You may have noticed that bright star coming up in the southeast just after dark. Look closely and you will see that it is not twinkling but rather shining with a steady even glow. That is a big clue that it is a planet, not a star. Jupiter, the largest planet in our solar system, is here to visit us this summer. In June, Jupiter is in what astronomers call opposition. Draw a straight line from the sun to the earth and continue farther and it hits Jupiter.
Opposition also means we are closest to the giant planet for the whole year, and it is a great time to look at it. The news media have been calling that to our attention and one article I read claimed that you could see all of its 79 moons with just a pair of binoculars. Now wait a minute. Most of those moons were discovered by billion-dollar, space-based telescopes like the Hubble orbiting telescope, or by rocket probes sent there by us. I do not think you are going to be able to see all of them yourself from your back yard with just some binoculars. Fake news even extends into outer space!
You might be able to pick out the four largest moons discovered by Galileo. You will need a very good, expensive pair and will have to hold them very steady. Try leaning up against something like a post on your porch. If you have one, a small telescope will work a lot better.
How did Jupiter get all those moons anyway? We only have one. It is the most-massive planet in the solar system, weighing more than all the other planets put together. More mass means more gravity and more gravity means that it can pull in more meteoroids, asteroids and comets, most of which crash into the planet but occasionally some are captured and become moons.
The four moons you can see are fun to watch. Night after night they will change their positions. Galileo noticed their movements and decided they were revolving around Jupiter, a very novel concept for his time. Taking that idea a step further, he concluded that the earth was revolving around the sun. That idea was so radical that the Inquisition found him guilty of heresy and placed him under house arrest for the rest of his life.
Did you know that Jupiter almost became a star? It has just about the same ingredients as our sun — hydrogen, helium and just a dash of some of the other elements. All it needed was to have picked up more mass during the formation of the solar system. More mass would mean more gravity and more pressure in its core to start nuclear fusion, the process that makes stars shine. It would even have had its own solar system, those 79 moons becoming 79 planets.
Other things out there
Look to the right of Jupiter for a reddish-orange star. That is Antares, one of the largest stars we can see with the naked eye, a red super giant star in the constellation of Scorpius. When we look up at the night sky, we only see it as two-dimensional. We do not get to see the true depth of the night. Antares is actually millions of times farther away from us than Jupiter.
Saturn is out there too, a little to the left and below Jupiter. It will look similar, yellowish, shining steady, not twinkling, but not nearly as bright as the giant planet. Of course, it is famous for its magnificent rings, which can easily be seen through that small telescope. While you are looking at it see if you can spot its largest moon, Titan, the only other world in our solar system with rivers and lakes. They are not made of water, however, but rather liquid methane. Sound cold? You bet it is, hundreds of degrees below zero! Titan will appear to be just a star very near the planet in a telescope.
High in the east, three bright stars form the Summer Triangle — Vega on top, Deneb on the lower left and Altair to the lower right. They will be in the sky all summer and most of the fall. Look for the Milky Way going from north to south through Deneb and Altair and then on to kind of near Saturn. Later in the summer or later at night is a great time to spot it when the Milky Way traverses the heavens high overhead.
The bright star Arcturus is high in the south, shining with a distinctive orange light. Both the dippers are visible in the north.
In a little over a month, the August meteors will be racing across the sky. I hope you enjoy these balmy summer nights and maybe you can stay up late enough to see some stars!