Tuesday, March 12, 2013
The Ellensburg sky for the week of 3/16/13
Saturday: Has there ever been life on Mars? Astronomers don’t know. But the Mars Curiosity Rover just drilled up some strong evidence that Mars was hospitable to life in the past. The first drilling assignment for Curiosity found clay-like minerals that form in the presence of water. Moreover, the water probably had a nearly neutral pH. According to project scientist John Grotzinger, “if this water was around and you had been on the planet, you would have been able to drink it.” For more information, go to http://goo.gl/S2hRn.
Sunday: 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.
While you are thinking about this, go outside at 8 p.m. and find the moon in the southwest sky. Jupiter is about two finger widths to the upper right of the moon and the bright star Aldebaran is about a half a fist to the lower left of the moon. Watch over the next four hours as the moon slowly moves above the line between Jupiter and Aldebaran. The overall motion of the three objects toward the western horizon is due to the rotation of the Earth. But since the moon orbits the earth, its actual motion can be detected. It is one of the few objects that we can see move in the sky over a matter of hours.
Monday: Saturn is one fist above the southeast horizon at midnight. By 6 a.m., it is all the way over into the southwestern sky, nearly two and a half fists above the horizon.
Tuesday: Arcturus is three fists above the east horizon at 11 p.m.
Wednesday: 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 3:02 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”.
Thursday: So far this week, I have written about Saturn, Mars, and Jupiter. Do you even care about these planets or does another planet really catch your fancy? If you’d like to know what most people’s favorite planet is, go to http://www.pbs.org/wgbh/nova/pluto/favorite.html and click on “Launch Interactive”. The public TV special called “The Pluto Files” has set up a website in which astronomers give a 30-second pitch for why a certain planet is their favorite. After listening to the pitch, you may vote for your favorite planet. Of course, you may also do what most people do for political elections: vote for the candidate with the best name or the one with the most interesting campaign slogan. So whether you carefully consider each planet or simply “Swoon for Neptune”, “Jump for Jupiter”, or “Pick Uranus”, go to “The Pluto Files” and vote. Saturn will be holding a campaign rally tonight at 11 p.m., nearly two fists above the southeast horizon.
Friday: The bright star Vega is about one fist above due northeast at midnight.
The positional information in this column about stars and planets is typically accurate for the entire week.