For years, I’ve glanced up in the north at this time of year and spied the two stars marked on today’s chart, Rastaban and Eltanin in the constellation Draco. They’re noticeable because they’re relatively bright and so near each other. There’s always that split-second when I ask myself with some excitement what two stars are those?
It’s then that my eyes drift to blue-white Vega nearby . . . and I know, by Vega’s nearness, that they are Rastaban and Eltanin in the Dragon’s Head.
In other words – because the stars stay fixed relative to each other – Vega is always near these stars. Vega, by the way, lodges at the apex of the Summer Triangle, a famous pattern consisting of three bright stars in three separate constellations, also prominent at this time of year.
Speaking of Rastaban and Eltanin, one of you asked, What are constellations?
The answer is that they’re just patterns of stars on the sky’s dome. The Greeks and Romans, for example, named them for their gods and goddesses, and also for many sorts of animals. In the 20th century, the International Astronomical Union (IAU) formalized the names and boundaries of the constellations. Now every star in the sky belongs to one or another constellation.
The stars within constellations aren’t connected, except in the mind’s eye of stargazers. The stars in general lie at vastly different distances from Earth. It’s by finding juxtaposed patterns on the sky’s dome that you’ll come to know the constellations – much as I identify Rastaban and Eltanin at this time of year by looking for the star Vega.
From tropical and subtropical latitudes in the Southern Hemisphere, the stars Rastaban and Eltanin shine quite low in the northern sky (below Vega). In either hemisphere, at all time zones, the Dragon’s eyes climb highest up in the sky around 1 a.m. (2 a.m. daylight-saving time) in early June, 11 p.m. (midnight daylight-saving time) in early July and 9 p.m. (10 p.m. daylight-saving time) in early August. But from temperate latitudes in the Southern Hemisphere (southern Australia and New Zealand), the Dragon’s eyes never climb above your horizon but you can catch the star Vega way low in your northern sky.
By the way, South America has it over North America for spotting the close pairing of the waning crescent moon with Mars tomorrow morning (June 7, 2013). Start your search at least 45 minutes before sunrise. If you have them, bring along binoculars. At more easterly longitudes (South Africa, Asia, Indonesia, Australia and New Zealand), look for Mars a short ways below the moon.
Although northerly latitudes are at a big disadvantage when it comes to tomorrow’s paring of the moon and Mars, people at mid-northern latitudes get to view the Dragon’s eyes all night long!