![]() ![]() Estimate the subgroup of the spirals, and measure the major and minor axes of the ellipticals so that you can calculate n and find the subclass. When there is more than one galaxy in the image, use the finding chart to identify the galaxy in question. Examine the images of each of the galaxies listed in the table below.Where d is the galaxy's distance (in Mpc), H is Hubble's constant (with a modern value of about 65 km/s/Mpc), and the speed v is found from the Doppler shift of the galaxy. He interpreted the observed spectral shift as a Doppler shift, and determined that all galaxies (except a few very close ones that are in the same group of galaxies as the Milky Way) are receding from the Milky Way Galaxy with speeds proportional to their distances: He used the redshift of spectral lines from distant galaxies (calculated by Slipher) whose distances could be determined by other means (for example, by Cepheid variable observations or measuring the angular sizes of HII regions). In the late 1920's, Edwin Hubble discovered one of the most fundamental properties of the universe, namely that it is expanding in all directions with a speed proportional to the distance. The entire problem is not yet well understood, and many explanations rely heavily on the postulated existence of dark matter. Dense clusters have much higher percentages of elliptical galaxies, indicating that dense galaxy formation regions are more likely to form ellipticals. We do know that there is a correlation between the environment and the type of galaxy that formed there. Recent observations made by Hubble Space Telescope do show more spirals in distant clusters of galaxies, however, there are also many more distorted galaxies and blue irregulars with enormous star formation rates. If this is true, then we would expect to see more spiral galaxies as we look farther out into the universe (that is, back in time). Because there is little evidence of star formation in elliptical galaxies, and because they seem to have extremely small angular momentum, it was thought that perhaps elliptical galaxies are much older than spirals. The relationship between galaxy types is not clear. Quasar 3C273, for example, is moving away from us at 43,700 km/s! These quasars are moving away from us at extremely high velocities. However, their redshifts are so high that we know that they can not be stars. These galaxies are so distant in fact, that the quasars look like stars in most images. Quasars are the bright, superluminal cores of very distant active galaxies. Irregular galaxies come in two flavors: Irr I's are resolvable into individual stars, and Irr II's are not. It is thought that many irregulars were once spiral or elliptical, but that a close encounter with a larger galaxy disrupted the organization of the material by gravitational forces. ![]()
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