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Re: What do stars look like in your eye?
From: Frank Reed CT
Date: 2004 Apr 24, 13:44 EDT
From: Frank Reed CT
Date: 2004 Apr 24, 13:44 EDT
Jim T wrote:
"I wonder where my right eye's biological optics stand compared to experienced sextant-users."
We could swap for a week and compare... <g>
And:
"Venus last night was simply a bigger star-like image. Frank Reed suggested putting the center of Venus on the moon's limb and accounting for SD, but there is no way that I could see that with my biological and physical optics. Is that average or bad?"
Just to clarify, the suggestion was to center Venus on the limb OR account for SD by bringing the limb of Venus to the limb of the Moon (not "and"). With the other planets, there's little question that you should center the image on the limb and that's probably the best advice with Venus, too.
I would recommend taking a look at Venus through a pair of binoculars so that you have a better idea of what you should be seeing through your sextant's telescope. Venus, right now, is 0.5 AUs away from the Earth and approaching quickly. It's 8000 miles across so its angular diameter is 8000/46500000 or 1/5812. To convert that angle to minutes of arc, you multiply by 3438 (a number worth remembering!). That yields about 0.6 minutes of arc. This should be resolvable as a small disk through your sextant. Of course Venus right now displays less than a full disk. It's a waning crescent roughly 40% full. It will look like a tiny moon. If you see something else through your sextant --a spikey point as you've described-- try using one of your sextant's shades to reduce the planet's dazzling brightness. You should also check the focus of your sextant's telescope.
Frank E. Reed
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"I wonder where my right eye's biological optics stand compared to experienced sextant-users."
We could swap for a week and compare... <g>
And:
"Venus last night was simply a bigger star-like image. Frank Reed suggested putting the center of Venus on the moon's limb and accounting for SD, but there is no way that I could see that with my biological and physical optics. Is that average or bad?"
Just to clarify, the suggestion was to center Venus on the limb OR account for SD by bringing the limb of Venus to the limb of the Moon (not "and"). With the other planets, there's little question that you should center the image on the limb and that's probably the best advice with Venus, too.
I would recommend taking a look at Venus through a pair of binoculars so that you have a better idea of what you should be seeing through your sextant's telescope. Venus, right now, is 0.5 AUs away from the Earth and approaching quickly. It's 8000 miles across so its angular diameter is 8000/46500000 or 1/5812. To convert that angle to minutes of arc, you multiply by 3438 (a number worth remembering!). That yields about 0.6 minutes of arc. This should be resolvable as a small disk through your sextant. Of course Venus right now displays less than a full disk. It's a waning crescent roughly 40% full. It will look like a tiny moon. If you see something else through your sextant --a spikey point as you've described-- try using one of your sextant's shades to reduce the planet's dazzling brightness. You should also check the focus of your sextant's telescope.
Frank E. Reed
[ ] Mystic, Connecticut
[X] Chicago, Illinois
