Go outside at 10 tonight and look straight up. Find the three bright stars that make a triangle in the center of the sky. These three stars, Vega, the western-most, Altair, the southern-most, and Deneb, the eastern-most, make a pattern commonly called the Summer Triangle. Vega, the brightest of the trio, marks the handle of Lyra, the harp. A line drawn from Deneb to Vega and extended that same distance ends in the constellation Hercules, the great hero of Greek mythology.
Move straight south from Vega by the width of one fist plus a finger held at arm’s length. That spot, near the Lyra-Hercules border, is the solar apex, the spot in space toward which our solar system is moving.
Everything in our Milky Way orbits the center of the galaxy. As with any other orbital motion, like Earth around the sun, galactic orbits aren’t perfectly circular. Our orbital speed around galactic central point is 137 miles per second, or 492,100 miles per hour. At that speed, it takes us some 250 million years to make one complete galactic orbit. Stars in the same part of the galaxy orbit at roughly the same speed, but not exactly.
The deviation of the sun’s orbit from the average of the stars around us is 36,910 miles per hour, and it is at that speed that we fly toward the solar apex.
If you really want to know where you’re headed, go out tonight and look straight out of our planet’s “front windshield,” south of Vega near the Lyra-Hercules border.
• The planets Mars and Saturn have been relatively close together in our evening sky for weeks. Mars, being closer, appears to move faster than does more distant Saturn.
The planets generally move eastward relative to the background stars in their orbits. Since last May, when both Saturn and Mars showed up in our night sky, Mars was west of Saturn. Over the past three months, Mars has been moving east faster than Saturn and on Wednesday, Mars passed Saturn in the constellation of Libra.
At 8 p.m. Sept. 28, with Mars now in Scorpius and Saturn still in Libra, the moon will move to a spot in Libra half way between Saturn and Mars, making an interesting visual pattern low in the southwestern sky.
In addition to these three, Vesta and Ceres, the two brightest asteroids, will be close to Saturn. Vesta and Ceres are the targets of study for NASA’s Dawn spacecraft.
Dawn studied Vesta from August 2011 to May 2012, and will arrive at Ceres next February.
While these are the two brightest asteroids, you still need a telescope and a dark location to see them.
On that same evening, Mars will sit directly above the star Antares, the heart of the Scorpion.
Ares is the Greek name for Mars, and Antares literally means “not Mars.” The two shine with nearly equal brightness, with Mars slightly brighter. Both sport a reddish-orange tint, so when the two are seen close together in the sky, like this night, they look almost like twins. So the star was named “not Mars” to distinguish it from Mars.
• If our solar system decides to take a right turn at Vega, we’ll be the first to let you know. Learn what’s up and upcoming in the sky in the daily presentation of “Tonight’s Sky” in the Kirkpatrick Planetarium Star Theater. Call 602-3761 or go to www.sciencemuseumok.org for more information and show times.
• The Oklahoma City Astronomy Club meets at 7:30 p.m. Sept. 12 at Science Museum Oklahoma. For more information on the astronomy club, visit www.okcastroclub.com.
• Planet visibility report: Mars and Saturn open the month low in the southwest after sunset, both in Libra. By mid-month, Mars moves into Scorpius. Mercury is also up at sunset, but will be very difficult to spot in the evening twilight.
Jupiter rises about three hours before the sun while Venus, which has been the brilliant “Morning Star” for months, finally plunges into dawn’s glow, preparing to soon become the “Evening Star.”
Full moon occurs Sept. 8 with new moon on Sept. 24.
Wayne Harris-Wyrick is director of the Kirkpatrick Planetarium at Science Museum Oklahoma. Questions or comments may be emailed to firstname.lastname@example.org.