The Evening Sky in March 2017
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The Evening Sky in March 2017
Bright planets are low in the east and west at the beginning of the month. Venus (not shown on the chart) might be seen from places with a low western skyline, setting 40 minutes after the Sun at the start of the month. It sets steadily earlier, disappearing by mid-March. Golden Jupiter rises in the east around 9:30 pm at the beginning of the month. By mid-month it is up at dusk. The near-full Moon will be near Jupiter on the 14th and 15th. Less obvious is Mars (not shown), looking like a medium-brightness red star above the western skyline at dusk. It sets about 80 minutes after the sun throughout the month. On March 1st the thin crescent Moon will be level with Mars and above Venus. The Moon is by Mars again on the 30th.
Jupiter is the biggest planet by far. Its mass is greater than all the other planets put together. In a telescope it shows parallel stripes. These are zones of warm and cold clouds, made narrow by Jupiter's rapid rotation. Any telescope shows Jupiter's disk with its four bright 'Galilean' moons lined up on either side. They are roughly the size of our moon. Sometimes one or two moons can be seen in binoculars, looking like faint stars close to the planet. Io, the smallest and closest to Jupiter, has massive volcanoes. The other moons have crusts of ice, some with oceans beneath, around rocky cores. Jupiter is 680 million km from us in March.
Northwest of overhead is Sirius the brightest star in the sky. It is fainter than star-like Venus and Jupiter. Southwest of the zenith is Canopus, the second brightest star. Below Sirius are Rigel and Betelgeuse, the brightest stars in Orion. Between them is a line of three stars: Orion's belt. To southern hemisphere star watchers, the line of three makes the bottom of 'The Pot'. Orion's belt points down and left to a V-shaped pattern of stars. These make the face of Taurus the Bull. The orange star is Aldebaran, Arabic for the eye of the bull. Continuing the line from Orion down and left finds the Pleiades or Matariki star cluster.
Sirius is the brightest star in the sky both because it is relatively close, nine light years* away, and 23 times brighter than the sun. Rigel, above and left of Orion's belt, is a bluish supergiant star, 40 000 times brighter than the sun and much hotter. It is 800 light years away. Orange Betelgeuse, below and right of the line of three, is a red-giant star, cooler than the sun but much bigger and 9000 times brighter. It is 400 light years from us. The handle of "The Pot", or Orion's sword, has the Orion Nebula at its centre; a glowing gas cloud many light-years across and 1300 light years away.
Near the north skyline are Pollux and Castor marking the heads of Gemini the twins. Left of Jupiter is the star cluster Praesepe, marking the shell of Cancer the crab. Praesepe is also called the Beehive cluster, the reason obvious when it is viewed in binoculars. The cluster is some 500 light years from us.
Crux, the Southern Cross, is in the southeast. Below it are Beta and Alpha Centauri, often called 'The Pointers'. Alpha Centauri is the closest naked-eye star, 4.3 light years away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away. Canopus is also a very luminous distant star; 13 000 times brighter than the sun and 300 light years away.
The Milky Way is brightest in the southeast toward Crux. It becomes broader lower in the southeast toward Scorpius. Above Crux the Milky Way can be traced to nearly overhead where it fades. It becomes very faint in the north, right of Orion. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. We are 30,000 light years from the galaxy's centre.
The Clouds of Magellan, LMC and SMC are high in the south sky, easily seen by eye on a dark moonless night. They are two small galaxies about 160 000 and 200 000 light years away.
Saturn rises in the southeast around 1 a.m. at the beginning of the month; at 11 pm by the end. It looks like a lone bright star, cream-coloured, shining with a steady light. Well above it is Scorpius with orange Antares, marking Scorpio's body. A telescope magnifying 20x shows Saturn's rings. The rings are at their most 'open' now. Saturn is 1500 million km away in mid-March. The Moon is below Saturn on the 20th.
*A light year (l.y.)is the distance that light travels in one year: nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes four years to reach the nearest star, Alpha Centauri.