Thursday, April 12, 2012

The Ellensburg Sky for the week of 4/14/12

Saturday: This week is International Dark Sky week, a time during which people around the world are encouraged to turn off any unnecessary outdoor lights in order to temporarily reduce light pollution. Light pollution is the adverse effect of unwanted light including sky glow, glare, and light clutter. If you think that there is not much sky glow, or wasted light, in the world, look at the nighttime image of the Earth at While turning off a few unnecessary outdoor lights for one week will not solve the problem of light pollution, International Dark Sky Week will raise awareness of the issue. You can do your own dark sky test. At 10 p.m., look in the sky starting at the southwest horizon, moving to about halfway up in the western sky and back down to due north. If you can see the faint glow of the Milky Way Galaxy, you are observing from a dark site. And if you can force yourself to stay awake or if you get up before sunrise or stay up very late any night this week, be on the lookout for meteors coming from nearly straight overhead near dawn. The Lyrid meteor shower is active for the next two weeks.

Sunday: Saturn is opposition tonight. That doesn’t mean that Saturn is a teenager. Opposition means that Saturn is on the opposite side of the Earth as the Sun. When an object is in opposition, it is at its highest point in the sky during the darkest time of the day. Thus, opposition is typically the best time to observe a planet. Saturn is about three and a half fists above the south horizon at 1 a.m. It is one fist above the east-southeast horizon at 9 p.m.
If you remember this column from 2/23/2008, 3/8/2009, 3/21/2010, and 4/4/11, you know that Saturn was also in opposition on those dates. Thus, it is in opposition about two weeks later each year. Two weeks is about one twenty-fourth of a year. This implies that it takes Saturn about 24 years to make one orbit around the Sun and get back in line with the same stars again. Saturn’s actual orbital period of 30 years matches this approximation quite well.

Monday: Avast ye matey. Swab the poop deck. Pirates love astronomy. In fact, the term “poop” in poop deck comes from the French word for stern (poupe) which comes for the Latin word Puppis. Puppis is a constellation that represents the raised stern deck of Argo Navis, the ship used by Jason and the Argonauts in Greek mythology. Argo Nevis was an ancient constellation that is now divided between the constellations Puppis, Vela and Carina. The top of Puppis is about a fist and a half to the left of the bright star Sirius in the south-southwest sky at 9 p.m. Rho Puppis, one of the brightest stars in the constellation, is about one and a half fists above the south-southwest horizon at this time.

Tuesday: The nighttime stars take little more than an instant to rise. The Moon takers about two minutes to rise. That’s absolutely speedy compared to the constellation Virgo which takes four hours to rise. The first star in Virgo rises at 4:30 in the afternoon today. Spica, the brightest star in the constellation, rises at 7:30. By 9 p.m., Spica is a fist and a half above the southeast horizon.

Wednesday: Mercury will be as far away from the Sun in the sky as it will get this orbital cycle. This "farthest away" point is known as the planet's greatest elongation. Since Mercury is in morning sky, it is west of the Sun and this occurrence is called the greatest western elongation. This morning will be the best mornings to observe Mercury for the next few weeks. Mercury is about a half a fist above the east horizon at 6 a.m., between the horizon and the Moon Over the next few weeks, Mercury will move toward the Sun in the sky. By early June, it will be visible in the evening sky.

Thursday: Jupiter is fading in the evening sky. It is less than half a fist above the west-northwest horizon at 9 p.m.

Friday: At 10 p.m., Venus, the brightest point of light in the night sky, is two fists above the west-northwest horizon and Mars is five and a half fists above the south horizon.

The positional information in this column about stars and planets is typically accurate for the entire week.

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