I happened to be out the other evening, and paused with the hope of catching an Aquarid or two streaking crossing the sky. The ‘peak’ of the Delta Aquarid meteor shower began last Wednesday, and will end this Saturday with the shower tapering off through the first week or so of August.
It was about a half hour after sunset, a little early for meteors as the stars were not yet visible, but planets Saturn and Mars in the south were, as was Jupiter, low in the west. Well, one star was out: half way up in south west I spotted Arcturus, the brightest star in the northern sky, and fourth overall.
Arcturus is an orange star estimated to be about the size of our own sun. It shows up early in the evening for a couple of reasons. First, it’s less than 37 light years away, virtually in our back yard, but that’s not the main reason. At 6-8 billion years of age, Arcturus has become a senior, and is burning up the last of the hydrogen fuel in its core at an enormous rate. The result is that it outputs 110 times as much light as the Sun, and 180 times as much energy. From our viewpoint, it’s a nice bright star; in reality, Arcturus is a nuclear furnace turned up to maximum.
It’s also bright enough to be seen in the day time, if you know where to look, so it’s not surprising it appeared in Babylonian star catalogues as early as 1100BC. Its prominence and placement in the summer sky also made it a major guide star for Polynesian sailors, and a major component in the development of star-based navigation.
Although Arcturus’s brightness makes it stand out at night, there are other contenders around, so as the skies darken and more stars come out, you can always find it by following the curve of the Big Dipper’s handle to the left. This location probably also led to its name: the Greek word ‘Arktouros’ translates as ‘Bear Guard’ or ‘Watcher of the Bear’, which would be its neighbour The Big Dipper, officially Ursa Major, or “The Great(er) Bear”, in Latin.
Arcturus is closely tied with our early history and helped open up the world to exploration, as did several other stars and star patterns. In present times, we view stars for pleasure, but to a sailor in a double-hulled canoe in the middle of the Pacific some 3000 years ago, this was the closest thing to GPS he had.
Arcturus will remain prominent from your back yard in the southwest and western sky through September. If you have a chance, try and get out and say thanks.
