Wednesday, September 11, 2013
The Ellensburg sky for the week of 9/14/13
Saturday: “Excuse me, do you have the time?”
“No, but the Big Dipper does.”
You can use the orientation of the Big Dipper to tell time with a precision of about 15-30 minutes. First, find the two stars at the far end of the Big Dipper cup, the stars that do not touch the handle. Draw an imaginary line segment starting at the North Star and passing through the two Big Dipper cup stars. Now, draw a big circle around the North Star. Your circle is a 24-hour clock. Number the circle from 0 hours at the top, counterclockwise to 12 hours at the bottom of the circle, and back up to 24 hours at the top. (O hours and 24 hours are the same on this clock because the day is 24 hours long.) The hour number on the big circle closest to where your imaginary line intersects this circle is called your raw time. Due to the location of the Big Dipper compared to the rest of the stars, the time nearest the intersection (the raw time) is correct for March 6. For any other night, subtract two times the number of months the current date is after March 6 from the raw time. For example, let’s say the imaginary line between the North Star and the Dipper stars is pointed to the right. That means the raw time is 18 hours or 6 p.m. If you made this observation on October 6, which is seven months after March 6, you would subtract two times seven or 14 hours from the raw time. Thus, the time for November 6 is 18 hours minus 14 hours or 4 hours. In other words, 4 a.m. Don’t forget to convert for daylight savings time if needed. For a more complete set of instructions, go to http://goo.gl/02HmA. There is a simple “star clock” template and instructions at http://goo.gl/SFKrE. Use this paper star clock whenever you watch is broken.
Sunday: Venus and Saturn are close together in the early evening sky for the next few days. At 8 p.m., Venus is about a half a fist held upright and at arm’s length above the west-southwest horizon. Saturn is less than a half a fist to the upper left of Venus. Over the next few evenings, Saturn will move down toward Venus in the sky.
Monday: Let me tell you the story of the ghostly white figure that rises early in the morning in early autumn. It appears to be a huge dim glow of white light that rises up from the east in the pre-dawn sky. No, I’m not writing about the ROTC student who has early morning physical training. I’m describing 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 sky with no haze or light pollution to see the zodiacal light that will be visible for the next few weeks or so. At its brightest, the zodiacal light rivals the light of the central Milky Way.
Tuesday: If you stay up late, you can see Jupiter rising just before 1 a.m. If you get up early, say 6 a.m., you can see Jupiter five fists above the east-southeast horizon and Mars three fists above the eastern horizon.
Wednesday: Shine on, shine on harvest moon, up in the sky. It’s just like a full moon in January, February, June and July. The only difference is that near the Autumnal Equinox (also known as the first day of fall), the full moon rises close to sunset resulting in a full night of light for the harvest. The harvest moon looks more orange than usual when it is near the horizon because of the dust kicked up from the harvest. The dust scatters the white light reflecting off of the Moon resulting in slightly more of the red and orange components of the white light reaching your eyes. Although the Moon has a dull yellow color whenever it is near the horizon owing to light scattering off of dust and atmospheric particles, the effect is more noticeable for the harvest Moon. Tonight’s full moon, which isn’t completely full until tomorrow at 4 a.m., is in the constellation Pisces the fish. For more information about the harvest moon, go to http://earthsky.org/space/harvest-moon-2.
Thursday: “One world, group hug, love everyone” philosophy: political borders are human-made and can’t be seen from space. Real world, pragmatic discovery: some human-made political borders CAN be seen from space. Since 2003, India has illuminated its border with Pakistan to prevent illegal crossings. In August, astronaut Ron Garan took a picture of the boarder from the International Space Station. For more information, including the photo, go to http://goo.gl/mY8xG.
Friday: Sirius, the brightest star in the nighttime sky, is two fists above the southeast horizon at 6 a.m.
The positional information in this column about stars and planets is typically accurate for the entire week.