Stellar charts for the Earth Hour 2021, Saturday, March 27, 21 h of local time (may be summertime for some southern latitudes)

The Moon will be just 1 day before full, so very bright indeed. Therefore we offer just all-sky maps for stars brighter than 5.5 mag and not any detailed ones for fainter stars.

Very bright – what does it mean in terms of illuminance? Everybody knows that around full moon under clear sky, there is a plenty of light to walk or ride a bicycle.. Quantitatively, that plenty means typically 1/10 of a lux, one decilux, 1 dlx. As much as from a candle 3 m from its flame. During the Earth Hour, 20:30 till 21:30, Moon will become high enough to illuminate the landscape even a bit more, by 1.2 dlx at 50° and even by 1.7 dlx at the equator. Around midnight, by 2 dlx. This is so much light that outdoor lighting becomes obsolete under the open sky. So, you may let the lights off not just till morning, but if weather allows, till Tuesday! Moonlit landscape is marvelous... And if there are clouds around Moon, they may have nice changing colours, it may be a nice view

You may namely admire not just the landscape, but also the space over you, ‘skyscape’. During the evening, you can notice how the stars travel in the sky. Moon moves more slowly than Mars and fixed stars, each hour it lags its own diameter, 1/2 degree.

Ecliptic is marked, Moon and Mars are a bit north from it.

In might be nice to observe how Sirius, unlike Mars, twinkels. There is so much light from it that it produces flashes with vivid colours. Actually, each eye gets those changes independently. If you look to proximity (converge your sight, like to a finger on a stretched arm) to see the star twice, creating a "double star" this way, each of the two images twinkles individually, uncorrelated with the other.

Still another way of observing this phenomenon – scintillation – caused by the turbulence of our atmosphere when observing a distant point-like source, is using a pair of binoculars or a telescope. If you wiggle it slightly, you can resolve quick time changes into a colourful light path across the field of view. And if you defocuse the instrument enough, so that the star becomes a disk? That disk, this is actually the illuminated aperture of your telescope (a lens or a mirror). Colour patches will be moving on it. And you can cast a shadow by your fingers, putting your open hand before the telescope into the path of the Sirius light. (Of course, any bright fixed star low in the sky, so that we observe it through a lot of air, is good for that. Like Rigel or, for southern latitudes, Canopus.)

And last, a telescope will show not just those pronounced dark areas on the Moon, the seas filled with a dark lava from the mantle, but also bright dots of the youngest craters. As their surface has not been exposed to cosmic rays so long, the regolith, ‘Moondust’ did not become darkened as much as longer exposed grains of regolith. From some large craters, there are even rays of material expelled by the impact. From Tycho, far south, the rays go almost over whole lunar sphere.
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[PARENTDIR]Parent Directory  -  
[DIR]CZ-latitude50/2021-03-27 13:34 - s českou legendou / Czech text
[DIR]Mar27/2021-03-26 14:57 - see subdirectory A for all-sky maps

The maps have been created similarly to the whole series for Globe at Night. They are made for various amounts of light pollution of the sky. The level of pollution can be guessed from how many stars are visible. The fainter a star is, the more "magnitudes" it has; the threshold values are given in maps.

Moon position is not for a local time, but for 21 h of central European time, i.e. for 20:00 UTC. So Japan will see the Moon more toward right along the ecliptic, Alaska will it have quite a lot to the left.

Jeník Hollan, CzechGlobe