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Astro Twilight

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Alot of people talk about astro darkness, and proper darkness etc and it can be a bit confusing if you don't know what people are on about so I found this nice simple explanation of what it all means, the proper terminology and some facts about when you can expect your nice dark skies to return.

Hope it helps :)

http://astro.ukho.gov.uk/nao/miscellanea/twilight/

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There is a nice iPhone app called Sunrise Clock which shows these times in a couple of different ways, very useful

post-6762-137346313687_thumb.jpg

Stu

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That is nice Stu, thanks for sharing. I'll add that to the iPad, they don't appear to do one for android :(

I wrote a Windows widget to work with SteveL's twilight calculator.

Cheers Ant

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The good news for people who live in cities is that the greater your local LP, the lesser the effect of long summer twilight.

You can still get some cracking viewing done even if the sky isn't completely dark - or as dark as it could possibly get - just like it's possible to observe quite successfully when the Moon is up.

Just take care choosing your targets.

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thank you for this graham, great link. have been following 7 timer for the last couple of days it says. 8/7/13 civil twilight begins 03.58 ends 22.35, today it says civil twilight begins 04.03 ends 22.32. so that sounds better I think.

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Thanks for the app tip.

If I'm reading it right, we don't get full darkness (the astro time) until 20th July...

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Yep, that's about right. It shows as 21st for me but it will vary depending on where you are.

Stu

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I just looked it up, Astronomical Twilight is "when the sky is dark enough for all astronomical observations".

And for completeness:

  • Astronomical twilight is the time when the center of the sun is between 12° and 18° below the horizon. From the end of astronomical twilight in the evening to the beginning of astronomical twilight in the morning, the sky (away from urban light pollution) is dark enough for all astronomical observations.

Civil Twilight

  • Morning civil twilight begins when the geometric center of the sun is 6° below the horizon (civil dawn) and ends at sunrise.
  • Evening civil twilight begins at sunset and ends when the geometric center of the sun reaches 6° below the horizon (civil dusk)

Nautical Twilight

  • Nautical twilight is the time when the center of the sun is between 6° and 12° below the horizon. In general, nautical twilight ends when navigation via the horizon at sea is no longer possible.

I try to learn something every day!

Edited by ibraidwo

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The joys of living nearer the equator.... I just checked Tanzania where we went last year, and even at this time of year, there is only a very short twilight and it gets dark early still.

post-6762-137352931844_thumb.jpg

Stu

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Yes, a little latitude goes a long way :cool: even in midsummer here, there are still 6 hours of astronomical darkness, 11 in midwinter (now!)

The down side to a shorter twilight are that if you haven't setup your kit quickly enough, you'd better have a good red torch :D

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