The Bighorn medicine wheel is a huge circular structure of stones and lines in the Bighorn Mountains of Wyoming, Western USA.

It was built by the original inhabitants of North America. Bighorn is one of a number of medicine wheels spread across the United States and Canada. East of Carmangay, Alberta, are the remains of another medicine wheel on Sundial Hill, for example. This name suggests that the wheels might have some relation to the apparent movement of the Sun. The wheels have always been associated with early American Indian understanding of astronomy, and by surveying the Bighorn medicine wheel, Dr John Eddy of the High Altitude Observatory in Boulder, Colorado, was able to make a connection between the rocks on the ground and the movement of the Sun and stars.

The great red ball ofthe Sun

Believing the wheel to be an observatory, he and his family climbed to it before dawn in June 1972, on the morning of the summer solstice - the first day of summer. He suspected that a cairn of rocks outside the wheel marked a spoke that would point to the sunrise. “The direction of the first glow told us we could not be far wrong. Then the great red ball of the Sun appeared, exactly in line with the cairn.”

At the time of the solstice, when the Sun is at its highest, the builders, “believed the growing power of the Earth is strongest”. The medicine wheel might be a model for the Sun dance, giving it its shape and geometry.

The dawn rising

Dr Eddy recorded the places of all the other cairns at the Bighorn wheel. Perhaps each one marked an astronomical event. He wondered if they recorded the dawn rising of stars - the few minutes when a very bright star appears over the dawn horizon before it disappears in the growing sunlight. These star appearances change from year to year; and so the cairns would no longer be in line with any current dawn risings. But if they had once lined up with the stars, it would be possible to calculate, very accurately, when the medicine wheel was in use.

Dr Eddy found that the brief flash of the bright star Aldebaran would have been visible in line with two cairns around 1700AD. Other bright stars would have been marked by other cairns. This tied in well with a piece of tree branch found in the central cairn and dated around 1760. Native Americans had made careful observatons of the sky, he concluded, and recorded them in this giant wheel.

Teaching astronomy to children

The national curriculum expects that pupils will be taught that the Sun, Earth and Moon are approximately spherical; how the Sun appears to change position - and so shadows - during a day; how the Earth turns, resulting in day and night; and how the Earth orbits the Sun annually, and the Moon the Earth monthly.

This involves us in teaching children three really tough concepts:

* The Sun, Earth and Moon are incredibly big - and very different in size from each other.

* The Sun, Earth and Moon are incredibly distant from each other.

* The Sun, Earth and Moon are moving - both as a group and relative to one another.

It is little wonder that children have real difficulties with these ideas. Added to this, pupils have their own ideas about astronomy. formed before and while we are teaching them about it. These ideas interfere with new ideas. They are very hard to challenge.

There are also practical problems in teaching astronomy. Most astronomical objects are visible only at night. Urban visibility is poor, due to light pollution from the glare of street lamps. Astronomical events take place very slowly. And astronomical objects cannot be manipulated, so investigations involving factors and fair testing are impossible. There are some practical answers to these issues: First-hand experience

Give children opportunities to experience the night sky by:

* involving parents in making observations with their children - best done in spring or autumn, when days are shorter but it is not too cold.

* using the school journey or a residential visit, when children may not be in a hurry to sleep, anyway.

* setting up an after-school club. One teacher arranged for older children to come back for one-hour Star-gazer Club meetings when she had to stay at school for agovernors’ meeting.

Vicarious experience

* Modelling, using balls and torches, gives some indication.

* Using secondary sources - books, videos and CD-ROMs - as well as Internet sites, can help; but note the page-spread syndrome. Because pictures have to be fitted on a double-page spread or a screen, distances are collapsed and relative sizes lost.

* Simulating, using games. The best of these involve pupils moving as planets and the Moon.