Seasonal Changes Due to the Sun

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Sun's Seasonal Movement Across the Sky

Activity: Stellarium-Web

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

Change the date at the bottom right of the page to early July (Winter in the southern hemisphere).
Play the time forward and observe the path the Sun appears in the sky.
- - Which direction does the Sun appear to rise from?
  - Which direction does the Sun appear to set in?
  - How many hours of daylight do we have on this day?
Using the controls on the bottom left of the screen, change the date to late December (Summer in the southern hemisphere).
Again, play time forward and observe the path the Sun takes as it moves across the sky.
- - Which direction does the Sun appear to rise from?
  - Which direction does the Sun appear to set in?
  - How many hours of daylight do we have on this day?

Although a day is 24 hours long, not every day has 12 hours of daylight and 12 hours of night.

The amount of time we spend in sunlight and night time depends on two things:

Where we are on Earth
Where Earth is as it revolves (orbits) around the Sun.

In New Zealand (southern hemisphere) the path of the Sun changes with the seasons:

In winter, the Sun rises in the northeast and sets in the northwest
In summer, it rises in the southeast and sets in the southwest.

This affects both how long the Sun is in the sky and the direction and length of shadows throughout the year.

The Sun's path from southeast to southwest in the summer is longer than the Sun's path from northeast to northwest in the winter.
This is why we have more daylight hours in the summer, and shorter daylight hours in the winter.

Activity: Changing Path of the Sun with Changing Seasons

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 'Course of the Year' left and right to change the month/season, but keep the latitude at -37° and the longitude at 175°. What do you observe, and why? What does these model settings represent?
Observe the direction of the Sun's path, the angle of the Sun in the sky and the shadow formed at different months/seasons of the year (January summer, April autumn, July winter and October spring).

The Earth's Tilt

We get different amounts of daylight hours over the course of the year because the axis (the imaginary line that connects the north and south poles) of our planet isn't straight up and down. Instead, it is tilted 23.5°.

As the Earth moves around the Sun during a year, the southern hemisphere faces the Sun more directly in December. In June, this reverses; and the southern hemisphere faces the Sun less directly. The way we face the Sun causes us to experience more direct sunlight and longer days in the summer, and less direct sunlight and shorter days in the winter.

During March (autumn) and September (spring), the Earth is tilted neither towards nor away from the Sun, so all locations on Earth receive the same number of daylight hours. As our planet continues in to revolve around the Sun, each hemisphere starts experiencing different daylight hours, depending on if it is now facing more toward or more away from the Sun.

This view shows the southern hemisphere (as seen from over Antarctica) during December. The red arrow points to New Zealand.

Would you say we are spending more time in daylight or night time?

This view shows the southern hemisphere (as seen from over Antarctica) during June. The red arrow points to New Zealand.

Would you say we are spending more time in daylight or night time?

Activity: Seasons

Control the motion of the Earth as it revolves around the Sun. Work out how the Earth’s revolution and the tilt of its axis determine seasons in the different hemispheres. Work out how the Earth’s revolution and the tilt of its axis determine day length in the different hemispheres. Examine the heating effect of the Sun. Compare seasons at different locations on the Earth. For example, work out that when it is summer in China, it is winter in Australia.

Click on this link: https://www.scootle.edu.au/ec/viewing/L5774/L5774/index.html

https://www.earthspacelab.com/app/seasons/

Matauranga Māori

Te Papatūānuku's (the Earth's) tilt makes te Rā (the Sun) appear to rise in different directions over the year. Māori astronomers passed down these observations by telling the story of how te Rā (the Sun) moves between two wives over the course of the year.

In Pipiri / winter, Māori astronomers observed that te Rā rises next to a blue star in the northeast. This blue star is Hinetakurua, the personification of Sirius (the brightest star in our night sky). Pipiri is the first lunar month of the Māori year (approx. June).

In summer, Māori astronomers observed that te Rā rises near a red star in the southeast. This red star is Hineraumati, ther personification of Antares. Antares is a red supergiant star in the constellation of Scorpius.

Transcript

Our ancestors believed that the Sun is the eldest to the celestial bodies and his rising in the early morning signified life and wellbeing. On the flipside, the setting of the sun in the evening was a sign of death. But what part did the sun play in the division of time?

The sun is said to have two wives, Hieraumati and Hinetakurua. Hinetakurua is a star that can be seen rising in the predawn sky in the east during the month of Pipiri that signals winter. She is the reason winter is called takurua. (Note: In the Māori lunar calendar (Maramataka), Pipiri is the first month of the year, roughly equivalent to June.)

During the winter solstice Matariki rises in the morning slightly north of the sun. Our ancestors believed Matariki signalled to the Sun that his time in the sky with his winter wife had come to an end, and it was time to return to the east to be with his summer wife.

It is said that Hineraumati dwells on the Earth, she is personified in the warm soil that encourages the growth in the summer seasons. She is the reason summer is called raumati.

Our ancestors knew that when the Sun started his journey back to either Hineraumati or Hinetakurua, this is known as 'the turning point of the sun'. These two turning points are known by western knowledge bases as the summer and winter solstices. This is the Sun's connection to how our ancestors divided the year into seasons. His movements across the horizon throughout the year signalled the summer and winter solstices.

Earth Over the Year

This changes the seasons - a time of year that has a general pattern to the weather. The changing seasons affects living things on our planet, and many animals and plants change their activitiy to accommodate for these seasonal changes. For example, plants may drop leaves to grow more slowly; animals may migrate to a new location or change how much they sleep and eat. The cycle of the different seasons repeats every year; caused by the Earth's revolution (orbit) around the Sun.

Glossary

Key terms and definitions.

autumn: The season between summer and winter, when temperatures start to cool and leaves may fall from trees; from March to May in NZ.

hemisphere: One half of a planet, divided into northern and southern sections by the equator.

latitude: The measurement of how far north or south something is from the equator.

revolution: The movement of one object around another, like Earth orbiting the Sun.

spring: The season between winter and summer, when temperatures start to warm and plants begin to grow again; from September to November in NZ.

summer: The warmest season of the year, when days are longest and the Sun is high in the sky; from December to February in NZ.

tilt: On an angle; the Earth’s axis is on a 23° angle.

winter: The coldest season of the year, when days are shortest and the Sun is low in the sky; from June to August in NZ.

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