In 1988 a team at the University of Southern Queensland participated in an international project, that discovered the atmosphere surrounding the planet Pluto. The project was organised by G.L. Blow of Carter Observatory, Wellington, N.Z. A simultaneous observation was made by the Kuiper Airborne Observatory.
On 9 June 1988 a small star passed behind Pluto as seen from Australia and New Zealand, and various observatories in these countries measured the intensity of the starlight as this event (called an occultation) proceeded.
If Pluto had no atmosphere (like the Moon) we would expect the starlight to 'snuff' out suddenly as the star passed instantaneously behind the planet, but if an atmosphere existed, then it should slowly darken the starlight as it passed through an increasing thickness of air.
And that's exactly what happened! Here is the light curve as measured at our Darling Downs observatory (higher is brighter, lower is darker; the intervals between vertical lines each represent ten seconds):
The slope is also obvious in a diagram made by a moving average of every twenty measurements.
