Comet gives closer look at 1910 photos

November 2, 1985

Study of old photos will help chart way through the comet’s maelstrom

GOOD OBSERVATIONS, and good records have always proved useful in astrononmy. Over the years it is amazing how often a new theory insight has been helped by examining existing observations.

When a faint Saturn-like ring around the planet Jupiter was discovered by the Voyager spacecraft, everyone was amazed; except for S.K. Vsekhsuyatskij who, two decades before, had published observations of the shadows of the rings cast on the surface of Jupiter. Unfortunately, at the time, this significant discovery went almost unnoticed.

Now the photographs of Comet Halley taken in 1910, the last time the comet was in our skies, are being reworked to find detail that the original observers never dreamed was there. The difference is that the astronomers of 1910 did not have the benefit of computers, so they had no way of seeing all of the information in the pictures they were taking.

Great astronomer

One of the great astronomers of the early part of the century was George Ritchey of Mount Wilson Observatory in California. Among his many achievements, he was responsible for grinding the mirror of the 100-inch telescope — at the time the largest in the world.

It was through this mighty eye that our universe was transformed from a single galaxy, our Milky Way, to a cosmos populated with countless galaxies.

Comet Halley 1910 Ritchey / Larson

Top Photos taken June 2 (left) and June 5, 1910. With computer enhancements below.

Photographs of Comet Halley, taken by George Ritchey in 1910, were the result of the same kind of painstaking labor known to any astronomer today.

A telescope and a camera are technically the same thing. When it is a telescope, an eyepiece is placed at the viewing end, and the astronomer can look at the image created by the telescope.

When it is a camera, a film plate is placed at the locus the telescope. The advantage of film is that it can soak-up light over a long period of time and reveal more than the eye can see. It is the astronomer’s job to make sure that the telescope never wavers from the object during the exposure. An astronomical exposure may take from a few minutes to several hours.

The process of controlling the telescope during photography is called ‘guiding’. This is necessary because the sky is always moving due to the rotation of the earth.

Telescopes have clockwork motor systems to drive the telescope across the sky at the same rate as the stars. Because of the slight magnifications, small adjustments are always required. The astronomer borrows some of the light coming through the telescope for an eyepiece. This eyepiece has a dimly illuminated pair of cross-hairs. The object photographed, or a nearby star is placed in the cross-hairs, and the astronomer keeps it there by speeding up or slowing the telescope

It is a tedious and exact job, and there is no room for error.

Comets are more difficult to photograph than most objects In the sky because they move independently of the stars.

This fall, when Bill Peters was in Arizona researching material for the planetarium show The Comet Adventure, he obtained a remarkable series of photographs from astronomer Stephen M. Larson.

Precisely guided

As part Of their preparation for the new pictures that will be taken of Comet Halley, Larson and his colleagues used 1910 photographs, and a computer to see if they could find new ways to process photographic data. Fortunately, those pictures were taken by George Ritchey. His guiding was so precise that the pictures preserved detail that he never saw.

Look closely at the accompanying pairs of pictures. They are the head, or coma, of Comet Halley as taken by Ritchey on the nights of June 2 and June 5, 1910. The top version are the images as Ritchey saw them, just hazy balls of light. Below each is the computer enhancement. There is much more detail.

In each picture there are a number of wavy streaks. These are stars. During the exposure the telescope was following the comet, which was moving compared to the stars. Each of the little ripples in the star-trails is a correction that Ritchey made at the telescope.

Many more stars

The computer pictures show many more stars. They also have some spurious shadow images of the stars that can sometimes be seen as black lines.

The really interesting features are the jets, and shells of comet material. The picture taken June 2 shows a jet appearing from the bottom of the nucleus, the next day the stream is much longer, and fainter. If the jet is not as violent, it forms a spiral as the comet rotates.

The energy for this material being ejected from the surface of the comet is the heat from the sun. We are seeing the comet-version of a volcano. The gases in the jets are accelerated to speeds of one to two kilometers per second. The sun-warmed surface of a comet must be a dynamic and exciting place.

Both the European Space Agency spacecraft, Giotto, and the Soviet probes, Vega 1 and Vega 2, will fly into the head of the comet, and try to get close to the nucleus. These jets could be fatal to the delicate craft. Larson will be analyzing, and he will recommend the safest route through the danger zone.

In 1985 Robert Ballantyne was director of the Manitoba Planetarium. His weekly column in the Winnipeg Free Press, called Sky Watch, focused on the return of Comet Halley.

© 1985 Robert Ballantyne and The Winnipeg Free Press

Sky Watch - Robert Ballantyne | Winnipeg Free Press


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