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Thread: sunspot orientation / time of day dependence

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    Default sunspot orientation / time of day dependence



    Hello everyone,

    Been doing some simple solar observations with solar binoculars. i like to check what i see with spaceweather. I've noticed the orientation of sun spots seems to rotate based on the time of day I observe. It's probably kind of obvious, but in what way does the apparent orientation of a spot change throughout the day? Does it depend on the observer's location on the earth? say for example in the morning there is sunspot near the 1 o'clock position. In the evening, it will be the same distance from the edge, but will have rotates to say the 7 o'clock position. Is that just because of the earth's rotation and it would make a full rotation every 24 hours?

    Thank you!

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    Default Re: sunspot orientation / time of day dependence

    Sunspots rotate with the Sun as the Sun rotates on it's axis. This allows the sunspots, from our perspective, to travel across the disk, out of sight, and sometimes to come back around again. That is movement 1.

    Now, the main thing you are noting is due to Earth's rotation, movement 2. The exact same effect occurs with the Moon, planets, constellations, and deep sky objects. When a full Moon rises, you can see prominent crater Tycho on the 3 o'clock position as it rises in the east, at 6 o'clock when the Moon passes over the meridian, and then at 9 o'clock as it settles into the west.

    Same with the equatorial bands on Jupiter, the orientation of the Andromeda galaxy, and the rising and setting of constellations. Orion, for instance, climbs out of bed from lying on his right side, walks across the sky only to lie down again on his left.

    You will also have a 3rd movement due to Earth's orbit of the Sun. This is what causes the sky to change over the year as our night side looks out upon different parts of our galaxy as we swing around our star.
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    Default Re: sunspot orientation / time of day dependence

    On a longer time scale, months say, you may notice the direction of the sunspots’ travel across the sun’s disc (Bryan’s “movement 1”) appears to change. This is because the Earth’s orbit is at an angle to the Sun’s axis of rotation. You can see what this will look like by overlaying a Stonyhurst grid on the Sun with Les Cawley’s TiltingSun2 software:--

    https://www.atoptics.co.uk/tiltsun.htm.

    Here’s a gif I made with TiltingSun to illustrate the apparent wobble over the course of a year:--

    https://www.dropbox.com/s/xyd3q689gx..._2016.gif?dl=0
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