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 Post subject: Omega Sunrise
PostPosted: Mon Sep 21, 2020 7:48 am 
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Needs to sheet in the jib a bit...
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 Post subject: Equinox in the Sky
PostPosted: Wed Sep 23, 2020 8:33 am 
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 Post subject: ISS Transits Mars
PostPosted: Wed Sep 23, 2020 8:35 am 
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 Post subject: Enceladus in Infrared
PostPosted: Thu Sep 24, 2020 7:21 am 
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 Post subject: Moon over Andromeda
PostPosted: Fri Sep 25, 2020 9:27 am 
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PostPosted: Sun Sep 27, 2020 12:10 pm 
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Can I take this opportunity to ask why astronomical photos so rarely indicate the angular field of view? Is it because the target audience is comprised mainly of people who already know 'how big' things are and those who don't care?


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PostPosted: Wed Sep 30, 2020 7:40 am 
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For many of the images posted, the angular field of view is fractions of arc seconds. It doesn't mean much, and astronomers don't commonly use, angular field if it would read 1.3E-5 arc seconds for a galaxy cluster. A good number of the APOD descriptions will give angular field of view for larger objects, particularly those that are faint to the naked (can I say naked on this forum :shock: ) eye. Even Jupiter (and Saturn, both of which are currently prominent in the night sky), as large as it appears, ranges only from 29.8 to 50.1 arc seconds. So, at best, it would take ~72 Jupiter diameters to make one degree in the night sky. If I remember correctly (long odds here), a fist held at arms length is about 10 degrees (could be 15, don't clearly remember), so holding your fist out next to an object in the sky will allow you to "ballpark" the angular field of view.
Does this help or confuse (hint, I'm better at the latter than the former....)?

dave boling

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PostPosted: Wed Sep 30, 2020 7:42 am 
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 Post subject: Lightning over Colorado
PostPosted: Wed Sep 30, 2020 7:44 am 
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PostPosted: Wed Sep 30, 2020 7:46 am 
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PostPosted: Wed Sep 30, 2020 7:48 am 
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APOD video
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PostPosted: Wed Sep 30, 2020 7:50 am 
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Yet another APOD video
dave boling

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PostPosted: Fri Oct 02, 2020 10:45 am 
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daveboling wrote:
For many of the images posted, the angular field of view is fractions of arc seconds. It doesn't mean much, and astronomers don't commonly use, angular field if it would read 1.3E-5 arc seconds for a galaxy cluster. A good number of the APOD descriptions will give angular field of view for larger objects, particularly those that are faint to the naked (can I say naked on this forum :shock: ) eye. Even Jupiter (and Saturn, both of which are currently prominent in the night sky), as large as it appears, ranges only from 29.8 to 50.1 arc seconds. So, at best, it would take ~72 Jupiter diameters to make one degree in the night sky. If I remember correctly (long odds here), a fist held at arms length is about 10 degrees (could be 15, don't clearly remember), so holding your fist out next to an object in the sky will allow you to "ballpark" the angular field of view.
Does this help or confuse (hint, I'm better at the latter than the former....)?

dave boling

Thanks. It's a question I had been thinking of asking on this thread for years. I guess what I actually like to know is what the angular diameter of the things I am being shown. I asked about angular field of view as that seems analogous to a map scale - which by convention is always there to help us tell if we are looking at a contour map of a mountain or a molehill. The trouble with space is that it looks much the same however much we enlarge it. I posted prompted by the Andromeda galaxy image because there we were given a sense of scale. Without the moon it could have been like a picture from Hubble of a speck of light or less to the naked eye rather than something that is actually quite 'big in the sky' but not seen like that without a little image processing.

I guess unless one is an astronomer then for most of us it's just awesome eye candy.


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PostPosted: Mon Oct 05, 2020 9:08 am 
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 Post subject: Biking to the Moon
PostPosted: Mon Oct 05, 2020 9:11 am 
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