U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. ... Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts.
Explanation:
Barchans
Barchans are a crescent-shaped shifting sand dune. Barchans face the wind predominantly from one direction. They are found in sandy deserts.
The astrolabe is an inclinometer, that is considered to ba analog calculator that is capable of solving the several different types of the astronomy and is mostly used measuring the altitude and the navigational aspects of the celestial bodies day and night and it was used in the Islamic golden age and the middle ages. It is also helpful in determining the land and the sea latitude.
