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Interacting Galaxies Arp 147
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Photo taken by the Hubble Space Telescope

The image shows two gravitationally interacting galaxies that happen to be oriented so they appear to form the number 10. Arp 147 appears in the "Atlas of Peculiar Galaxies," compiled by Halton Arp in the 1960s and published in 1966.

Facts of interest about the image

The left-most galaxy, or the "1" in this image, is relatively undisturbed apart from a smooth ring of starlight. It appears nearly on edge to our line of sight. The right-most galaxy, resembling a “0,” exhibits a clumpy, blue ring of intense star formation.

Classroom activity

Included is an inquiry-based classroom activity that focuses on the image and text.


This Hubble Space Telescope image shows a pair of interacting galaxies that appears to form the number 10. The text describes the image and provides a brief explanation of why astronomer Halton Arp compiled his catalogue of odd-looking galaxies in the 1960s. Includes an inquiry-based classroom activity.

11-12, but the material can be adapted for use in other grades at the teacher's discretion
How to use in the classroom

Teachers can use this lithograph as:

An example of interacting galaxies. Use the inquiry-based classroom activity called In Search of Peculiar Galaxies that is included with the PDF lithograph.

An engagement tool in an inquiry-based lesson. Have students study the images on the lithograph. Ask them to write down as many questions as they can about the features visible in the images. The students questions can be used in a variety of ways. Here are a few suggestions:

  • Ask students to find the answers to their questions by reading the back of the lithograph and/or the related materials listed below.

  • Have students exchange papers so that each student has someone else's questions. Then have students find the answers to the other students' questions by reading the back of the lithograph and/or the related materials listed below.

  • Ask for volunteers to read the questions as someone records them on the blackboard or on an overhead transparency sheet. Ask students to raise their hand if they have the same question or something similar. Count the number of raised hands and record it next to the question. Once all the students questions have been added to the list, ask them to search for the answers to their questions in the text on the back of the lithograph. When they complete that task, ask them to decide if each of their questions was answered completely, answered partially, or not answered at all. Go through the original list and place an "A" in front of the questions that were answered completely, a "P" for those that were partially answered, and an "N" for those that were not answered at all. Determine if the most commonly asked questions were also answered completely. Encourage students to do further research to find answers to the unanswered questions.

A content reading tool. Have students read the back of the lithograph and write a quiz for the class.

Related materials