Wednesday, March 15, 2017

The Ellensburg WA sky for the week of 3/18/17

Saturday: The elusive Mercury is a half a fist held upright and at arms length above due west at 7:40 p.m. The much brighter Venus is about one fist to the upper right of Mercury.

Sunday: Mars is two fists above due southwest at 8:30 p.m.

Monday: 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 3:30 a.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”.

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 above the horizon, to the right of the bright star Procyon four and a half fists above the south horizon, through Capella six fists above the west horizon, through W-shaped Cassiopeia three fists above the northwest horizon, and down to due north where the bright star Deneb sits just above the horizon.

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 Proxima Centauri, the closest known star other than our Sun. It is about 12% of the mass of the Sun. Last year, astronomers even announced the discovery of an Earth-sized planet orbiting Proxima Centauri indicating that even very small starts can have planets. 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

Thursday: Jupiter is one fist above the east-southeast horizon at 10 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 9:32 p.m., 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

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