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Astronomy – What can we see in the night sky?
What is light?
Light arrives on our planet after a speedy trip from the Sun, 149 million km away.
Light travels at approx. 300,000 km per second, so the light you're seeing now was
still tucked away in the Sun about eight minutes ago.
The Math: Light travels at approx. 300,000km/sec
60sec in a minute = 300,000x60 =18,000,000km/min
149,600,000km (sun to earh) / 300,000 (speed of light) = 498.7sec or 8.3min
Example 1: Take a head torch and flash it up at the tarp or over to a tent.
Q?: If light could curve around the earth and land back at this headtorch/tarp/tent (if
in a vacuum and unhindered) – how long do you think it would take?
The circumference of the earth is 40,075km.
A: It would take 0.13sec to travel the entire distance around the earth.
Another way of saying this is that in one second, light could travel the
circumfrerence of the earth (40,075km) 7.5 times.
So, if Light takes 0.13seconds to travel the same distance as the circumference of the
earth, and about 8min to travel from the Sun to the earth… then how long has it
taken to travel from our closest star to your eyes? How long would it take to travel
to other planets from the sun?
Stars
Stars are the most numerous objects visible in the sky. On a clear dark night, you’ll
see about 3,000 stars with your unaided eye. Every star you see belongs to our own
galaxy, the Milky Way, which holds some 200 billion stars altogether.
Take a look at the stars on the next clear night. Aside from differences in brightness
from star to star, you will also see differences in color. Some stars, like Rigel in the
constellation Orion, are blue. Others, like Altair in Aquila, are white. Arcturus, a
bright star in the northern spring sky, is yellow-orange. Yet others, like Betelguese in
Orion or Antares in Scorpius are a deeper orange-red.
The closest neighboring stars to our sun Alpha
(one of the pointer stars
to the Southern Cross) which is actually three closely positioned stars. They are a
little over 4 light years away (The distance measured in the time light takes to travel
that distance because the number in kilometers would be ridiculously large – about
9.5 trillion km)!
Constellations and Stories
Every people group on earth have used the night sky to convey information. From
telling the seasons, to navigating the seas; from conveying morals and myths to
telling the time.
Indigenous Australians saw figures and created stories not only from the visible parts
of the sky, but also from the dark parts of the sky.
Dark patches in the sky
Unlike Greek celestial tradition, which focuses almost exclusively on stars, Aboriginal
astronomy focuses on the Milky Way and often incorporates the dark patches
between stars.
The Emu in the Sky, a story common to many Aboriginal groups, is
an example of this — its body is made up of the dark patches in the Milky Way. The
Boorong people saw the same dark patches as the smoke from the fires of
Nurrumbunguttias, the old spirits. The Kaurna people saw the Milky Way — called
Wodliparri or hut river — as a large river where a Yura (monster) lives in the dark
patches.
To the Ngarrindjeri people, the dark shape formed by the Southern Cross
is the stingray Nunganari and the pointers are Ngarakani, or sharks.
The emu in the sky
During the Dreaming, a blind man lived with his wife in the bush. Every
day he told his wife to go out and hunt for emu eggs for him to eat. Even
though his wife tried hard to please her husband, he was always angry
with her, telling her that the eggs were too small.
One day while she was out hunting, she came across some very large
emu tracks. She thought of her husband and how angry he got, and
followed the tracks all the way to the nest. She found a huge emu there
and threw stones at it to get at the eggs, but it stood up and ran towards
her and killed her.
The blind man became hungry and worried about his wife. He felt
around the camp until he came across a bush with some berries on it
and ate some of them. Suddenly he could see. He made some spears
and a woomera and set off to find his wife. He followed her tracks and
finally saw the huge emu and the body of his wife. He speared the emu
and banished its spirit to the Milky Way, where it can still be seen today.
— a story from Papunya, Northern Territory
—
This constellation is made up of dark nebulas, rather than by stars in the milky way
(warrumbul).
In Autumn, the Emu stretches from the South to the South-east, giving the
impression the Emu has legs and appears to be running (female emu birds chase the
males during mating) this time indicates mating season and egg laying. Emu eggs will
be ready to eat. In Winter, the Emu appearance changes with the legs disappearing,
so now it is the male Emu sitting on its nest, hatching the new chicks. This time is
also for egg collections. In late winter, the Emu becomes indistinct, with the body
shape now representing an emu egg. This indicates the chicks are hatching and eggs
are no longer available. In Spring, the Emu appears to be sitting on the horizon. This
is interpreted as the Emu sitting in a waterhole, which indicates the waterholes are
full (typical after the winter rains). Later in Summer the Emu dips even lower. Now
the Emu is believed to have left the waterhole (the usual case as the country
becomes dry in the summer months). The Emu in the Sky will not be visible again
until its head peaks above the horizon in late summer, followed by the body in
March.
The Kulin People, who come from the region around the city of Melbourne, and the
Wotjalbaluk People of western Victoria have a creator being named Bunjil the eagle.
Bunjil is represented in the sky by the star Altair (Alpha Aquilae) in the constellation
Aquila. There are no prizes for guessing that Aquila is another eagle in the sky, but
one of the classical 88-constellations as used by astronomers today. Bunjil has two
wives in the form of black swans that sit either side of him represented by the stars
Tarazed (Gamma Aquilae) and Alshain (Beta Aquilae).
To be found within The Dreaming there are many stories throughout the diversity of
Aboriginal groups which speak of eagles.
For example, the Kaurna People of the Adelaide Plains have an eagle constellation
known as Wilto. The Southern Cross represents the foot of this stellar raptor which
can be easily seen from the southern hemisphere.
Finding the South Pole using the Southern Cross
The Southern Cross is one of the best known asterisms in the night sky, and the most
familiar star pattern in the southern hemisphere.
Composed of five stars forming the shape of a cross, it is the most distinctive feature
of the constellation Crux, the smallest constellation in the sky. The Southern Cross is
notable for containing two bright stars, Acrux and Gacrux, that point the way to the
Southern Celestial Pole.
To find south:
1. Find the Southern Cross.
2. Draw an imaginary line through the long axis of the Southern Cross beginning
with the
star that marks the top of the cross. (Note: during summer, the Southern
Cross is low
in the sky and therefore upside-down).
3. Extend the line four and a half times the length of the cross.
4. This will bring you to the point in the sky called the South Celestial Pole.
5. From this point, drop a line vertically down to the horizon. This gives you the
direction
of true south. Compasses find magnetic north/south, not true north/south –
a compass needle will show magnetic south to be 11 ̊ west of true south
when measured from Victoria.
Alternate: This method involves using the two bright Pointer stars (Alpha Centauri
and Beta Centauri) that lie near the Southern Cross in the constellation of Centaurus.
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After step 2 above, draw a perpendicular bisector between the two Pointers,
that is, a line starting at the mid-point between the two Pointers and coming
out at right angles. This line should cross the line you drew in step 2.
The intersection of these two lines is close to the South Celestial Pole.
Phases of the Moon Diagram