The Physics
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Diameter of the Sun

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Bibliographic Entry Result
(w/surrounding text)
Namowitz, Samuel N., and Nancy E. Spaulding. Heath Earth Science. Lexington, MA: Heath, 1994: 398. "The sun's diameter, 1,380,000 kilometers, is about 110 times Earth's diameter." 1.38 × 109 m
Ridpath, Ian. Stars and Planets. New York, NY: DK Publishing, 1998: 26. "The sun has a diameter of 865,000 miles (1.39 million km). Next to the sun, the Earth is just a tiny dot." 1.39 × 109 m
Bertotti, Bruno, and Paolo Farinella. Physics of the Earth and the Solar System. Dordrecht, Netherlands: Kluwer Academic Publishers, 1990: 256. "The sun is a gaseous mass M of 2·1033 g, 743 times heavier than the total planetary mass, with a radius R=7·1010 cm and a mean density 1.4 g/cm3." 1.4 × 109 m
Wild, JP. Focus on the Stars. London: Heinemann, 1976: 73. "The sun is located in a nondescript place within a spiral arm of the Galaxy about 30000 light years from the galactic centre; its diameter is 1.39 × 106 km and its mass is 1.99 × 1030 kg (332,000 times the Earth's mass)." 1.39 × 109 m
Friedman, Herbert. The Astronomer's Universe. New York: Norton, 1998: 120. "Our star is approximately 865,000 miles in diameter, about 109 times the diameter of the Earth." 1.39 × 109 m

The sun was made from an enormous cloud composed of dust and gas that had a diameter of one trillion miles. Gravitational forces within the cloud caused the gas and dust particles to contract similar to the way gravity pulls everything on earth towards its center. The packed particles in the center of the cloud formed a dense core which later became the sun. Heat was produced as a result of the collapse of the particles and nuclear reactions further heated them up to form the sun.

The sun has a diameter of 865,000 miles or 1.39 million kilometers. Its diameter is 109 times the diameter of earth. Despite its seemingly huge size in comparison to earth, the sun is actually considered a small star and is classified as a yellow dwarf.

The sun is mainly composed of hydrogen and helium. Other atoms exist in the sun, but they make up less than 1% of the sun. The sun can be divided into three regions. The thermonuclear core is about 25% of the solar radius. The radiation zone, where energy is transported out from the core through x-rays and ultraviolet light makes up 55% of the radius. The convection zone, which is the outer layer, transfers heat through turbulent motion and occupies the remaining 20% of the solar radius. Astronomers predict that the sun will develop into a red giant, which means that there will be an increase in diameter. Following that transformation, the sun will shrink to a white dwarf and then a black dwarf, which are both about the size of earth, after billions of years.

Amy Chan -- 2004

Bibliographic Entry Result
(w/surrounding text)
Namowitz, Samuel N. and Spaulding, Nancy E. Earth Science. Evanston, IL: McDougal Littell Company, 1999. "Compared to Earth, the sun is enormous. It has a diameter of 1,400,000 kilometers, which is more than three times the distance from Earth to the moon, the longest distance humans have traveled in space. It would take a jet flying at three times the speed of sound more than two months to fly all the way around the sun." 1.4 × 109 m
"Sun" Columbia Electronic Encyclopedia. 6th ed. Columbia University Press, 2003. "The sun is approximately 865,400 mi (1,392,000 km) in diameter, and its volume is about 1,300,000 times that of the earth." 1.392 × 109 m
Sinnott, Roger. Senior Editor, Sky and Telescope Magazine. Electronic Mail. 20 May 2004. "The value of the Sun's radius to be used for astronomical purposes is 696,000 km. That means the diameter is 1,392,000 km." 1.392 × 109 m
Tuma, Jan K. Handbook of Physical Calculation. New York: McGraw-Hill Book Company, 1976.
Sun Data SI System FPS System
Constant Value Value
Mean radius 6.960 (05) 4.325 (05)
  Unit Unit
  km mi
1.392 × 109 m
The Amazing Structure of the Sun. National Aeronautics and Space Administration (NASA), 2003. "The diameter of the Sun is about 1,390,000 km. The average diameter of the Earth is 12,740 km. About 109 Earths could be placed side-by-side along the diameter of the Sun." 1.39 × 109 m

The Sun is located at the center of the solar system, where nine planets in addition to moons, comets and asteroids rotate around it. Our planet, Earth, rotates around the Sun about 93,000,000 miles away. Earth is significantly smaller than the sun, within an incredible diameter about 1,400,000,000 meters (109 times that of the Earth).


The linear measurements (converted from the angular measurements) of the sun of photosphere (the sun's surface) are necessary to determine the diameter of sun. The angular diameter can be measure best by using Picard's telescope during a solar eclipse or by recording Mercury's time as it pass in front of the sun.

In about eight billion years it is estimated that the sun's radius (and consequently its diameter) will increase greatly due to the large amount of heat that the sun produces. This increase in heat will also change the sun's intensity by 10%, and will most likely have a very disastrous impact on Earth.

Emily Louick -- 2004