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Stargazing: Interesting Observations on the Sun

The Sun is Earth’s local star. It looks much bigger, brighter and hotter than the stars you see at night, but that’s only because you’re much closer to the Sun than you are to the other stars.

For example, say that you got into a spaceship – the fastest ever built – and flew towards the next-closest star, α Centauri. In a few million years after you arrive there, if you look out of your spaceship window, α Centauri will look just like the Sun does from Earth; if you look back at the Sun, it will appear as a speck of light in the black night sky.

Never look directly at the Sun. You could permanently blind yourself. Use a filtered telescope or project it onto a card.

Stargazing: Sunspots

When you see the Sun through a filtered telescope or projected onto a card, you may at first glance think it’s just a boring, featureless object – but look more closely! Those tiny black specks are sunspots, cooler regions of the Sun’s surface. They may not look like much, but even the smallest visible sunspot is bigger than the Earth.

If you’re looking through a telescope that’s safely fitted with a solar filter, look out to the edge of the Sun (the part that astronomers call the limb), and you may be able to see small loops (prominences), arcs or jets (flares) of gas. This gas has been blown off the surface of the Sun in an eruption caused by the Sun’s magnetic field lines becoming tangled and then snapping.

Stargazing: The Sun’s aurorae displays

If a particularly powerful eruption happens on the Sun, a large cloud of gas may blast from its surface. When this blast happens, the charged particles can fly through the solar system, and some of them even hit the Earth. But don’t panic; these particles are mostly harmless, and their main influence is seen high in the atmosphere where they make the air molecules glow. When this blast happens, stargazers at far northern or southern latitudes may observe the aurora. In the north, it’s called the aurora borealis, or Northern Lights; in the south, it’s known as the aurora australis, or Southern Lights.

At their most dramatic, aurorae can look like giant colourful curtains of fire in the sky. Their most common colour is green, but you may also see reds, blues or purples mixed in, too. And they move around in the sky, shimmering and flowing. Displays of aurorae are some of the most beautiful natural phenomena and well worth making the effort to see, but astronomers can’t predict them much more than a couple of days in advance, which makes planning for them tricky!

If you do hear of a good display coming, then you should look north if you’re in the northern hemisphere and south if you’re in the southern hemisphere. A good clear horizon free of light pollution will help you see them.

Websites such as Spaceweather.com let you keep an eye on the Sun’s activity and can alert you when a good display of the aurora is due. Different cultures have different names for aurorae. For example, in Orkney, in the north of Scotland, they’re known as the Merry Dancers.

Stargazing: Solar eclipse

One of the most stunning of all natural phenomena is a total solar eclipse. An eclipse occurs when the Moon passes in front of the Sun, perfectly blocking out the disk of the Sun. When an eclipse happens, you see the Sun’s beautiful outer atmosphere, called the corona or crown. The corona is there all the time; it’s just that the Sun’s light normally drowns it out. That an eclipse happens at all is just a huge coincidence.

The Moon just happens to be the right size and distance from the Earth so that it appears to be exactly the same size as the Sun in the sky. The Sun is much bigger than the Moon (its diameter is 400 times greater than the Moon’s), but it’s also much farther away (400 times farther from Earth than the Moon), and these factors conspire to make an eclipse possible.

If the Moon was a bit smaller or farther away from Earth, it wouldn’t block out all the Sun’s disk in an eclipse. If the Moon was a bit bigger or closer to Earth, then it would more than cover the Sun’s disk, and you wouldn’t see the corona nearly as well.

Eclipses are very rare from individual places on Earth, but a total solar eclipse occurs somewhere on Earth at least every few years. In addition to total solar eclipses, you can also see partial eclipses, when the Moon only blocks out part of the Sun’s disk. These aren’t quite as impressive as total eclipses, but still well worth watching out for.

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