Astronomical Twilight?

[coffee_prince]

Tonight is the first clear weekend in weeks, but a problem I have is that it is not dark enough last time I was looking... is it because I am not gazing at the best time, or is it just a fact of Summer viewing?

I have been looking up Astronomical Twilight, it ends tonight at 23:35 in my city. So from then on can I assume this will be the darkest time of the day to be viewing as the sun will be at least 18 degrees below the horizon, or am I reading it wrong?

Thanks

[virtualpilot45]

No, If you are on +1hr (due to BST etc) the darkest time will be 01:00. If you are on the standard time (GMT etc) it will be 00:00. The sun will then be more or less exactly in the north, at its lowest in the horizon (or south if you are in the southern hemisphere).

The end of astro twilight means dark enough anyway though

[pete_l]

Depending on how much light pollution you have (you mention a city, so I'm assuming that's a substantial number of people) the actuality of astronomical twilight may not make a lot of difference

Personally, I wouldn't wait until the clock strikes the end of Astronomical Twilight before venturing out, as you will still have setting up to do, eyes to get dark-adapted and even when it's not strictly the darkest there will still be plenty of things to view. You probably won't even notice the difference within an hour of the "official" start. So add on your setup time and go for it earlier than when the professionals would turn their multi-million-pound instruments towards their research targets.

Another thing that can make a difference is the amount of humidity/moisture in the air. This has the effect of reflecting light of the extremely small water droplets - either from streetlights, or the Moon or the not-fully-dark sky and making the night (any night) seem not so good.