Where: above the northern horizon
When: during hours of darkness throughout May 2013.
What: a comet - dust, rock & frozen volatile gases held together by ice, which is released to form a tail as the sun heats it up
How: no longer naked eye visible but ideal for telescopes and astrophotography from May onwards, when it will be visible in darker skies
Name: C/2011 L4 (PANSTARRS) or Comet Pan-STARRS
The chart below shows the progress of the comet at midnight each night during June 2013:
Comet Pan-STARRS continues to be visible through medium and large scopes and I'd recommend using at least a 4" scope to spot this wander as it continues its exit from the inner solar system.
Having put on a nice display since March, the comet is now more than twice as far away from the sun as the Earth. But a camera attached to a scope will show the tail continues to streak across the sky as it heads for the orbital distance of Mars.
Pan-STARRS is making its way through Ursa Minor this month so, while quite dim at around magnitude +11 all month, it will be high in the sky and observable whenever it's dark.
The 19th June is a very good night to observe or image the comet as it will be just half a degree away from magnitude +2 star Kochab in Ursa Major. This will make it much easier to locate or provide an interesting contrast on photographic images.
What have I missed?
Observers in both hemispheres have already been treated to a view of this comet with the naked eye as it made its closest approach to the sun (known as perihelion) on 10th March.
As it got closer to the sun, the outer ice and gases began to warm up and turn from a solid into a gas to produce an ionised gas tail which shoots directly away from the sun, and a dust tail which curved gently. Most comets have a tail of some sort and the differing composition makes each comet's tail different from the last.
We can't predict with any accuracy how bright or long a comet's tail will each night as it moves away from the sun (especially a distant traveller like C/2011 L4, which has journeyed 5 trillion miles to make its first ever dive into the inner solar system from the Oort Cloud), but the images taken so far have shown us that Comet Pan-STARRS was a stunning sight with binoculars and through a camera lens throughout March & April.
I estimated its brightness as mag 1 on 13th March and mag 8 on 5th May, but by the end of June it was getting really dim and only visible with a 4" telescope or larger. It has, however, kept its nebulous coma and tail which will help you distinguish it from field stars. This tails has now smeared out into a huge streak that covers many degrees of arc in the sky.
Here's a guide to observing and photographing C/2011 L4 (Pan-STARRS):
So where and when should I look?
Although no longer applicable to Pan-STARRS, please be careful not to point a telescope or binoculars on the sun (even at sunset) as you can cause permanent eye damage and even blindness. You're unlikely to see the vast majority of comets while the sun is visible so, to be safe, only use a scope once the sun has fully set.
11th-12th March 2013
Even with clear skies, observing the comet on these nights was tricky. The comet was at its brightest during these evenings but it was still close to the sun and proved difficult to discern so low on the western horizon in the glow of dusk. But looking west immediately after sunset, and above the point in the sky where the sun was, did allow some photographers to take some lovely images.
On the 12th, the comet made a beautiful companion to the left of a very slender crescent moon. This provided a handy aid to pinpointing the comet as the skies weren't dark enough to see it clearly enough without the moon for reference.
13th-16th March 2013
I recommended this period as possibly being the most favourable for taking a good look on the western horizon for an hour or so after sunset with binoculars.
A pair of binoculars or a telescope allowed us to see more of the coma (the fuzzy 'atmosphere' of the comet itself) and the tail. This was also be a great time to photograph the comet (for advice on imaging Pan-STARRS, see further below).
During this period the comet provided more beautiful images as it moved away from the sun that brought it to life. It matched the predictions that suggested it would be visible to the naked eye for that part of March, dimming from magnitude +2 to magnitude +4 and as the comet progressed upward in the sky, and it began to stand out against darker skies around 7-7:30pm. The darker the skies you observe from, the longer you'll be able to enjoy this spectacle. Of course, a pair of binos or a scope will also let you observe the comet beyond its naked eye visibility.
We expecting this comet to be a stunning sight throughout April despite moving out of naked eye visibility and it didn't disappoint.
As the comet hung in the sky later in the evenings it provided more hours of darkness to observe the comet - the contrast counteracting the dimming object. Using binoculars or a telescope, you were in for a real treat all month.
We caught the magnitude +5 comet rounding the Andromeda galaxy in the period from 3rd-5th April and some of the images of this on Flickr were quite breathtaking. In binoculars, we saw the comet and the galaxy in the same field of view, and a very small refractor (70mm or smaller aperture) allowed us to image these two diffuse objects together.
But... under very dark skies we stood a good chance of seeing them together as two faint smudges with the naked eye - looking for a nearby companion to the already familiar smudge of the Andromeda Galaxy, we were disappointed to find Pan-STARRS had dimmed a little too much to make this possible where we tried.
We thought C/2011 L4 would remain visible through binoculars throughout April and through a scope until late May - perfect for viewing at AstroCamp. Luckily it did and we were indeed able to view this distant wanderer. During this time the comet climbed higher in the sky and, therefore, allowed us to see it against the blackness of the night sky later in the evening.
May, however, will be the astrophotographer's ideal time to image the comet with a telescope and long camera exposures. We saw with a small scope at magnitude 8 on 5th May and others saw it on 10th May with large binoculars, so it's still well worth hunting down.
How can I photograph C/2011 L4?
You'll need a camera with manual exposure, ISO & aperture settings, such as a DSLR but you might want to have a go with a fully automatic camera too if the comet is particularly bright or your camera has long exposure settings.
You'll also need a tripod or a means of keeping your camera perfectly steady for exposures of up to 10 seconds - even the slightest vibration in your shots will cause blurring.
You'll want to set your camera up to face the western horizon with either a standard or a zoom lens and focus it on the comet if your camera allows (or a very distant object if not). You can do this manually or with the automatic setting, but turn the automatic focus off once you've got the focus right.
If your lens has an infinity focus setting, take a test shot to be certain.
If you're using a DSLR, use the manual (or 'M') setting and:
- Set the ISO to 400
- Set the aperture to the lowest f number possible
- Set the exposure length to the highest you can without overexposing the image and inducing blurring.
Take a 5 second exposure and lower the ISO if the image is overexposed. Raise the ISO if it's too dark.
As the sky darkens, try increasing the exposure length to 10 seconds and adjust the aperture and ISO to get the light/dark balance right.