Bright planet Jupiter with the stars Castor and Pollux above (left), constellation Auriga and Taurus (middle) with the open cluster M45 Plejades (right), and constellation Orion rising from the ocean. Additionally, there is also heavy airglow visible to the naked eye. Airglow is a faint emission of light by a planetary
atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes
the night sky never to be completely dark, even after the effects of starlight
and diffused sunlight from the far side are removed. This phenomenon originates
with self-illuminated gases and has no relationship with Earth's magnetism or
sunspot activity, causing aurorae.
On planet Earth
Feldspar, sometimes spelled felspar, is a group of
rock-forming aluminium tectosilicate minerals, also containing other cations
such as sodium, calcium, potassium, or barium. The most common members of the
feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali
(potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust
and 41% of the Earth's continental crust by weight.
Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many kinds of sedimentary rocks.
