Astropedia 14.3: How do massive stars help keep interstellar gas stirred up? Why O-type supergiant are stars likely to be associated with large-emission nebulae whereas solar-type stars are not? Why do planetary nebulae often have simple nearly spherical forms whereas typical emission nebulae such as the Orion Nebula are ragged and irregular?
Massive stars help keep interstellar gas stirred up due to supernova explosions. The explosions scatter elements all over the interstellar medium thus keeping gases such as hydrogen and helium stirred up. O type stars have large and hot emissions due to hot supernova explosions whereas; solar-type stars are always cooling and shrinking. Planetary nebulae are simple sphere-shaped balls of gas and fluorescent material released by a star at the end of its life. They are main sequence stars whose gases are not continually stirred up, but instead, they have nebulas that slowly emit gas more evenly thus creating a round planetary
Astropedia 14.4: Why are O and B stars the brightest in open clusters? Why are red giants the brightest stars in globular clusters? If you saw the galaxy from a great distance which would be brighter open or globular clusters? Which would be redder? Which would be farther from the galactic disk?
Hot blue O and B Stars are the brightest because they were formed more recently and burn their fuel fast so they can't last long. Majority of the stars in the clusters are faint since the clusters are invariably very old -more than ten billion years old. Red giant stars are the brightest since they are in the process of dying or due to collision with smaller stars.From a distance, open clusters would be brighter than globular clusters because these kind of clusters are much older and burn their fuel more slowly. They are redder in color and much further away from the galactic disk
Astropedia 15.1: During what percentage of recorded human history (define as you think appropriate) have people not know that we live in an isolated galaxy of stars similar to other remote galaxies? How large did people think the universe was during most of recorded history?
For most of human history, people did not know that there were other galaxies with similar stars as the earth. More than 90% of the population only knew the earth. Humans believed that universe was the planets and the solar system was only composed of the sun.
Astropedia 15.8: Which type of galaxy tends to be biggest? Which type can be the most luminous? Which type contains the fewest young stars? Why do almost all galaxies have a stellar mass-to-light ratio higher than 1?
IC 1101 is the biggest galaxy. The most luminous galaxy is the Wise J224607.57-052635.0. Spiral galaxies contain the fewest young stars. The mass-to-light ratio of galaxies is higher since the mass of other materials such as isolated stars and star clusters are included.
A supernova was discovered by Chuck and John Faranda in 1998. The brightest magnitude was 12.1. How distant is the galaxy NGC 3368 if the standard magnitude is -19.6?
What is the recessional velocity of this galaxy if the Hubble Constant is 72 km/s/Mpc?
The distance will range between 15m and 20m.
v = Ho d,Where: V= recession velocity
d= is the distance to the galaxy
Ho = the Hubble constant (72 km/s/Mpc)
The galaxy's distance is based on the assumption used by Hubbles "the standard ruler" assumption.
V =72 km/s/Mpc 12 Mpc
= 880 km/s
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