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Eroica
2005-Jun-25, 09:56 AM
Exploring the Night Sky with Binoculars[/i],]Nu [Draconis], which is a wide double; each component is of magnitude 4.9, and the 'twins' are identical. Keen-sighted people can distinguish them both with the naked eye.
Is this true? The separation between the two components is only about 61 arcseconds, and this hasn't changed by more than a second or two in the past few decades.


About the closest star separation that the eye can distinguish is 4 minutes of arc (240 seconds of arc). Twice this distance, or an 8-minute (480 seconds) apparent field angle, is a more practical value for comfortable viewing.

2005-Jun-25, 10:46 AM
Exploring the Night Sky with Binoculars[/i],]Nu [Draconis], which is a wide double; each component is of magnitude 4.9, and the 'twins' are identical. Keen-sighted people can distinguish them both with the naked eye.
Is this true? The separation between the two components is only about 61 arcseconds, and this hasn't changed by more than a second or two in the past few decades.


About the closest star separation that the eye can distinguish is 4 minutes of arc (240 seconds of arc). Twice this distance, or an 8-minute (480 seconds) apparent field angle, is a more practical value for comfortable viewing.

But Tycho Brahe's observations typically had an error of about 2 minutes of arc and at least some writeups claim he achieved 1 arc-minute (see
http://galileoandeinstein.physics.virginia.edu/lectures/tycho.htm )

Champion_Munch
2005-Jun-25, 02:47 PM
Exploring the Night Sky with Binoculars[/i],]Nu [Draconis], which is a wide double; each component is of magnitude 4.9, and the 'twins' are identical. Keen-sighted people can distinguish them both with the naked eye.
Is this true? The separation between the two components is only about 61 arcseconds, and this hasn't changed by more than a second or two in the past few decades.


About the closest star separation that the eye can distinguish is 4 minutes of arc (240 seconds of arc). Twice this distance, or an 8-minute (480 seconds) apparent field angle, is a more practical value for comfortable viewing.

I always thought that it was 1 minute of arc, for the people with the best vision (some even claim to be able to distinguish the phase of Venus with the naked eye, but it's easy to be manipulated when you already know what orientation it's gonna be :P).

with regards

Ilya
2005-Jun-25, 10:25 PM
I always thought that it was 1 minute of arc, for the people with the best vision (some even claim to be able to distinguish the phase of Venus with the naked eye, but it's easy to be manipulated when you already know what orientation it's gonna be :P).

with regards

There is a story (not certain of its veracity) that Gauss once showed Venus to his mother through a telescope, expecting to surprise her -- as Venus was in a crescent phase. Instead, she showed no surprise at all, just asked why in the telescope the crescent was pointing the wrong way. Apparently, old Frau Gauss had eyes that good.

Extra-keen vision does occur, and is not even all that rare -- that's why optometrists' charts have the line for 20/15 vision, and sometimes for 20/10 as well.

Chip
2005-Jun-25, 11:04 PM
Stephen O'Meara observed dark radial features or "spokes" in Saturn's rings before Voyager's cameras obtained images of them. :o

gopher65
2005-Jun-26, 12:08 AM
I always thought that it was 1 minute of arc, for the people with the best vision (some even claim to be able to distinguish the phase of Venus with the naked eye, but it's easy to be manipulated when you already know what orientation it's gonna be :P).

with regards

There is a story (not certain of its veracity) that Gauss once showed Venus to his mother through a telescope, expecting to surprise her -- as Venus was in a crescent phase. Instead, she showed no surprise at all, just asked why in the telescope the crescent was pointing the wrong way. Apparently, old Frau Gauss had eyes that good.

Extra-keen vision does occur, and is not even all that rare -- that's why optometrists' charts have the line for 20/15 vision, and sometimes for 20/10 as well.

I believe that story. I've heard people could see some of the phases of Venus with their naked eye. Personally I can't, but then again without glasses I can't see my hand clearly unless it is ~1.5 inches from my eyes:P.

TriangleMan
2005-Jun-26, 04:29 PM
Extra-keen vision does occur, and is not even all that rare -- that's why optometrists' charts have the line for 20/15 vision, and sometimes for 20/10 as well.
My vision is slightly better than 20/20. 8)

Champion_Munch
2005-Jun-27, 03:22 AM
Extra-keen vision does occur, and is not even all that rare -- that's why optometrists' charts have the line for 20/15 vision, and sometimes for 20/10 as well.
My vision is slightly better than 20/20. 8)

I finally got myself some glasses a few months ago, and now the sky looks amazing! About the time I realised I couldn't see anything was when I was at the astrofest (2 hours away from the city) and I was looking at the Pleadies - I thought it was just a cloud. #-o

Just to make sure it wasn't just me, when I came back home, I asked one of my mates how many stars he could make out in that 'cloud' - he said he saw 7. This guy knows absolutely nothing about astronomy. :(

When people called it the "seven sisters", I always thought it must have been only able to have been seen in prestine conditions...not from my very backyard.

Anyway, now I can see good and the number of naked eye stars has tripled! :D

with regards