Set your alarm clocks. Early tomorrow morning Australian sky watchers will be treated to two beautiful celestial events that will make getting out of bed before the crack of dawn worthwhile.
Not only is the annual Eta Aquariid meteor shower at its peak, but there’s a beautiful comet in the sky.
The best time to see these two separate, but spectacular, events is probably between 4.30 and 5.00AM. Experts say the meteor shower is best viewed between 2AM and 5AM, but the comet is likely to be most visible for half an hour before 5.
Why the excitement about Comet SWAN
Comet SWAN was discovered in early April by Michael Mattiazzo, an amateur astronomer from Swan Hill in Victoria, while he was sifting through data from NASA’s Solar and Heliospheric Observatory.
“Everyone is getting really excited because this is the biggest comet we’ve had in a long time and its particularly photogenic,” says astrophotographer and astronomer Dylan O’Donnell.
So how bright will it get?
We’re not entirely sure, says Jonti Horner, an astronomer at the University of Southern Queensland.
While the comet may be bright enough to see with your eyes by the time it comes closest to Earth on May 12, at the moment it’s still a bit dim unless you live in a dark sky area.
But even if you can’t see it with your eyes, it’s so big it’s easy to pick up in a camera, says Mr O’Donnell, who has been observing it from his backyard in Byron Bay.
“I haven’t been able to see it with my naked eye, but my camera with its long exposures really reveals the whole thing,” he says.
Here’s what we know about this celestial visitor and how you can catch it.
Where to see it
At the moment Comet SWAN is predicted to reach a brightness of around magnitude 2.5 — that’s around the same as the fourth brightest star in the Southern Cross ƍ (Delta) Crucis over the next week.
But the light is diffuse, so it won’t look that bright — it’ll look like a green fuzzy blob on the eastern horizon with the naked eye.
Although it is getting brighter, it is also getting closer to the horizon each day as it moves towards the Sun, which will make it harder to see in the dawn twilight.
The other factor to take into account is light from the Moon.
Juggling all these factors, the best time to see the comet may be tomorrow morning between 4.30 – 5.00 AM, after the Moon has disappeared.
The Moon will be full on May 7, and will be in the sky all night from then making the comet harder to see in the dawn twilight.
“[The Moon is] going to start to wash out this view we have of the comet so we’re taking every opportunity we can to get in while its darkest,” Mr O’Donnell says.
Tomorrow morning also coincides with the Eta Aquariid meteor shower, in the same area of the sky for extra viewing pleasure.
The comet will disappear below the horizon around May 17 in the Southern Hemisphere.
Where did it come from?
Comets are balls of ice and dust that zoom in from the outer reaches of our solar system.
Some comets such as Halley’s comet, which is responsible for the Eta Aquariids meteor shower, come from an area out beyond Neptune and Pluto known as the Kuiper Belt.
But Comet SWAN is flying in from a zone in the furthest reaches of our solar region known as the Oort Cloud that stretches halfway to the nearest star.
“It’s coming in from 100,000 times further away than the distance between the Earth and the Sun,” explains Professor Horner.
The comet is travelling on a very elongated orbit that is approaching Earth from the south, which is why we get a better view of it as it travels in towards the Sun.
Once it has swung around the Sun on May 27, people in the northern hemisphere will get their best view.
“Comets are usually a bit better on their way out than on their way in,” Professor Horner says.
But the comet will be on the far side of the Sun, and the Northern Hemisphere is heading into mid-summer so the comet will appear in the dusk and will be harder to see.
“If this had come six months later the Northern Hemisphere would have got a spectacular show as it passed.”
“They’ll get a decent show, but we [in the Southern Hemisphere] are getting our best view of it over the next week.”
It is travelling so fast, it is unclear at this stage if it will ever return to our solar system or just shoot through.
And, even if it can be contained by the gravity of our solar system, it won’t be back for hundreds of thousands of years or longer.
What does it look like now?
As comets move closer in towards the Sun they heat up and the solids turn into gas and form a fuzzy halo around the nucleus known as a coma.
“Then the solar wind and solar radiation act on that gas and dust to push it away from the Sun and that’s how you get the tail,” says Professor Horner.
The tail of a comet always points away from the Sun.
“So when the comet is coming in [towards the Sun] the head’s in front and the tail is behind, but when it is going back outwards, the tail’s in front and the head is behind.”
Comets usually have two tails — a gas tail and a dust tail — or they can have multiple tails if the nucleus is spinning.
The gas or ion tail, which appears a blueish-green colour, is created by the effect of ultraviolet radiation stripping away electrons.
Dust tails tend to occur as the comet gets closer to the Sun. They are usually yellowish as they reflect sunlight; and curved as they’re affected by radiation pressure, which is not as strong as the solar wind.
Comet SWAN currently looks like it is more gassy than dusty, says Professor Horner.
“It looks like this comet is actually kicking off a lot of gas,” he says.
“The gas tail has a kink in it because as you go through areas where the solar wind changes direction or is a bit gusty you get kinks and changes in the tail,” he said.
While the tail of Comet SWAN has been largely straight it has started to curve over the past couple of nights, Mr O’Donnell says.
“The last measurement I took showed an 11 degree tail. To give you some perspective that’s about 20 times the size of the full moon so it is huge,” he says.
Why are some comets brighter than others?
The last truly bright comet in the sky was Comet McNaught in 2007, a multi-tailed comet which cut a swathe through the evening twilight and could clearly be seen.
“The hope is that Comet SWAN as it moves closer to the Sun will continue to ablate material and become really, really bright,” Mr O’Donnell says.
Last month, before Comet SWAN suddenly appeared on the scene, astronomers had their hopes pinned on a comet called ATLAS.
This comet was a fragment of the Great Comet of 1844 that rocked up 180 years after the main event, Professor Horner says.
“It was very bright initially because being a chip off the old block it exposed a lot of volatile material from within the comet that hadn’t been previously exposed so it looked like it was much bigger.”
But smaller comets are more fragile than big ones, and it disintegrated as it got closer to the Sun.
Latest reports suggest Comet SWAN is starting to dim, but it is unclear whether it will go the same way as Comet ATLAS.
We don’t know how big Comet SWAN is because it was discovered when it was already blowing gas.
Usually, the bigger the comet the brighter it is, but small comets can also be very bright if they have lots of gas and dust coming off them.
“It’s fair to say it’s not going to be tens of kilometres across because … we probably would have found it earlier a bit further out.”
How to get a good shot of Comet SWAN
- Try to find a dark spot in your backyard away from street or house lights.
- After you’ve given your eyes 5 – 10 minutes to acclimatise to the dark, look directly to the east. “If you just point your camera dead east and take a long exposure you will find that green blob,” Mr O’Donnell says.
- You don’t need any special camera, but DSLRs are preferred.
- You can use any type of lens, but a long or a wide focus lens will give you the best results. “If you are using the longer lens you can get right into that nucleus and see the detail in the tail,” Mr O’Donnell says. But if you want to capture the whole tail then a wide-angle lens is better.
- Use as high an ISO as possible, but if you use too high an ISO the image will be grainy. “I use 3200 for this comet,” Mr O’Donnell says.
- The aperture should be as wide open as possible – the lower the number the better
- Shutter speed will depend upon your lens. “If you are shooting wide then you can do 30 second exposures, but if you’re using a long lens and you’re zooming in I wouldn’t go more than 8 – 10 seconds.
- Do a few test exposures first to see if you are capturing all of the comet. “If you centre the comet in the middle you might find that you’re chopping off the tail at the edge of the frame.”