NEBULA
VOLUME 44 I ssue 2
PAGE 10
THE SUN: OUR AMAZING STAR
by Chris West
Our nearest star, the Sun, is by
far the most important source of
energy for life on Earth. Its di-
ameter is about 109 times that of
the Earth, and its mass is about
330,000 times that of Earth, whilst
accounting for about 99.86% of
the total mass of the Solar System.
About three quarters of the Sun’s
mass consists of hydrogen, the rest
is mostly helium, with much
smaller quantities of heavier ele-
ments, including oxygen, carbon,
neon and iron.
The Sun is a G-type main-
sequence star, (G2V), based on
spectral classification, and it is
informally referred to as a yellow
dwarf by astrophysicists.
It
formed approximately 4.6 billion
years ago from the gravitational
collapse of matter within a region
of a large molecular cloud. Most
of this matter gathered in the cen-
tre, whereas the rest flattened into
an orbiting disc that became, even-
tually, the Solar System that we
know today. The central mass be-
came increasingly hot and dense,
due to the effects of gravity, even-
tually initiating nuclear fusion in
its core. The consensus among
astrophysicists is that all stars form
through this process.
The Sun is middle-aged, and has
not changed dramatically for over
4 billion years, and will remain
fairly stable for a further 5 billion
years. However, after hydrogen
fusion in its core is shut off, the
Sun will start to fuse helium to
carbon, and will undergo severe
changes and become a red giant. It
is calculated that the Sun will
eventually become sufficiently
large and bloated as to engulf the
current orbits of Mercury, Venus
and possibly Earth. The star which
sustains all life on Earth will, ulti-
mately, destroy all life, including
humanity, should our far descend-
Hertzsprung-Russell Diagram: an important tool for determining
how stars evolve (image: NASA/GSFC)
ants choose to remain here on our
planet.
The English proper noun, Sun,
developed from Old English,
Sunne, and may be related to,
South. Similarities to English,
‘Sun’, appear in other Germanic
languages, including Old Frisian,
Sunne, Old Saxon, Sunna, Middle
Dutch, Sonne, modern Dutch, Zon,
and modern German, Sonne. The
English weekday, Sunday, stems
from Old English, Sunnandaeg,
“Sun’s day”, from before A.D.
700, and is, ultimately, a result of a
Germanic interpretation of Latin
dies solis, itself a translation from
Greek. The Egyptians worshipped
the sun god, Ra, from at least the
4 th Dynasty of Ancient Egypt. In
the form of the Sun disc, Aten, the
Sun enjoyed a brief resurgence
during the Amarna Period, when it
became the preeminent, if not on-
ly, divinity for the Pharaoh Akhe-
naton. Other cultures, including
the Hindu, Japanese and Aztec,
had a rich tradition of Sun wor-
ship.
Coming back to the present, of
course there is almost an infinity
of other stars – about 200 billion in
our Galaxy, alone. But that bril-
liant, yellow/orange ball of ionized
gas in our skies cannot help but
have a special place in our hearts
and minds, in our science, litera-
ture and mythologies. Our Sun
sustains all life on our planet, as
well as driving our weather and
climatic systems. By studying our
Sun, we will, in addition, learn
much more about the other stars,
and vice versa. Our Sun is an end-
lessly fascinating object of study in
its own right, and the future will
have much, much more light to
shed, pardon the pun, on our clos-
est star.