Wednesday, March 16, 2016
The Ellensburg WA sky for the week of 3/19/16
Saturday: Look up in the sky. It’s a plane. It’s a bird. No, it’s the vernal equinox. The vernal equinox!? Spring starts at 9:30 p.m. Pacific Daylight Time. The first day of spring is often called the vernal equinox. This label for the day is misleading. The vernal equinox is actually the point in the sky where the Sun’s apparent path with respect to the background stars (called the ecliptic) crosses the line that divides the stars into north and south (called the celestial equator). This point is in the constellation Pisces the fishes. At the vernal equinox, the Sun is moving from the southern region of background stars to the northern region. Since the Sun crosses the vernal equinox at night, tomorrow will actually be the first full day of spring.
Because the Earth slowly wobbles like a spinning top, the vernal equinox is slowly moving into the constellation Aquarius. By the year 2597, the vernal equinox will reach the constellation Aquarius and the “Age of Aquarius” will begin. Until then, we’ll be in “the age of Pisces”.
Sunday: Geometry lesson in the skies: triangles. Mars is about two and a half fists held upright and at arms length above the south-southwest horizon at 6 a.m. Mars is the right hand point of the triangle. Antares is the bright object about one fist to the lower left of Mars. Saturn is about a fist and a half to the left of Mars. Mars is about twice as bright as Saturn and Saturn is about twice as bright as Antares.
Monday: Tonight is a great night to show yourself that the Moon changes its position throughout the night. When the Sun sets, Jupiter is to the upper left of the Moon low in the eastern sky. See how many fingers you can fit between the Moon and Jupiter. Try it again at midnight and at 6 a.m., just before the pair sets. You should notice the two getting farther apart in the sky. That's because the Moon is close enough to the Earth that its actual motion affects where we see it in the sky. The distant stars also move but they are so far away, it can take many centuries to detect their motion.
Bonus activity: try to spot Jupiter just to the left of the Moon even before the Sun sets.
Tuesday: The Milky Way is pretty easy to spot on the early spring sky. Just look up. Everything you see in the sky, including that bird that just startled you, is in the Milky Way. But, even the path of densely packed stars in the plane of our galaxy that look like a river of milk is easy to find. Look due south at 9 p.m. Follow the fuzzy path just to the left of the bright star Sirius two fists held upright and at arm’s length above the horizon, to the right of the bright star Procyon four and a half fists above the southwest horizon, through Capella five fists above the west horizon, through W-shaped Cassiopeia, and down to due north.
Wednesday: Astronomers are often fascinated with large objects. Planets that could fit 1000 Earths (Jupiter). Stars that would fill up the entire inner Solar System (Betelgeuse). Galaxies with 400 billion stars (Milky Way). But what about the smallest objects? One of the smallest stars is Centauri, the closest known star other than our Sun. It is about 12% of the mass of the Sun. The smallest theoretically possible star would be about 7.5% of the mass of the Sun. Any smaller and it could not support fusion reactions. For more on small stars, go to http://goo.gl/EHBdOX.
Thursday: Orion is getting lower and lower in the nighttime sky. Its second brightest star, Betelgeuse, is only two fists above the west-southwest horizon at 11 p.m.
Friday: If you want to put somebody off, tell her or him to wait until Deneb sets. At Ellensburg’s latitude of 47 degrees, Deneb is a circumpolar star meaning it never goes below the horizon. At 10:22 tonight, it will be as close as it gets to the horizon, about two degrees above due north. Watch it reach this due north position about 4 minutes earlier each night.
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.