A15 – Universe

A15 – Universe

Some of the objects listed following are generally considered to be single (individual) astronomical objects; others are thought of as collections of many individual astronomical objects. Match these to the appropriate category.
Single astronomical objects:
Comet, Star, Planet

Collections of astronomical objects:
Supercluster, Solar System, Milky Way Galaxy, Galaxy

Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.
Red Giant or Supergiant Starts:
Very cool but very luminous
Found in the uppper right of the H-R diagram

Main-sequence stars:
The majority of stars in our galaxy
The Sun, for example
A very hot and very luminous star

White dwarfs:
not much larger in radius than Earth
Very hot but very dim

The history of the universe can be divided into seven major phases. Taken together, these phases make up the cosmic evolutionary scheme—the continuous transformation of matter and energy that has led to the appearance of life and civilization on Earth.
Rank the phases in the history of cosmic evolution from earliest to most recent.
– Particulate – primal energy into elementary particles
– Galactic – atoms into galaxies and stars
– Stellar – stars into heavy elements
– Planetary – elements into solid, rocky planets
– Chemical – elements into building blocks of life
– Biological – molecules into life itself
– Cultural – advanced life forms into intelligence

Taken together, these phases make up the cosmic evolutionary scheme. Starting with the initial matter and energy, the universe progresses through stages of particulate, galactic, stellar, planetary, chemical, biological, and cultural evolution.

Imagine a photon of light traveling the different paths in the Milky Way described in the following list. Rank the paths based on how much time the photon takes to complete each journey, from longest to shortest.
Longest to Shortest:

across the diameter of the galactic halo – 200,000 light years
across the diameter of the galactic disk – 100,000 light years
from the sun to the center of the galaxy – 26,000 light years
across the diameter of the central buldge – 20,000 light years
through the disk from top to bottom – 1,000 light years

The light-travel time converts directly to a distance in light-years, so you can think of this question as a simple variation on Part A, but with the added choice of the thickness of the disk (from top to bottom). The correct answer shows that the halo is larger in diameter than the disk, which is larger than the bulge, and that the Sun is within the disk but outside the bulge. The disk is quite thin compared to its diameter (typically only about 1,000 light-years in thickness), which makes it relatively flatter than a typical pancake.