by Ann » Thu Jun 28, 2012 7:10 am
I think this is an excellent picture!
The description given by the APOD Robot is very satisfying, but a few things can be added. First, the fact that Alpha Centauri looks so overwhelmingly bright, even though it is the intrinsically faintest of all stars apart from the Sun that look bright and obvious to the naked eye. Fascinatingly, 99% of all naked-eye stars are brighter than the Sun, but 95% of all stars in the Milky Way are fainter than the Sun!
In this Sun-centered view of the universe - sorry about that -
all the white dots making up the constellations represent stars that are intrinsically brighter than the Sun. The rare bright stars in the sky shine so brightly that they are seen over vast distances and dominate the sky, whereas all stars similar to the Sun look faint and insignificant - all of them except the Sun and Alpha Centauri. The Sun is only eight light minutes away, and Alpha Centauri, at four light-years, is the second nearest star to the Earth in the cosmos. What a coincidence that both the Sun and Alpha Centauri are G-type hydrogen-fusing dwarfs of similar brightness!
![Image](http://jumk.de/astronomie/img/alpha-centauri.jpg)
Alpha, Beta and Proxima Centauri. Photo: ESO
The fact that Alpha Centauri is a multiple star is a fact that we don't have say much about here, except that it's a pity that today's excellent APOD isn't wide enough to show Proxima Centauri, the probable third member of the Alpha Centauri system. But this ESO photo shows the glare of the Alpha A+B Centauri system, with the tiny, ultrafaint red dwarf in a very wide orbit around the two main components.
I guess that Proxima Centauri would have showed up in today's APOD if the picture had been wide enough to include it, but the tiny star would have looked insignificant indeed!
In the ESO picture, you can see the clusters NGC 5617 and, faintly, Pismis 19. You can also see cluster Trumpler 22, which is visible in today's APOD below Pismis 19. But in the ESO picture you can't see planetary nebula Hen 2-111 very well, certainly not its outer halo. The supernova remnant which is seen in today's APOD is also invisible in the ESO image. Photographer Marco Lorenzi has used an Ha filter to tease out these fascinating details in the background of Alpha Centauri.
The wonderful deep-sky jewels seen in Marco Lorenzi's image have nothing to do with Alpha Centauri itself. We happen to see the clusters and the remnants of dead stars in the same direction as we see Alpha Centauri. But Alpha Centauri is our next-door neighbour, while the deep-sky wonders belong to the rich treasure trove of the distant Milky Way.
The Milky Way is like a city in the distance, while Alpha Centauri is like a small cottage a few steps away.
Ann
I think this is an excellent picture! :D
The description given by the APOD Robot is very satisfying, but a few things can be added. First, the fact that Alpha Centauri looks so overwhelmingly bright, even though it is the intrinsically faintest of all stars apart from the Sun that look bright and obvious to the naked eye. Fascinatingly, 99% of all naked-eye stars are brighter than the Sun, but 95% of all stars in the Milky Way are fainter than the Sun!
[float=left][img]http://www.indiadaily.com/images/editorial/2656_320.jpg[/img][/float] In this Sun-centered view of the universe - sorry about that - [i]all[/i] the white dots making up the constellations represent stars that are intrinsically brighter than the Sun. The rare bright stars in the sky shine so brightly that they are seen over vast distances and dominate the sky, whereas all stars similar to the Sun look faint and insignificant - all of them except the Sun and Alpha Centauri. The Sun is only eight light minutes away, and Alpha Centauri, at four light-years, is the second nearest star to the Earth in the cosmos. What a coincidence that both the Sun and Alpha Centauri are G-type hydrogen-fusing dwarfs of similar brightness! :shock:
[float=right][img]http://jumk.de/astronomie/img/alpha-centauri.jpg[/img][c][size=80]Alpha, Beta and Proxima Centauri. Photo: ESO[/size][/c][/float]The fact that Alpha Centauri is a multiple star is a fact that we don't have say much about here, except that it's a pity that today's excellent APOD isn't wide enough to show Proxima Centauri, the probable third member of the Alpha Centauri system. But this ESO photo shows the glare of the Alpha A+B Centauri system, with the tiny, ultrafaint red dwarf in a very wide orbit around the two main components.
I guess that Proxima Centauri would have showed up in today's APOD if the picture had been wide enough to include it, but the tiny star would have looked insignificant indeed!
In the ESO picture, you can see the clusters NGC 5617 and, faintly, Pismis 19. You can also see cluster Trumpler 22, which is visible in today's APOD below Pismis 19. But in the ESO picture you can't see planetary nebula Hen 2-111 very well, certainly not its outer halo. The supernova remnant which is seen in today's APOD is also invisible in the ESO image. Photographer Marco Lorenzi has used an Ha filter to tease out these fascinating details in the background of Alpha Centauri.
The wonderful deep-sky jewels seen in Marco Lorenzi's image have nothing to do with Alpha Centauri itself. We happen to see the clusters and the remnants of dead stars in the same direction as we see Alpha Centauri. But Alpha Centauri is our next-door neighbour, while the deep-sky wonders belong to the rich treasure trove of the distant Milky Way.
[url=http://upload.wikimedia.org/wikipedia/en/6/6a/Genting_view.jpg]The Milky Way is like a city in the distance,[/url] while Alpha Centauri is like a small cottage a few steps away.
Ann