Adler Planetarium CyberSpace

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Quick Facts

Rotation Period (at equator):
25.38 Earth days

Diameter: 864,400 miles

Mass: 4.38499439 x 10³⁰ pounds

Temperature (surface): 10,000°F

Temperature (core): 27,000,000°F

Distance to Earth: 93 million miles

The Sun

Our nearest star, the Sun is the center of the Solar System. Generating huge amounts of heat and light energy, it is the Solar System's power plant. The Sun is the source, directly or indirectly, of almost all of the energy we use.

Our Sun is just one of billions of stars. Studying the Sun helps us to learn more about stars in general. It is approximately 4.6 billion years old (middle-aged).

Scientists think that the Sun began when a huge, slowly spinning cloud of dust and gas collapsed under its own weight. Pulled together by its own gravity, this dense region began to shrink. As the cloud shrink the gas in the center became hotter and hotter, nucleur fusion began, and our star was born.

Image at right: The Sun (courtesy of NASA).

DID YOU KNOW?

By visiting Adler's Doane Observatory you can view the Sun's photosphere and chromosphere.

The Sun's layers (Original image from NASA)

Features

Like all stars, the Sun is a huge ball of very hot gas composed of hydrogen and helium. It is a nearly perfect sphere. The Sun is extremely hot - about 10,000°F (or 5,5000°C or 5,800°K) at the surface and 27,000,000°F (or 14,999,982°C or 15,000255°K) at the core. The visible surface of the Sun is called the photosphere, which is mostly composed of hydrogen and helium.

The Sun's atmosphere has two transparent layers: the chromosphere and the corona. With solar telescopes and space-based instruments, scientists can study other features of the Sun like sunspots and prominences.

Our Sun has spots! Sunspots, that is.

Sunspots are really just dark, cool regions on the Sun's surface. Sunspots come and go, and over time scientists have observed that our Sun has an 11-year cycle of sunspots. Scientists have known about sunspot activity for hundreds of years. Even Galileo made sketches of them.

At the peak of the 11-year cycle, dozens of planet-sized sunspots can be seen at the same time. At the minimum of the 11-year cycle, the sunspots disappear completely. Currently, the sun is at a 100-year low in sunspot activity. This puzzles astronomers since the solar minimum should have ended about a year ago, but hasn't. No one knows why this is, but astronomers are not worried. The Sun has gone through quiet phases before, and it has always returned to normal eventually.

See Galileo's sketches of the Sun at the Galileo Project website.

SOHO: The International Solar and Heliospheric Observatory (Courtesy of NASA)

Missions

The first American expedition to the Sun was the Pioneer 5 satellite launched by NASA in 1959. It took measurements of the Sun's diameter and solar wind and observed the surface activity of our star. Pioneer 5 was the first spacecraft of its kind to study sun phenomena.

The largest mission to investigate the Sun was SOHO, the Solar and Heliospheric Observatory, a joint effort between the United States and the European Space Agency. The spacecraft left Earth in 1995 and is still operating, sending back some of the best images ever taken of the Sun.

Learn more about missions to the Sun at NASA's Solar System Exploration.

Apollo 13th Patch featuring Apollo (Courtesy of NASA)

Myths, Stories, and More

Throughout history, human beings have been fascinated by the Sun. The Romans called the golden orb Sol. Apollo replaced the Titan Helios as the sun god, but the Greeks continued to refer to both.

Our star has inspired mythological stories in cultures around the world, including the ancient Egyptians, the Aztecs of Mexico, and Native American tribes of North America and Canada. The Sun continues to be a dominant force in our lives today.

Discover more stories about the Sun at Windows to the Universe.

Size of Earth in relation to the Sun (Courtesy of NASA)

Earth Matters

The Sun has a mass 332,900 times greater than the mass of Earth, and it is 109 times Earth's diameter. If the Sun were the size of a soccer ball, the Earth would be about the size of a pea!

Radiant energy from the Sun lights up our daytime sky and makes life possible on our planet, even though the Sun is 93 million miles away. It powers photosynthesis in green plants and drives the seasons, ocean currents, weather and climate.

Learn more about Sun-Earth connections from NASA's Sun-Earth Viewer.