Denmark the 22 proposals have been agreed upon by a parliamentary majority. Denmark shares strong cultural and historic ties with its Scandinavian neighbours Sweden and Norway. It has historically been one of the most socially progressive cultures in the world. In 1969, Denmark was the first country to legalise pornography, and in 2012, Denmark replaced its "registered partnership" laws, which it had been the first country to introduce in 1989, with gender-neutral marriage. Modesty and social equality are important parts of Danish culture. The astronomical discoveries of Tycho Brahe (1546–1601), Ludwig A. Colding's (1815–88) neglected articulation of the principle of conservation
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