July 1, 2007 Astronomers say that this July planetary orbits have lined up so that people on Earth can see a rare convergence of Venus and Saturn in the night sky. Just after sunset they will appear in the west, looking like a double star, with Venus appearing much brighter. The two planets are actually hundreds of millions of miles apart, but during July they will appear to be very close from our vantage point on Earth.
We all like to wish upon a star. In July, you may think you're wishing on a double star -- but what you're really seeing is Venus and Saturn. The planet Venus is named after the goddess of love and come July first, this earth neighbor will look like it's trying to kiss the planet Saturn in the evening sky.
"They are going to be so close together -- less than a degree apart -- that when you stick out your arm and cover it with your pinky, you can cover them both -- they are that close together," says Kelly Beatty, executive editor of Sky and Telescope Magazine.
That line of sight is actually an optical illusion. "They are not physically close. It's just that as they pass each other through space, from our perspective, they appear to be very close together in the sky," Beatty explains.
Planets circle the sun in orbits that are very far apart, so they can never collide. But as they move across our sky, every so often, one planet will look like it's slowly overtaking another one, creating what seems like a near miss.
"We don't often see things that bright in the sky, that close together. And the funny thing is that in this day and age, we aren't used to looking at the night sky and these things strike us as odd." Through a telescope, Venus will look like tiny a crescent moon and Saturn -- 850-million miles farther away -- will be surrounded by its famous rings.
"Saturn will be a lot fainter than Venus, a hundred-times fainter, but you will still see them ... it will look like a double star in the sky," Beatty says. You'll be able to catch that double star if you look up into the western sky soon after the sun goes down. The next time you'll get a clear view of such a celestial treat will be February 1st of 2008.
The American Astronomical Society and the American Meteorological Society contributed to the information contained in the TV portion of this report.
BACKGROUND: In July, two major planets -- Venus and Saturn -- will look very close to each other in the night sky. They will be at their closest on June 30th, looking as though they were as near each other as the Moon is wide. This happens because both planets are getting noticeably lower in the sky as they move around in their orbits.
ABOUT VENUS: Venus -- dubbed "the jewel of the sky" because it is brighter than the brightest stars -- is often called Earth's sister planet by astronomers because they are similar in size, mass, density and volume. But the similarities end there. Venus has no oceans and has a heavy atmosphere made up mostly of carbon dioxide. This causes an intense greenhouse effect: sunlight passes through the atmosphere to heat the planet's surface, but the heat radiating back out is trapped by the carbon dioxide in the atmosphere. So Venus is hotter than Mercury, with a surface temperature of about 900 degrees. The surface of Venus is mostly vast plains covered by lava flows and mountainous regions; there is no liquid water on the surface. The surface is also scarred by impact craters, and there are hundreds of large volcanoes dotted about the surface. Venus rotates once every 243 Earth days, by far the slowest rotation of any of the major planets.
ABOUT SATURN: Saturn has been known since prehistoric times. It is one of the gas giants, and is the sixth planet from the sun, and the second largest in the solar system, exceeded only by Jupiter. Saturn is composed primarily of hydrogen, with smaller amounts of helium and other trace elements. Its interior is made of a small core of rock and ice, surrounded by a thick layer of metallic hydrogen and a gaseous outer later. Saturn is best known for its prominent system of rings, which are mostly comprised of ice particles, rocky debris and dust. Astronomers believe the rings may have been formed from larger moons that were shattered by impacts from comets and meteoroids. The planet also has at least 62 moons; most of them are quite small, but the largest is Titan, which is bigger than the planet mercury and is the only moon in the entire solar system to have a significant atmosphere.
HOW TELESCOPES WORK: A telescope, in its most basic form, is a long tube with a lens on either end that magnifies distant objects. One lens is concave, the other convex, and the light that enters bends, or refracts. The concave lens collects as much light as possible, and a convex lens redirects the rays so that they all converge back to one point. And that point is where you get an image of any object in front of the lens. The reason we have difficulty seeing objects that are far away is they don't take up sufficient space on the eye's retina for the retinal sensor to detect them. A "bigger eye" would enable us to collect more light from the object to create a brighter image, and then magnify part of it so that it stretches over more of the retina. A telescope is an extension of the human eye; in this case, it gathers light from dim, distant objects in the sky so we can see them more clearly.