Ellipse – Mallaband-Brown

Sunlight streaming through the window Shines on Christmas cards and books, ornaments my sewing kit. As the sun rises it also travels south in the sky in winter. Then in the afternoon it appears to move downwards and West. So because of the way the earth is tipped on its axis the position on the sky moves in arcs that tip further south in the winter and further north in summer. So the sun appears overhead eventually.

If the Earth was rotating on a vertical axis at 90° to the plane of the solar system, then day length would stay the same all over the world. 12 hours day and 12 hours night. There would be no seasons. There would probably be no poles as all parts of the earth would receive the same amount of heat from the sun.

Instead the tip of the axis means that the day length changes over the years. So at the solstices the earth has turned to have its poles either closest or furthest apart from the sun. It’s also complicated by the earth travelling in an elliptical orbit round the sun. In the summer in the North of the world the sun is actually slightly further away from the earth than in the winter.

Anyway enough of celestial mechanics. Don’t get me started on the moon! Happy Boxing day. X

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There was an eclipse today in some parts of the world. Not here though. This was an annular eclipse, where the moon doesn’t fully cover the sun and leaves a ring of sun shining behind the moon.

So why does this happen. In normal eclipses the moon appears to be the same size as the sun so its completely covered. That is because the moon is something like 40 times smaller than the sun, but also 40 times closer to us. So they have the same apparent size in the sky. But with an annular eclipse the Sun can be slightly closer or the moon slightly father away. Why? Because the Earth rotates round the Sun in an ellipse, which is an oval with two focal points. The sun sits on one focus, but the Earth orbits around both. That means sometimes it is further away from the sun and sometimes closer Then it also means the moon is further away from the sun or slightly closer to it. The moon rotates round the earth in the same way in an elliptical orbit. So sometimes it is closer to, and sometimes further away. If you add the two positions up further to the sun and further away from the earth you get an annular eclipse.

I can’t explain it more clearly. It is most difficult to think your way through how it works but I hope this makes sense.

Mallaband-Brown

Tag: Ellipse

Sunlight

Annular Eclipse