Lecture Question #1

Lecture Question #2

Our Place in the Universe

Before embarking on a tour through the vast topic of Astronomy, it is important to create a framework to put it all into perspective.  You all come to this class with preconceptions about the Universe and our place in it, but many of these preconceptions are not accurate, since they come from our perspective on the Earth, which is but one planet orbiting one star in a vast galaxy of stars.  This perspective leads intelligent people to certain "obvious" truths that are quite wrong.  Some of the wrong ideas that plagued our forebearers, such as that we live on a flat Earth that is the center of the Universe, you have been already been taught are wrong.  But while you know that the Sun, not the Earth, is the center of the solar system, many of you probably have only a hazy idea of how our planet fits into the larger picture of the galaxy and the Universe.  A full understanding is a humbling experience, as the words of Carl Sagan make clear.

So let us begin by looking at how the Earth fits into the spatial framework of the Universe.  We will start with the small and nearby, and end with the large and distant, by writing down our cosmic address.  We start with the familiar postal address represented by the following picture of the Earth as seen from space, with Newark, NJ located as shown. The familiar postal address is:

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA

But the Earth is only one of nine planets orbiting the Sun--the center of the solar system--so our cosmic address had better say which planet we are on:

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA
Earth

But specifying the planet is not enough--these nine planets orbit our star, the Sun, but we now know of at least 98 130 135 other planetary systems around other stars, and we have reason to believe that most stars have planets.  Once we colonize other planets (or make contact with alien civilizations), we are going to have to use addresses that are more specific.  Since there are about 100 billion stars in our galaxy, our cosmic address had better specify the solar system!

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA
Earth
Solar System

This address ought to be enough for awhile.  We can explore all of the 100 billion stars of our galaxy, and this address will be enough to find us.  But eventually, who knows, we may enlarge the postal system to include other galaxies!  The official name of our galaxy is the Milky Way Galaxy, so our more complete address is:

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA
Earth
Solar System
Milky Way Galaxy

How many galaxies are there?  There may be as many as 100 billion galaxies, (they are not all counted!) each with up to 100 billion stars!  Galaxies are not spread uniformly in the Universe, however, but are found in groups and clusters.  Our galaxy is one of the largest members of a group of galaxies known as the local group, along with the Andromeda Galaxy (shown below) and several other galaxies (two others can be seen in the same photo).

We need to specify our group, to distinguish from other clusters of galaxies, such as the giant Virgo Cluster.  The address becomes:

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA
Earth
Solar System
Milky Way Galaxy
Local Group

As it turns out, galaxies show even larger groupings, or clusters of clusters, known as superclusters.  As the postal system grows to galaxies outside the local group, we will need to specify which supercluster our group belongs to.  We refer to it as the local supercluster.  So now the address is:

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA
Earth
Solar System
Milky Way Galaxy
Local Group
Local Supercluster

The overall structure of superclusters can be mapped in surveys such as the one below, from the 2dF Redshift Survey. This structure makes up the visible universe.  We now believe that other universes are possible, although we can never reach them or know anything about them other than what we deduce from physical laws.  So the absolutely complete address is:

Samantha Student
NJIT
323 M L King Blvd
Newark, NJ  07102-1982
USA
Earth
Solar System
Milky Way Galaxy
Local Group
Local Supercluster
The Universe

Lecture Question #3

Lecture Question #4