The seasons are probably the most noticeable thing that occurs as the Earth revolves around the Sun. The seasons are caused by the tilt of Earth’s axis with respect to the Sun. That means as the Earth rotates around the Sun, the latitude where the Sun is directly overhead changes during the year.
Laboratory Tools
We will be using the Seasons and Ecliptic Simulator from the University of Nebraska-Lincoln. The main panel shows the Earth and Sun in either an orbit view or the celestial sphere. The upper right panel shows either the angle the Sun’s rays make with the Earth (view from side) or where the Sun is overhead on the Earth (view from Sun). You need to click the box for show subsolar point to see point where the Sun is overhead. In this panel there is also a stick figure with which you can change the latitude of the observer. The bottom right panel shows either the angle the Sun’s rays make with the Earth’s surface at the observer’s location (sunlight angle) or how spread out the Sun’s energy is on the Earth’s surface (sunbeam spread). The panel at the bottom shows the day of the year and allows you to start and stop the animation. You can also drag the redline to the day of your choice.
Also we will be using the Daylight Hours Explorer from University of Nebraska-Lincoln. Note that there are instructions for how to download this that you should ignore, it will run perfectly fine in your browser. The explorer shows the amount of day and night for each day of the year for a latitude specified in the Settings box. There is also a Globe box that shows the Earth as a globe.
Assignment
Using the Seasons and Ecliptic Simulator start by placing your observer on the equator. Let the simulation run for a year. Observe the way the Sun’s rays change over the year. Describe what the observer sees over the year. What will be the hottest and coldest days of the years (based only on sunlight) for this observer?
Now move the observer to the North Pole. Again observe the Sun’s rays and also the sunbeam spread. Describe the motion of the Sun in the sky for this observer. How long is the observer in total darkness? What angle above the horizon is the Sun on summer solstice?
Now move the observer to New York City, latitude 41 degrees. Describe how the motion of the Sun changes for this observer. Now switch to the Daylight Hours Explorer. How much daylight is there on the longest day in New York City? How about the shortest? What latitude to you have to reach to see 24 hours of daylight?
Questions
- Why is it always colder at the poles then on the equator even though one can have 6 months of 24 hours of daylight?
- If you live on the equinox is it more correct to say you have four seasons or two?
- What would the seasons be like if the Earth’s tilt was 90° instead of 23.5°?
