Page 118 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

DEEP SKY

GALAXIES AND CLUSTERS

THE UNIVERSE IS FULL OF STARS THAT GROUP TOGETHER INTO
CLUSTERS LARGE AND SMALL, AND VAST COLLECTIONS CALLED
GALAXIES, WHICH COME IN ALL MANNER OF GUISES

New stars form within the much smaller, containing only away, while the Hyades is only cluster are made of stars.
hazy confi nes of emission a few dozen members. 150 lightyears away. Globular star clusters are
nebulae. Over an incredibly You can see some pretty One thing the stars in open spherical in shape and consist
long time, all of an emission fi ne open clusters using only clusters do as they age is of hundreds of thousands of
nebula’s gas is either pulled your eyes, such as the famous drift apart. This means that stars at least – indeed some
into new stars or pushed Pleiades – also known as the younger clusters are a more have several million members.
away into space by their Seven Sisters – and the Hyades, tightly knit community. Taking Unlike young open clusters,
radiation, revealing a new both in the constellation of our two friends in Taurus as which sit within the main
stellar family – an open Taurus, the Bull. We know an example, the compact body of the Milky Way Galaxy,
star cluster. that these and other open star Pleiades is around 100 million these ancient globular clusters
How many stars there clusters are families due to years old, but the looser Hyades live in a halo around it and
are in an open cluster depends the similar make-up of the has been around for about are tens of thousands of
on the amount of gas and stars and because they move 790 million years. lightyears away from us.
dust in the original nebula. through space together. We know our Galaxy is
The oft-mentioned Orion Although hundreds of GREAT GLOBULARS surrounded by around
Nebula is a great example of star clusters are visible Now, just to make things more 160 globular clusters. You can
an emission nebula that will through a small telescope, interesting, there’s another spot a few with the naked eye,
produce a massive open star the brightness of these two sort of star cluster known as a like M13 in the constellation
cluster in the future, possibly is due to their relative globular. They have nothing to of Hercules, but they are best
containing around 1,000 closeness to Earth. The do with open clusters; the only seen through binoculars or a
stars. Some star clusters are Pleiades is 380 lightyears similarity is that both kinds of small telescope.
N.A.SHARP/REU PROGRAM/NOAO/AURA/NSF, NASA/ESA/AND THE HUBBLE HERITAGE TEAM (STSCI/AURA)-ESA/
GALACTIC VARIETY

There are estimated to be 100 billion galaxies in our Universe – these are the main types
HUBBLE COLLABORATION, NASA/ESA/AND THE HUBBLE HERITAGE TEAM (STSCI/AURA) X 3

SPIRAL BARRED SPIRAL ELLIPTICAL IRREGULAR
These galaxies take the shape These are similar to spiral The elliptical class may include Irregular galaxies don’t fi t
of a fl attish disc with a central galaxies, except the arms start the largest of all galaxies, but into any particular class. A
bulge. The disc itself is made from a bar-like structure that they are rather structureless galaxy of this type has probably
of curving arms of dust, gas stretches out from the centre. collections of old stars. They been involved in a collision
and stars that sweep out Astronomers believe the Milky typically have a lot of globular with another galaxy, which
from the centre. Way is this type of galaxy. clusters in their outer regions. has twisted its appearance.
118 skyatnightmagazine.com 2012