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Solar System, page 2 Astronomy - The Sun planet Mercury

Sun, taken from SOHO Mass: 1.989 X 1030 kg (332 830 Earths)
Radius (equatorial): 695 000 km
Mean density: 1.410 g cm-3
Rotational period: 36 days (poles), 25 days (equator), 27 days (interior)
Escape velocity: 618.02 km s-1
Apparent magnitude: -26.7
Surface temperature: 6000C
Chemical composition: hydrogen (92.1%), helium (7.8%), oxygen (0.061%), carbon (0.030%), nitrogen (0.0084%), neon (0.0076%), iron (0.0037%)


The Sun is the largest body in the Solar System. It is classified as a yellow G2 star. Most of other stars are in fact fall into this category. The Sun is essentially a huge ball of very hot gas, consists mostly of hydrogen. The gas, among other matter holds together by gravitational field. Deep inside the Sun's core, the field is so strong that the hydrogen would undergo thermonuclear fusion. This is what causing the Sun to give out heat, radiation and charged particles (Solar wind).

The surface of the Sun, or photosphere appears yellowish, corresponding to a temperature of about 5500C. Sunspots are dark depressions on the photosphere with a typical temperature of 4000C. However, deep in the core, the temperature can reach up to 15 000 000C. Every second, about 700 000 000 tons of hydrogen are converted to helium at the core, with 5 million tons of matter being converted into energy. The energy takes about a million year to travel to photosphere via convection process.

Just above photosphere is an upper layer of Sun's atmosphere called the chromosphere. It is bright red in color, which can be detected in red H-alpha light. This is where the solar energy begin its way out into space. Faculae and flares arise in the chromosphere. In addition, masses of hydrogen clouds called prominences also appear that can easily extend tens of thousands of kilometers away from chromosphere.

At the outer part of chromosphere is the corona, a blanket of very hot gas with a temperature in the excess of 1 000 000C. It is only visible during solar eclipse. Alternatively, a coronagraph, instrument to study corona, can be used. An occulting disk is used to cover the sun surface to create a kind of ecllipse. Disks of different sizes can be used so that fainter corona can be observed.

A basic overview of the Sun.


Click here to view Sun's latest images.

solar prominence Huge sweeping prominence, at the lower left. Every feature in the image traces magnetic field structure. The hottest areas appear white while darker red areas indicate cooler temperature.

Credit: SOHO/EIT 304. SOHO is a project of ESA and NASA.

Illustration of sun's storm on Earth's magnetosphere. Solar wind distorts the Earth's magnetosphere (and that from rest of the Planets). Sun's magnetic storms are illustrated here. The Earth's magnetic field is distorted but shields most of the effect of Sun's storms. Sun's storms occur quite frequently and a really strong burst from the Sun directed towards Earth may damage satellites, disrupt communications and even cause blackout. Next time if your cellular phone is not working, don't blame your provider to quickly! The culprit could be the Sun. (Credit: SOHO, a project of ESA and NASA.)

Comparison of Sun's activity Comparison of two EIT (Fe IX-X 171) images. Left image was taken in Jan. 1997 which shows low solar activity. Right image shows dramatic increases of the activity, on Nov. 1998.

Credit: SOHO/EIT. SOHO is a project of ESA and NASA.


Solar and Heliospheric Observatory (SOHO) - Space-based solar observatory, a joint project from ESA and NASA.

Ulysses Mission - Space-based exploration over the Sun's poles, a joint project between ESA and NASA.

Yohkoh - Solar observatory satellite observing solar atmosphere in X-ray. A joint project from Japan, the USA and UK.

Transition Region and Coronal Explorer (TRACE) - Imaging solar corona and producing temporal data of Sun's atmosphere.

Solar system, page 2 Planet Mercury


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