Explore the Sun

Facts About Our Closest Star

A Source of Light and heat, the sun is a giant ball of glowing gas. It is about 100 times the diameter of the Earth. When you are ready, click back to return to the Student Center or click below to explore again.

The Sun is a Star
Sunspots
Eclipses
Terms

The Sun is a Star

The sun with solar prominence The picture at left shows the sun with a huge solar prominence. Special cameras were used to take the picture. Do not ever view the sun without special eye protection or filters. Staring at the sun can permanently blind your eyes!

The sun is mostly hydrogen with about 10% helium and other elements. The nuclear reaction in the core changes the hydrogen to helium and releases tremendous amounts of energy as light, heat, x-rays, and high speed particles. As this happens the constant churning of the gases causes an intense magnetic field and other effects. Sunspots, solar winds, prominences and flares are some of these effects.

The Sun is 100 times bigger than the Earth We think of the Earth as a huge place. The diameter of the Sun is about 100 times wider than the Earth as can be seen in the diagram at left. Our Sun is an average size star but it has 98% of all the mass of the solar system. Some stars are as small as the Earth while others can be 500 times bigger than our Sun.

Rocky Earth-like planets are really hard to find around other stars because they are lost in the glare of the star. See below for more on discovering other planets.

Corona seen during an eclipse We can only see the outer layers of the sun during eclipses or with special cameras on orbiting spacecraft like SOHO. The outer portion or corona reaches far out into the solar system.

The picture at right shows the corona. Not seen is the solar wind which also influences the Earth's magnetic field and auroras. The solar wind is predicted to extend more than 50 A.U. (50 times the distance from the sun to the Earth. One Astronomical Unit is 149,597,870 km.) which is a really huge distance.

Aurora or Northern Lights Solar flares can sometimes leave the sun and zoom towards Earth. When the high speed particles from the sun contact the Earth's magnetic field it produces a lighting effect known as the aurora. Here it is seen from the Space Shuttle in orbit.

New! Click here to find out about "The Professor's Telescope", a new book by Chris Moreau, one of our advisors. Take an adventure with Eric to Saturn!

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Gravity and You
Your weight on Earth is determined by your mass and Earth's mass. Would you weigh more or less on the Sun?

Planet Names
Why are the planets named for Roman gods? Is there a story or myth about the sun? Click image or here for Planet Myths and Lore.

Are There Planets Like Earth Around Other Suns?
The first planet outside of our solar system was discovered around 51 Pegasi, a small star in the constellation Pegasus. Since then more than 100 planets have been found. For more information on how astronomers discover new planets click image or here NASA/JPL Planetquest.

Quick Facts about the Sun

Topic

Data

Diameter

1,391,940 km

Mass

1.989 x 10³⁰ kg

Surface Temperature

6400 K

Interior Temperature

15.6 x 10⁶ K

Rotation

25 Days

Composition

Hydrogen and Helium

Magnetic Field

Very Large and Active

The Sun is a Star | Sunspots | Eclipses | Terms | Top

Sunspots

Close up view of sunspots Sunspots are areas where the cooler areas show up darker than the surrounding surface. The sunspot cycle is about 11 years from almost no activity to solar maximum. The solar maximum in the year 2000 is giving astronomers a chance to study these strange spots.

Some sunspots are larger than the diameter of the Earth and can reach up to 20,000 km in diameter. Most last for a few days and different ones can be seen as the sun rotates. Static in radio broadcasts and satellite transmissions are related to sunspot activity. This is due to strong magnetic fields.

The Sun is a Star | Sunspots | Eclipses | Terms | Top

Eclipses

Lunar Eclipse Diagram The picture at right shows what happens during a Lunar Eclipse. The diagram is not to scale, that is, the Earth is much farther away and smaller than it is shown here. (See The Sun is a Star , above.) Because the moon's orbit is slightly tilted by 5 about degrees, eclipses do not happen every month but vary from 6 months to 30 months apart. As the moon reaches line A it begins to enter the Earth's shadow. Part of the sun is still shining on it so it is not totally dark. At line B the moon is about half dark. Some of the sun's light seeps through the Earth's atmosphere and turns the shadow reddish. At C the moon is coming out of the darkest part of the shadow. At D the moon is fully lit again. It takes about 5 hours to move from line A to line D.

A Solar Eclipse is similar except that the moon is much smaller than the Earth so it does't completely shadow it. The diagram at left shows the moon's shadow covering part of the Earth. Lines A and B are where the sun's light is blocked by the moon. Again, the drawing is not to scale. Solar eclipses happen from about 9 to 30 months apart.

Click image or here for a 262K NASA animation of the eclipse. The background is a light color so you can see the shadows. Behind the moon there is a darker cone of shadow that makes a black dot on the Earth known as the totality. If you are standing in this part of the shadow, the sky turns as dark as night for about two minutes or so.

The Diamond Ring Effect The Diamond Ring

Just before the moon completely covers the sun, mountains on the moon allow a bit of light to peek through creating this beautiful diamond ring effect at right. This image was taken by an Apollo Mission crew as they went behind the moon on their way back to Earth.

Bailey's Beads are a similar effect that look like a string of pearls along the edge of the shadow.

The table below lists some recent and future total eclipses for North America. There are occasions where the eclipse is only partial so are not listed here. Find out more dates at the US Naval Observatory's Official Times and Dates site.

Recent and Future Eclipses

Total Solar Eclipses 21 June 2001

4 Dec 2002

23 Nov 2003

8 Apr 2005

29 Mar 2006

1 Aug 2008

Total Lunar Eclipses 9 Jan 2001

16 May 2003

9 Nov 2003

4 May 2004

28 Oct 2004

3 Mar 2007

The Sun is a Star | Sunspots | Eclipses | Terms | Top

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Star information for elementary students.
Ask NASA about stars.
Ask a NASA astronomer.
Parts of a star.

Terms

Here are some basic terms used for describing the sun. Find more astronomical terms in the Glossary.

Astronomical Unit: The average distance between Earth and the Sun, 1.5 x 10⁸ km.
Aurora: The glowing light from solar particles interact with Earth's magnetic field.
Comet: One of the small, icy bodies that orbit the sun that make tails of gas and dust when they get close to the sun.
Ecliptic: The path the Sun seems to follow in the sky.
Light-year: The distance light travels in a year.
Lunar Eclipse: The name of the event when the Earth comes exactly between the Sun and the moon.
Orbit: The path an object takes as it moves around another object.
Rotation: An object spinning about its center.
Solar Eclipse: The name of the event when the moon comes exactly between the Sun and Earth.

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