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MASON ASTR 302 - Infinite Space and Absolute Time

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Infinite Space and Absolute TimeHubble demonstrated that the spiral nebulae are far beyond the Milky WayGalaxies were classified according to their appearance by Hubble and placed in a diagram.The disks of spiral and barred spiral galaxies are sites of active star formationElliptical galaxies are nearly devoid of interstellar gas and dust, and so star formation is severely inhibitedAstronomers use various techniques to determine the distances to remote galaxiesThe Distance LadderMasersThe Hubble law relates the redshifts of remote galaxies to their distances from the EarthThe Hubble law is v = H0dGalaxies are grouped into clusters and superclusters Our Galaxy is a member of a poor, irregular cluster called the Local GroupColliding galaxies produce starbursts, spiral arms, and other spectacular phenomena The gravitational effects during a galactic collision can throw stars out of their galaxies into intergalactic space Most of the matter is dark matter.Gravitational lensing of remote galaxies by a foreground cluster enables astronomers to glean information about the distributiGalaxies formed from the merger of smaller objects Whether a protogalaxy evolves into a spiral galaxy or an elliptical galaxy depends on its initial rate of star formation The darkness of the night sky tells us about the universe – this is known as Olbers’ ParadoxThe universe is expanding The Hubble law describes the continuing expansion of spaceThe redshifts that we see from distant galaxies are caused by this expansion, not by the motions of galaxies through spaceThe redshift of a distant galaxy is a measure of the scale of the universe at the time the galaxy emitted its lightThe expanding universe emerged from a cataclysmic event called the Big BangThe observable universe extends about 14 billion light-years in every direction from the EarthThe microwave radiation that fills all space is evidence of a hot Big BangThe background radiation was hotter and more intense in the pastThe abundance of helium in the universe is explained by the high temperatures in its early historyThe shape of the universe indicates its matter and energy contentIf ρ0 is greater than ρc, the density parameter Ω0 has a value greater than 1, the universe is closed, and space is spherical If ρ0 is equal to ρc, the density parameter Ω0 is equal to 1 and space is flat (with zero curvature)If ρ0 is less than ρc, the density parameter Ω0 has a value less than 1, the universe is open, and space is hyperbolic (with nObservations of temperature variations in the cosmic microwave background indicate that the universe is flat or nearly so, witObservations of distant supernovae reveal that we live in an accelerating universePrimordial sound waves help reveal the character of the universeJargonKey WordsInfinite Space and Absolute TimeThe “Discovery” of GalaxiesAt the beginning of the 20thcentury, what we now call spiral galaxies were referred to as “spiral nebulae” and most astronomers believed them to be clouds of gas and stars associated with our own Milky Way. The breakthrough came in 1924 when Edwin Hubble was able to measure the distance to the “Great Nebula in Andromeda” (M 31) and found its distance to be much larger than the diameter of the Milky Way. This meant that M 31, and by extension other spiral nebulae, were galaxies in their own right, comparable to or even larger than the Milky Way. Edwin P. Hubble (1889-1953)M31 - The Great Spiral Galaxy in AndromedaThis nearby galaxy in the Local Group of galaxies, of which the Milky Way is a member, is 2.9 million light years away. (NOAO/AURA Photos)The Nuclear Bulge of M31(NOAO/AURA Photos)Note that you find young stars along the spiral arms. M32 and NGC 205, both dwarf elliptical galaxies, are in the bottom center and upper right.The Outer Disk of M31(NOAO/AURA Photos)Hubble demonstrated that the spiral nebulae are far beyond the Milky Way• Edwin Hubble used Cepheid variables to show that spiral nebulae were actually immense star systems far beyond our Milky Way GalaxyTypes of Galaxies I. SpiralsSpiral galaxies are so-named because of the graceful shapes of arms emanating from a bright central nucleus. Spirals are classified according to how tightly or loosely wound the arms are, and it turns out that the brightness of the central nucleus is correlated to the tightness of the arm. The galaxies M 104 (below) and M 51 (right) respectively show tightly and loosely wounds. Notice the effects of dust in both galaxies. (NOAO/AURA Photos)Barred Spiral GalaxiesThe spiral galaxies M 91 (left) and M 109 (right) have bars across their nuclei from which spiral arms unwind. In virtually all spirals (barred or not) the galaxies rotate such that the spiral arms trail behind in the rotation. The Milky Way is known to be a barred spiral galaxy. (NOAO/AURA Photos)Types of Galaxies II. EllipticalsElliptical galaxies lack spiral arms and dust and contain stars that are generally identified as being old. The elliptical galaxies M 32 (below) and M 110 (right) show varying degrees of ellipticity. (NOAO/AURA Photos)Types of Galaxies III. IrregularsIrregular galaxies lack any specific form and contain stars, gas and dust generally associated with youth. The irregular galaxy at top right is the Large Magellanic Cloud, a satellite of the Milky Way located about 170,000 light years from the Sun. It is about 60,000 light years across. The bright reddish feature in the upper right is a region of star formation. The galaxy at the bottom is an irregular galaxy in Sagittarius.(NOAO/AURA Photo)Galaxies were classified according to theirappearance by Hubble and placed in a diagram.Properties of GalaxiesProperty Spirals Ellipticals IrregularsMass/M of Sun 109 to 4x1011 105 to 1013 108 to 3x1010 Luminosity/L of Sun 108 to 2x1010 3x105 to 1011 107 to 3x109Diameter (light years) 16x103 to 8x105 3x103 to 7x105 3x103 to 3x104% of galaxies 77% 20% 3%National Optical Astronomy Observatory imagesFrom this table, you should take note of which galaxies are the most and least massive, most and least luminous, and largest and smallest in size.The disks of spiral and barred spiral galaxies are sites of active star formationElliptical galaxies are nearly devoid of interstellar gas and dust, and so star formation is severely inhibitedAstronomers use various techniques to determinethe distances to remote galaxiesStandard candles, such as Cepheid variables and the most


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