Stars that travel in the same direction around a concentration of mass are characteristic orbits found in the arms of spiral galaxies Besides shape color is what characteristic clearly separates elliptical galaxies from spiral galaxies the size of the region responsible for powering an AGN is Solar System size According to Hubble s law as the distance of a galaxy increases its recessional velocity increases Type Ia supernovae be used to determine a galaxy s distance because Type Ia supernova have approximately the same luminosity Type Ia supernovae can be used to measure the most distant objects Astronomers use galactic redshift as a measure of distance distance indicators from closest to farthest parallax main sequence fitting Cepheids Type Ia supernovae the Milky Way Galaxy is a barred spiral galaxy RR Lyrae stars are used to determine distances to globular clusters the radio region of the electromagnetic spectrum is best used to study structure in the Milky Way The distance to the center of the Milky Way cannot be measured directly because clouds of dust and gas obscure our view No globular cluster has zero heavy elements so we know that at least one generation of stars formed and died before the Milky Way s globular clusters formed Open star clusters primarily inhabit the disk part of spiral galaxies we can look in the disk of the Milky Way to find lots of gas and dust the rotation curve of the Milky Way suggests that it contains a large amount of matter NOT in the form of stars most of the mass in our galaxy is in the form of dark matter The inverse of the value of H0 is a time the increasing in space between galaxies increases redshifts of distant galaxies The Big Bang occurred everywhere in the universe The existence of the cosmic microwave background radiation tells us that the early universe was much hotter After the Big Bang photons began to travel freely through the universe Observations of Type Ia supernovae in distant galaxies have shown that the expansion of the universe is increasing the discovery of dark energy was unexpected because the gravity provided by the mass contained within the universe was predicted to slow the expansion By the time the universe was a few minutes old the majority of the normal matter in the universe was hydrogen and the remainder was mostly helium superclusters are the largest Our Milky Way Galaxy is a member of the Local Group the Virgo cluster and the Virgo supercluster the large scale structure of the universe looks like a sponge with many large holes gravity is responsible for shaping the large scale structure of the universe the visible parts of galaxies form only in the densest parts of dark matter halos cold dark matter halos provided the gravity to form galaxy fragments in the early universe Structure formation in the universe proceeds hierarchically meaning that small objects collapse then merge to form larger objects Structure formation in our universe proceeds from the bottom then moves up the Cambrian explosion occurred 500 million years ago The phylogenetic tree of life was established using DNA sequencing All terrestrial life is carbon based Terrestrial life is carbon based and requires water as its solvent cyanobacteria and other photosynthesizing organisms have allowed Earth to have a large amount of oxygen in its atmosphere astrobiology is the study of the origin evolution distribution and future of life in the universe
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