Wednesday, March 14, 2018
The Ellensburg WA sky for the week of 3/17/18
Saturday: Ask someone which day in March has the same duration day and night. Go ahead, ask someone. Why are you still reading this? I can wait. If that person said the first day of spring, they are wrong. Today, three days before the first day of spring, is the date in which day and night are closest in duration. There are two main reasons for this. First, the atmosphere acts like a lens, bending light from the Sun above the horizon when the Sun is actually below the horizon. This makes the Sun appear to rise before it actually rises and appear to set after is actually sets. Second, spring starts when the center of the Sun passes through the point called the vernal equinox. But, the Sun is not a point. The upper edge of the Sun rises about a minute before the center of the Sun and the lower edge sets a minute after the center of the Sun. Thus, even if we didn’t have an atmosphere that bends the sunlight, daytime on the first day of spring would still be longer than 12 hours.
Sunday: The Moon, Venus, and Mercury make a small triangle a little less than a fist held upright and at arm's length above due west at 7:45 p.m. Bright Venus is at the apex of the triangle and Mercury is at the upper right.
Monday: 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.
Tuesday: 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 9:15 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 northern and southern celestial hemispheres (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.
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”.
Wednesday: At 6 a.m., Saturn and Mars are both one and a half fists above the south-southeast horizon.
Thursday: Jupiter's atmospheric winds are much deeper and longer lasting than those on Earth, according to data from NASA's Juno mission. This mission has taken exceptionally close and detailed images of Jupiter, including a "family" of nine cyclones near the north pole. Even Jupiter's gravity is pattern is mush stranger than originally thought. For more information about these findings, as well as breathtaking images, go to https://goo.gl/u1ve1w. For more information about Jupiter, stay up until midnight and look just above the east-southeast horizon. Or get up at 6:30 a.m. and look two fists above the south-southwest horizon.
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 https://nightsky.jpl.nasa.gov/planner.cfm.