Why the Sun Appears to Move

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Papatūānuku Spins Eastward (from West to East)

Our place on Papatūānuku, as it spins, affects what we see in the sky. As Papatūānuku spins from west to east (eastward), we see te Rā appear to move the other way - from east to west (westward).

Activity: Stellarium-Web

Use the interactive below or click on this link: https://stellarium-web.org

Play time forward (right-hand menu) and note the path te Rā takes across the sky.
Change the location to somewhere on the equator (left-hand menu). Again, play time forward and observe the path of te Rā as it moves across the night sky.
Change the location to somewhere in the Northern Hemisphere (left-hand menu). Again, play time forward and observe the path Te Rā takes as it moves across the sky.

Our View of the Sun

From Papatūānuku, te Rā looks like it moves across the sky in the daytime and is not visible at night. Long ago, we used to think that te Rā moved around our planet, but as astronomers carefully studied the way things appear to move in our night sky, they updated their ideas bit by bit. Eventually they came to realise that things appear to move across our sky because our own planet is spinning while we stand on it.

Te Rā lights up one half of Papatūānuku, and as Papatūānuku spins on its axis (an imaginary line that connects the North and South poles), different parts of the planet turn to face toward and continue to turn away from te Rā. When we look up at the sky, we are looking away from Papatūānuku. As shown in the images, at sunrise we would see te Rā appear to our side, then as Papatūānuku spins, we see te Rā cross high over our heads. In the afternoon, te Rā then seems to move lower and lower in the sky before setting in the west.

Other places on Papatūānuku also see te Rā appear to move from the east across the sky to the west, but te Rā might cross higher or lower in the sky depending on which part of Papatūānukuy they are at.

Activity: Our View of the Sun

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.
Observe the direction of the Sun's path, and the angle of the Sun in the sky at different times of the day (sunrise, noon, sunset).

Tracking Angles in the Sky

We can track how much te Rā moves aross our sky by separating our sky view into different angles. We place 0° at the horizon - the line in the distance where land meets the sky. Directly over our heads is 90° from the horizon.

We can then divide the sky up further from east to west also, allowing us to precisely measure and track how much of the sky te Rā appears to move through over the course of the day. These measurements allow us to predict where it will be in the future.

The pictures below show you how different widths of your hand can be used to measure angles of the sky.

Hold your hands at arm's length in front of your face.

The width of the tip of your little finger at arm's length is about 1°
Raise your three middle fingers to measure 5°
Clench your fist to measure 10°
One full hand-span is 20°

Movement of Other Stars

What about other stars? How do they appear to move over the course of a night?

The Earth is still spinning at night! At night, any stars that rise in the east will also appear to cross the sky and set in the west. Here is a timelapse of what that looks like, as taken by Mark Gee, a well-known astrophotographer in Aotearoa.