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Astronomy newsletter March 2010 |
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From December untill now we had some good stargazing times, thanks to clear
nightskies. |
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Although Taurus and Orion still can be seen, they have shifted further to
the west. The Southern Cross is rising in the |
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south-east and Mars, the red planet, shines
bright in the north. |
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| Mars |
| Often
referred to as the red planet beacause of its red appearance due to
iron-oxide (rust). |
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normally so far away that even with a large telescope it appears just as a
tiny red dot. This rocky and dusty |
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is much cooler than Earth, since its orbit around the Sun is (avarage) 50%
further away. |
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temperatures vary from -133°C at the poles during winter, to a pleasant 27°C
on a summers day. |
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The avarage distance from the Sun to Mars is
1,52 AU (Astronomical Unit). 1 AU is the distance between the Sun
and |
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the Earth, which is about 150
million km. |
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The closest distance to Earth is 56 million
km and |
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400 million km is the ditance furtherst from
Earth, |
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which it will reach on 30 March. |
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Mars orbits the Sun in 687 days so a year is
almost |
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twice as long as on Earth. |
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The largest volcano
in our Solarsystem, Olympus |
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Mons (Latin for Mount Olympus) is on Mars and
rises |
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24 km above the surrounding planes. |
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Mars has 2 moons: Phobos and Deimos. Both are
small |
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and Phobos orbits
so fast that is rises and sets twice a |
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day, seen from
Mars' surface. |
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Life on
Mars? |
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In 1938
Orson Welles created panic when he announced in an American radio drama (War
of the worlds), the invasion of |
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the
Martians. People gathered on the streets because they really believed that
New Yersey was under attack! |
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In July
1976 the Voyager 1 captured this picture of some hills in the Cydonia
region. |
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NASA released this picture under the
impression that it would |
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make a light-hearted story but there was a
much greater |
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public fascination
then they had expected. |
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Just above the centre a face can be seen and
this led to |
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numerous speculations about life on Mars. |
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Only much later new
pictures of this region with better |
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equipment showed
that the "face" was nothing more then |
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lightfall on the
landscape. |
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There is however
overwhelming proof that there was lots of |
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water on Mars once.
A part of it is now locked away in the thin |
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polarcaps but what happened to the most of it? One theory is that it lies in
the permafrost, just below the surface. |
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This
month on NGC a documentary can be seen on terraforming on Mars. A process to
create a new earth-like world by |
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melting
the ice and thus forming an atmosphere. Science-fiction or future? |
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On a personal note, I estimate the chances of
anything coming from Mars a million to one.... |
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The Southern Cross. |
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Only vissible in the southern hemisphere and
used to navigate since one can determine the (celestial) south using this |
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constellation. At this time of year Crux can be seen in the south-east. |
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The 2 bright stars
on the left of the picture are Hadar |
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(or beta Centauri)
above and Rigel Kentaurus (or alpha |
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Centauri) below.
Together they form the "pointers", so |
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called because they point out the Crux. |
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Rigel is actually a
triple star consisting of 2 sun-like stars |
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called alpha
Centauri A and alpha Centauri B, and a tiny |
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red-dwarf star
called Proxima Centauri. This one is the |
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closest star to the
Sun, only 4, 24 lightyears. |
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Just left of the
Cross you can see a dark patch. This is |
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a dark nebula
called the coalsack. It is a cold cloud of |
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dark
hydrogen that blocks the light of stars behind it. It is at about 500
lightyear distance. |
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Between
the coalsack and the left star of the Cross lies the jewelbox which is an
open starcluster about 7.000 lightyears |
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away. Even with your binoculars you can
easily see the glowing jewels in the nightsky. |
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African lore. |
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The coalsack was named "the old bag of night"
by the Nyae !Kung Bushmen. |
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The /Xam Bushman new the Pointers (Alpha and
Beta Centauri) as male lions and the three brightest stars in Crux as
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lionesses. |
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What is a star? |
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A star
is a rotaing sphere of plasma, hot ionised gas. |
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After a
newborn stars's core is heated by gravitational contracttion, nuclear fusion
of hydrogen into helium takes place. |
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The energy produced builds up enough pressure
to balance the enormous forces of gravity, and a normal star like our sun
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settles
into a long stable period of existence. |
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A photo of our sun,
taken by the SOHO space probe. |
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The hottest areas
appear almost white, while the darker red |
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areas indicate
cooler temperatures. |
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A huge plasma cloud
erupting on the surface can be seen top |
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right. |
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The age of the sun
is estimated on 4,6 bilion years. |
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It has another 5
billion years to go before it peters out and |
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becomes a white
dwarf star. |
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Nothing to be
worried about yet! |
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The
sun's surface is called the photosphere and is about 500 kilometers thick. |
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It
takes lightwaves 8 minutes to travel the distance from the sun's surface to
the Earth (150 million km). |
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The sun
has 6 regions. |
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1) the
core |
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2) the
radiative zone |
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3 the
convective zone in the interior |
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4) the
visible surface known as the photosphere |
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5) the
chromosphere |
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6) the
outermost region, the corona |
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The sun
is magnetically active. It has a strong, ever-changing, magnetic field that
varies continuously and reverses direction |
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once
every 11 years so south becomes north and vice versa. |
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Sunspots on the surface are areas with strong magnetic fields that are
cooler and thus darker then the surrounding area. |
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This is
the reason they appear as almost black spots when viewed through a
telescope. |
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A solar
flare, also called "solar prominence" occurs when magnetic energy that has
build up in the solar athmosphere |
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is
suddenly released. These flares take on the appearance of a huge "flame"
rising up from the surface of the sun. |
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If you
line them up one by one a 110 Earths will fit into the diameter of the sun
and 1,3 million crushed-up Earths can fit |
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into
its volume. |
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The
brightest star we can see in the nightsky at this moment is Sirius in Canis
Major. |
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Sirius A is the
bright star we see (top left) while Sirius B is |
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a (massive) white dwarf. (the small blue one
on the right) |
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Sirius A is about twice as massive as our sun
and it is |
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25 times more luminous. |
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Sirius B weighs almost twice the solar mass
but is only |
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about the size of the Earth. |
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March and April Highlights: |
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25
March: Moon lies about 4° west of M44 (the Beehive open cluster) with Mars
some 4.5° north-west of this. |
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30
March: Full moon |
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11
March: Mars at aphelion (farthest distance from the sun) |
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11
March - 16 April: Delta Pavonids meteor shower (02:00 - 04:30) |
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12 - 12
April: At 05:00 a cresending moon can be seen together with Jupiter. Uranus
and Neptune will be binocular objects. |
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14
april: New moon |
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28
April: Full moon |
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From Balule: Clear skies! |
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