Astronomical unit
Astronomical unit
An astronomical unit (AU, au, a.u., or ua) is a unit of length, roughly the distance from Earth to the Sun. It is used primarily for measuring distances within the Solar System or around other stars. The astronomical unit is approximately equal to 149,597,870.7 kilometers (92,955,807.3 miles).
Definition[edit]
The astronomical unit was originally conceived as the average distance between the Earth and the Sun. However, due to the elliptical nature of Earth's orbit, this distance varies over the course of a year. The current definition, adopted by the International Astronomical Union (IAU) in 2012, is based on the length of the semi-major axis of Earth's orbit around the Sun.
Historical Context[edit]
The concept of the astronomical unit dates back to the early astronomical observations of the Ancient Greeks, who attempted to measure the distance between the Earth and the Sun. The first reasonably accurate measurement was made by the astronomer Giovanni Cassini in 1672, using the parallax method with observations of Mars.
Modern Measurement[edit]
Modern measurements of the astronomical unit are made using radar reflections off planets and other celestial bodies, as well as observations of the motion of spacecraft within the Solar System. These methods have allowed for a highly precise determination of the AU.
Usage[edit]
The astronomical unit is commonly used to express distances within the Solar System, such as the average distance from the Sun to Mercury, Venus, Mars, Jupiter, and other planets. It is also used in the study of exoplanetary systems to describe the distances of planets from their host stars.
Related Units[edit]
Other units of distance used in astronomy include the light-year, which is the distance light travels in one year, and the parsec, which is equivalent to about 3.26 light-years.
See Also[edit]
References[edit]
External Links[edit]
Ad. Transform your health with W8MD Weight Loss, Sleep & MedSpa
Tired of being overweight?
Special offer:
Budget GLP-1 weight loss medications
- Semaglutide starting from $29.99/week and up with insurance for visit of $59.99 and up per week self pay.
- Tirzepatide starting from $45.00/week and up (dose dependent) or $69.99/week and up self pay
✔ Same-week appointments, evenings & weekends
Learn more:
- GLP-1 weight loss clinic NYC
- W8MD's NYC medical weight loss
- W8MD Philadelphia GLP-1 shots
- Philadelphia GLP-1 injections
- Affordable GLP-1 shots NYC
|
WikiMD Medical Encyclopedia |
Medical Disclaimer: WikiMD is for informational purposes only and is not a substitute for professional medical advice. Content may be inaccurate or outdated and should not be used for diagnosis or treatment. Always consult your healthcare provider for medical decisions. Verify information with trusted sources such as CDC.gov and NIH.gov. By using this site, you agree that WikiMD is not liable for any outcomes related to its content. See full disclaimer.
Credits:Most images are courtesy of Wikimedia commons, and templates, categories Wikipedia, licensed under CC BY SA or similar.
Translate this page: - East Asian
中文,
日本,
한국어,
South Asian
हिन्दी,
தமிழ்,
తెలుగు,
Urdu,
ಕನ್ನಡ,
Southeast Asian
Indonesian,
Vietnamese,
Thai,
မြန်မာဘာသာ,
বাংলা
European
español,
Deutsch,
français,
Greek,
português do Brasil,
polski,
română,
русский,
Nederlands,
norsk,
svenska,
suomi,
Italian
Middle Eastern & African
عربى,
Turkish,
Persian,
Hebrew,
Afrikaans,
isiZulu,
Kiswahili,
Other
Bulgarian,
Hungarian,
Czech,
Swedish,
മലയാളം,
मराठी,
ਪੰਜਾਬੀ,
ગુજરાતી,
Portuguese,
Ukrainian
