Tuesday, August 25, 2015
The Ellensburg WA sky for the week of 8/29/15
Saturday: School starts next week so it is time for a little geometry review. A square is a four-sided figure with four equal sides and four right angles. Go outside at 10 p.m. tonight with notebook in hand to sketch one. The Great Square of Pegasus is balancing on its corner two and a half fists held upright and at arm’s length above due east. The top corner of the square is two fists above the bottom corner. The other two corners are to the left and right of the line segment connecting the top and bottom corners. Hum. I guess that’s why it is called a square.
Sunday: Neptune is in opposition last night. But that doesn’t mean it is difficult to get along with. In fact, for a planet, being in opposition means it is easy to get along with.… Or, at least easy to observe. Opposition means that Neptune 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 night. Neptune is three fists above the south-southeast horizon at midnight. You’ll need binoculars to see it but you can use the Moon and the bright star Fomalhaut as a guide. First find Fomalhaut, one fist above the south-southeast horizon. Then fine the moon. Next, draw an imaginary line straight up from Fomalhaut and straight to the right from the Moon. Neptune will be found where those two lines cross.
Monday: Geometry review, part 2. Go outside at 10 p.m. tonight with notebook in hand. (Good teaching involves a little repetition.) You’ll have an easy time seeing your notebook because the moon is just a little past full. A triangle is a polygon with three corners and three line segments as sides. A good example is the Summer Triangle made up of the bright stars Vega, Deneb and Altair. Vega, the brightest star in the triangle, is a little bit southwest of straight overhead. Deneb is a little bit east of straight overhead and Altair is five fists held upright and at arm’s length above the south horizon.
Tuesday: Have you been excited to learn all of the new discoveries from the NASA spacecraft that traveled hundreds of millions of miles visit a dwarf planet that we knew little about and to return images of the surface that stunned astronomers and amateur space enthusiasts? And then have you been even more excited that this spacecraft continues to orbit the dwarf planet? Wait. What? Didn’t New Horizons fly by Pluto? Of course it did. I’m talking about the other dwarf planet mission: Dawn’s trip to the asteroid and dwarf planet called Ceres. If you have binoculars and a clear southern horizon, you will find Ceres one fist above due south at 10:15 p.m. Move your binoculars straight up from due south. On the way, you’ll encounter a line of three stars, each one getting successively dimmer than the one below it. With this line at the bottom of your binocular field of view, Ceres will be near the top of your field. If you are not sure which one is Ceres, visit that same spot a few nights in a row. Ceres will be the point of light that changes position from night to night. For more information about Ceres, go to http://goo.gl/Zsstrr.
Wednesday: The Ellensburg Rodeo is a “Top-25” rodeo. What does it take to be a “Top-25” star? There are many ways to rank stars. The most obvious way for a casual observer to rank stars is by apparent brightness. The apparent brightness is the brightness of a star as seen from Earth, regardless of its distance from the Earth. Shaula (pronounced Show’-la) is the 25th brightest star in the nighttime sky as seen from Earth. It represents the stinger of Scorpius the scorpion. In fact, Shaula means stinger in Arabic. Shaula has a visual brightness rating of 1.62. Sirius, the brightest star has a visual brightness rating of -1.46. (Smaller numbers mean brighter objects.) The dimmest objects that can be seen with the naked eye have a visual brightness rating of about 6. There are approximately 6,000 stars with a lower numbered visual brightness rating than 6 meaning there are 6,000 stars visible to the naked eye. Shaula is a blue sub-giant star that radiates 35,000 times more energy than the Sun. It is 700 light years away making it one of the most distant bright stars. Shaula is a challenge to find because it never gets more than a half a fist above the horizon. Look for it tonight about a half a fist above the south horizon, a little bit west of due south, at 8:30.
Thursday: Saturn is two fists above the south-southwest horizon at 8 p.m.
Friday: It’s Labor Day weekend. Time to go to the lake. A Martian lake. In 2010, astronomers found a chloride salt deposit on Mars. Geologists recently used images taken from spacecraft and models of the terrain to determine that the deposits sit at the bottom of a depression that has apparent inflow channels on the high side of the depression and an outflow channel on the low side. A salty deposit in a low-lying area does not automatically mean there was a lake there. But there are other lines of evidence that suggest that Mars was much warmer in the past. Get up at 5:30 a.m., put on your bathing suit and look for Mars one fist above the east-northeast horizon. It is a half a fist to the left of a much brighter Venus.
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 http://nightsky.jpl.nasa.gov/planner.cfm.