Thursday, March 12, 2015
The Ellensburg WA sky for the week of 3/14/15
Saturday: Has there ever been life on Mars? Astronomers don’t know. But the Mars Curiosity Rover has been digging up some strong evidence that Mars was hospitable to life in the past. At the end of 2012, the first drilling assignment for Curiosity found clay-like minerals that form in the presence of water. In December 2013, scientists announced the strongest evidence yet for an ancient fresh-water lake in Gale Crater. Planetary geologist John Grotzinger said that Earth microbes could have thrived in this lake if they were placed there. Earlier this month, astronomers at the European Southern Observatory’s Very Large Telescope in Chile found evidence that Mars was once had an ocean that held more water than the Arctic Ocean and covered a greater percentage of Mars’ surface than the Atlantic Ocean does on Earth. In brief, they came to this conclusion after analyzing the chemical signature of light that passes through the Martian atmosphere. For more information about this ancient ocean and the method of discovery, go to http://goo.gl/bOqD4U. Mars is about one fist held upright and at arm’s length above the west horizon at 8 p.m., about a fist below the bright planet Venus. By the way, the name of the observatory in Chile really is Very Large Telescope. See for yourself at http://www.eso.org/paranal.
Sunday: Jupiter is five and a half fists above the southeast horizon at 9 p.m.
Monday: Vega is a half a fist above the northeast horizon at 11 p.m.
Tuesday: 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. 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.
Wednesday: 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.
Thursday: Saturn is about two and a half fists above the southern horizon at 6 a.m.
Friday: 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 3:45 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”.
Those of you lucky enough to be sailing in the North Atlantic or Arctic Oceans this morning will witness a total solar eclipse. Just east of Iceland, the eclipse happens at about 9:45 a.m. Europe and North Africa will see varying degrees of a partial solar eclipse.
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.