Variable stars

It is not very well known that more than half the stars in the night sky vary in brightness…

It is strange to think that so many stars vary in brightness, but of all the stars that do, most only vary by a small amount. Often this is almost undetectable with the human eye. Even our own Sun is a variable star over its 11-year cycle. As the number of sunspots increase and decrease so does the light output.

However, there are some stars which have a huge change in brightness, going from a moderately bright star in our skies

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Types of giant stars

Red supergiant

The biggest red giants are the largest stars in the universe, swollen to diameters of a billion kilometres or more by changes in their cores as they near the end of their lives. As they swell in size and brighten to hundreds of thousands of times solar luminosity, their surfaces cool to a distinctive red colour. But many scientists say these stars are supergiants rather than true hypergiants.

Yellow supergiant

Yellow supergiants seem to be a rare intermediate stage, though again they get their name from their size and brightness rather than their mass. They seem to be

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The Big Dipper.

Let’s take a closer look at one of the most easily recognisable patterns of stars in the northern hemisphere.

The Big Dipper goes by several different names, including the ‘Plough’ and the ‘Saucepan’. It is, though, very recognisable with its bowl-shaped pattern of four stars connected to a ‘handle’ of three more. This is a group of stars which has been recognised from time immemorial and by nearly all cultures around the world.

It is not a constellation in its own right, but just an easy-to-spot pattern of stars which form part of the larger constellation of Ursa Major, or

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Tarantula

BIGGEST NEBULA

The largest known nebula in the universe is many times larger than the Oort cloud and far more massive, with a star cluster at its core which is 450,000 solar masses alone. The Tarantula Nebula is right on our cosmic doorstep in the Large Magellanic Cloud (LMC), which is one of several satellite galaxies orbiting around the Milky Way itself. With a diameter of roughly 800 light years, the Tarantula Nebula (which also goes by the names 30 Doradus and NGC 2070) is a seething cauldron of starbirth containing millions of Suns’ worth of star-forming material, approximately 160,000

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Star classification

One of the most useful tools for classifying stars is the Hertzsprung-Russell (H-R) diagram. It plots stars according to their surface temperature and colour or ‘spectral type’ (on the horizontal axis) and their luminosity (on the vertical axis). When a large number of randomly selected stars are plotted, a pattern soon emerges: most stars are arranged along a diagonal ribbon known as the ‘main sequence’, that runs between the faint, cool and red and the bright, hot and blue. Luminous cool stars and faint hot ones (‘red giants’ and ‘white dwarfs’) occupy regions to either side of the main sequence

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Searching for monster stars

In 2010, Professor Paul Crowther and his team discovered the most massive known single star, R136a1.

Can we start by asking what first drew your attention to the R136 star cluster?

Well, it’s probably the prime target for anyone looking for the most massive stars – it’s the most obvious place to look really because it’s the most massive young star cluster in our part of the universe. It’s about the same size as the famous Orion Nebula, but while that’s got a couple of thousand stars, R136 probably contains 100,000 stars or more, if you could see them all.

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How to identify constellations

Being able to recognise the constellations in the night sky can be a lot of fun and also very useful.

From ancient times, mankind has seen patterns in the stars. Getting to know these star patterns can help you feel at home in the night sky and being able to recognise just a couple can help you find many others and help you become familiar with them.

In the past, every culture had its own way of seeing patterns in the stars. These patterns, or constellations, were connected with stories and folk legends. In the west we have settled on

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How do we know the composition of distant stars?

What stars are made of is determined through the help of spectroscopy.

This involves the study of a star’s spectrum which is created by the electromagnetic radiation that it emits. Spectroscopy can not only derive the chemical composition of distant stars and galaxies, but can also determine their temperature, density, mass, luminosity and relative motion.

Stars emit at all wavelengths across the electromagnetic spectrum, along with many discrete absorption lines at certain wavelengths. These lines, which appear black on a colourful emission spectrum, result from a deficiency of observed photons at those particular wavelengths since its light is absorbed. It

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Galaxy classification

Edwin Hubble’s monumental discoveries revealed that the universe consists of a variety of vast galaxies that exist far beyond our Milky Way galaxy.

Edwin Hubble can be ranked as one of the great astronomers, whose discoveries are as important as those of Nicolaus Copernicus and Galileo Galilei.

In 1919, he began working at the Mount Wilson Observatory in California. A few years later, he used the newly built 2.5-metre (100-inch) Hooker Telescope to study Cepheid variable stars located in spiral nebulas. From these observations, he found that they must exist far beyond the Milky Way. In 1925, he presented his

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Exploring the stars

Could we travel to this distant neighbour and what problems would we encounter on the way?

Although Proxima Centauri is sometimes referred to as Alpha Centauri C, we aren’t yet sure how it fits in with Alpha A and B. The stars in the binary system orbit around a common centre of gravity, and range from being 1.67 billion kilometres (1 billion miles) to 5.3 billion kilometres (3.3 billion miles) apart due to the eccentricity of their orbit. They’re relatively similar and Sun-like.

By contrast, Proxima is smaller, redder, weaker and much further from the other two stars. Visually it

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