Name _______________________________ Date _____________________ Period ________________
The Angular Size of the Sun and Moon
Part 1: The Moon’s Angular Size
During a full Moon, if you were to hold a dime, with a diameter of 1.7 cm, at a distance of 188 cm from your
eye it would just barely cover the full Moon.
Dime
Moon
Diameter
Dime
Eye
Distance
The angular size of the moon is approximately equal to the diameter of the dime divided by the distance from
the dime to your eye.
This will tell use the angular size in degrees. To find the angular size in arcminutes you would have to multiply
the angular size by 60.
1) Find the angular size of the Moon in degrees.
2) Find the angular size of the Moon is arcminutes.
3) How does the angular size of the Moon, as seen from Earth, compare with the angular size of your
index finger held out at arm’s length? (If one has a larger angular size, write which one that is and also
include how many times bigger it is.)
Part 2: The Sun’s Angular Size
On a sunny day you can discover the Sun’s angular size by poking a small hole in a piece of paper and holding
the paper perpendicular to the rays of light from the Sun. As you lift the paper higher you will notice that the
shadow of the paper has a small hole of light that gets bigger.
In your group poke a small hole in a piece of paper and go outside with the class. Hold the paper, with the
hole, height in the air and angle it so the shadow on the ground has a near perfect circle of light passing
through the hole. Measure a straight line distance from the shadow to the hole in the paper. Also measure
the diameter of the circular light that is passing through the hole onto the shadow on the ground.
4) Record the distance from the hole to the shadow on the ground in cm.
(Remember a meter stick is 100 cm long.)
Distance: ___________________
5) Record the diameter of the circular light passing through the hole on the ground in cm.
Diameter: ___________________
6) Now use the equation below to find the angular size of the Sun in degrees.
7) Find the angular size of the Sun in arcminutes.
8) How does the angular size of the Sun as seen from Earth compare with the angular size of your index
finger held out at arm’s length? (If one has a larger angular size, write which one that is and also
include how many times bigger it is.)
9) Compare the angular size of the Sun and Moon as seen from Earth.
a) Is one angular size a lot greater (more than twice) than the other? If so which is bigger?
b) If the angular size of the Sun and Moon as seen from Earth are about the same size, predict what
you would see if the Moon passed in front of the Sun.
c) If the angular size of the Sun was a lot greater than that of the Moon as seen from Earth, predict
what you would see if the Moon passed in front of the Sun.
1.6 Daily and Annual Motions Questions
1) Suppose the ecliptic were not tilted with respect to the celestial equator. How would the
length of the day and night vary throughout a year at a given location?
2) Why do we see different stars at different times of the year?
3) Explain why the Sun and stars appear to rise in the East and set in the West each day.
4) Does the Moon appear to rise in the East and set in the West?
Explain how you are sure of your answer.
5) Each day the Sun seems to be slowly drifting to the East. Explain this apparent motion of the
Sun.