Student worksheet

Sizes: Using a pinhole camera to measure the Sun or Moon
Equipment Required
• Sheet of card
• Sheet of white paper or a screen
• Blackout for a window (e.g. black card that can be sellotaped over a window)
• Sellotape or masking tape
• Aluminium foil about 3cm x 3cm
• Pin or sharp point
• Ruler
• Scissors
• Candle or other light source
Making the Pinhole Camera
• Cut a square about 2cm x 2cm in the centre of the sheet of card.
• Put the aluminum foil over the 2cm square hole and tape it to the
sheet of card.
• Use a pin or similar to make a small hole in the foil.
• Your sheet of card complete with pinhole is your “pinhole
camera”.
Using the Pinhole Camera
1. First check that you get an image with your pinhole camera.
• Place a lit candle (or other light source) in front of the pinhole
and then turn out all other lights.
• Hold a sheet of white paper or a screen a few centimeters from
the back of the camera (as shown in this figure).
• You should be able to see an image of the candle flame (or
other light source) on the screen.
• Measure accurately and record the height of the image
My image was ______________ cm high.
• Measure accurately and record the distance between the image
and the pinhole camera.
The distance between my image and the pinhole camera was ______________ cm.
• Measure accurately and record the distance between the candle or light source and the
pinhole camera
The distance between my candle and the pinhole camera was ______________ cm.
Dr Lisa Jardine-Wright, Cavendish Laboratory December 2007

Things to find out
• What happens to the size of the image as you move the sheet of paper or screen further
away from the pinhole, but keep the candle in the same place?
________________________________________________________________________
________________________________________________________________________
• Try drawing a graph of image height (vertical axis) against the distance of the paper or
screen from the pinhole camera (horizontal axis).
• Look at your graph – what do you think it tells you?
• For each pair of measurements, calculate the result when you divide the height of the
image by the distance between the camera and the screen or paper.
• Multiply the result of the division calculations by the distance between the candle and the
pinhole camera.
Height of image cm
× ·distance between the candle and the pinhole cm
Distance to screen from pinhole cm
= _________________________ cm
= Height of the candle flame or light source
• Measure the height of your candle flame or light source.
My light source is _____________________cm high
How similar are the your two values for the height of the light source _________________
2. Finding the diameter of the Sun or Moon.
It is very important that no one looks directly at the sun, as this will damage the retina in
the eye. The pinhole camera is a safe way to observe the sun, since you only need to
look at the image on the screen, not directly at it.
• Black out a window that faces
the Sun or Moon, and cut a
square about 2cm x 2cm in the
centre of the blackout material.
• Put the foil over the square
hole and tape it to the blackout
material.
• Use a pin or similar to make a
small hole in the foil.
• Turn out all the lights in the
room.
• Hold a sheet of white paper or
a screen as far from the
pinhole as possible.
• You should now be able to see
an image of the Sun or Moon on the paper or screen – if it isn’t clear enough, try blacking
out more windows to reduce the light in the room or experiment with the size of your
pinhole.
Dr Lisa Jardine-Wright, Cavendish Laboratory December 2007

• Measure accurately and record the distance between the pinhole and the white paper or
screen.
The distance between my image and the pinhole camera was ______________ cm.
• Measure accurately and record the diameter of your images of the Sun or Moon (using the
same units).
The diameter of my Sun or Moon image is ______________ cm.
• Now we will calculate the real diameter of the Sun or Moon from your measurements.
Calculation
• The diameters of the moon and the cut-out semi-circle are in the same proportion as the
distances between your eye and the moon and between your eye and the window.
Diameter
Distance from Earth of Sun or Moon × Diameter
of Sun or Moon =
Distance to Screen from Pinhole
of Image
• The distance of the Earth from the Sun is 149,600,000km
• The distance of the Earth from the Moon is 384,400 km
• You will need to make sure that you change all your distance measurements to the same
units, e.g. metres.
o Remember there are 100cm in 1m and 1000m in 1km.
• Fill in the blanks in the boxes below
Diameter
of
________ in km =
km
×
cm
cm
Diameter of ________ in km =
km
Things to think about
• How many times bigger is the Sun than the Moon?
________________________________________________________________________
________________________________________________________________________
• Why do you think that they appear to be about the same size to us?
________________________________________________________________________
________________________________________________________________________
Dr Lisa Jardine-Wright, Cavendish Laboratory December 2007