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    Perihelion today, greatest SD
    From: Frank Reed
    Date: 2013 Jan 2, 09:41 -0800

    Perihelion this year occurred a bit earlier than average, about twelve hours ago as I write this. The Earth is now moving away from the Sun and we won't be this close to it again until next year at this time. Currently we're moving away from the Sun at a snail's pace of about 10 mph. By the end of the week, we'll be moving away at over 100 mph, and in three months, the speed away from the Sun will peak at around 1100 mph. After that the outward motion slows down again and in early July the Earth will be at aphelion, its maximum distance from the Sun.

    Naturally this is all connected with the changing semi-diameter of the Sun during the year which is about about 0.3 minutes of arc bigger than average today and will be about 0.3 minutes of arc smaller than average in July. Can you measure a change in the Sun's SD of only 0.3 minutes of arc? Try measuring the SD of the Sun today and see what you get. Do remember to use sufficient shades!


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