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The Guide to the Universe

The Guide to the Universe

The Guide to the Universe

The latest special edition from BBC Sky at Night Magazine, The Guide to The Universe takes you on a journey from the Solar System to the edge of space to encounter the familiar and exotic objects that make up the Universe. Beautifully illustrated throughout, with expert and clear-cut descriptions, it will give you a new perspective on our place in the vastness of space.

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United Kingdom
Immediate Media Company London Limited
R 164,27

in this issue

2 min
open clusters

CLINGING TO the spiral arms of our Galaxy are the giant molecular clouds (see page 80). Vast drifts of interstellar gas and dust, they are lightyears wide and outweigh stars millions of times to one. They’re also where stars are born. Usually, a giant molecular cloud splits up as it falls in on itself under gravity, with each of the fragments forming a separate multiple-star system or even just a single star. But in some cases, the cloud fragments are so enormous that they give birth not just to multiple stars, but entire assemblages of them, known as open clusters. The Milky Way is estimated to contain around 1,000 open clusters, scattered randomly around its arms. They vary greatly in their size and in their contents. Some contain a few dozen stars…

2 min
comets & comet clouds

THE LAST class of objects in the Sun’s family is the comets. Perhaps the most famous one is Halley’s Comet, named after Edmond Halley, the astronomer who first correctly calculated its orbit. He examined historical comet sightings and realised that what was thought to be several comets was in fact a single object returning every 76 years. Comets, he proved, like planets, are objects that orbit the Sun with strict periodicity. Like asteroids, comets are relics of the Solar Nebula, but their compositions are different. Asteroids formed close to the Sun, so are stony or metallic. Comets were fashioned much further out, where ices dominated. Probes have shown comets to be ‘dirty snowballs’, loosely packed chunks of ice, mixed with grit and riddled with voids, filled with gasses. They measure a…

2 min
large-scale structure: superclusters and voids

THERE SEEMS to be no end to the structure of the Universe and no limit to the force of gravity. Its influence can link objects together on truly mind-boggling scales. Stars are grouped into galaxies; galaxies are combined into clusters; and, incredibly, galaxy clusters are subject to even larger aggregations. These are called superclusters – clusters of clusters of galaxies. Just as the Milky Way belongs to the Local Group of galaxies, so the Local Group is but one of at least 100 galaxy clusters that comprise the so-called Local Supercluster. Also called the Virgo Supercluster because many of its galaxies reside in the Virgo constellation, it stretches across a phenomenal 110 million lightyears and houses tens of thousands of individual galaxies. It is somewhat flat, shaped like an ellipse. The…

2 min
t tauri stars: stellar adolescents

THE T TAURI phase in a star’s development is extremely violent. The young star is still undergoing gravitational contraction, but it is not yet hot enough to drive thermonuclear reactions. However, with sufficiently hot surface temperatures around 4,000˚C, virtually all its gases are electrically charged. In a normal gas, atoms are electrically neutral because they are made up of equal quantities of positive and negative charges bolted together. But if the gas is hot enough, the heat shakes the atoms apart. This process is known as ionisation and the charged atomic fragments are called ions. So, a T Tauri star, like a true star, is a gigantic ball of electrically charged gas – a plasma. Compared to a star like the Sun, the average T Tauri is typically a few times…

2 min
barred spiral galaxies: the dominant spirals

Scan to see an animation of the Milky Way Galaxy THE MILKY Way is an example of a spiral galaxy. More precisely, it belongs to a subclass called the barred spirals. They make up more than half of all spirals, perhaps as many as two-thirds, so they are predominant. Barred spirals are similar to their regular siblings in almost every way. Both classes have bright spiral arms encrusted with rich star-forming regions full of young stars; both have nuclear bulges filled with geriatric, reddish stars; both are flat and rotate about the central hub; and both are surrounded by halos of globular clusters, each containing up to a million individual stars. The difference is that in a barred spiral galaxy the spiral arms do not begin at the centre and wind outwards.…

2 min
giants: geriatric stars

SUBGIANTS MAY be dramatic, but they are puny compared to the stars that they are destined to become. A subgiant’s core is contracting all the time, heating up as it does. Once the core temperature is high enough, so much energy is generated that the radiation pushes on the star’s outer layers and puffs them up to even greater dimensions. With a typical diameter of a few dozen to hundreds of times larger than a normal mains-equence star, and 1,000 to 10,000 times brighter, these stars are known as red giants. When the Sun reaches the end of its life, it will expand into a red giant, with an expected diameter of around 200 times its current size – easily large enough to engulf the innermost planets, possibly including Earth. Eventually,…