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In this activity you will calculate the Sun's diameter with a hands-on simple experiment done with simple, household materials and -of course- without looking directly at the Sun. You will just need to learn how to calculate ratios, a mirror, a stop-watch, and 20 min of a sunny day.
Students will:
The Sun is the centre of our Solar System, provided all of the light and heat needed to support all living things on our planet. Our lives are dominated by the movement of the Earth relative to the Sun, we use these movements to measure time: one day is the length of a full rotation of the Earth on its own axis and one year is a full orbit of the Earth around the Sun. However, many people do not possess an accurate idea of the scale of the Sun relative to the Earth.
The Sun moves across the sky at a constant rate because of the rotation of the Earth.It takes 24 hours for the Sun to travel 360 degrees, all the way around the sky and return to the same position it was in the previous day.
By measuring how fast the Sun moves you can work out how big the Sun appears in the sky and how big it is.
You can find additional Information about the Sun: https://en.wikipedia.org/wiki/Sun
In this activity, you have been measuring how long it takes the Sun to move a distance equal to its own diameter across the sky. The Sun will take 24 hours to travel 360 degrees all the way around the sky and return to the same position it was in on the previous day. The speed it travels at is:
360 degrees/24hours: = 360 deg/(24x60) minutes = 0.25 deg per minute = 0.00416 degrees per second or 1/240 degs per second
Calculate the size of the Sun as an angle:
Average duration (in seconds) × 1/240 (degrees per second) = _ _ _ degrees
Congratulations! You have calculated the angular size of the Sun.
You can use your value for the angular size of the Sun to calculate the physical size of the Sun.
Your number for angular size converted into radians × distance from Earth to the Sun = size of the Sun
Angular size × (pi/180) × 92 955 887.6 miles =______miles ORAngular size × (pi/180) × 149 598 000 km =______km
Congratulations! You have measured and calculated the diameter of the Sun in miles/kilometers!
The activity concludes when all the steps have been completed and a size for the Sun has been calculated (and compared with a value listed in a text book). If there are multiple groups doing this activity, collect all the answers and see how much variation there is.
This activity can be used to start a discussion about many other astronomical concepts, such as size scales in the Solar System or unit conversions.