by Ann » Thu Jan 30, 2020 6:15 am
Nice picture!
- Double Cluster and comet.png (285.36 KiB) Viewed 2389 times
Double Cluster in Perseus (at 7,000 light-years) and comet
(at a number of light-hours). Photo: Rolando Ligustri.
As a diehard lover of blue things, I would of courser have liked the Double Cluster to look a little bluer, especially since there are many intrinsically blue stars there. But I can't complain. The Double Cluster is 7,000 light-years away from us, and the stars are quite reddened. The brightest stars in cluster NGC 869 (right) belong to spectral classes B2Ia and B3Ia. Their intrinsic color index
should be something like -0.15, but they are so reddened that their color index (as seen from our location) is about +0.50 instead.
I posted the beautiful picture of the Alpha Persei Cluster because I wanted to give you an idea of how reddened the stars of the Double Cluster really are. While the Double Cluster is some 7,000 light-years distant, the Alpha Persei Cluster appears to be located between 500 and 600 light-years away. The Alpha Persei Cluster is barely reddened at all, and its brightest star, Mirphak, has a spectral type of F5Ib and a color index of +0.48. In other words, the hot B-type supergiants of NGC 869 of the Double Cluster appear to be exactly the same color as mid-F-type lesser supergiant Mirphak. All because of the reddening caused by 7,000 light-years of an extremely tenuous "soup" of dust particles between ourselves and the Double Cluster.
Illustration: Michael Hague.
There appears to be virtually no dust between ourselves and the Alpha Persei Cluster, so I guess that the old woman tossed up in a blanket has already been up there, far higher than seventeen times as high as the Moon, and swept the nearest 500 light-years in the direction of Alpha Perseus free of cobwebs of the sky!
I admire MarioSS' image, and I think he captured the colors of the stars of the Alpha Persei Cluster perfectly. Note the whiteness of Alpha Persei (center) and the blue-tinted Delta Persei near bottom of the image.
The comet seen in the APOD displays a properly green coma and what looks like a short yellowish dust tail.
Ann
Nice picture! :D
[float=left][attachment=0]Double Cluster and comet.png[/attachment][c][size=85]Double Cluster in Perseus (at 7,000 light-years) and comet
(at a number of light-hours). Photo: Rolando Ligustri.[/size][/c][/float] [float=right][img2]https://2.img-dpreview.com/files/p/TS560x560~forums/63381280/2c92ec2eaf274d1491f4f23a3ccdcdf5[/img2][c][size=85]Alpha Persei Cluster at ~500 light-years.
[url=https://www.dpreview.com/forums/thread/4447752]Photo: MarioSS.[/url][/size][/c][/float]
As a diehard lover of blue things, I would of courser have liked the Double Cluster to look a little bluer, especially since there are many intrinsically blue stars there. But I can't complain. The Double Cluster is 7,000 light-years away from us, and the stars are quite reddened. The brightest stars in cluster NGC 869 (right) belong to spectral classes B2Ia and B3Ia. Their intrinsic color index [i]should[/i] be something like -0.15, but they are so reddened that their color index (as seen from our location) is about +0.50 instead.
I posted the beautiful picture of the Alpha Persei Cluster because I wanted to give you an idea of how reddened the stars of the Double Cluster really are. While the Double Cluster is some 7,000 light-years distant, the Alpha Persei Cluster appears to be located between 500 and 600 light-years away. The Alpha Persei Cluster is barely reddened at all, and its brightest star, Mirphak, has a spectral type of F5Ib and a color index of +0.48. In other words, the hot B-type supergiants of NGC 869 of the Double Cluster appear to be exactly the same color as mid-F-type lesser supergiant Mirphak. All because of the reddening caused by 7,000 light-years of an extremely tenuous "soup" of dust particles between ourselves and the Double Cluster.
[float=left][img2]https://i.pinimg.com/originals/3f/d0/9a/3fd09a9fcfb9577da8947145ca147c13.jpg[/img2][c][size=85]Illustration: Michael Hague.[/size][/c][/float]
There appears to be virtually no dust between ourselves and the Alpha Persei Cluster, so I guess that the old woman tossed up in a blanket has already been up there, far higher than seventeen times as high as the Moon, and swept the nearest 500 light-years in the direction of Alpha Perseus free of cobwebs of the sky!
I admire MarioSS' image, and I think he captured the colors of the stars of the Alpha Persei Cluster perfectly. Note the whiteness of Alpha Persei (center) and the blue-tinted Delta Persei near bottom of the image.
The comet seen in the APOD displays a properly green coma and what looks like a short yellowish dust tail.
Ann