" being a glowing ball of gas; then you might expect the

by Allen Wootton
so Terrace Contributor.
TERRACE —During July we should be able to see a lot
of the Sun. For this reason, I. will concentrate on the ~

- Sun for this month’s article, —

For an astronomical object, the Sun is quite close to
us (only 150 million km away). Light, which travels at -
the incredible rate of 300,000 km each second, takes just
over 8 minutes to travel this distance. For comparison,
light from the next nearest star to the Earth, Proximal

Y

Centauri, takes 4.2 years to arrive. .

There is nothing to indicate that the Sun is anything
other than a typical, and: very average, star. About 75
percent of its huge mass is the element hydrogen, The
Test is mainly the element helium with less than 1 percent .
being composed of oxygen, carbon, and other elenients.

_ All this mass is contained in a ball that is about 1.4

million kilometres across and: ‘about 6,000 degrees
celsius at the surface... .

_ Other stars are'much too far away for usto be able to’
see their surface features. It is possible, however, to see.
features of the Sun and I have included a photo. that

shows some: of them.

The photo is one of a series I took a few years ago”
over a period of about a month. If you look carefully
you will notice that the edge is quite well defined and .
that the edge is dimmer than the centre. The sharp, well.
defined edge is surprising if you think of the Sun as just .

light to trail off gradually instead of forming a well
defined: boundary. That the boundary is relatively sharp
and indicates that the light from the Sun comes from
quite’a ‘thin layer’ neat’ the surface. ‘This layer ‘is called:
the photosphere. The dimmer edge occurs because light
from that.region has to travel through more of the
cooler outer atmosphere of the Sun and more of the
light islosttous. . . | - _ a
“You ¢an also clearly. see. sunspots on. the photo. .’
Sunspots have been known’ since: antiquity although.
through much of European history their existence was:
‘ignored for it was assumed:that the Sun must ‘be a
“‘perfect’” sphere with no blemishes of any-kind.. Now
sunspots are known. to. be cooler regions on the Sun’s-.
surface.. Sunspot temperatures are. about 4000 desrees..
celsius. — still very warm.— and.while' they look small _
their average size is about 10,000:km in diameter (about
the size-of the Earth) and large ones of up to 150,000 kin.

‘diameter have. been recorded:. As well, sunspots are. . |

regions of: unusually © high” magnetic’ field, many _

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“ASTRONOMY CALENDAR -

thousands of times that of the Earth’s magnetic field,
It is thought that sunspots result from.the interaction
of convection currents below the surface of the Sun and

‘magnetic fields that result from its rotation, Because-of

this interaction, material from below the surface is forc-
ed up to form the sunspot. This material is cooler
because of its high magnetic field and low gas density.

Sunspots appear in cycles of about 11 years in length.
At the start-of.a cycle there are a few sunspots and they
appear some distance either side of the Sun’s equator.

Later in the cycle there will be a lot of sunspots nearer.

the equator. Towards the end of the cycle there are few
sunspots and they will be very near the equator. When I
took the picture it was near the height of the current

sunspot cycle. Now it is near the end: of the same cycle.

so there are few sunspots. Using the apparatus shown in

- the pictures, I was able to see one.large one a few:days. :

ago, however.

The apparatus I used is safe‘as long as you do not |
look at the sun through the binoculars. To do so would:

Terrace Review — Wednesday, July 8, 1987 15 oF

destroy your eyesight. You must look only at the Sun’s
image that is formed on the cardboard screen behind the |
binoculars. Note that one lens of the binoculars ‘is.
covered with cardboard so.as to make only one image so.
that there is a,region of shadow behind the binoculars.
The camera tripod just allows you to.aim the binoculars |

‘at the Sun.

I hope you have a chance to look at the Sun, You. _
might enjoy trying to find how long it takes to make one:
rotation by following the movement of a. sunspot. —
Please be. very: careful with any apparatus you.use for
viewing the Sun, however. Have a good month, ©

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