Halley's Comet: 
Stereoscopic Photograph

Stereoscopic astrophotography 

by John Wattie 

Halley, the comet that flipped.

As Halley's comet crossed the southern hemisphere sky in April 1986, it was at its closest to Earth.

Some observers were surprised how small the tail seemed.  Even respected astronomers claimed the tail had "turned off". They forgot that comet tails always point away from the sun.

The Milky Way further confused people's view. The diaphanous tail was visually lost against the similar grey blur of the Milky Way, but clearly visible in 3D photographs, such as this.

The author took a series of pictures most nights as Halley passed by, showing how the comet "flipped over".

Why Halley flipped.

As explained by the author in "The New Zealand Annual" for 1986, Earth moved between the sun and the comet.

•  In early March the long comet tail pointed south.
•  While the comet was at its closest, the tail pointed away from both Sun and Earth. 
• Finally the tail elongated again and pointed north.
• The tail did not really shorten then grow. All that changed was the angle we viewed it from.

This stereoscopic picture of Halley, against the Milky Way of southern Scorpio, shows the tail pointing back from the bright nucleus. The tail is a fan of debris, evaporated from the icy nucleus and blown away from us into space by light pressure from the sun. Here we see the fan end-on.

 X Stereo

U Stereo Big  / Small 

RIGHT

LEFT 

RIGHT

LEFT