The Ellensburg, WA sky for the week of 9/24/16

Saturday: Last week you hung out on Titan’s lakes and dunes. Now dream about Enceladus’ ocean. Wow, that’s a lot of liquid in the Saturn moon system. Titan’s lakes are made of methane. But astronomers think there is a liquid water ocean beneath the icy surface of Enceladus.  Read all about it at http://goo.gl/6E0sHp. Saturn and its moons are one and a half fists held upright and at arm’s length above the south-southwest horizon at 7:30 p.m.

Sunday: Did you time the exact length of the day and night on Thursday, the first day of autumn? They were not equal in duration. Many people think that the day and night are the same duration on the autumnal equinox. The day is a little longer than the night for two reasons. First, the Sun is an extended object so even when the lower half has set, the upper half is still above the horizon lighting the sky. The second, and more influential, reason is that the atmosphere acts like a lens, bending light from the Sun above the horizon when the Sun is actually below the horizon. Day and night are closest in duration today.

Monday: Jerry Seinfeld gave his best friend some good advice to see Mars this week: “You’ve got to go downtown George. Just like the song says.” Just like the downtown, or core, of a distant city has a glow from human-made light, the “downtown”, or core of the Milky Way galaxy has a glow from starlight. And this week, Mars is lined up right in the middle of this glow; one and a half fists above the south-southwest horizon at 8 p.m. Read more about the glow at https://goo.gl/3IVGcy.

Tuesday: Aldebaran, the bright orangish star in the constellation Taurus, is one fist above the east-northeast horizon at 11 p.m.

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 morning to observe Mercury for the next few weeks. Mercury is nearly a fist above due east at 6:15 a.m. Over the next few weeks, Mercury will move toward the Sun in the sky. By early December, it will be visible in the evening sky.

Thursday: To the people of Ancient Greece, the stars that are about five and a half fists above the east-northeast horizon at 10 p.m. were known as Cassiopeia and Andromeda, a mythological queen and her daughter. But not all cultures imagined the same pictures in the sky. To the people of Polynesia, the stars of Cassiopeia and Andromeda represented a dolphin, called Kwu. Cassiopeia formed its tail, the brightest stars of Andromeda formed its fins, and its fainter stars outlined the dolphin’s body.

Friday: The moon almost directly between the Earth and Sun today. That means you won’t be able to see it. But that does not mean it doesn’t exist. Contrary to the belief of toddlers and immature politicians, just because you can’t see something doesn’t mean it doesn’t exist. (Note a double negative statement followed by a triple negative statement. I’m not unsorry about that.) Now, back to the science. What would happen to the earth if the moon really didn’t exist? In that 2013 blockbuster Oblivion, aliens destroy the moon and Tom Cruise survives. But the long-term effects on the earth would be devastating to life, as we know it. The moon stabilizes the spin axis of the earth keeping the seasons fairly uniform over time. For more information on what would happen to the earth if the moon were destroyed, go to http://goo.gl/4EbzLa. For more information on Thomas Cruise Mapother IV, go to http://en.wikipedia.org/wiki/Tom_Cruise.

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.