Star
For further reference: A light year is the distance travelled by light in a vacuum in one year (approximately 9,460,730,472,580.8 kilometers or 5,878,625,373,183.6 miles). In this article, distances will be in light years unless otherwise specified.
Stars viewed from the Hubble Space Telescope. Retrieved from the U.S. Public Domain.
A star is an astronomical object that consists of a sphere of luminous plasma held together by its own gravity. The Sun is the closest star to Earth, but numerous others are visible to the naked eye from Earth during the night, appearing as fixed, luminous points. However, although thousands of stars can be viewed from Earth, most of the stars in the universe, including all stars outside our galaxy, are invisible even with the most powerful telescopes.[1][2][3]
For the majority of the life of an average star, thermonuclear fusion of hydrogen and helium occurs within the star's core, releasing energy that transverses the outer layers of the star and radiates into outer space, causing the star to shine and emit various types of electromagnetic radiation. During a star's lifetime, almost all of the 92 naturally occurring elements are produced within the star by stellar nucleosynthesis and, for high-mass stars, by supernova nucleosynthesis when the star explodes.[1]
Contents
Astral Measurement
Although astral parameters can be expressed using SI units, it is most convenient to represent characteristics of stars, including mass, luminosity, and radii, based upon solar units, which are based upon characteristics of the Sun. In 2015, the International Astronomical Union defined the set of nominal solar values, which can be used to describe astral parameters:[1]
- nominal solar luminosity: \(L_{\bigodot} = 3.828 \times 10^{26} \text{ Watts}\)
- nominal solar radius: \(R_{\bigodot} = 6.957 \times 10^8 \text{ meters} = 6.957 \times 10^5 \text{ kilometers}\)
- nominal solar mass: \(GM_{\bigodot} = 1.3271244 \times 10^{20}\text{ m}^3\text{/s}^{2}. \)
As described by Everipedia,[1]
Large lengths, such as the radius of a giant star or the semi-major axis of a binary star system, are often expressed in terms of the astronomical unit, approximately equal to the mean distance between Earth and the Sun (150 million km or approximately 93 million miles). In 2012, the IAU defined the astronomical constant to be an exact length in meters: 149,597,870,700 meters.
Stars within the Universe
Astronomical Objects Within the Observable Universe (approximate):
There are approximately
- 10 million superclusters
- 25 billion galaxy groups
- 350 billion large galaxies
- 7 trillion dwarf galaxies
- and 30 sextillion (30 billion trillion) stars
within the universe.[4]
\(\)
Closest Stars to the Solar System:[5][6][7]
| Star Name(s) | Distance from Earth | Star Name(s) | Distance from Earth | ||
| 1 | Proxima Centauri | 4.24 light years | 21 | DX Cancri | 11.83 light years |
| 2 | α Centauri A and α Centauri B | 4.37 light years | 22 | Tau Ceti | 11.89 light years |
| 3 | Barnard's Star | 5.96 light years | 23 | GJ 1061 | 11.99 light years |
| 4 | Luhman 16A and Luhman 16B | 6.59 light years | 24 | WISE 0350−5658 | 12.07 light years |
| 5 | WISE 0855−0714 | 7.27 light years | 25 | YZ Ceti | 12.13 light years |
| 6 | Lalande 21185 | 8.29 light years | 26 | Luyten's Star | 12.37 light years |
| 7 | Sirius A and Sirius B | 8.58 light years | 27 | Teegarden's Star | 12.51 light years |
| 8\(\hspace{5mm}\) | Luyten 726-8 A and Luyten 726-8 B\(\hspace{10mm}\) | 8.73 light years\(\hspace{30mm}\) | 28\(\hspace{5mm}\) | SCR 1845-6357 A/SCR 1845-6357 B\(\hspace{10mm}\) | 12.57 light years |
| 9 | Ross 154 | 9.68 light years | 29 | Kpteyn's Star | 12.78 light years |
| 10 | Ross 248 | 10.32 light years | 30 | Lacaille 8760 | 12.87 light years |
| 11 | Epsilon Eridani | 10.52 light years | 31 | WISE 0535−7500 | 13.00 light years |
| 12 | Lacaille 9352 | 10.74 light years | 32 | Kruger 60 A/Kruger 60 B | 13.15 light years |
| 13 | Ross 128 | 10.92 light years | 33 | DEN 1048-3956 | 13.17 light years |
| 14 | WISE 1506+7027 | 11.01 light years | 34 | UGPS 0722-05 | 13.26 light years |
| 15 | EZ Aquarii A/EZ Aquarii B/EZ Aquarii C | 11.27 light years | 35 | Ross 614A/Ross 614B | 13.35 light years |
| 16 | Procyon A/Procyon B | 11.40(2) light years | 36 | Wolf 1061 | 13.82 light years |
| 17 | 61 Cygni A/61 Cygni B | 11.40(3) light years | 37 | Van Maanen's Star | 14.07 light years |
| 18 | Struve 2398 A/Struve 2398 B | 11.53 light years | 38 | Gliese 1 | 14.23 light years |
| 19 | Groombridge 34 A/Groombridge 34 B | 11.62 light years | 39 | Wolf 424 A/Wolf 424 B | 14.31 light years |
| 20 | Epsilon Indi A/Ba/Bb | 11.82 light years | 40 | 2MASS J154043.42-510135.7 | 14.40 light years |
Stellar Classification and Evolution
Classification of Stars
Stellar Formation within Nebulas
Mass-dependent Evolutionary Stages
Characteristics and Structure of Stars
The Hertzsprung-Russell Diagram
The Hertzsprung-Russell diagram and the specific regions where certain star types (e.g. giants, supergiants, etc.) are found. Retrieved from the U.S. Public Domain.
Various color spectrums relating to certain stars (labeled). Retrieved from the U.S. Public Domain.
The Hertzsprung-Russell diagram is a 2-dimensional scatterplot showing the relationship between stars' absolute magnitudes (also known as luminosities or brightnesses) and their effective temperatures (which correlates to the stars' colors). The diagram was created independently by Ejnar Hertzsprung and Henry Norris Russell (hence the name "The Hertzsprung-Russell diagram") in 1910 and represented a major step towards the complete understanding of stellar evolution.[6][8]
The horizontal axis of the Hertzsprung-Russell diagram represents a star's temperature, which directly correlates to the spectral type or spectral class (color) of the star. Astronomers recognize 7 different spectral types or temperature divisions of stars, which are also used in the Hertzsprung-Russell diagram:[9]
| Spectral Type | Color | Surface Temperature | Mass (Sun = 1) | Luminosity (Sun = 1) | Examples |
| O | Blue | Over 25,000 K | 60 | 1,400,000 | 10 Lacertra |
| B | Blue | 11,000 - 25,000 K | 18 | 20,000 | Rigel |
| A | Blue | 7,500 - 11,000 K | 3.2 | 80 | Sirius |
| F | White | 6,000 - 7,500 K | 1.7 | 6 | Canopus |
| G | Yellow | 5,000 - 6,000 K | 1.1 | 1.2 | Sun, Capella |
| K | Orange | 3,500 - 5,000 K | 0.8 | 0.4 | Arcturus |
| M | Red | Under 3,500 K | 0.3 | 0.04 | Antares |
References
- Everipedia, E. Star. Retrieved April 7, 2018, from www.everipedia.org/wiki/Star/
- The Gale Group, I. Star - UXL Encyclopedia of Science, Encyclopedia.com. Retrieved from www.encyclopedia.com/science-and-technology/astronomy-and-space-exploration/astronomy-general/star
- Fernie, J. Star - Encyclopædia Britannica. Retrieved from www.britannica.com/science/star-astronomy
- Atlas of the Universe, I. The Universe within 14 Billion Light Years - The Visible Universe. Retrieved from www.atlasoftheuniverse.com/universe.html
- Tate, K. The Nearest Stars to Earth (Infographic) - Space.com. Retrieved from www.space.com/18964-the-nearest-stars-to-earth-infographic.html
- University of Wisconsin-Madison, I. The Closest Stars to the Earth - The 26 Nearest Stars. Retrieved from www.astro.wisc.edu/~dolan/constellations/extra/nearest.html
- Atlas of the Universe, I. The Universe within 12.5 Light Years - The Nearest Stars. Retrieved from www.atlasoftheuniverse.com/12lys.html
- Wikipedia, I. Hertzsprung-Russell diagram - Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Hertzsprung–Russell_diagram
- Enchanted Learning, I. Star Classification - Zoom Astronomy. Retrieved from http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml