## The Universe At Your Fingertips Activity: Cosmic Calendar

Source: The Cosmic Calendar is adapted with permission from Carl Sagan's book The Dragons of Eden (copyright © 1977 by Carl Sagan) and from his television series Cosmos. This version was first written by Therese Puyau Blanchard and the staff of the Astronomical Society of the Pacific in 1994 and later revised and updated by Andrew Fraknoi. © copyright 2010 Astronomical Society of the Pacific.

Students (and adults) have a lot of trouble envisioning the history of the universe, from the Big Bang, 13.7 billion years ago, through the development of various structures in the cosmos and the evolution of life on Earth, to the present moment. In this activity, students will equate the full span of cosmic time with one calendar year, and see where different cosmic events fall on a 12-month time scale.

#### What Will Students Do?

Students first brainstorm about the key events in the history of the universe and then put them in order. They will use a 12-month calendar hung from a clothesline or posted on the wall to show the whole class their estimates of what the order of events is and when each event falls on the "cosmic calendar." Younger students then uncover the answer for some key events. Older students are given the instructions and a worksheet to figure out the answers for themselves.

#### Tips and Suggestions

• Most teachers are content to have students calculate the first entries in the time line to an accuracy of one day. However, if you are emphasizing the math component of the activity you can figure out the remainder (the fractional part of the day) and then convert these to hours, minutes, seconds.
• The later entries, involving human activities, do require calculating much smaller units of time. See the hints and answer key for teachers which is part of the activity.
• Some geology and earth science teachers do this activity using the history of our planet Earth as equal to one year. Once they understand the idea of such a calendar by analogy activity, students can make their own calendar for Earth history.

#### What Will Students Learn?

Concepts

• The Big Bang
• History of the Universe
• Ratios

Inquiry Skills

• Ordering
• Calculating
• Organizing
• Visualizing

Big Ideas

• Scale
• Evolution
• Models and simulations

### Cosmic Calendar

by Therese Puyau Blanchard, Andrew Fraknoi, and the staff of the Astronomical Society of the Pacific

Astronomers estimate that the universe began some 13.7 billion years ago in the explosion of space, time, matter, and energy we call the Big Bang. Such a number is hard to visualize. Most students have difficulty grasping how large a span of time this is compared to their own lifetimes or to the events they read about in history.

One way to visualize large expanses of astronomical time is to draw an analogy between the time since the creation of the cosmos and a more familiar span of time, like a year. Geology educators have used this technique for a while, but in astronomy the idea was pioneered by Cornell University astronomer and popularizer of science, Carl Sagan. In Chapter 1 of his Pulitzer-prize winning book, The Dragons of Eden (1977, Random House hard cover; Ballantine paperback), Sagan proposed compressing the history of the universe into one year and then seeing where in that year various events of interest fall. Since the book was written, we have better information about a number of the time spans Sagan originally used, but the technique of figuring out "the cosmic year" remains a particularly powerful educational tool.

Depending on the age and mathematical ability of the students or audience, you can either provide the dates for this visual analogy or have students calculate them. The necessary information and materials for both options are provided below.

#### Materials Needed:

• 12-month calendar (either one for the whole class or one for each group; the larger the better)
• Clothesline and clothespins (optional, but recommended)
• Large cards or signs for each major event, with the date of the event written on the back (covered by a sheet of paper) [for older students, let them make these cards or signs instead of providing them]
• Cosmic Calendar Events hand-outs
• A large sheet of construction paper for each group of students
• Glue
• Scissors
• Blank sheets of paper
• (Optional, for students doing calculations) Cosmic Time Line Events Worksheet, Cosmic Time Line Events Calculations Sheet, and Backward Calendar Count Table (included in hand-outs)

#### Procedures

1. Present the concept of a time line by displaying the 12-month calendar, with the months hung along a wall or across the room on a clothes line. (The clothes-line calendar strung along the whole classroom allows step 6 to be especially dramatic.)

2. Explain the visual analogy: that the first moment of January 1st of our one-year "Cosmic Calendar" represents the "Big Bang," which is the beginning of cosmic time. Explain that "today" is represented by the last possible moment on December 31st. Thus, this "cosmic year" represents the entire history of the universe. Now we want to see where different historical events fall on our calendar of cosmic time.

3. Depending on your students' background, either brainstorm with them or divide them into small groups to brainstorm about some of the important events that happened between the Big Bang and now. Encourage them to take a "big picture view" and focus some of their attention on events in the universe at large and not just those on Earth. Accept all suggestions at first to be sure everyone gets a chance to participate and then have them narrow down the number of events to be manageable.

4. If you have not done so already, now divide the class into groups and distribute a Cosmic Calendar Events handout to each group. Have groups cut and place the list of events on the handout onto the large piece of construction paper to create one long time line. (Note: There is nothing sacred about this particular list of events. You can give students a shorter list, a longer list, or a different list, depending on their backgrounds and your curriculum. Later, you can have them do research and find how long ago events that they add to the list happened. )

5. Each group should then take the major events listed on the Cosmic Calendar Events hand-out and decide on the probable order of occurrence by putting the events in the right sequence. When every group has decided on the order of the events, you can have a full-class discussion and see if groups agreed on the order. Groups can adjust their own order based on the full-class discussion.

6. Now we want to become more specific and try to figure out where each event would actually fit within our "cosmic year." So, for example, where in the year would the origin of planet Earth lie? Would it be early in January, in the spring, in the fall, etc? If each group has its own 12-month calendar, have the groups place each event they cut out next to the month they predict the event occurred. Groups that finish first can also try to predict the day of the month for some events. (If there is only one calendar for the whole room, then just have students keep notes on the months and dates they predict; perhaps by pasting each event to a sheet of blank paper and writing their estimate of the month and day in pencil on the sheet.)

7. Then, select volunteers to be a "living time line." Give each volunteer a larger sign or picture for one of the major events (these signs need to be prepared in advance; on the back you can put the correct Cosmic Calendar date for that event and then cover it up with a flap, or just leave the answer for later). Ask volunteers to stand under the predicted month on the clothesline calendar or next to the month on the wall calendar for their event. (At this point, the class is still using their own estimates for where each event falls on the calendar, and has not yet been given the answers.) When the volunteers have found their places, each one should say their event and their estimate of the date aloud, starting with the earliest.

8. Hold a class discussion on the order of the events portrayed. A student who disagrees with the order or placement of a certain event may change places with the person holding that card, if the class agrees. Continue the discussion until a majority of the students agree with the order of events.

9. Now it's time to see how well the students did. For younger students, if the large sign or poster each volunteer in the "living time line" is holding has the "answer" under the flap on the back, have them uncover the answer and read aloud the actual calendar date for that event one by one. If necessary have them re-position themselves on the time line. Leave time for discussion, especially for those event dates where students were considerably off.

10. For older students, have the volunteers write their estimates for each event in pencil on the class calendar. Then have everyone sit down and assign different groups to do the calculations of where various key events fall on the time-line. Have them use the Cosmic Time Line Events Worksheet in this activity. Instructions for doing the math are on the Cosmic Time Line Events Calculations Sheet. Once the answers are done, volunteers should go back up to the class calendar and correct any estimates that need correcting and re-position themselves. Leave time for discussion.

11. Point out some of the significant events and discuss these questions:

• Humans arrived on the scene only about 8 minutes ago according to our model. How does this change your perspective on our cosmic importance?
• Dinosaurs ruled the Earth for almost two hundred million years— from December 26 to December 30 on our time line. They died out long before humans came on the scene. Does this change your thinking about dinosaurs?
• Were you surprised by when the Earth and the Sun were formed in the "cosmic year? If there are older stars than the Sun out there (and there are many), might they have older life-forms on them?
• It took a long time between the beginning of life on Earth and the rise of humans. Did you think before this activity started that the time for us to evolve was that long?

NOTE: It's important for students to understand that science is a "progress report" and is always updated as new experiments and observations become possible. While the dates in the attached worksheet are our current best estimates, new information may become available about some of the ideas presented in the table. Older students may want to do some research using reliable web sites and books about the latest estimates.

#### Extensions

1. Have students write up and illustrate their own cosmic time lines in their notebooks, and include information and scale drawings.

2. Have students work in groups to design mobiles using hangers and string to fit the events on the class clothesline.

3. Do research to find additional events for the time line. If necessary, enlarge a part of the Cosmic Calendar to study shorter time periods. Other events could include: first life on land, first primates, the invention of writing, etc.

4. Designate an entire hall in the school as a cosmic time line. Have students create drawings and captions to describe the major events and hang these along the time line. Have one group make a poster to explain the time line concept to other students in the school.

#### Note for the Teacher or Activity Leader

We have included a Cosmic Time Line Events Worksheet with Answers for your use (included in hand-outs). In the calendar calculations,

1 calendar day = 37.5 million years
1 calendar hour = 1.56 million years
1 calendar minute = 26,050 years
1 calendar second = 434 years.