Astronomy Unit 7 km s per The overall diameter of the galaxy is estimated at 30 kpc The mass of a nearby galaxy can be estimated by use of the mass luminosity ratio A good two dimensional analogy for a closed finite expanding universe is the surface of an expanding balloon with dots in its surface The red shift in spectral lines of the distant galaxies is correlated to the galaxy s distance The larger the distance the larger red shift When we can find the distance independently we find the further away a galaxy is the less red shift incorrect The recent measurements of Hubble s constant are about 50 100 km sec per Mpc One of the revisions of Hubble s constant was found in a study of the ultraviolet brightness of galaxies by OAO 1 The new value is in the range of 50 100 Mpc The Big Bang theory is a cosmology cosmogony After the red giant stage a star approaches the white dwarf stage During this time it may undergo a period of instability nova supernova Most stars become variable stars after the red giant stage A variable star has a predictable period of brightening and dimming Such a variable is called a regular variable A variable star has an unpredictable period of brightening and dimming Such a variable is called an irregular variable The period of RR Lyrae stars range from 3 7 days The period of Cepheid I stars range from 1 to 100 days Another name for Cepheid I stars is classical Cepheids Another name for Cepheid II stars is W Virginis Cepheids The galactic coordinate measured in the plane of the Milky Way is galactic longitude The Sun s motion in the galaxy is roughly on a circle centered at the galactic center The Sun is about 7 9 kiloparsecs from the galactic center The time it takes the Sun to travel around the galaxy is about 2 3 x 10 8 years Spiral arm stars that are farther from the galactic center than the Sun do not move as rapidly about the galactic center as we might have expected them to move This is termed the differential rotation of the arms The overall diameter of the galaxy is estimate at 30 kpc The rotation of a nearby galaxy can be determined by Doppler shifts The distance of a nearby galaxy can be determined by Cepheid variables and novae The mass of a nearby galaxy can be estimated by use of the mass luminosity ratio A galaxy that appears as a flattened disk of stars with an arm like structure is called a spiral galaxy A galaxy that appears as a somewhat flattened disk of stars with little internal structure is called a n elliptical galaxy A Mpc is smaller than a ly incorrect 1 megaparsec 10 6 parsecs There is evidence that even clusters of galaxies cluster correct Galaxies are never found in clusters of galaxies incorrect All distant clusters of galaxies are red shifted correct The more distant a galaxy is from us the more the light from it is red shifted When we can find the distance independently we find the further away a galaxy is the less the red shift incorrect The red shift in spectral lines of the distance galaxies is correlated to the galaxy s distance The larger the distance the larger red shift If r represents the distance to a cluster of galaxies and v represents its velocity of recession the formula v H r is a statement of Hubble s law The red shift in the spectral lines of external clusters of galaxies is most commonly held to be Doppler shift For very distant clusters of galaxies Hubble s relation is between the red shift and the corrected apparent magnitude When we get to large distances Hubble s law must be changed or extended since we would need to assume a cosmology to convert red shift to velocity So we plot the red shift versus the distance wrong plot the red shift versus the apparent magnitude Although all the distant clusters of galaxies are receding from us they are receding faster the further away they are so we are not the center of the universe correct Since distant clusters of galaxies are receding from us we are at the center of the universe incorrect Hubble s law is useful for finding the distances of clusters of galaxies The distance to distant clusters of galaxies is obtained from The Hubble relation Before the Big Bang an observer would have seen the universe as a small hot object incorrect According to all Big Bang models the primeval fireball could have been viewed from outside and would have looked small hot and dense The period of Cepheid II stars range from 3 to 50 days The pulsating variables are a class that have average absolute magnitude between 1 5 and 5 are Cepheid I As a class the pulsating variables that have average absolute magnitude of about 5 are RR Lyrae Most of the RR Lyrae variables in our galaxy are found in globular clusters The variable stars that are used as distance indicators are Cepheid RR Lyrae The Cepheid I variables in our galaxy are found only in the spiral arms correct Misleading the fireball possibly filled all space Cepheid II