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Decoding an Extraterrestrial Message

  • Planétarium
Decode an extraterrestrial message!
Photo: Planétarium de Montréal
Zeiss projector.

Tabs group


Description of the activity

Decode an extraterrestrial message!


By the end of this activity, students will be able to:

  • Transpose a message made up of zeroes and ones onto a grid.
  • Interpret the image constructed.
  • Create “messages” made up of zeroes and ones in order to transmit the information to other students.

Equipment needed by the student

  • A copy of the handout “Decoding an Extraterrestrial Message.”
  • Pencils


Make one copy of the handout Decoding an Extraterrestrial Message for every student.


  1. Tell students they’ll see the transcription of a message recently picked up by a radio telescope at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, at a frequency of 1420 MHz. The message comes from extraterrestrials. What will the message look like? Will we be able to decode it? To understand it? To answer these questions, your students will try to decode and understand this message from the stars.
  2. Pass around the handout. Point out that the message is made up of two symbols: zeroes and ones. Do we know any machines that use only two symbols to process data and communicate to each other? Fax machines and computers, of course! These machines use only zeroes and ones to exchange information. 
  3. Ask students to count the number of zeroes and ones in the message. The message consists of 22 zeroes and 13 ones (hence, 35 “bits” of information in total). How is the number 35 special? It’s not a prime number, but its divisors are (35 can be divided only by itself and the primes 1, 5 and 7). This suggests a way to “organize” the information. Students may obtain good results if they lay out the zeroes and ones on a grid containing five rows and seven columns, or seven rows and five columns.
    We already use a similar technique to transmit black-and-white images by fax or satellite. The images are first “broken down” into a very tight grid. Each of the squares is represented by a one or a zero, depending on whether it is black or white. This produces a long series of zeroes and ones that the receiving fax reorganizes to recreate the image. Is this technique what extraterrestrials hope to see us use?
  4. To clarify this notion, ask students to place the zeroes and ones on a 5 x 7 or 7 x 5 grid. You can divide the group into two, the first group using the first grid (five rows and seven columns) and the second group using the second grid (seven rows and five columns). You can also have each student complete the two grids.
    Students must transcribe the message line by line. They begin in the top left corner and move right, darkening the squares representing a one and leaving blank the squares representing a zero. They then move to the front of the second row and continue. So that they don’t forget a zero or one (which would completely ruin the message), suggest that they check off the “bits” of the message as they move each bit to the grid. Give them a few minutes to complete this exercise after making sure they’ve all understood the procedure.


Adapted from Decoding an Extraterrestrial Message, developed by Roberta Vaile of the SETI Institute in California

Category of activity

  • Enrichment activity

Sub-category of activity

  • Class activity

Grade level

  • Elementary cycle three
  • Secondary cycle one
  • Secondary cycle two

Number of students per group

Individual activity or in pairs


30 minutes

Activity Sheets

Decoding an Extraterrestrial Message[PDF - 385.04 KB - 8 pages]

Schedules for teachers

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