Why the Sun and Stars Appear to Move

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

Earth Spins Eastward (from West to East)

Our place on Earth, as it spins, affects what we see in the sky. As Earth spins from west to east (eastward), we see the Sun 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 the Sun takes across the sky.
Change the location to somewhere on the equator (left-hand menu). Again, play time forward and observe the path of the Sun 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 the Sun takes as it moves across the sky.

SIMULATION QUESTIONS

What was similar about the way the Sun appeared to move across the sky for the different latitudes on Earth?
What was different about the way the Sun appeared to move across the sky for different latitudes on Earth?

Our View of the Sun

From Earth, the Sun looks like it moves across the sky in the daytime and is not visible at night.

Long ago, we used to think that the Sun 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.

The Sun lights up one half of the Earth, and as the Earth 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 the Sun.

When we look up at the sky, we are looking away from the Sun. As shown in the images, at sunrise we would see the Sun appear to our side, then as the Earth spins, we see the Sun cross high over our heads. In the afternoon, the Sun then seems to move lower and lower in the sky before setting in the west.

Other places on Earth also see the Sun appear to move from the east across the sky to the west, but the Sun might cross higher or lower in the sky depending on which part of Earth 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).

Do all locations on Earth see the Sun take the same path in the sky each day? In the example below:

Which stick figure is seeing the Sun directly overhead?
Which stick figure is seeing the Sun shining at an angle over their head?
Which stick figure is seeing the Sun quite low in the sky, off to their side?

Our location on Earth also affects how high or how low the Sun crosses the sky during the middle of the day.

People near or on the equator see te Rā cross the sky almost directly overhead, while people near the poles see te Rā cross quite low in the sky.

Tracking Angles in the Sky

We can track how much the Sun 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 the Sun 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.

Pictured: Navigator Bruce Blankenfield using his hand to measure the altitude of the Sun aboard Hōkūle’a. (Science Learning Hub)

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 (westward). Here is a timelapse of what that looks like, as taken by Mark Gee, a well-known astrophotographer in Aotearoa.

Matauranga Māori

Transcript from the Video

Today, most of the world has conformed to a universal system of time that is built around a western solar calendar. This system of time gives us our days, our weeks and our months and seasons. This system of time is based on the position of the sun and the movement of our planet around the sun. One revolution around the sun happens once a year. Māori also followed the sun to divide the year and measure time, but not in isolation of other markers. Māori also observed the changing phases of the moon, the movements of the stars, the migration of fish species, the song of bird species, the sound of insect species, the flowering of plants and even the changing cycles of the weather.

All of these phenomenon were part of a time division system that enabled Māori to divide the year. There were many signs that informed this sytem. Moreover, the sings were specific to the community of the observer. which meant there were variances across districts. Essentially, Māori had many different calendars and divisions of time that regualted the days, months and seasons of the Māori year.

Māori would meet at different times throughout the year to discuss the lessons of the recently past seasons and to determone the bounty of the impending seasons. These gatherings and their associated knowledge were known as whakamoe tau meaning to know the seasons or more correctly to decide upon the seasons.

Whakamoe tau is the practice of reading the signs of the environment. By understanding thes signs our ancestors were able to divide the year into days, months and seasons.