26-07-2008 So Where Have You Been Today? (Article 147)

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Simon Kenny
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26-07-2008 So Where Have You Been Today? (Article 147)

Post by Simon Kenny » Tue Dec 30, 2008 9:33 pm

So Where Have You Been Today? (Article 147)

Perhaps to the shop, to work or just stayed in? It is often a good idea to take a different perspective — let’s look at the bigger picture. Imagine yourself, sitting on your favourite chair, located above the centre of our Galaxy, the Milky Way Galaxy, looking down on the Galaxy.

You will notice four motions: the whole galaxy is moving through space, the Galaxy is rotating about its centre, the Earth, located towards the outer edge of the Galaxy is rotating around the Sun and the Earth itself is rotating about its own axis.

Let’s take the Earth’s rotational motion. At the equator, it is about 0.5 Km/s or 1800 Km/hour but if you live at the North Pole you will simply pirouette, just like a ballerina or ice skater. At our position on the Earth’s surface, the rotation velocity is about 0.3 Km/s.

The earth rotates around the sun at about 30Km/s, while the Sun, including the whole solar system rotates around the centre of the Galaxy at about 230Km/s. However, we need to take account of the fact that the Earth’s rotation will be in the same direction as the galaxy’s rotation for six months (230Km/s +30Km/s) while for the remaining 6 months of an Earth year it will be in the opposite direction (230Km/s —30Km/s). Let’s take 230 Km/s.

The Milky Way forms part of a group of galaxies known as the Local Group, which has a velocity of about 40 Km/s through space. Finally, if you could move even further away, there is a fifth motion where the Local Group is moving, as part of the Local Super Cluster of galaxies (the Virgo Super Cluster), at about 600 Km/s. If the velocities are simply added: 0.3 Km/s + 30Km/s + 230Km/s + 40 Km/s + 600Km/s, which in round figures equals 900 Km/s or 3240000 Km/hour. That is some roller coaster.

As to where we are headed and at what velocity, it’s a bit more complicated. The velocities cannot simply be added, as above, and the direction is towards, what cosmologists call, the Great Attractor.

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