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In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-dark) matter in the universe is either hydrogen or helium, and astronomers use the word "metals" as convenient shorthand for "all elements except hydrogen and helium".
This article is a list of notable unsolved problems in astronomy. Problems may be theoretical or experimental. Theoretical problems result from inability of current theories to explain observed phenomena or experimental results. Experimental problems result from inability to test or investigate a proposed theory.
It is not just heavy metals which can be toxic; other metals (for example beryllium and lithium) can be toxic too. [266] Sleeping in a closed room with an electric fan running does not result in "fan death", as is widely believed in South Korea among older people. [267] [268] As of 2019 this belief was in decline. [269]
The following is a list of notable unsolved problems grouped into broad areas of physics. [1]Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result.
The remaining 4.9% [11] comprises all ordinary matter observed as atoms, chemical elements, gas and plasma, the stuff of which visible planets, stars and galaxies are made. The great majority of ordinary matter in the universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10% of the ordinary matter ...
Space has fascinated humanity for centuries - from the mystery of the stars to the groundbreaking discoveries that push the boundaries of our understanding. Whether you're an armchair astronomer ...
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets.
This is gravitational-wave astronomy. Gravitational-wave astronomy can test general relativity by verifying that the observed waves are of the form predicted (for example, that they only have two transverse polarizations), and by checking that black holes are the objects described by solutions of the Einstein field equations. [114] [115] [116]