Weekend sky watch: Polaris and dippers
Posted June 15, 2012
One of the first patterns many learn to find in the night sky is the Big Dipper. This weekend look for it after sunset to the north. This time of year, it looks to be tipped on end, emptying its contents. If you look again before sunrise, the Big Dipper will have rotated counter-clockwise until the bowl appears level.
The Big Dipper consists of brighter stars so it's visible even in light-polluted areas. The stars at the end of the Big Dipper (Merak and Dubhe) are known as the pointer stars. You can follow the line they create to the right to find Polaris, the pole star, over 400 light years from Earth.
Polaris, the pole star appears to stay relatively still as the other stars rotate throughout the night.
Photographers create star trails, beautiful images of swirling stars, by leaving the camera shutter open for several minutes at a time. At the center of each star trail photo is Polaris, barely leaving a smudge.
Polaris forms the tip of the handle of the Little Dipper. From Polaris, follow the two dim stars in the handle up to the bowl of the dipper. That bowl has two stars that you'll probably be able to make out (Kocab and Pherkad) and 2 dimmer stars (which have boring numbers instead of traditional Arabic names) which will be visible only in darker rural or suburban skies.
The dippers have been recognized for as long as we've been looking up at the night, but different cultures saw different things.
The indigenous people of Scandinavia saw the stars in the Big Dipper as forming a bow and arrow. Ancient India associated the seven stars with seven rishi or sages. Europeans saw the grouping of stars as a butcher's cleaver or plough. The Navajo saw it as part of a larger constellation forming a man who rotated in the night sky through the summer. Further north, the Inuit saw the Big Dipper as a Caribou.
In modern astronomy, the big and little dippers aren't constellations but are technically asterisms. The Big Dipper is part of the constellation Ursa Major (big bear) and the Little Dipper is part of
Ursa Minor (little bear).
The Big Dipper and Polaris so dominate the night sky that they inspired a seventh-grade student to base his design of his state flag on them. What state flag was based on his creation? Post your answer in the comments, and I will recognize the correct choice next week.
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.