Delta2 Lyrae is the brightest member of (to me, at least) one of the most beautiful open clusters in the summer sky, Stephenson 1. Close by is the 5th magnitude Delta1 Lyrae, once thought to be paired with Delta2 in a binary system, but now known to be simply a fellow member of the open cluster. (Interestingly enough, at least 2 other members of the cluster are binary companions of Delta2, but they are both 10th magnitude stars, and not so easy to distinguish amongst all the clutter. Stephenson 1 consists of perhaps 33 stars in all, spans a whopping 38 light years across, and is about 900 light years distant from us.
I have a particular fondness for Stephenson 1, because eons ago when I was a rank beginner in amateur astronomy, like so many other newbies I gravitated towards the bright and splashy objects out there, and this cluster was not only one of the easiest to find, it was also among the most visually appealing. (It still is.) In addition to containing stars of greatly differing magnitudes splattered across the field of view, its members span the visible spectrum in color. So in one field of view, you can enjoy red, blue, yellow, and pure white stars sprinkled in an alluring array - downright gorgeous. Its proximity to brilliant Vega, the Ring Nebula, and the Double Double (Epsilon Lyrae) are added bonuses. So it's no wonder that over the years I've returned to this unappreciated gem again and again. (I recommend using a widefield eyepiece for maximum effect.)
Delta2 Lyrae is quite the giant. Were it to replace the Sun in our own Solar System, it would swallow up the Earth! It's that big. It pours out more than 10,000 times the energy of our own Sun, and weighs in at a bit more than 7 solar masses. But its greater mass has caused it to speed through its life cycle, leaving the Main Sequence in a relatively short time to bloat up into a red giant. It is thought to have an inert core of carbon and oxygen (having run through its available supply of hydrogen), with all the action now taking place in two concentric shells outside the once active core. In the first shell, helium is being fused into carbon. In the outer shell, the star's remaining hydrogen is still being fused into helium. This is a very weird (and short lived) period in a star's life cycle. When enough helium has built up in the outer shell, it periodically "dumps" it onto the inner shell, causing a phenomenon known as a helium shell flash. This causes a shell of gas to be expelled from the star. Repeated flashes can result in a star being surrounded by a whole series of such shells, extending outward for truly colossal distances.
So don't just admire the (undeniable) beauty of Delta2 Lyrae. Try to imagine all the wild stuff going on within it.
I just got back from tonight's star party, at which I spent maybe a good 20 minutes (and maybe more) with my scope fixed on Stephenson 1. I started observing as soon as Vega popped into view not long after sunset. At first, all I could see was the single star of Delta 2 Lyrae. After a few minutes, there were one, maybe two other stars in the field of view. 15 minutes later, there were stars sprinkled all over the place. But look up naked eye? Only Vega was visible - everything else required the light gathering power of my telescope. It was an excellent tutorial in why we have these things in the first place.
ReplyDeleteAt that point, I moved on to other targets, but I did come back for another look once the sky was fully dark. Wow! The cluster was now clearly discernible amidst the background stars, and as colorful as ever.
Unfortunately, the light polluted skies of suburban Howard County do not allow one the full effect one gets by observing Stephenson 1 (or anything else, for that matter) under truly dark skies. Be sure and put it on your list of "must sees" when you get the chance to be under such.