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Classified in Physics
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Cepheid variable stars: variable starts with pulsation periods of 1 to 60 days whose period of variation is related to their luminosity.
Dark matter: nonluminous matter that is detected only by its gravitational influence
Elliptical galaxies: are round or elliptical, contain no visible gas and dust and lack hot, bright stars
Spiral
Galaxies: contain a disk or spiral arms. Their halo stars are not
Visible, but presumably all spiral galaxies have halos. Contain gas and
Dust and hot bright O and B stars
Irregular galaxies: are a chaotic mix of gas, dust and stars with no obvious nuclear bulge of spiral arms
Local group: the small cluster of a few dozen galaxies that contains our milky way
Active galatic nucleus (AGN): the centers of active galaxies that are emitting large amount of excess energy
Olbers's paradox: the conflict between theory and evidence regarding the darkness of the night sky
Isotropy: the observation that, in its general properties, the universe looks the same in every direction
Homogeneity: the observation that, on the large scale, matter is uniformly spread throughout the universe
Dark energy: the energy believed to fill empty spaces and drive the acceleration of the expanding universe
the
Elements-namely ordinary baryonic matter out of protons and neutrons as
Well as are only a small part of the content of the universe.
Cosmological obsersations say that 72% of the universe is dark energy,
23% is dark matter and 4.6% is visible baryonic matter which is stars,
Planets and living beings. Dark matter has not yet been detected in a
Particle physics detector and the nature of the dark energy is not yet
Understood
Hydrogen and helium are 74% and 24% of all baryonic matter un the universe.