I was at work a week or so ago and one of my co-workers asked me about a formation of stars he had been looking at in the night sky and was interested in my identifying it for him.
The particular formation he was asking about is one known as the “Summer Triangle” and is a grouping that I’ve written about many times at this time of year. It has been rising steadily in the eastern sky and is now almost overhead and very observable from our vantage point here in southwest Iowa.
Once you see it you won’t have any problem understanding why astronomers gave it the name they did with three very bright stars forming what appears to be a huge isosceles triangle.
The three alpha stars marking the corner points of the triangle are Deneb (Alpha Cygni) located in the constellation of Cygnus the Swan that is the northern most point. The next star in the triangle and which is the brightest is Vega (Alpha Lyre) in the constellation of Lyra the Lyre. It lies just to the lower right of Deneb. Further down and slightly to the left will be Altair (Alpha Aquilae) in the constellation of Aquila, the Eagle.
As I said, the “Summer Triangle” is a huge isosceles form, or nearly so, and shouldn’t present any problem locating since it can be found in an area of the sky that is fairly uncluttered with other bright stars.
Although each of the three stars appear almost uniform as far as colors are concerned, Vega is actually a blue-white star and shines at us from 27 light years. Deneb, on the other hand, has a yellowish color when viewed through a telescope and estimates place this star at just over 1,500 light years away. It is a gigantic star much, much larger than our own Sun.
Last but certainly not least is Altair in the constellation of the Eagle.
Altair is 10 times as bright as our Sun but it is difficult to see this brilliance from 18 light years away.
Another feature of the “Triangle of Summer” is that one of its members, Vega, once held the position as north star a location that is now occupied by Polaris. Due to the wobbling of Earth on its axis, over a very long period of time the axis points at a different position in space. In just over 13,000 years, Vega will once again become our north star.
Vega has another feature that is not shared by any other star in the heavens. Over a year’s time as Earth rotates, Vega passes almost directly over six capitals around the world … three of them in the United States. The U.S. capitals are District of Columbia, Denver, CO, and Sacramento, CA. The three other major capitals are Lisbon, Portugal, Athens, Greece and Beijing, China.
Some readers may think that the tremendous amount of heat that has been baking southwest Iowa for the past week or so is due to Earth being closer to the Sun at this time of year. Not so!
On Thursday, as Earth moves in its orbit around the Sun, it reaches a position in relation to the Sun known as aphelion. On that date we will be 94.5 million miles away from the Sun, our most distant position
Believe it or not, in January of 2020 in the dead of winter, Earth will reach that point in its orbit known as perihelion when we will be 3.1 million miles closer to the Sun than we are now.
You may ask, “If we are closer to the Sun, why isn’t it hotter”.
It is because at that time of year Earth’s orbital position is tilted in relation to the Sun and, as a result, the major portion of the Sun’s rays strike Earth and are reflected back into space.