Wednesday, August 1, 2012
The Ellensburg sky for the week of 8/4/12
Saturday: It’s a moonless August morning. The first remnant of dawn has not appeared yet. Suddenly, you notice a large softly radiant pyramid of light in the east sky. The base of this ghostly triangle is along the east horizon and the peak stretches two or three fists held upright and at arm’s length above the horizon about two hours before sunrise. Don’t be scared. It’s not really a ghost. It is an effect called the zodiacal light. This light comes from sunlight reflecting off dust grains in our solar system. The effect is the most visible when the band of constellations called the zodiac makes a steep angle with the horizon. You need a clear dark sky with no haze or light pollution to see the zodiacal light. At its brightest, the zodiacal light rivals the light of the central Milky Way. This is one of the best times of year to see the zodiacal light in the morning.
This is also one of the best times of the year to see meteors. The Perseid meteor shower peaks later this week.
Sunday: Saturn, Mars, and Spica make a small, nearly equilateral triangle about one fist above the west-southwest horizon this week.
Monday: Let’s all sing the galactic black hole monster song: “D is for dusty, that’s good enough for me. D is for dusty that’s good enough for me. D is for dusty that’s good enough for me. Oh dusty, dusty, dusty starts with D.” Astronomers know that spiral galaxies such as our own have super massive black holes in the center, black holes that are billions of times the mass of the Sun. They thought they got to be this massive by mergers where two galaxies collide and the gas, dust and black holes at the center of each colliding galaxy form a larger central black hole. But many distant galaxies show no signs of galactic mergers. Astronomers think the black holes at the center of these galaxies grew simply by snacking on the gas and dust that comes from supernova explosions and normal star formation. Just like the Cookie Monster gains weight by snacking on individual cookies rather than eating a cookie factory. Cookie crumbs, I mean dust, block your view of the center of our galaxy. It is about one fist above due south at 10 p.m., between the constellations Sagittarius and Scorpius. For more information, go to http://goo.gl/GRrWa.
Tuesday: Arcturus is two and a half fists above due west at 11 p.m. This star, whose name means bear watcher, is the brightest in the sky’s northern hemisphere. It follows Ursa Major, the Great Bear, around the North Star. Arcturus is the closest giant star to Earth and is one of the few stars whose diameter can be measured directly.
Wednesday: Had the script been written a little differently for a well-known Robin Williams movie, we might have heard Mr. Williams shout, “Goooood Morning Orion the hunter”. Orion is typically thought of as a winter constellation. But, it makes its first appearance in the summer sky. The lowest corner of Orion’s body, represented by the star Saiph (pronounced “safe”), rises at 4:30 a.m., well before the Sun. By 5 a.m., Orion’s belt is about one fist above the east-southeast horizon.
Thursday: The two brightest points of light in the sky are hanging out together. At 5 a.m., Venus is about two and a half fists and Jupiter is about four fists above the east horizon.
Friday: The Perseid meteor shower hits its peak late for the next few nights. The meteors appear to come from a point just below the W of the constellation Cassiopeia. This point is about two and a half fists above the northeast horizon at 11 p.m. By dawn, this point is about seven fists above the northeast horizon. If you fall asleep or forget to set your alarm, you will be able to observe this shower from about 11 p.m. to dawn for the next three nights in about the same location in the sky. The Perseid shower is one of the longest lasting showers. With dark skies, you can see up to 100 meteors per hour in the late night and early morning hours all week. Unfortunately, the early morning waning crescent moon will obscure all but the brightest fireballs. As your Mother might say, dress warm and sit in a comfortable chair for maximum enjoyment. These meteors are sand to pea-sized bits of rock that fell off of Comet Swift-Tuttle. They are traveling about 40 miles per second as they collide with the Earth and burn up in the atmosphere. For more tips about meteor watching, go to http://goo.gl/6glPq.
The positional information in this column about stars and planets is typically accurate for the entire week.