What it shows
The height of the Pole Star above the horizon is nearly equal to your latitude in the northern hemisphere. A homemade angle measurer can show your place on Earth.
The science
The Pole Star, Polaris, lies almost exactly above the Earth’s north pole of rotation, within about 0.7 degree. At the north pole it would be straight overhead, and at the equator it is on the horizon. At any place the angle of the Pole Star above the northern horizon is nearly equal to the latitude. The tilt of the Earth’s axis, and not the star itself, is the reason. Polaris is faint, so use the Great Bear or Cassiopeia pointers to find it.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A protractor with a hole at its centre
- A drinking straw taped along its straight edge
- A thread of 20 cm with a nut as a plumb weight
- A star chart or a free sky app to find the Pole Star
- A torch with a red cover for reading
- A notebook
- An atlas or phone map for the latitude of your town
Safety
For this project: An adult must come along for night work. Choose a safe open space away from roads and wear mosquito protection.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Tape the straw along the straight edge of the protractor and fix the thread at the centre hole so that it hangs freely over the scale with the nut at the end.
Learn to find the Pole Star: draw a line through the two stars at the end of the Great Bear’s bowl and extend it five times their gap. Check the star chart.
Stand in an open place and look through the straw at the Pole Star so that you can see the star along the straw.
Ask a friend to read where the thread crosses the scale while you hold still. If the protractor shows 90 at the straight edge, the angle of the star is 90 minus the reading, or read the right scale carefully.
Repeat the reading five times and take the average.
Check your latitude with the atlas or phone map and compare.
Estimate the error, for example plus or minus 2 degrees, and think about how a steady hand and a straight straw could improve it.
Use the daytime noon Sun on an equinox as a second method: latitude is about 90 degrees minus the Sun’s altitude on that day.
What you should see
A measured angle that is within a few degrees of the latitude of your town, such as about 28 degrees for Delhi or 13 degrees for Bengaluru.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is the Pole Star useful for finding north?
It lies almost exactly above the Earth’s north pole, so it stays in the same place in the sky.
2What is the angle of the Pole Star at the equator?
Nearly 0 degrees, on the horizon.
3Why does the Pole Star not move while others circle it?
It lies on the Earth’s axis of rotation, so it turns in a tiny circle.
4Can you use this in the southern hemisphere?
No, because the Pole Star cannot be seen there.
Take it further
Photograph the sky with a phone on a tripod for 30 seconds to catch short star trails turning round the Pole Star.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Earth, Space and Geography Models
Solar system, seasons, eclipses, volcanoes and the water cycle explained
Science projects
Investigatory Projects for Class 11 and 12
Topics, method and report structure for physics, chemistry and biology