Star Spy: picking south
FREIDL HALE - TEKAPO STARLIGHT
South Pole in the sky
If you go out and face south at about 11pm at the beginning of the week, perhaps 9.30pm by the end of the week, you will see the sky as it appears in Fraser's photo above.
There is a point in the sky above the horizon, level with the Cross at that hour, that is true south.
If you were standing at the South Pole this point would be directly above your head.
This empty yet important point is called the South Celestial Pole (or SCP) and, unfortunately for us here in the south, there is no bright star to mark it as there is for the northern pole.
If you think of it as the centre of a clock, the Southern Cross is at about three o'clock.
The SCP is directly south of you, wherever you are located, so it can help you find your way if lost at night.
It is also interesting as all the stars appear to rotate clockwise around it. Actually it is we here on Earth doing the rotating, in the other direction on our planet's north-south axis.
Earlier in the evening the Southern Cross will be higher and pointing a little downward, around two on this celestial clock.
The Clouds of Magellan
Since there is no moon this week, if you can find a dark area away from town lights, you can see two apparently puffy white clouds floating in the sky near the pole. They are dim, but should be visible if you give your eyes a few minutes to adjust to the darkness.
If you watch for a few minutes you will notice that the clouds don't seem to dissipate or change their shape as you might expect.
This is because they are actually galaxies, and very close neighbours to our own Milky Way Galaxy.
They have been known since ancient times to Arab tribes, so that in 964 the Persian astronomer, Al Sufi, called the larger cloud al-Bakr, "'the sheep' of the southern Arabs", in his Book of Fixed Stars.
The two clouds are more recently known as the Clouds of Magellan because they were observed on Portuguese explorer Magellan's around-the-world expedition in the 1500s.
These galaxies are rather shapeless and much smaller than our galaxy, so are referred to as irregular dwarf galaxies. The large one appears to occupy about the same amount of space as the Southern Cross, perhaps the size of a child's fist held up toward the sky.
Until recently believed to be in orbit around the outside of our galaxy, the Magellanic Clouds are now thought likely to be moving toward us, pulled by our strong gravity.
In Star Spy, we have looked at a few bright stellar nurseries in our own galaxy, but none so large or luminous as the Tarantula Nebula in the LMC.
In fact, this enormous bright starburst region is the largest and most active star-forming area known, not only in the Milky Way, but in the entire "Local Group" of about 50 galaxies including our own.
This is in spite of the fact that the Milky Way and at least 2 other galaxies in the group have around 10 times the mass of the LMC.
Fraser's picture of the Tarantula Nebula is a five-minute exposure through his 400mm camera lens.
Note that this week Mars will pass between Saturn and Spica and the two planets will set together at about 11pm on Tuesday.
- © Fairfax NZ News
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