The Sun is the star at the centre of our Solar System. The Earth and the other planets orbit the Sun, which makes up 99% of the Solar System's mass. Sunlight and heat from the Sun support all life on Earth. Without the Sun, there would be no life at all.
What is the Sun?
The Sun is an average star, just like countless others in the Universe. It was formed from a cloud of gas and dust, plus material thrown out by one or more exploding stars. Now, in middle age, the Sun burns yellow and quite steadily - giving the Earth daylight and fairly constant temperatures. Besides heat and light, the Sun sends out deadly gamma rays, X-rays and ultraviolet rays, as well as infrared and radio waves.
How big is the Sun?
The Sun is a small to medium sized star 1,392,000 km in diameter. It weighs just under 2000 trillion trillion tonnes.
How old is the Sun?
The Sun is a middle aged star. It probably formed about 4.6 billion years ago. It will probably burn for another 5 billion years and then die in a blaze so bright that the Earth will be scorched right out of existence.
How hot is the Sun?
The surface of the Sun is a phenomenal 5500°C, and would melt absolutely anything. But its core is thousands of times hotter at over 15 million°C.
What makes the Sun burn?
The Sun gets its heat from nuclear fusion. Huge pressures deep inside the Sun force the nuclei (cores) of hydrogen atoms to fuse together to make helium atoms, releasing vast amounts of nuclear energy.
‘The Sun's visible surface
is called the photosphere.
It is a sea of boiling gas
that gives the heat and light
we experience on Earth.’
What is the Sun's crown?
The Sun's crown is its corona, its glowing white hot atmosphere. It is seen only as a halo when the rest of the Sun's disc is blotted out by the Moon in a solar eclipse.
What is the Sun's orbit?
While the Solar System orbits the Sun, the Sun itself is orbiting the centre of our Galaxy, the Milky Way. The Sun is moving at an orbital speed of 251 km every second. It takes the Solar System about 225 to 250 million years to complete one orbit of the Galaxy.
‘Solar prominences form
in about a day
and
may last as long as
several months.’
What are Sunspots?
Sunspots are dark blotches seen on the Sun's surface (right). They are thousands of kilometers across, and usually occur in pairs. They are dark because they are slightly cooler than the rest of the surface. As the Sun rotates, they slowly cross its face - in about 31 days at the equator and 27 days at the poles.
What are Solar Flares?
Flares are eruptions on the Sun's surface that release energy into space with the power of one million atom bombs for about five minutes. Solar prominences are giant flame-like tongues of hot hydrogen that loop up to 32,000 kilometers into space.
‘The northern lights often
appear as a greenish glow
or a faint red. They can
occur as arcs or bands.’
What is solar cycle?
The average number of sunspots and flares seems to reach a maximum every 11 years. Some scientists think that these peaks in the Sun's cycle are linked to stormier weather on Earth.
What is a solar eclipse?
A solar eclipse is when the Moon moves in between the Sun and the Earth (shown on the left), creating a shadow a few hundred kilometers wide on the Earth.
‘During an eclipse,
the Moon's shadow
can be seen
on the Earth.
Up to five eclipses
occur each year.’
What is the solar wind?
The solar wind is the stream of particles constantly blowing out from the Sun at hundreds of kilometers per second. The Earth is protected from the solar wind by its magnetic field, but at the poles the solar wind interacts with Earth's atmosphere to create the aurora borealis or northern lights, and the aurora australis or southern lights.
What is a transit on space?
Mercury and Venus are the two planets closer to the Sun than the Earth. Occasionally, they can be seen crossing, or in transit over, the face of the Sun. Mercury crosses 13 or 14 times a century; Venus crosses twice every 120 years.
‘The last transit
of Mercury
took place on
November 8, 2006.’
Collected by: Uttar Tamang
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