1 star Star-chart for Sept 2015 (2 sheets, east & west)*
1 piece of string (just the right length)
*Note: These star-charts are good for September, 2015. You will need new star-charts for other months. You can find these at Stardome by clicking here. Some excellent star-guides, star-charts with lots of additional information and things to look for, can be found here.
First, you need to make a sextant: A sextant is a tool for measuring the altitude (in degrees) of a star above the horizon. Sextants were used by sailors for navigation, until they were replaced by radio and GPS.
To make a quadrant = a simple sextant for your experiments.
- Find a washer or small clip (any small weight will do) and loop your string through it, so that the string is doubled up, open ends together at the top.
- Tape the open ends of the string (together) to the midpoint of the protractor on the flat end. You have just made a plumb line!
- Make a sight guide by taping your protractor to a ruler, so that the straight edges align. If you put a piece of paper between the protractor and the ruler, it’s easier to see the numbers.
Celestial Treasure Hunt!
To get your feet wet, you should use your starchart find all of these stars and constellations (and one planet) in the New Zealand night sky.
|Southern Cross||Beta Centauri||Scorpius||Sagittarius|
Find the Southern Celestial Pole & your Latitude!
The Southern Celestial Pole is the point in the night sky around which all stars seem to rotate. If you can find this, then you can figure out which direction due south is, and you can figure out your latitude. You will need your sextant, starcharts, transparency film and a Vivid or Sharpie marker.
- Find the Southern Cross and the two pointer stars Alpha and Beta Centauri. Draw them on your transparency to the left, near the top.
- Draw a line connecting the two pointer stars.
- Draw a line through the long arm of the cross. Draw a second line perpendicular to the one that joins the two pointer stars.
- Where these two lines intersect is the South Celestial Pole! You found it!
Now you know the direction South. Does what you found match what your compass says?
Your latitude tells you how far south (or north) you are on the globe. These are the lines that go around the globe horizontally on the diagram below. Once you’ve found the Southern Celestial Pole, you can find latitude with your sextant. It will tell you how far south you are on the globe.
- Hold your ruler up to your eye, and look along its top edge. Point the ruler in the same direction as you are looking at the Southern Celestial Pole point in the sky.
- Measure the angle on the protractor – use the scale that goes from 0 to 90 deg (on the picture above, that’s the inner scale). Either have a friend tell you where the string crosses the protractor or put your finger on it carefully. What did you find? Now, subtract the number you got from 90-degrees. That’s your latitude!
Go online (do a quick check with this page) and see what it should be where you are when you did the measurement. Did you get the same answer? Why or why not? Get everyone in your group to try it. Did you all get the same answer?
Tracking a Celestial Object
Now you are ready for something a bit more tricky – tracking a celestial object in the night sky over time, to map out its path. First, choose your object. You might start with something big and easy like the moon, and work your way up to a particular star, planet or a comet.
- Find south (use compass or Southern Celestial Pole) Record your object’s compass direction.
- Now use your sextant to determine its altitude angle. The altitude angle is the angle that the line connecting your eye and the celestial body makes relative to the horizon. To find the altitude angle, you sight your chosen celestial body along the ruler and record the angle indicated by the string. That is the zenith angle. The altitude angle = (90o – zenith angle)
- Log your sightings. There is an example data table here that you can use. Try looking every 30 minutes one night for a few hours. What do you find? Try looking at the same time each night for a week or more. Now what do you find?
Keen to know more: The night sky has fascinated people from the very beginning of, well, people! There is so much information out there for you to explore. Try looking up latitude and longitude to find out about how to navigate on earth. Try looking up star tracking, the universe and galaxies for more about what’s out there. And do your own experiments!! What if you track two or three objects at the same time – maybe a planet and a star? Do you see the same thing? Why or why not? Never stop asking and answering questions!!
A couple of interesting (and reputable) sites you could visit:
Report your results!
Real scientists tell other people what they have found, and discuss what it might mean. You can do this below. Enter what you found as text, photos or video. Chat with others doing this experiment. Compare results. Learn stuff!