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TRANSCRIPT
Hubble National Teach-In
Nationwide Galaxy Count The Nationwide Galaxy Count is a project to get students, teachers, and schools from across the country to collaborate on estimating the number of galaxies in the observable universe. The Hubble Ultra Deep Field One of the Hubble Space Telescope's most important images is the Hubble Ultra Deep Field (HUDF). The HUDF is the deepest visible light view of the universe, where “deep” is an astronomy term for seeing very faint light. This extremely long exposure, combining about 11 days of Hubble observations, shows a vast number of galaxies stretching across the universe. There are so many galaxies in the HUDF that counting them by hand would be a very long and very repetitive task. In fact, astronomers write specialized computer programs to identify and count the galaxies (and stars) in images like these. Furthermore, the HUDF image shows only a very small patch of the night sky. One cannot help but wonder, if there is such an abundance of galaxies in this tiny region, how many galaxies are there across the entire universe? The Nationwide Galaxy Count attempts to address that question through a collaborative project. Sampling and Estimation The basic idea is to use representative sampling to estimate the number of galaxies in the HUDF and the universe. If one counts the galaxies in a small region (a sample), one can then estimate the number of galaxies in a larger region. This extrapolation is just a multiplication by the ratio of the region sizes. For example, if the larger region is 10 times the size of the smaller region, then it can be estimated to have 10 times the number of galaxies. For this estimate to be accurate, the sample region must be an average (or representative) region of the whole.
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The Hubble Ultra Deep Field For the HUDF, we have created 100 sample regions that we call “cutouts”. These HUDF cutouts are numbered from “00” to “99”. Each HUDF cutout contains an appreciable number of galaxies, but not so many that it is too arduous to count by hand. The HUDF cutouts are available in 10 PDF files with 10 HUDF cutouts in each. These files can be downloaded from the Hubble National Teach-In web page. Nationwide Galaxy Count is at the bottom of the page.
http://hubble25th.org/go/Teach-In
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Materials - Pens or Pencils - 1 Recording Sheet per group (located in this packet)
This activity can be completed with or without a computer
To complete the activity with a computer
o Download the HUDF cutouts http://hubble25th.org/go/Teach-In
o Place the files in a directory students can access.
To complete this activity without a computer o Download and printout the HUDF cutouts
http://hubble25th.org/go/Teach-In o Files can be printed in color or black and white
NOTE: Due to the differing contrast of a computer screen and a printout, one may get different counts. This is a good point to discuss or even test with students.
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Instructions
1. Assign students in groups of two or three. Have the group choose a HUDF cutout. The conversations that ensue when working as part of a team are an essential part of science.
2. The students are then are to count the galaxies. Before counting, the students need to consider:
a. Be Random - The PDF files are listed in numerical order, which
means that human nature may lead them to choose the first image in the first PDF file. It will not make for good statistical sampling, if everyone does HUDF cutout #00. Choose a random number between 0 and 99.
b. What to count – In this activity, students need to count the galaxies of their HUDF cutout. Galaxy is defined on the Amazing Space website as
A galaxy is a collection of stars, gas, and dust bound together by gravity. The smallest galaxies may contain only a few million stars, while the largest galaxies have thousands of billions of stars. Galaxies are classified or grouped by their shape. Round or oval galaxies are elliptical galaxies and those showing a pinwheel structure are spiral galaxies. Others are called irregular because they do not resemble elliptical or spiral galaxies.
As a visual guide to the three main galaxy shapes, there is a graphic organizer available at this link:
http://amazing-space.stsci.edu/resources/organizers/galaxy.php
For the HUDF, most of the galaxies will not be the big beautiful ones seen on posters. The HUDF is dominated by small and irregularly-shaped galaxies. The reason for this will be discussed during the Hubble National Teach-In.
c. What not to count - The HUDF does contain some stars. The
bright ones are easily identifiable by the plus sign (“+”) shaped diffraction spikes emanating from their center. Some of the faint stars are indistinguishable from galaxies. Our advice is to ignore anything with diffraction spikes, and count the rest as galaxies.
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One question we get is: “How small of an object in the image qualifies as a galaxy?” It can be difficult to assess whether a splotch is a small galaxy or just one piece of a larger galaxy. For this exercise, those decisions are up to the students. In fact, working through such questions is where the process of science really happens. Anyone can count, but it requires some thought to determine what to count.
3. Have students record their observation on the recording sheet. If
possible, have students count galaxies in additional HUDF cutouts.
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Data Submission Submit your data via email by April 17, 2015. Basic instructions are on the Hubble National Teach-In web page.
http://hubble25th.org/go/Teach-In Please provide the grade level, school, and zip code. You may provide a teacher’s name, but please do not send us any student information. Here is an example email:
To: [email protected] From: [email protected] Subject: data for Nationwide Galaxy Count Here is the data from Miss Marple’s 7th grade class at Christie Middle School. Our zip code is 13579. HUDF cutout #47 galaxy count 73 HUDF cutout #73 galaxy count 47 …
We will compile and combine the data from all participants and present the results during the Hubble National Teach-In on April 24, 2015.
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Student National Galaxy Count Data Table
HUDF Cutout # Galaxy Count
What to count In this activity, you are counting the galaxies in a HUDF cutout.
Galaxy is defined on the Amazing Space website as
A galaxy is a collection of stars, gas, and dust bound together by gravity. The smallest galaxies may contain only a few million stars, while the largest galaxies have thousands of billions of stars. Galaxies are classified or grouped by their shape. Round or oval galaxies are elliptical galaxies and those showing a pinwheel structure are spiral galaxies. Others are called irregular because they do not resemble elliptical or spiral galaxies.
What not to count The HUDF does contain some stars. The bright ones are easily identifiable by the plus sign (“+”) shaped diffraction spikes emanating from their center. Some of the faint stars are indistinguishable from galaxies. Ignore anything with diffraction spikes, and count the rest as galaxies.
8 Teacher Nationwide Galaxy Count Data Table
00 34 68
01 35 69
02 36 70
03 37 71
04 38 72
05 39 73
06 40 74
07 41 75
08 42 76
09 43 77
10 44 78
11 45 79
12 46 80
13 47 81
14 48 82
15 49 83
16 50 84
17 51 85
18 52 86
19 53 87
20 54 88
21 55 89
22 56 90
23 57 91
24 58 92
25 59 93
26 60 94
27 61 95
28 62 96
29 63 97
30 64 98
31 65 99
32 66
33 67