Northern sky
The northern sky , North Star ( s ) sky or northern starry sky is that half of the night sky , the north of the celestial equator is located and thus all points with a positive declination comprises (→ equatorial coordinate system ). From the North Pole the northern sky can be seen entirely; the further south the observation site, the less it is visible.
With good visibility, around 2000 stars in the northern sky are freely visible, with binoculars it is around 20,000 to 40,000. In large cities, even when the night sky is cloudless, you can only see around 100 to 500 stars, depending on the extent of air and light pollution . The brightest in the northern sky is a apparent magnitude of -0.05 like Arcturus in the constellation Bootes (the boat). Wega in the lyre (lyre) and Capella in the carter (Auriga) are almost as bright . The brightest stars are all bigger than our sun .
The northern sky shows slightly fewer stars than the southern sky , because the center of the Milky Way is about 20 ° south of the celestial equator in the constellation Sagittarius . The three stars of the so-called summer triangle belong to the northern sky, four of those of the winter hexagon . Seven of the 14 brightest stars of 1st magnitude are in the northern sky, seven in the southern sky.
The exact center of the northern sky is the celestial north pole as an extension of the earth's axis . Less than 1 ° next to it is the current North Pole Star , Polaris in the constellation Little Bear (Ursa Minor), around which the neighboring constellations seem to revolve. The conspicuous stars of the Big Dipper in the constellation Great Bear (Ursa Major) and also those of Cassiopeia remain visible all year round as circumpolar at observation locations at higher geographical latitudes . They are facing each other, roughly in the middle between them is the North Star, to which the extended connecting line of the outer box stars of the Big Dipper points as a pole point .
Across the northern sky, the dim power band pulls Milky Way - including through the constellations Gemini (Gemini), Perseus , Cassiopeia and Swan (Cygnus), where she apparently shares. Orion , the well-known winter constellation of the northern hemisphere , passes over to the southern sky , near whose belt stars the celestial equator runs.
While at the equator you can see exactly half of the northern sky at any time of the year or night, you can see 70–80 percent of the northern sky at observation locations in mid- latitudes in Europe and part of the southern sky when looking south.
