Astronomy Picture of the Day 3-23-03

NASA ^ | 3-23-03 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2003 March 23

Alpha Centauri: The Closest Star System
Credit: 1-Meter Schmidt Telescope, ESO

Explanation: The closest star system to the Sun is the Alpha Centauri system. Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star. The bright stars Alpha Centauri A and B form a close binary as they are separated by only 23 times the Earth- Sun distance - slightly greater than the distance between Uranus and the Sun. In the above picture, the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light. The Alpha Centauri system is not visible in much of the northern hemisphere. Alpha Centauri A, also known as Rigil Kentaurus, is the brightest star in the constellation of Centaurus and is the fourth brightest star in the night sky. Sirius is the brightest even thought it is more than twice as far away. By an exciting coincidence, Alpha Centauri A is the same type of star as our Sun, causing many to speculate that it might contain planets that harbor life.

[petuniasevan]

Unfortunately it's not visible from much of the Northern Hemisphere. US residents will be out of luck unless they live in extreme south Florida or extreme south Texas, or in Hawaii.

Note the difference in brightness between the close binary pair and Proxima.

The Sun And Its Nearest Neighbors	Sun	Alpha Centauri A	Alpha Centauri B	Proxima
Color	Yellow	Yellow	Orange	Red
Spectral type	G2	G2	K1	M5
Temperature	5800 K	5800 K	5300 K	2700 K
Mass	1.00	1.09	0.90	0.1
Radius	1.00	1.2	0.8	0.2
Brightness	1.00	1.54	0.44	0.00006
Distance (light-years)	0.00	4.35	4.35	4.22
Age (billion years)	4.6	5 - 6	5 - 6	~1?

Note that Proxima is not thought to have planets which could harbor life. There are several reasons for this. Some are speculation; others are solid fact. Perhaps the most compelling reason is that it IS a red dwarf. To keep a planet warm enough for liquid water, it would have to orbit Proxima so closely (4 to 9 million miles distant) that it would become tidally locked with one side always facing Proxima. Even if there WERE a narrow habitable zone, there is still a problem with the star. Flares on a red dwarf are just as big as on our own sun. They are proportionately much greater in magnitude in relation to the size of red dwarfs. So a close-in planet could also suffer occasional toastings in all kinds of radiation. All in all, Proxima is not a good place to look for life.

[petuniasevan]

[petuniasevan]

With all the war reporting my attention has been directed to that subject. It took me 3 hours to complete APOD as I kept running back to the TV to watch the Umm-Kasr firefight.

So I apologize in advance if I post late in coming days or weeks.

[firewalk]

Thanks for the ping
and for putting up the thread everyday

[RightWhale]

While it is true that many are trying to keep some of their ordinary routine intact these days, it isn't necessary to keep it all going. Was listening to NPR today and wondering if they broadcast from the same planet we live on. Maybe they inhabit a habitable zone at Alpha Centauri.