Star Spy: The Egg and the Zodiac
FREIDL HALE-TEKAPO STARLIGHT
We’ve used the Small Magellanic Cloud (SMC) as a ‘land’ mark to assist in finding other objects, and learned that Tucana may be trying to hatch it, but it is actually a very interesting object in its own right.
Called a dwarf galaxy, it is only about 7000 light years across, pretty small when compared to the Milky Way’s breadth of over 100,000 light years.
It is also called an irregular galaxy because it lacks a distinctive shape.
The SMC is about 200,000 light years distant from Earth, below (south) of the Milky Way.
To put that into some perspective, that is around two of our galaxy-widths away, which makes it like a tiny house just a couple of doors down the street from our mansion.
But it is a galaxy, complete with all the things that go with that; clouds of gas, clusters of stars, stellar nurseries, and hundreds of millions of stars of all sizes, ages, temperatures, and lifespans.
The Small Magellanic Cloud has been traveling for a very long time with its companion, the Large Magellanic Cloud, and the two appear to exchange material in a “bridge” of gas that stretches between them.
Called the Magellanic Stream, it also sheds gas to its close mega-neighbour, our Milky Way Galaxy.
According to some recent observations the Magellanic pair are traveling too fast to have originated in our Local Group of Galaxies.
They are moving in a curved path and are likely to swing past the Milky Way in the distant future.
The bright globular cluster 47 Tucanae appears in our sky right next to the SMC, but there is no connection between them as 47 Tuc is just 17 thousand light years away in our own galaxy.
Another, similar but more distant globular cluster of stars, NGC 362, sits even closer to the SMC in our sky.
NGC stands for New General Catalogue. Created in 1888 (not as new as the name implies), it is a well-known and comprehensive catalogue of deep space objects. 47 Tuc is NGC 104.
We have seen that the ecliptic is the path followed in the sky by the Sun, Moon and planets.
The Zodiac, consisting of the 12 celestial houses of the Sun, also lies along this path, although use of the term Zodiac is now limited mostly to astrology and horoscopes.
I hope that you all were able to see this striking view of the Moon with Jupiter that Fraser captured last week.
This was possible because the Moon’s orbit around the Earth is only off a few degrees from the ecliptic, bringing it very close to the path of the planets.
As we orbit the Sun, the ecliptic is always in motion above the surface of the tilted Earth.
You may have noticed that the Sun does not always rise and set in the same places on your horizon. The same is true for the Moon and planets.
These points shift a little to the north and south of true east and west throughout the year.
To find your true east and west you need to check where the Sun rises and sets on the Equinoxes, in September and March.
- © Fairfax NZ News
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