Hubble Deep Field Galaxy Estimate

This is one of my favorite exercises in the Astronomy course. One large area of the science standards is knowing our place in space and getting a proper perspective. Well, the Solar System Scale Model gives you a sense of where Earth is relative to the other planets and the nearest stars. This lab will give you a perspective Earth's larger home as a member of the Milky Way relative to other galaxies in the Universe.

The image above is the Hubble Ultra Deep Field. It is the deepest look ever into the most distant areas of the Universe. The Hubble Telescope's Advanced Camera for Surveys' wide-field camera snapped 800 exposures over four months, from Sept. 24, 2003 to Jan. 16, 2004. Each exposure averaged 21 minutes in length, bringing the total exposure time to 1 million seconds! The total image is described as "looking through an 8 foot-long straw" at a tiny patch of the night sky and seeing what is in that limited amount of sky. Click on the link in this paragraph to learn more. When the imaging process was completed, this photo is what greeted astronomers! In the image at the top of this page, objects that have four little points are foreground stars in the Milky Way. Every other dot is a galaxy! In this lab will you study this image and estimate the total number of galaxies in the Universe.

The first thing you are asked to do is make a guess as to the number of galaxies you think are in the entire Universe. Once you have made this guess, write that number down someplace for later reference. Now, the next step is to enter the practice area for the galaxy estimate. Please go to the Ultra Deep Field Lab page. When you arrive there, do the galaxy counts as you are instructed. When you have collected those counts, you will be asked to return to this page and enter the values into the boxes found below. A WARNING. THE IMAGE ON THE PAGE YOU WILL CONNECT TO IS A 3.5MB IMAGE. IT IS HUGE! I hope your computer can manage an image of this size because there is no other way to really count the galaxies unless I give you the full resolution image ... and I even cut it down a bit from the original 6000x6000 format into a 4000x4000 format or else my webpage builder would not let me move it into the course.

You need to fill in the two blanks below correctly or else nothing that you work on will arrive to me via the internet.

Your Name:

E-mail Address (Required):

1) What is your guess of the number of galaxies in the Universe?

2) Please enter the galaxy counts in the boxes below?

Random Box Area #1

Random Box Area #2

Randon Box Area #3

Random Box Area #4

Random Box Area #5

Random Box Area #6

Add up the numbers that are in these boxes and then divide that number by the number of boxes that you counter. Enter that number below:

3) . The number you have here is the average number of galaxies in each 10 x 10 cm box.

Multiply this average number by 100. This will give you a value for the total number of galaxies estimated to be in the Hubble UltraDeep Field image. Enter that number below:


Astronomers estimate that there are 12.7 million of these patches that make up the entire sky all around the planet. Multiply the estimated number of galaxies in the Hubble UltraDeep Field Estimate. This is what you have estimated the total number of galaxies in the Universe to be. Enter this last number below:


Now, please respond to these final questions and your lab work will be completed.

6) As you look in the image, there are many different types of galaxies. What types of galaxies were you able to find.

7) Astronomers believe that all of the galaxies in the Universe comprise only 4% of what is really out there. What do astronomers believe the rest of the Universe is made of?

8) If some of the galaxies in this image are 10 billion light years away, what does that mean we are actually looking at when we take a picture of those galaxies?

9) Astronomers had to use the Infrared Camera to make this image since the more distant galaxies are not visible to us in the light spectrum between 400 and 700 nanometers. Light has always been shining from these distant galaxies, but their light has been shifted from visible wavelengths into infrared wavelengths. Why have the more distant galaxies had their light shifted from visible to infrared wavelengths? What has caused this shift to occur?

10) Final calculation. Scientists think that the average galaxy may have 150 billion stars. You made an estimate of the total number of galaxies in the Universe. Take that number from above and multiply it by 150 billion, and enter that number in the box below.

This is a reasonable estimate of the total number of stars in the Universe. Even if only a tiny fraction of those stars have planet systems, that makes for an incredibly huge number. Hopefully, you are now thinking about your significance and also about whether we are alone or not in this vast Universe. It is difficult for anyone to comprehend just how incredibly huge the Universe is, and while it is theorized that the visible stars and galaxies make up only 4% of the actual Universe, it is still a pretty impressive number of stars. I have included a link to my public school teaching on Roacblocks to Intelligent Life. It is my contention that we are alone in the Universe.



You can now go back to the Moodle Site.

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