All About Space Astronomer Book - 2014 UK

contains an unusual number of red giants. At a mere 25,000 light years

this is the closest galaxy known, and stars have been torn from it by the

gravitational pull of our own Galaxy, producing a ring of stars around the

Milky Way known as the Monoceros Ring.

Grus the Crane, adjoins Piscis Austrinus, the Southern Fish – the

constellation which has Fomalhaut as its brightest member. Also

near the zenith are two large but rather barren constellations,

Capricornus, the Sea Goat and Aquarius, the Water Bearer. Aquarius

is distinguished by two well known planetary nebulae, NGC 7009

(Caldwell 55), the Saturn Nebula, and NGC 7293 (Caldwell 63), the

Helix Nebula. Curiously, neither of these planetaries are in Messier’s

catalogue, whereas M73, also in Aquarius, is merely a grouping of

four stars.

The Magellanic Clouds

Now let us turn to those superb objects the Magellanic Clouds, which

are satellite galaxies of the Milky Way. Both are prominent to the

naked eye and any small telescope will show tremendous amounts of

detail in them. They are particularly important because they contain

objects of all kinds and for most purposes we can regard them as

being the same distance from us, though this is not strictly true. The

Large Magellanic Cloud is 169,000 light years from us, and crosses

the border between Dorado, the Swordfish, and Mensa, the Table. It

contains the magnificent Tarantula Nebula, a gaseous nebula which

would cast shadows if it were as close as M42 in the Sword of Orion.

In 1987 a supernova blazed up in the Tarantula and became an easy

naked eye object.

The Small Magellanic Cloud is 197,000 light years away, and

contains several hundred million stars. It lies in Tucana, and gives the

impression of being associated with the globular cluster 47 Tucanae. It

contains a number of Cepheid variables, and it was by studying these

that Henrietta Swan Leavitt established the vitally important Cepheid

period-luminosity law. As they are so prominent to the naked eye,

both Magellanic Clouds must have been seen in ancient times, but the

first mention of them was by Al-Sufi in 964AD. They were described by

the crew members of Ferdinand Magellan’s voyage round the world in

1519, hence the name.

Both clouds have been classed as irregular galaxies and in each

case there are indications of a rather ill defined central bar. They are

certainly not spirals. The Milky Way galaxy contains a number of other

dwarf satellite galaxies of which the closest is the Canis Majoris dwarf.

It is hard to detect because it lies behind the plane of the Milky Way and

SPRING (SOUTHERN HEMISPHERE)

In spring we have the Square of Pegasus reasonably high in the northeast

but Andromeda is always very low down and it is by no means easy to

locate the Andromeda Galaxy M31. Fomalhaut in the Southern Fish is

practically at the zenith and one can appreciate how bright it really is. It

is a particularly interesting star because it is the centre for a system of

planets, and one of these has actually been imaged.

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