Explanation of the Characteristics of our Sun by Ron Kurtus - Succeed in Understanding Astronomy. Key words: solar system, stars, planets, galaxy, Earth, universe, meteors, comets, Physical Science, School for Champions. Copyright © Restrictions

# Characteristics of our Sun

by Ron Kurtus (revised 11 April 2009)

The Sun is the center of our solar system, with 9 planets, asteroids and other objects rotating around it. One of 100 billion stars in our galaxy, the Sun provides light and heat to the orbiting planets. It is extremely large compared to the Earth. The temperature inside the Sun is extremely high, being driven by nuclear fusion reactions. The surface of the Sun gives off visible light, charged particles and occasionally high energy particles.

Questions you may have include:

• What are some statistics about the Sun?
• What are characteristics of the Sun?
• What are some surface effects observed on the Sun?

This lesson will answer those questions.

Note: Click the Play button to hear the text being read.

Time = 6 min. 22 sec.

## Statistics

The size and mass of the Sun and its distance to the Earth are as follows:

### Size

The Sun is 1,390,000 km in diameter. That compares with 12,756 km for diameter of the Earth. In other words, the diameter of the Sun is over 100 times the diameter of the Earth.

In June, 2004, Venus passed in front of the Sun, as seen from the Earth. Since the diameter of Venus is only slightly less than that of Earth (12,104 km), you can get an idea of the relative size of the Earth or Venus compared to the Sun from the following photograph:

The planet Venus just passing in front of the Sun

### Mass

The mass of the Sun is about 2 x 1030 kilograms (2 followed by 30 zeros). It is one of the larger stars in our Milky Way galaxy. The median size of stars in our galaxy is less than half the mass of the Sun. In comparison, the Earth is 6 x 1024 kg. This means that the mass of the Sun is over 300,000 times greater than that of the Earth.

### Distance

The Sun is 149,600,000 km (92 million miles) from the Earth. Since the speed of light is 303,000 km/sec (186,000 miles/second), it takes the light slightly over 8 minutes to get from the Sun to the Earth.

The distance of the Sun to the Earth is called an Astronomical Unit (AU) and is sometimes used to denote large distances that are less than a light year.

## Characteristics

The Sun consists of about 70% Hydrogen, 28% Helium and 2% of metals such as iron. Other characteristics are its rotation, temperature, and radiation.

### Rotation

The Sun rotates on its axis, which is approximately the same axis that most of the planets revolved around the Sun. Since the Sun is primarily very hot gas, the surface at the equator rotates once every 25.4 days. The rotation near the poles is around 36 days. Also the surface swirls in high and low pressure areas, similar to those that occur on Earth.

The rotation of the Sun and the inclusion of iron in its core cause it to have a magnetic field, which is considerably more than the Earth's magnetic field.

### Temperature

Its temperature is extremely hot, with the surface being about 5000° C and the center core at 15,600,000° C. The high temperature in the core, along with extreme pressure from the Sun's mass, result in nuclear fusion reactions. Two Hydrogen nuclei (protons) combine with two neutrons to form a Helium nucleus plus a release of energy.

The energy released from the fusion reactions near the Sun's core is in the form of very high frequency electromagnetic waves called gamma rays.

As this radiation moves towards the Sun's surface, it is absorbed by atoms in the Sun's interior, increasing their kinetic energy. After absorption, the rays are then re-emitted at lower frequencies. This process continues until the radiation reaches the Sun's surface. By that time it is primarily visible light.

## Surface effects

The surface of the Sun is called the photosphere. Some areas of the Sun's surface are hotter than the average 5000° C temperature and some are cooler. The cool areas look dark in comparison with the surrounding regions. They are called sunspots and are at about 3800° C.

The chromospheres lie above the photosphere. Above that is the corona which extends millions of kilometers into space and is visible only during a total solar eclipse.

Stormy surface of the Sun, with jets of material

### Solar wind

The Sun continually emits a stream of charged particles consisting mostly of electrons and protons. This is called the solar wind. Most of these particles are blocked by the Earth's upper atmosphere or attracted to the magnetic poles. The solar wind is the reason that the tails of comets always face away from the Sun.

### Solar flares

Occasionally, solar flares on the Sun's surface shoot out streams of high energy particles. They can cause such problems as power line surges and radio interference. They also result in the Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights), where the charged particles cause the atoms in the atmosphere to give off a glow.

Northern Lights

## Summary

The Sun is the center of our solar system, with 9 planets and is one of billions of stars in our galaxy. The Sun provides light and heat to the orbiting planets. It is extremely large compared to the Earth and is 92 million miles away. The temperature inside the Sun reaches 15 million degrees, being driven by nuclear fusion reactions. The surface of the Sun gives off visible light, charged particles and occasionally high energy particles.

Have fun in the sun

## Resources and references

Author's Credentials

### Websites

Nine Planets - A great multimedia tour of the Solar System from the University of Arizona

The Sun: a pictorial Introduction - pictures and explanations from the High Altitude Observatory

Astronomy Resources

## What do you think?

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.

## Students and researchers

www.school-for-champions.com/astronomy/sun.htm

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Physical Science

Astronomy topics

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