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The use of light/dark hemispheres
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Gerald Kelleher
Jan 3, 2023, 5:23:52 AM1/3/23
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The first Sun-centred astronomers were keen to account for observations that didn't make sense in a geocentric framework, and to a large extent, they did. Using a telescope to account for why Venus doesn't change its appearance significantly to a slower-moving Earth using its phases is one such use of the light/dark hemispheres relative to the central Sun-
http://www.masil-astro-imaging.com/SWI/UV%20montage%20flat.jpg
"But the telescope plainly shows us its horns to be as bounded and distinct as those of the moon, and they are seen to belong to a very large circle, in a ratio almost forty times as great as the same disc when it is beyond the sun, toward the end of its morning appearances.
Sagr; Oh, Nicholas Copernicus, what a pleasure it would have been for you to see this part of your system confirmed by so clear an experiment!
Salv; Yes, but how much less would his sublime intellect be celebrated among the learned! As I said before, we may see that with reason as his guide, he resolutely continued to affirm what sensible experience seemed to contradict. I cannot get over my amazement that he was constantly willing to persist in saying that Venus might go around the sun and be more than six times as far from us at one time than at other times as at another and still look always equal when it should have appeared forty times larger." Galileo
A variation of this approach is when Mercury and Venus are behind the Sun ( not possible to observe in Galileo's era) as they show us their full light hemisphere-
https://www.youtube.com/watch?v=w2uCtot1aDg
When Mercury shows up within a day or so, it will be barely visible as it moves faster than the change in position of the background stars as it shows its dark hemisphere to us and on rare occasions ( planetary transit) it is totally dark-
https://www.youtube.com/watch?v=0yNzSwlnQ2Q
So, keep an eye out for Mercury overtaking the slower-moving Earth in a few days and enjoy this new type of astronomy made possible with satellites and the internet-
https://sol24.net/data/html/SOHO/C3/96H/VIDEO/
http://www.masil-astro-imaging.com/SWI/UV%20montage%20flat.jpg
"But the telescope plainly shows us its horns to be as bounded and distinct as those of the moon, and they are seen to belong to a very large circle, in a ratio almost forty times as great as the same disc when it is beyond the sun, toward the end of its morning appearances.
Sagr; Oh, Nicholas Copernicus, what a pleasure it would have been for you to see this part of your system confirmed by so clear an experiment!
Salv; Yes, but how much less would his sublime intellect be celebrated among the learned! As I said before, we may see that with reason as his guide, he resolutely continued to affirm what sensible experience seemed to contradict. I cannot get over my amazement that he was constantly willing to persist in saying that Venus might go around the sun and be more than six times as far from us at one time than at other times as at another and still look always equal when it should have appeared forty times larger." Galileo
A variation of this approach is when Mercury and Venus are behind the Sun ( not possible to observe in Galileo's era) as they show us their full light hemisphere-
https://www.youtube.com/watch?v=w2uCtot1aDg
When Mercury shows up within a day or so, it will be barely visible as it moves faster than the change in position of the background stars as it shows its dark hemisphere to us and on rare occasions ( planetary transit) it is totally dark-
https://www.youtube.com/watch?v=0yNzSwlnQ2Q
So, keep an eye out for Mercury overtaking the slower-moving Earth in a few days and enjoy this new type of astronomy made possible with satellites and the internet-
https://sol24.net/data/html/SOHO/C3/96H/VIDEO/
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