Proper star charts for GLOBE at Night

See 2011 for technical information and observing hints, 2012, 2014 and 2015 for current maps. Generally, maps for any year can be used, when they correspond better to the local sidereal time. Just the wandering stars (Saturn, Mars, Jupiter, or even Venus in all-sky maps) were elsewhere, perhaps brighter or fainter. Each chart has a common limit, objects giving less light to your eyes are omitted. Such a common limit may not correspond to the real visibility of stars, as the luminance of the sky is far from uniform at polluted sites (typically, it increases toward horizon). In such cases, compare just the centre of the chart with the sky – the margins of the chart should serve just for easier identification of the central region.

Charts have been prepared by J. Hollan, CzechGlobe.
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GLOBE at Night is a great campaign to attract everybody's attention to the wonder of the night sky. Thousands of generations of our human predecessors admired the sky, during day and night. The regularities of the behaviour of stars, including the wandering ones (Sun, Moon and another planets) were the basis of calendars, religions, of culture in general.

It's a pity that thousands of millions of people are devoid of the gift of the starry sky now. There are so many terrestrial lights which are so much stronger... The world is so much light-polluted... (What pollution is that? Light from non-natural sources. See ev. Declaration for an expert attitude.)

However, even in cities we can still see some stars. From a place with no glare, like a roof high over any lamps, this is possible even in the centre of any city, provided that clouds don't prevent it. Venus, Jupiter or sometimes Mars (like in 2012 winter and spring) are bright enough to be visible even when the air is strongly illuminated from below. Comparing the maps offered at this site with the sky above you, you can get a proxy indicator how much brighter the sky is than the natural moonless one. A proxy for a quantity called luminance (luminance: how much light goes towards your eyes from a piece of the sky – this is expressed in lumens per square metre, divided by the size of that piece – expressed in steradians; the result is in lumens per square metre per steradian, or shortly candelas per square metre).

On your site, is there still a huge difference between a full-moon sky, with the air dispersing the light from the Moon, and the moonless sky with little natural luminance and perhaps a large artificial component? If yes, then you should use the moonless night to see more stars. Not everybody is so fortunate, there are sites where Moon cannot add much to the all-the-time large luminance of the heavily polluted sky. Go and explore that for yourself! Actually, such comparisons of our maps with the real sky during nights with and without Moon may become an even better proxy for the artificial component of the sky luminance. The same holds for observation during civil, nautical and astronomical twilight. In my city, Brno, there is no perceptible change after the nautical twilight ends... What's the situation at your site? Does the sky get darker during nautical or even astronomical twilight, so that more stars become visible? Start observing during civil twilight already and proceed till astronomical night.

(The evening twilights: they start with the sunset, the civil one ends with Sun being at −6°, nautical at −12° and astronomical at −18°. Astronomical night is the time when the Sun is below −18°.)

Jenik Hollan