Wednesday, March 1, 2017

The Ellensburg WA sky for the week of 3/4/17

Saturday: Do you want to impress your friends by making a star disappear? On Saturday night at 6:30 p.m., the bright star Aldebaran is right above the first quarter Moon.  The Moon will move closer and closer to Aldebaran until, about 7:20 when it passes in front of Aldebaran. Because the dark part of the Moon first block, or occults, Aldebaran, it looks like the star just vanishes. By about 7:55 p.m., Aldebaran will pop out from the upper portion of the light side of the Moon. This motion with respect to the background stars is evidence that the Moon is orbiting the Earth.

Sunday: It’s getting dark. The last remnant of twilight has disappeared. Suddenly, you notice a large softly radiant pyramid of light in the western sky. The base of this ghostly triangle is along the west horizon and the peak stretches two or three fists above the horizon. It is 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. Look for the ghostly patch after twilight for the next few weeks.

Monday: It is often said that Earth is a water world because about 70% of the Earth’s surface is covered by water. What would it look like if all that water on the surface were gathered up into a ball? That “ball” would be about 700 km in diameter, less than half the diameter of the Moon. The Astronomy Picture of the day shows us right here

Tuesday: Two weeks ago, astronomers announced the discovery of six or seven Earth-sized planets orbiting the red dwarf star called TRAPPIST-1.  Three of these planets are in the so-called habitable zone of the star, the region where liquid water can exist. In addition, all seven are thought to be rocky. Before you get all excited about these being new Earths, realize that astronomers orbiting a distant star would say our Solar System has three Earth-like planets: Venus, Earth, and Mars. So “Earth-like” from a distance is not the same as “Earth-like” up close. Also, these planets are 39 light years way meaning a trip there would take thousands of years given today’s technology. But, it doesn’t hurt to go to to learn more information.

Wednesday: At 7 p.m., Venus is nearly one and a half fists held upright and at arm’s length above the west horizon and Mars is two and a half fists above the west-southwest horizon.

Thursday: In this busy world, it is important to know what time it is. We have many devises that give us the time. A phone. A computer. A watch. But who has time to build a phone, computer or even a watch. Not you. But everyone has enough time to build a simple Sun Clock. All you need is a pencil, a compass and a print out of the clock template. Go to for more information.

Friday: Jupiter is nearly one and a half fists above the east-southeast horizon at 10 a.m. By 5:30 a.m., Jupiter is all of the way over into the southwest sky and Saturn is two fists above the south-southeast horizon.

The positional information in this column about stars and planets is typically accurate for the entire week. For up to date information about the night sky, go to

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