The Earth in Space: Passing Time

# 1. Awareness of Time

Suggested Learning Intentions

• To understand that the passage of time is measured in specific units based on the movement of the Earth in space

Sample Success Criteria

• I can demonstrate that the passage of a day is determined by the length of time that it takes for the Earth to spin on its axis
• I can demonstrate that the passage of a year is determined by the earth’s movement around the sun, which takes approximately 365 days
• I can explain why we have leap years
• I can demonstrate that seasons are determined by the Earth’s orbit around the sun and the earth’s relative axial tilt
• I can describe that the passage of a month is determined by one cycle of the moon’s phases
• I can use manipulatives to demonstrate my understanding

Part A – Rotations and revolutions

To begin, ask students to think about the word ‘time’. Encourage them to respond to the following questions:

• How do we measure the length of a day and why?
• How long is a year, and how do you know?
• Why do you think different regions of the earth experience different seasonal conditions?

Ask students to turn and talk to the person next to them about their responses to these questions. After a few minutes, ask a few students to share. Record responses on the board or an anchor chart, and then invite students to explore the topic further.

Read the book ‘On Earth’ by G. Brian Karas to students, or alternatively watch a recorded video of the book being read.

• What is meant by 'rotation' and 'revolution' of the earth on its axis?
• What does it mean when we say the earth is tilted? Ask students to draw their response to this question.

Part A – Rotations and revolutions

This activity is based on an activity developed by Margaret Thomas.

Watch the Rotation and Revolutions video from Crash Course Kids.

Pair students, giving each pair a torch, a world globe (or a ball to represent the globe). Make the room as dark as possible. One student will be the sun, holding the torch. The other student will hold the world globe (or ball). This student will turn the ball around while walking around the sun (lit torch) which is being held by their partner. Tell the students that although they will not be able to rotate (turn) this many times with the ball, the earth will have made 365 ¼ turns by the time it completes one revolution around the sun.

Explain to students that a calendar records full days, so that when we have completed a calendar year of 365 days, the Earth is still a quarter of a day away from the starting point. The second year starts, but we are a quarter of a day out. After the second calendar year, we are another quarter of a day short, so altogether these two quarters make a half-day. By the end of the third year, we are three quarters of a day short of the actual start of the revolution and by the fourth year, we are a day short.

Ask the students to record their observations.

Watch a mini lesson about Day and Night (ABC iView, Series 2021, Episode 9 Science Year 3).

Working in small groups, students discuss the following questions and record their responses:

• What do you notice about night and day? What causes day to change into night?
• Which way does the Earth spin? (Hint: the east coast of Australia experiences sunrise before the west coast)
• What do you notice about the weather as the Earth moves around the sun?
• Describe the time measuring devices we use to measure and record the Earth’s rotations (days) and revolutions (years)
• What happens with the additional ¹/₄ rotation (¹/₄ of a day)?

If students do not come up with the answer to this last question, remind students that we add up those quarter days and then add one extra day every four years to the shortest month (February) to make up this extra quarter day each year, so that by the end of the fourth year, we are back to the start. The year with the extra day in February is called a leap year.

Optional Question:

• Do all countries start a new year on January 1? Learn about cultures that don't celebrate New Year's Day on January 1.

The Seasons

Explain to students that different regions of the Earth experience different seasons because of the tilt of the Earth's axis, which remains constant. Throughout the year as the Earth orbits the Sun, the axial tilt causes different parts of the Earth to receive the most direct rays from the Sun.

Explain that in December, the Sun shines directly on the southern hemisphere causing summer, and indirectly on the northern hemisphere causing winter. In June, the Sun shines directly on the northern hemisphere (summer) and indirectly on the southern hemisphere (winter). In March and September, the Sun shines equally on the northern and southern hemispheres, and we experience spring (September in the southern hemisphere) and autumn (March in the southern hemisphere).

Ask students to predict what seasons are experienced in places near the equator. Explain that near the equator, the Earth has a relatively steady angle of axial tilt all year round as it orbits the Sun. The equatorial region receives a fairly consistent level of direct rays throughout the year. As a result, the temperatures and seasons of places near the equator tend not to vary extensively.

Use a globe and torch to model how the axial tilt of the Earth causes the variation in seasons in the northern and southern hemisphere, and how this differs to the equatorial region. Watch Seasonal Variation: Tilt and Orbit (sign into ClickView using your department credentials). Encourage students to explore the seasons in other parts of the world and explain why they might be different to what we experience in Victoria.

Show students a video about different seasons recognised by some of Australia's Aboriginal and Torres Strait Islander Peoples. Ask students, ‘How do these seasons compare with the seasons that are determined by dates in the calendar?' Students could visit the Melbourne Museum website to explore the Eastern Kulin seasonal calendar which describes the seven seasons recognised by the Eastern Kulin people in Victoria.

Part B – Weeks and months

Ask students why they think months have different numbers of days, and how they think the idea of months and weeks as we know them were established.

After a brief discussion, invite students to explore this topic and watch a video about moon phases.

Explain that the moon orbits (revolves) around the earth, just like the earth revolves around the sun. It takes 29 ½ days for the moon to revolve around the earth. One revolution of the moon is the basis for the idea of a ‘month’. The reason why some months have a different number of days is because the revolution of the moon - a month - is 29.5 days, and the revolution of earth around the sun - a year - is 365.25 days.

As 365.25 cannot be divided equally by 29.5, the Ancient Romans assigned ten months, each with either 29 or 30 days; however this left 60 days unaccounted for. The calendar was changed over time to include two additional months, upon which our current Gregorian calendar is based. For more information see this link.

The moon goes through various phases. Seven days corresponds to the time it takes for the Earth’s moon to transition between each phase: full, waning half, new and waxing half. This is where the length of time for each week comes from.

• What instrument do we use to measure weeks and months?
• Did you see the moon last night?  What did it look like?

Part B – Weeks and months

Students work in pairs or small groups to make a floor calendar of the current month. Each group will need a large piece of paper, markers and a copy of the four main phases of the moon. Alternatively, you can ask students to draw each of these phases directly onto the calendar (See image below).

Students can read about the phases of the moon here. Note that there are four main and four secondary phases of the moon, but students will only work with the four main phases.

Students glue or draw last night’s phase of the moon onto yesterday’s date on the calendar. Ask them to place the other three phases of the moon onto the dates where they would expect each phase to have occurred in the past or to occur in the future.

Students can reflect on the following questions:

• How long does it take for the Moon to go through the four phases?
• Does this line up with the calendar month? Why or why not?
• Does each phase line up with each week in the month? Why or why not?

The aim is for students to realise that weeks and months are based on the moon’s revolution (orbit) and phases. In addition, the reason these are not exact has to do with the fact that the number of days that it takes the Moon to revolve around the Earth does not divide equally into the number of days it takes the earth to revolve around the sun. Length of weeks and months are based on approximations of the moon’s movement and phases.

Enable students by providing them with more information from this video about the four phases of the moon and when they occur to assist them in completing their calendar.

Extend students by exploring the four secondary phases of the moon and adding them to their calendars. Encourage students to consider whether all cultures use the same calendar.

This stage has focused on building up students’ awareness of time through an understanding that time can be thought of as the duration of an event from its beginning to its end. Some units of time, including the seasons, are based on the movement of the earth and moon in space. These different units of time can be measured by a calendar.

• A day represents the time (duration) it takes for the earth to complete one full rotation on its axis.
• A week represents the time (duration) it takes for the moon to transition between each phase.
• A month represents the time (duration) it takes for the moon to revolve (orbit) around the earth.
• A year represents the time (duration) it takes for the earth to revolve around the sun.
• Seasons are determined by the tilt of the earth’s axis, which always points in the same direction.

Assessing students’ understanding of these concepts by having a discussion with students and asking them to explain each of the above units of time. Evidence can also be obtained by observation of students as they demonstrate the rotation and revolution of the earth, as well as observing how they build the floor calendar together.

Students could draw and label diagrams representing the movement of the earth and the moon as another form of assessment. Students could also be given a Thinkboard with the following headings: Day, Week, Month, and Year where they describe each, using words and/or diagrams. A Thinkboard template is available in the Materials and texts section above.

Note that the units of time that represent portions of a day, and measured by the instrument of clocks, will be explored in a later stage.

ABC, 2021. Episode 9 Science Year 3: Day and Night. [Online]
Available at: https://iview.abc.net.au/video/ED2001V009S00
[Accessed 15 March 2022].

Behind the News, 2017. The Different Seasons in Australia's Indigenous Cultures - Behind the News. [Online]
[Accessed 15 March 2022].

Coach ONeal Science, 2020. On Earth by G. Brian Karas. [Online]
[Accessed 15 March 2022].

Coolman, R., 2014. Origins of the days of the week. [Online]
Available at: https://www.livescience.com/45432-days-of-the-week.htmlv
[Accessed 15 March 2022].

Crash Course Kids, 2015. Earth's Rotation & Revolution. [Online]
[Accessed 15 March 2022].

FreeSchool, 2016. Phases of the Moon: Astronomy and Space for Kids. [Online]
[Accessed 15 March 2022].

Happy Learning English, 2015. The Moon for Kids - Learning the Moon | Educational Video for Children. [Online]
[Accessed 15 March 2022].

Museums Victoria, n.d. Phases of the Moon. [Online]
Available at: https://museumsvictoria.com.au/learning/little-science/teacher-support-materials/phases-of-the-moon/
[Accessed 15 March 2022].

National Center for Families Learning, n.d. Why Don’t All Months Have the Same Number of Days?. [Online]
Available at: https://www.wonderopolis.org/wonder/why-dont-all-months-have-the-same-number-of-days#:~:text=The%20ancient%20Romans%2C%20like%20ancient,the%20month%20on%20the%20Moon.&text=Julius%20Caesar%20modified%20the%20Roman,extra%20day%20every%20fourth%20year
[Accessed 15 March 2022].

SBS News, 2015. 11 cultures that don’t celebrate New Year’s Day on Jan 1. [Online]
Available at: https://www.sbs.com.au/news/11-cultures-that-don-t-celebrate-new-year-s-day-on-jan-1
[Accessed 15 March 2022].

State Government of Victoria (Department of Education and Training), n.d. Day and night. [Online]
Available at: https://www.education.vic.gov.au/school/teachers/teachingresources/discipline/science/continuum/Pages/daynight.aspx
[Accessed 15 March 2022].

Thomas, M., 2018. A matter of time: an investigation into the learning and teaching of time in the middle primary years. Australian Catholic University: Unpublished Doctoral Thesis.

Thomas, M., 2020. A Matter of Time. Prime Number, 35(1).

Thomas, M., 2020. A Matter of Time (Part 2). Prime Number, 35(2).

Thomas, M., Clarke, D., McDonough, A. & Clarkson, P., 2016. Time: Assessing Understanding of Core Ideas: Opening up mathematics education research (Proceedings of the 39th annual conference of the Mathematics Education Research Group of Australasia). Adelaide, MERGA, pp. 592-599.

Thomas, M., Clarke, D., McDonough, A. & Clarkson, P., 2016. Understanding Time: A Research Based Framework: Opening up mathematics education research (Proceedings of the 39th annual conference of the Mathematics Education Research Group of Australasia. Adelaide, MERGA.

University of Iowa Department of Physics and Astronomy, 2017. Imaging the Universe. [Online]
Available at: http://astro.physics.uiowa.edu/ITU/labs/foundational-labs/observing-the-night-sky/part-6-moon-phases.html
[Accessed 15 March 2022].