What is Big?

Introduction:

As humans, we have a sense of large and small as it compares to us. Ants are small; the Empire State Building is large. However, even though it is obvious that the universe is big, it is sometimes hard to imagine just how big it really is.

Activity:

The two links below are to two videos that should help bring things into perspective. Watch them both now and respond to the following reflection questions.

Star Size Comparison:

Map of the Universe:

Reflection:

  1. Write a few sentences reacting to the Star Size Comparison and Map of the Universe videos. What surprised you? What did you learn? What did you notice?
  1. Wikipedia has many great articles about some of the stars in the video. Research the Sun, Arcturus, Pistol Star, and VY CanisMajoris. Fill in the data table below. We will be using Solar Units to fill in these tables which means that for radius, volume, brightness, mass, or any other measurement, the sun has a value of exactly 1. Those qualities in other stars are expressed in the number of suns it would take to make up that star (i.e. a star with 2 solar radii means that it has a radius twice the size of our own sun). Temperature is expressed in Kelvin.

Star Name / Mass (M) / Radius (R) / Luminosity (L) / Temperature (K)
Sun / 1 / 1 / 1 / 5,778
Arcturus / 1.1 / 25.4 / 170 / 4,286
Pistol Star / 27.5 / 306 / 1,600,000 / 11,800
VY CanisMajoris / 17 / 1420 / 270,000 / 3,490
  1. It is estimated that the Milky Way galaxy is a 100,000 light years in diameter and 2000 light years thick (assume here that it is a perfect cylinder). If that’s true, what is the percentage of volume that VY CanisMajoris takes up in the Milky Way? You will need to research some of the numbers you need on the internet. (Remember to convert all units—light years, solar units, etc.—to common units before calculating.)

The biggest star in the universe is 0.00000000000000000000003% the size of the Milky Way.

  1. The Milky Way galaxy is in a spherical (well not really, but let’s pretend) cluster of galaxies called the Local Group and has a diameter of 10,000,000 light years. What is the percentage of volume in the Local Group that is occupied by the Milky Way?

The Milky Way galaxy comprises 0.000003% of the Local Group.

  1. The most distant objects that we have observed in the universe are about 13 billion light years away from Earth. Assuming that the universe is spherical, estimate the percentage of volume that the Local Group occupies in the universe.

The Local Group occupies 0.00000000057% of the Universe

  1. Fill in the blanks to complete the following:

The radius of VY Canis Majoris is ___1420_____ times bigger than the sun’s radius. That star only occupies ______3E-23_____% of the Milky Way galaxy which only occupies ______3E-6______% of the Local Group which only occupies ______5.7E-9______% of the entire universe. In other words, we are really really really really really tiny.