2024 events

Sun 31st
16:30-17:00
Starlight Room

Determining the Eccentricity of the Earth's Orbit and the Tilt of the Earth's Axis

Stephen Broderick

St Ursula's College, Toowoomba

After working on Tycho Brahe's Mar's data for several years, Kepler was able to determine that the orbit of Mars was elliptical. Kepler correctly inferred that all planets travel in elliptical orbits. The eccentricity of the Earth's orbit took hundreds of years to be accurately determined. Today it can be calculated by using several images of the Sun from either the internet or by using a DLSR camera with a telescope. Ten weekly images of the Sun can be used to determine the perihelion and aphelion of the Sun, which in turn allows for the eccentricity of the Earth's orbit to be calculated.

A solargraph is made with a pinhole camera and displays the altitude of the Sun throughout the day on photographic paper. Solargraphs made over several days, weeks or a whole year reveal interesting information about the location’s length of daylight hours and maximum altitude of the Sun. From this information, you can accurately determine the tilt of the Earth’s axis and even the latitude of the location. Examples of solargraphs will be presented during the presentation.

Both of these activities have been used as assessment tasks in senior mathematics by the author.

Stephen Broderick has been a teacher of mathematics and science at St Ursula’s College for 38 years and was the mathematics coordinator for 22 years. Stephen is currently a T3 National Instructor with Texas Instruments (Teachers Teaching with Technology) and has presented workshops on STEM. Stephen is passionate about the connections between mathematics and astronomy and hopes to see Halley's comet again.