Astronomers can’t guarantee quality of celestial show

October 19, 1985

THE QUESTION THAT EVERYONE at the Manitoba Planetarium must answer several times every day is, “will I be able to see Halley’s Comet from Canada?”

THE COMET'S COURSE - image from Winnipeg Free Press 1985 Oct 19

THE COMET'S COURSE - image from Winnipeg Free Press 1985 Oct 19, click for full image

The best that we can promise is probably. Since we do not know exactly what is going to happen in the next few months let me share with you some of the drama that we are experiencing with the comet.

“Is it going to be another Kohoutek?” I am asked accusingly. Do you remember Kohoutek? In 1973 the media got hold of the idea that it could be the great comet of the century, but it didn’t turn out that way.

When scientists attempt to predict the performance of something like a comet, they will also express their margin of error. They did that with Comet Kohoutek. And the comet always remained within that margin.

Unfortunately, everyone was interested only in its potential to be spectacular. Actually it was a fine comet, easy for an amateur astronomer to observe, and well studied, even from Skylab. From the public’s point of view, it was almost impossible to find in the sky, and was therefore a fizzle.

So, now what about Halley? Here Is my prediction. From Manitoba, Comet Halley should be fairly easy to see In the western sky, at the end of evening twilight, in January. To be fair, it may be visible only with telescopes and binoculars. However, with three months to go, I am optimistic that you will be able to view it easily just by going outside and looking in the right direction.

This is what is happening. Since 1948, comet Halley has been falling towards the sun. From the outer part of the solar system, the Earth and sun seem very close together. In effect, the comet has been falling almost directly towards us.

That means that, from our point of view, the position of the comet has been almost stationary in the sky.

Knew location

Although we could not observe It — it was too far away, and too tiny — we knew that it was up there more or less between the constellations of Orion and Gemini. Each year, as we go around the sun, the comet seems to make a small loop in the sky. This little circle is due to our own movement. Each year the comet has come a little closer, and each loop is a little bigger.

Last August, as the Earth swung out from behind the sun, we headed toward the incoming comet for the first time. The earth circles the sun counter-clockwise, the comet goes clockwise. We pass Comet Halley on Nov. 27. Although this is one of our two close approaches to the comet, it is still small and quite far from us — more than half the distance to the sun.

Early this month the lazy loops of Halley’s path in the sky ended abruptly; the comet has begun a dash that will take it from the eastern sky, at dawn, to the western sky at twilight.

Now it is high in the sky, and well placed to observe. It is also so faint that you need a telescope of at least eight inches aperture (diameter of the main lens) just to glimpse it.

Here is the drama. It will continue to become brighter as it slides closer and closer to the sun. About Jan. 20 it will be so close to the sun that it merges with the evening twilight, and vanishes until it has gone around the sun. When it re-emerges, it will be too low in the sky to be seen from Canada.

The question is: will it be bright enough before that to be seen by naked eye?

Astronomers use a quaint method of measuring the brightness of an object with a system that has changed little since the days of ancient Greece. The brightest stars are called first magnitude, and the faintest that can be seen by the human eye are sixth magnitude.

The only real improvement is the agreement on the mathematical relationship between magnitudes. Each Increase in magnitude means the object is 2.512 times fainter. You might be interested to know that, although no one really likes the system, there is no discussion about making this awkward system metric.

When the Planetarium staff first observed the comet in August it was around 14th magnitude, and seemed a little dim compared to predictions.

This is when we decided that it was prudent to make no extravagant promises about the performance of Comet Halley. Recent observations have made us more optimistic.

Getting brighter

Right now, the comet Is still around 10th to 11th magnitude. It is still too early to judge when it will reach fifth magnitude, the point when we can all see it without binoculars.

Our best guess is that that should occur about Jan. 10. Therefore, we have a 10-day window, Jan. 10 to Jan. 20, to observe the comet without telescopes.

To complicate matters, there will be a waxing moon in the sky after Jan. 13. Its light will make it harder to see the comet.

So, this is our early prediction. We will revise it in about one month’s time. We are looking forward to observations in mid-November, when the comet is around ninth magnitude. At that time we should be able to have a much more accurate estimate.

We may be lucky. In January, we may be able to go outside see Comet Halley as a little wisp of light in the evening twilight. If not, and you still want to be sure to see the comet, you will have to learn how to use a pair of binoculars, or a telescope, and how to find faint things in the sky.

To develop those skills the Planetarium is running a lecture series called Comet Halley and the Universe. On Oct. 29 I will present the session on observing the comet. For details please contact the planetarium office.

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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