only because the great planet is close to us but because it’s available for our astronomical perusal all night long, since Jupiter and the sun are in opposite directions. That’s why this alignment is called opposition. Just like a full moon, Jupiter rises at sunset and sets at sunrise. It’s absolutely the brightest starlike object in the eastern half of the sky.
Jupiter will dominate the night skies right through the summer and beyond, but it will be a little challenging to check out with a telescope or binoculars. That’s because Jupiter will be making a fairly low arc across the southern sky as it tracks from east to west through the night. Even at its highest point during the midnight hour, it will be less than 25 degrees above the southern horizon. That’s a problem, because the closer any celestial object is to the horizon, the more of earth’s blurring atmosphere we have to plow through to see it. That’s especially a problem when there’s a lot more humidity in the air as there is in the summer.
Despite that, Jupiter is still a very worthy target through even the smallest of backyard telescopes. Jupiter is a tremendously large ball of mostly hydrogen and helium gas, over 300 times more massive than Earth. In fact, Jupiter is twice as massive as all of the other planets combined. Like the rest of the gas giants in the solar system it doesn’t have a solid surface, but is thought to have a rocky core about 10 to 15 times the mass of the Earth. Because of its colossal mass, Jupiter has a very strong gravitational force, so strong that even if the planet had a surface to stand on you wouldn’t be standing there long. The gravity of Jupiter would break you down to a pile of flesh and broken bones very quickly.
Jupiter’s gravity also causes the giant planet to produce energy. Jupiter’s interior gases are constantly being gravitationally compressed, which produces heat that oozes out of the planet. In fact, Jupiter produces more than one and half times the energy that it receives from the sun, mostly as infrared radiation. That heat drives the atmospheric winds hundreds of miles an hour, constantly ripping through Jupiter’s cloud tops.
When we see pictures of Jupiter from Galileo, New Horizon and other robotic spacecraft, you can see these complex bands of wind driven clouds mainly made of up methane, ammonia and other gases. The different colors are the result of gases being at different temperatures and densities. There are also several storms on Jupiter like the “Great Red Spot,” a storm that’s been raging for more than 300 years.
Through even a small telescope, you can see at least some of these cloud bands, especially two darker ones on either side of Jupiter’s equator. If your scope is larger, you might even see the famous Red Spot, although that’s usually really tricky to see. In fact, since Jupiter rapidly rotates on its axis once every nine hours, the Red Spot is not always visible.
Jupiter also has dozens and dozens of orbiting moons, four of which can easily be seen using just about any telescope, or even a cheap pair of binoculars. There are four larger moons, called the “Galilean” moons in honor of their discoverer Galileo in the early 1600s. These look like little stars that circle the planet in periods of two to 17 days. These moons are another story all by themselves, and I’ll have that next week in Skywatch.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the new book “Washington Starwatch,” available at bookstores and on his Web site, www.lynchandthestars.com.
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