Post
by Ann » Sun Sep 04, 2011 7:36 am
Comets are beautiful, and this APOD is beautiful.
The comet is now in the small constellation Sagitta, the Arrow, which is an interesting constellation. It is in the middle of the dust lane of the Milky Way, and you can expect interesting things to go on somewhere inside it. Things do happen, too, but generally "deep in the dust" of Sagitta and not on the "surface" of it.
All the bright stars of Sagitta, Alpha, Beta, Gamma and Delta are massive stars at respectable distances of 260 to 600 light-years, and they all shine between 200 and over 900 times the luminosity of the Sun. No puny little "Siriuses" here, which "only" emits 23 solar luminosities from a distance of barely 9 light-years!
Comet Garradd looks as if it has passed right over the face of M71, because its tail seem to point right at the globular. (But of course, a comet's tail does not so much point in the opposite direction of the comet's movement as it points in the opposite direction of the Sun.)
(By the way, what a pair: the globular cluster is about 12,000 light years away and the comet can't be more than, at most, a few light hours away. A light-half hour seems more probable to me.)
Note a line of stars that seems to curve away from the comet at lower right. The brightest of these stars is majestic O type star 9 Sagittae, which is so far away that Hipparcos couldn't measure a parallax for it. To me 9 Sagittae is the symbol of the amazing current goings-on in this deceptively quiet constellation, while the globular cluster is a reminder of glorious star formation events in the past. And the comet is a reminder of the liveliness of our own solar system, which is still alive and kicking after four and a half billion years. Yet like the constellation Sagitta, our solar system looks quiet and orderly, too, and in our case the reassuring quietness is no deception.
Ann
Color Commentator