The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe • H2
Page 1
What’s This Activity About?
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.
Cosmic Calendar
Activity H2
Grade Level: 6–12
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:
www.astrosociety.org
Concepts
• The Big Bang
• History of the Universe
• Ratios
Inquiry Skills
• Ordering
• Calculating
• Organizing
• Visualizing
Big Ideas
• Scale
• Evolution
• Models and simulations
What Will Students Learn?
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
Page 2
Cosmic Calendar
by Therese Puyau Blanchard, Andrew Fraknoi,
and the staff of the Astronomical Society of the Pacific
A
stronomers 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 recom-
mended)
• 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
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
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
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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),
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
Page 4
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. In the calendar calcu-
lations,
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.
© copyright 2010 Astronomical Society of the Pacific.
www.astrosociety.org
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
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Cosmic Calendar Events Handout
© copyright 2010 Astronomical Society of the Pacific
The Big Bang
The formation of first neutral atoms
Formation of first stars & galaxies
Formation of the thin disk of the Milky Way Galaxy
Formation of the Solar System
Formation of the Moon
Birth of life on Earth
First cells develop on Earth
First vertebrates (creatures with backbones)
First dinosaurs
First mammals
Death of the dinosaurs from giant impact
First bipedal hominids
(human-like creatures walking on two legs)
First humans (homo sapiens)
Development of agriculture (farming)
Development of the wheel for transportation
Invention of the telescope
Right now
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
Page 6
Cosmic Time Line Events Worksheet
© copyright 2010 Astronomical Society of the Pacific
Note: The symbol ~ in front of a number means “roughly” or “about”
Event
Number of
Years Ago
Number of
Days Ago on
Calendar
Date/Time on
Calendar
The Big Bang 13.7 billion 365 Jan. 1, 12 am
The formation of first neutral atoms
13.7 billion
(400,000 years
after the BB)
365 Jan. 1, 12:15 am
Formation of first stars & galaxies ~13 billion
Formation of the thin disk of the Milky Way Galaxy ~9 billion
Formation of the Solar System 4.56 billion
Formation of the Moon ~4.5 billion
Birth of life on Earth ~3.8 billion
First cells develop on Earth ~2 billion
First vertebrates (creatures with backbones) ~520 million
First dinosaurs 230 million
First mammals ~200 million
Death of the dinosaurs from giant impact 65 million
First bipedal hominids (human-like creatures walking
on two legs)
~4 million
First humans (homo sapiens) 200,000
Development of agriculture (farming) ~10,000
Development of the wheel for transportation ~6500
Invention of the telescope 400
Right now 0 0 Dec. 31, midnight
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
Page 7
KEY: Cosmic Time Line Events Worksheet with Answers
© copyright 2010 Astronomical Society of the Pacific
Note: The symbol ~ in front of a number means “roughly” or “about”
Event
Number of
Years Ago
Number of Days
Ago on Calendar
Date/Time
on Calendar
The Big Bang 13.7 billion 365 days Jan. 1, 12 am
The formation of first neutral atoms
13.7 billion
(400,000 years
after the BB)
365 days
plus 15 min.
Jan. 1, 12:15 am
Formation of first stars & galaxies ~13 billion ~347 days ~Jan. 19
Formation of the thin disk of the Milky Way
Galaxy
~9 billion ~240 days ~May 6
Formation of the Solar System 4.56 billion 122 days Sep. 1
Formation of the Moon ~4.5 billion ~120 days ~Sep. 3
Birth of life on Earth ~3.8 billion ~101 days ~Sep. 22
First cells develop on Earth ~2 billion ~53 days ~Nov. 9
First vertebrates (creatures with
backbones)
~520 million ~14 days ~Dec. 18
First dinosaurs 230 million 6 days Dec. 26
First mammals ~200 million ~5 days ~Dec. 27
Death of the dinosaurs from giant impact 65 million 1.7 days Dec. 30
First bipedal hominids (human-like
creatures walking on two legs)
~4 million ~2.5 hrs Dec. 31, ~9:30 pm
First humans (homo sapiens) 200,000 8 min Dec. 31, 11:52 pm
Development of agriculture (farming) ~10,000 23 sec Dec. 31, 11:59:37
Development of the wheel for transportation ~6500 ~15 sec Dec. 31, ~11:59:45
Invention of the telescope 400 1 sec
Dec 31, 1 second
before midnight
Right now 0 0 Dec. 31, midnight
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
Page 8
Cosmic Time Line Events Calculations
© copyright 2010 Astronomical Society of the Pacific
In this exercise, we want to set the age of the universe equal to one calendar year. Then we want to set up ratios to
figure out where in that calendar year significant events in the history of the universe would fall. (In this analogy,
the Big Bang happens in the first moment of Jan. 1 and NOW is the very last moment of Dec. 31.)
So our basic idea is that 13.7 billion years equal one calendar year (365 days). We’ll ignore leap years for this exercise.
We set up a ratio in the form:
Number of years ago an event happened = 	 x days
Number of years ago Big Bang happened 	 365 days
The number of years ago the Big Bang happened is 13.7 billion years = 13,700 million years.
When you’ve solved for x, the number of days ago (from Dec. 31) that an event should be placed on our calendar,
you then have to count the days backwards. To make that easier, we have provided a table that tells you on what
date any number of days counted backwards from Dec. 31 would fall. (You’re welcome.)
So, for example, the dinosaurs developed 230 million years ago. Setting up our equation,
230 million years = 	 x days
13,700 million years 	 365 days
	 x = 6.13 days (which we round off to 6 days ago)
Looking at the table of dates counted backwards, 6 days before the end of Dec. 31 puts the start of the dinosaurs on
Dec. 26.
Use the table “Cosmic Time Line Events Worksheet” which lists some of the key events in the history of the universe
and do the same kind of calculation for each event. At first, you can round off, but as you get to events closer
to the end, fractions matter.
So we want to figure out how many years of real time would make an hour on our cosmic calendar. If 13.7 billion
years = 1 calendar year, then one day on our calendar would be:
13,700 million yrs in a calendar year = 37.5 million years/calendar day
365 days in a calendar year
In the same way, divide by 24 hours in a day to figure out the number of years in a calendar hour and divide by 60
again to get the number of years in a calendar minute.
The Universe at Your Fingertips • Astronomical Society of the Pacific
Galaxies and the Universe H2 • Cosmic Calendar
Page 9
DaysoftheYear*
NumberofdaysbeforeDecember31st
12345678910111213141516171819202122232425262728293031
JAN365364363362361360359358357356355354353352351350349348347346345344343342341340339338337336335
FEB334333332331330329328327326325324323322321320319318317316315314313312311310309308307
MAR306305304303302301300299298297296295294293292291290289288287286285284283282281280279278277276
APR275274273272271270269268267266265264263262261260259258257256255254253252251250249248247246
MAY245244243242241240239238237236235234233232231230229228227226225224223222221220219218217216215
JUN214213212211210209208207206205204203202201200199198197196195194193192191190189188187186185
JUL184183182181180179178177176175174173172171170169168167166165164163162161160159158157156155154
AUG153152151150149148147146145144143142141140139138137136135134133132131130129128127126125124123
SEP12212112011911811711611511411311211111010910810710610510410310210110099989796959493
OCT92919089888786858483828180797877767574737271706968676665646362
NOV616059585756555453525150494847464544434241403938373635343332
DEC31302928272625242322212019181716151413121110987654321
*Doesnottakeleapyearsintoaccount.