Stars Sun: As a Star
article: Sun: As a Star
Introduction
Thanks to our proximity, we know quite a lot about our sun. In the most general terms, as for most other stars, it can be characterized by a few general parameters as follows:
Physical
| Mass | 1.989 x 10^33 grams |
| Age | 4.57 billion years |
| Central temperature | 15.6 million K (28,000,000º F) |
| Equatorial Radius | 695,990 km |
| Central density | 150 g/cm3 (8 × Gold density) |
| Equatorial Rotation Speed | 1.9 km/sec |
| Hydrogen Mass Fraction (X) | 0.7491 |
| Helium Mass Fraction (Y) | 0.2377 |
| Heavy Element Mass Fraction (Z) | 0.0133 |
| Surface Density | 0.000000207 grams/cm3 (0.00016 Earth air density) |
Our sun as seen from the SOHO satellite.
Spectroscopic
| Spectral Class | G2 IV |
| Luminosity | 3.826 x 10^33 ergs/sec |
| Solar Constant at Earth outside atmosphere | 1.3533 million ergs/cm2/sec |
| Surface Temperature | 5770 K (9,930 F) |
| Absolute Magnitude (Ultraviolet, Blue, Visual) | +5.51, +5.41, + 4.79 |
| Photometric Color (Apparent B-V magnitudes) | +0.62 |
| Apparent Magnitude (Ultraviolet, Blue, Visual) | -26.06, -26.16, -26.77 |
Solar Analog Stars
The sun has planets and a single known planet with a biosphere. Some astronomers feel that searching for stars that are as similar to the sun as possible, may increase the likelyhood of finding a planetary system with an alien biosphere...all other factors being equal (which they probably are not at the planetary scale!)
The star 18 Scorpii (HD 146233, HR 6060) is currently regarded as the nearest solar twin. Hall and Lockwood [2000] have been observing this star since 1995. The Calcium K-line data show a pronounced rise that suggests 18 Sco has a well-defined activity cycle that reached an apparent minimum in 1998 and showed a rapid rise through the most recent of the 2000 data. Comparison with contemporaneous solar data, obtained with the same instrument, suggested that the activity cycle of 18 Sco may be of greater amplitude than the Sun's and that its overall chromospheric activity level is noticeably greater than the Sun's. Other solar analogues include 37 Geminorum, 51 Pegasi, Beta Canum Venaticorum, and HD 98618.
Images of the Sun
The sun in X-rays.
This illustration shows the approximate size of Earth compared to the Sun. The giant coronal mass ejection in the image blasted off the Sun in October 2003. The image was taken by the international SOHO spacecraft. (Source: SOHO-NASA/ESA.)
"Solstice Celebration"
Taken from the EIT instrument onboard the space-based SOHO observatory, this image is a false-color composite of three images all made in extreme ultraviolet light. Each individual image highlights a different temperature regime in the upper solar atmosphere and was assigned a specific color; red at 2 million, green at 1.5 million, and blue at 1 million degrees C. The combined image shows bright active regions strewn across the solar disk, which would otherwise appear as dark groups of sunspots in visible light images, along with some magnificent plasma loops and an immense prominence at the right hand solar limb.
(Source: Astronomy Photo of the Day, June 20, 2004. Credit: SOHO - EIT Consortium, ESA, NASA)
References
- Solar System Abundances and Condensation Temperatures of the Elements, K. Lodders, ApJ 591 (2003) 1220–1247.
- Solar Analog Stars - Jeffrey C. Hall and G. W. Lockwood, 2000, The Astrophysical Journal, v. 545, p. L43–L45
External Links
- Solar Science: Sun Facts, New/Updated Pages, Recent Solar Physics News & Web Links – Solar Physics, Marshall Space Flight Center, NASA.
Preview Image
- "Solstice Celebration" - From the EIT instrument onboard the space-based SOHO observatory, the tantalizing picture is a false-color composite of three images all made in extreme ultraviolet light. View the full-size image. (Source: Astronomy Photo of the Day, June 20, 2004. Credit: SOHO - EIT Consortium, ESA, NASA)
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Sun: As a Star." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published November 26, 2007].
<http://www.cosmosportal.org/articles/view/138454/>
Comments
There are no comments.