Desert Studies: Overview of the Desert Night Sky
Are you aware that on any given night you can view approximately forty percent of the sky? That is, if you want to stay awake from sunset to sunrise. Most of us, however, are content with the night sky from just after sunset until nine or ten p.m. at the most. At least we on the desert can see the night sky. People in urban areas have to contend with lights “washing out” the night sky. Let’s explore some areas, and we’ll complete the survey next month.
Planet Earth requires twelve months and 365 1/4 days to orbit the Sun. We call this a year, although technically it’s a “solar (for Sun) year.” Earth’s axis is inclined 23 1/2 degrees to the plane of the orbit and this causes our seasons. On or about December 21 is the winter solstice (or the summer solstice, if you’re in the southern hemisphere). At this point the Sun is lowest in its arc across the sky and the days are shortest (longest in the south). On March 21 we reach one of the two equinoxes, which means “equal night.” The first day of spring and autumn. On or about June 21 is the summer solstice (winter in the south), and the Sun is highest in the sky.
The Moon requires about 29 1/2 days from new Moon to new Moon. The Moon is also inclined to the orbit of the Earth and Sun. This causes our Moon to be higher in the sky during the winter months and lower in the summer (and the opposite in the south). At the equinoxes, the Moon is halfway from one extreme to the other. Astronomers call these “eclipse season.”
What is an eclipse? We have two on Earth – the solar (or Sun) eclipse, when the Moon covers the Sun, and the lunar eclipse, where the Earth passes between the Sun and Moon and casts its shadow over the Moon. A solar eclipse can only occur at new Moon phase and a lunar eclipse only at full Moon. We have a total eclipse of the Moon on the night of February 20 and a partial eclipse on the Sun on August 1.
Ancient civilizations recognized five planets in our sky. The Greeks called them planets (for “wanderers”). The fire are (in order from the Sun) Mercury, Venus, Mars, Jupiter and Saturn. Neptune and Uranus are too distant and faint to be easily observed, and Pluto is no longer considered a planet. Mercury and Venus are “inferior” planets (closer to the Sun than Earth) and are only visible in fairly close proximity to the Sun. Mercury is elusive and hard to find. Venus is easier and is currently a morning “star” – not a star at all, in fact. It will be conspicuous in the morning until late February and then will be too close to the Sun to easily see.
Mars, Jupiter, and Saturn (and Neptune and Uranus) are “superior” planets, further out from the Sun than Earth. Mars and Saturn are currently evening “stars,” and visible most of the night. Mars is the reddish planet in Taurus, the bull. Saturn is in Leo, the lion, and its conspicuous rings are almost edge on this year. Jupiter is a morning “star” until late this year.
We will consider stars, constellations, and “asterisms” next month. Have fun observing and don’t get frost-nipped!