1.3 : The Sun

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What is the diameter of the Sun?
1.4 million km, just over 100 times the diameter of Earth.
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How does the Sun support life on Earth?
By providing heat, light and energy.
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What elements comprise the Sun?
Hydrogen (75%) and helium (25%), with trace amounts of other elements.
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What is the photosphere and what is its temperature?
The Sun's visible 'surface,' which has a temperature of 5800K.
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What components make up the Sun's atmosphere?
The relatively thin (2000km) chromosphere ('sphere of colour') and extensive corona ('crown').
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When can the chromosphere be observed and how does it appear?
Just before totality in a solar eclipse, at which point it appears as a slender red/pink ring.
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When can the corona be observed and how does it appear?
During an eclipse, the corona appears as a glowing region of ionised gas.
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What is the temperature of the corona?
2 million K, which is hot enough to cause X-ray emission.
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What provides the Sun with its energy?
Nuclear fusion reactions, in which hydrogen nuclei fuse together to make helium nuclei, in its central core.
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Why does the Sun lose matter?
It is converted into an equivalent amount of energy (E = mc^2), some of which is used to maintain the high temperature of the Sun's core while the rest is radiated outwards into space through the photosphere.
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How can the Sun be safely observed with a telescope?
By fitting the objective with a special high-quality H-alpha or Mylar filter.
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What is the safest way of observing the Sun?
An indirect projection method in which a pinhole camera, a pair of binoculars or a telescope focuses an enlarged image of the Sun onto a screen, which reduces the brightness to a safe level.
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How can the contrast of a projected image of the Sun be improved?
By casting a dark shadow onto the screen with a card or wooden baffle.
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What damage can be caused to a telescope by using it in solar observation and how can this be prevented.
Excessive amounts of light entering the telescope can partially melt the eyepiece. To prevent this, the objective lens should be partly covered with black card to reduce the amount of light entering the telescope.
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What are sunspots?
Small dark patches on the photosphere, roughly equal in diameter to Earth. They are cooler areas of the photosphere that correspond to strong localised magnetic fields, usually occurring in pairs or groups of opposite magnetic polarity.
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What is an umbra?
The central darker region of a sunspot, about 2000K cooler than the photosphere.
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What is a penumbra?
The lighter area surrounding the umbra, with a temperature about 200K cooler than the photosphere.
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How can it be proven that the Sun does not rotate as a solid body?
By tracking sunspot movement.
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How does the rotation period of the Sun vary?
It varies from 25 days at the equator to 36 days at the poles.
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How long can a sunspot last on the photosphere?
From a few days to several weeks.
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What is the solar cycle?
A regular 11-year cycle in which the number of sunspots on the photosphere increases to a maximum before falling again. The cycle typically displays an increasing number of sunspots that migrate towards the solar equator, terminating at 5-10°N/S.
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What information is represented on a Butterfly diagram?
A sunspot's latitude against time.
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What is the solar wind?
A steady stream of charged particles (mainly protons and electrons, with traces of ions of helium and other elements) flowing outwards in all directions from the corona at typical speeds of 400km/s.
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How do particles in the solar wind escape the Sun's gravitational pull?
They gain kinetic energy from the high temperature of the corona.
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How does the fast solar wind differ from the slow solar wind?
It is thought to originate from coronal holes (cooler regions of the corona close to the Sun's magnetic poles) where open magnetic field lines permit charged particles from the photosphere to escape more easily, at speeds of up to 850km/s.
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What are prominences?
Huge clouds of cooler gas in the Sun's atmosphere.
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What are filaments?
Prominences appearing as dark silhouettes against the brighter photosphere.
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What are solar flares?
Sudden releases of energy from the Sun.
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Other cards in this set

Card 2

Front

How does the Sun support life on Earth?

Back

By providing heat, light and energy.

Card 3

Front

What elements comprise the Sun?

Back

Preview of the front of card 3

Card 4

Front

What is the photosphere and what is its temperature?

Back

Preview of the front of card 4

Card 5

Front

What components make up the Sun's atmosphere?

Back

Preview of the front of card 5
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