The Coming of the Comet

Comets are not unusual in our solar system, but readily visible ones are. Dozens of comets are discovered every year, and a handful, most famously Halley’s Comet, are well-known repeat visitors to our skies. But to be visible and genuinely bright, comets must tread a celestial path that takes them close to both the Sun and the Earth, so they are simultaneously well-lit and easily seen by humans.

These are special events, and our current visitor, Comet Tsuchinshan-ATLAS is the brightest we have seen in a decade.

A few weeks ago, this comet was a naked-eye object in the morning sky, rising an hour or two before dawn. Now, after making a hairpin turn round the Sun, it is visible in the evening sky.

This weekend will be your best and possibly last chance to see it before it heads on out. Because the comet is now moving away from the Sun, it is higher in the sky with each passing night – but this also means it will become steadily fainter as it makes its million-year trek back into the outer reaches of the solar system.*

Luckily, while the Moon is close to full (and has been looking spectacular in the last few days), it is now rising an hour or so after sunset so the comet need not compete with its glow.

So here is how to see the comet before it leaves town. Firstly, time it right: at typical latitudes for the upper end of the North Island, sunset is around 7.40pm and the sky takes a further 30 minutes to get properly dark. So you’ll want to be at your comet-watching spot by around 8pm.

Secondly, find a good spot. The further away from bright city lights, the better the odds of seeing the comet. So get out of town, and head for a hill or a beach – somewhere with a clear view to the west, i.e. in the direction of the setting Sun.

If the weather cooperates and the clouds stay away, you will notice a spectacularly bright white “star” in front of you – this is the planet Venus.

The chart above looks due west and covers 1/4 of the horizon, as seen from Auckland at 8.30pm on the night of Saturday 19 October, 2024. The comet’s location is marked by the red dot, off to the right and just over halfway between Venus and the horizon. You are hoping to see its long thin tail, which will point upwards and away from the horizon.

The comet may already be challenging to find with the naked eye, but binoculars will help if you have them. And, while we are regularly exhorted to turn away from our screens to better enjoy an unfiltered connection with nature, modern phones can take seconds-long exposures of the night sky, which can reveal far more detail in the sky than our unaided eyes. (As I discovered for myself while aurora-watching earlier in the year.)

The further south you are, the more it will be a little more challenging to detect the comet, as the sun sets later and any comet is tough to spot in the twilight sky. Conversely, for Northern Hemisphere viewers, a quirk of planetary geometry puts the comet higher in the sky so it will be a little easier to see and perhaps for longer into the evening; Sky and Telescope (a venerable astronomy publication) provides a guide for northern observers.

In any case, it’s a good opportunity to get out and take the night air – plan your route, pack a picnic and a blanket, and check the weather before you go. There is never a bad time to look up at the stars.

Photograph of the comet in twilight
The comet in the morning sky, as seen from Murrays Bay, Auckland, New Zealand on September 28. By Alex Liang. [Wikimedia]

* There is actually a chance that after being jostled by the planets on its trip through the solar system the comet will have picked up enough speed to send it into interstellar space, i.e. beyond the solar system, never to return. Exciting, for the comet.

The header image is an early illustration of a comet from the Ausberg Book of Miracles.

I made the finder chart using Wolfram Mathematica.