Daily Patterns Due to the Sun

Navigate the knowledge tree: 🌿 Earth & Space Science ➡ Astronomy ➡ Observing the Sky from Earth

Day and Night

When the Sun is at its highest in the sky, it crosses an imaginary line drawn between north and south known as the meridian.

The time when the Sun crosses the meridian is defined as noon. The hours before noon are known as AM (an abbreviation for 'ante meridiem' which is Latin for "before the middle of the day") and the hours after noon are known as PM (an abbreviation for 'post meridiem' which is Latin for "after the middle of the day.")

As the Earth rotates (spins) on its axis, it moves about 15° every hour. This means that each hour, we see the Sun move through about 15° of the sky. This creates the basis of our times and day.

Time Zones

Activity: Night and Day Interactive

This online interactive will take you through a ride across the planet to investigate how the rotation of the Earth creates different time zones! Rotate an animated model of Earth to explore how rotation is related to night and the time of day. Experiment with the model to answer questions, e.g. what’s the time in Sydney when the Sun rises in New Zealand? Click on this link: https://www.scootle.edu.au/ec/viewing/L696/index.html

Since different parts of the Earth enter and exit daylight at different times, each part needs different times.

An area that agrees to all set their clocks by the same time is known as a time zone.

Since our planet takes 24 hours to rotate once, we have divided the planet into 24 sections or time zones. Each time zone is agreed to by countries that have the same longitude (an imaginary line that connects areas that are directly north or south of each other). The time zones are generally 15° of longitude wide.

Note: 360° / 24 sections = 15° per section

What time is it around the world?

Use the interactive below, or click on this link https://dayspedia.com/time-zone-map/ to see what time it is for different locations around the world right now:

What time is it currently in Western Australia?
What time is it currently in the United Kingdom?
Which areas are currently experiencing the middle of the night?
Why do youthink the United Kingdom is 12 hours different from us?

Shadows

Shadows happen when light is blocked. As the Sun moves across the sky, shadows change their length and/or point in different directions.

In the morning, when the Sun is low in the eastern sky, shadows are long and stretch to the west.
Around midday, when the Sun is highest, shadows become short and are found directly under objects.
In the afternoon, as the Sun moves lower in the western sky, shadows grow longer again, this time stretching toward the east.

Activity: Creating Shadows

In this activity, we will be using a torch and plasticine to simulate how people can mark the different times of the day using shadows. This is very similar to how a sundial works.

Fold an A4 paper in half, and then half again so that you have divided it into 4 quadrants.
Creat a person, tree or building out of plasticine and place it in the centre of the paper.
Mark the 4 directions on the edges of the paper: north, south, east and west.
Shine a torch from the north east direction toward the figurine and mark where the shadow is on the paper.
Move the torch higher above the paper, shine it toward the figurine again, and mark the new position of the shadow.
Continue moving the torch through different positions as it crosses from north east to north west, marking where the shadow is on the paper each time.

Questions:

On your model, when is the shadow the longest?
Which quadrant of the paper shows where the shadow is in the morning? Label those shadows with "Early morning, late morning etc."
Label the shadow that represents midday, when the Sun crosses the meridian.
Which quadrant of the paper shows where the shadow is in the afternoon? Lable those shadows with "early afternoon, late afternoon, etc."

Activity: Putting it all together! Day and Night, Timezones and Shadows

Use the interactive below or click on this link: https://www.earthspacelab.com/app/solar-time/#google_vignette

Enter a latitude of -37° and a longitude of 175° to view the Sun's path from Auckland, New Zealand.
Now, move the slider for 'longitude' left and right, but keep the latitude at -37°. What do you observe, and why? What do you think changing the longitude represents? What places on Earth do you think this represents?
Observe the direction of the Sun's path, the angle of the Sun in the sky and the shadow formed at different times of the day (sunrise, noon, sunset).