Tycho Brahe (Martian crater) Tycho Brahe (Martian crater) Tycho Brahe is a nearly ovular crater on Mars named after the Danish astronomer Tycho Brahe (1546–1601). It is located in the Cerberus hemisphere around 49.8° south and 213.9° west, in an area which is south of the Martz crater and east of the Hellas Basin. It measures approximately 105 kilometers in diameter from east to west. The name was adopted by IAU's Working Group for Planetary System Nomenclature in 1973. The crater is crossed by Eridania Scopulus, an escarpment. Other nearby named craters are Huggins to the east, far south is Vinogradsky and northwest is
Planetary nebula the universe they theoretically contained smaller quantities of heavier elements. Known examples are the metal poor Population II stars. (See Stellar population). Identification of stellar metallicity content is found by spectroscopy. A typical planetary nebula is roughly one light year across, and consists of extremely rarefied gas, with a density generally from 100 to 10,000 particles . (The Earth's atmosphere, by comparison, contains 2.5 particles .) Young planetary nebulae have the highest densities, sometimes as high as 10 particles . As nebulae age, their expansion causes their density to decrease. The masses of planetary nebulae range from 0.1 to 1