How to see Comet Johnson in the spring night sky

Here’s how to see Comet Johnson, which is on view in the night sky and easy to find with binoculars, providing you have clear, dark conditions. Its full name is Comet C/2015 V2 Johnson. It is currently brightening as it crosses the northern constellation of Bootes, the herdsman.

Comet Johnson C.2015 V2
The track of Comet Johnson (C/2015 V2) across the sky during May and June 2017. Positions are shown for 22h UT, with the dates in the format month-day (e.g. 06-02 for June 2nd). You will need binoculars to spot it. Chart by Skymania using Cartes du Ciel.

It is possible that Comet Johnson will just become visible with the unaided eye in June if it reaches 6th magnitude. However, comets are usually fuzzy objects, so a blur at this brightness will be less easy to make out than a star.

If you have binoculars, the comet will actually be easier to spot against the starry background because its fuzzy appearance will help you immediately to distinguish it from a star. Our chart on this page will help you see Comet Johnson for yourself. (You can locate the constellations using our all-sky map for the month.)

Throughout May, Comet Johnson will move southwards through Bootes and towards the constellation of Virgo. It is travelling through an area of sky that is well away from the Sun, so you will be able to see it against a dark sky if the weather is kind.

The Moon, whose glare can be bright enough to drown out fuzzy comets when it is near Full phase, is waning in the morning sky during the second week of May. This makes conditions favourable for comet-spotters over the next week or two. We mentioned Comet Johnson in our earlier article on comets to see this spring.

Observers who have recently observed Comet Johnson report it as showing two tails, more or less at right angles to each other. These are the classic twin tails of a comet – an ion (or gas) tail, and a dust tail.

Comet Johnson
Comet C/2015 V2 Johnson, photographed remotely on May 16th, using a 150 mm refractor in New Mexico, 300 second exposure. Image credit Robin Scagell/Galaxy

Comet Johnson’s dust tail is the more pronounced at present, appearing as a short stubby extension, while the ion tail is much more delicate and reveals itself in photographic exposures lasting a few minutes.

The strange geometrical arrangement of the two tails is due to the particular orientation of Comet Johnson as it passes us on the opposite side of the sky to the Sun.

Remember that comets are notoriously unpredictable. They are often compared to cats because both have cats and both do what they want to do. There is always the chance that the comet will become brighter than expected, but it could also fizzle out.

The good news is that Comet Johnson’s head,or coma, seems to be well condensed (less fuzzy) judging by the photos,so it should not be difficult to see. In photos, the coma appears green but do not expect to see any colour with just your eyes.

Comet Johnson will be less easy, though not impossible, to see from southern hemisphere locations such as Australia, New Zealand, South Africa and South America, during May, due to its high northern declination. Of course, there it will be autumn, or fall.

This will be humans’ first and only opportunity to spot this comet, which was formed in the icy zone of objects far beyond Pluto. That is because it is now on a hyperbolic orbit around the Sun which means it will escape the Solar System altogether. So don’t you miss the chance to spot Comet Johnson!

See what else is in the night sky for northern and southern observers.

How to photograph Comet Johnson

You can photograph Comet Johnson for yourself if you have a camera that is capable of taking manual exposures lasting more than a few seconds. You will need to keep the camera steady, preferably by mounting it on a tripod, and pointed towards the stars of Bootes.

Open the camera lens to its widest aperture if you can and set the camera’s “film speed” (or ISO rating) to a high number of 400 or above so that it is more sensitive to faint light. If you have no light pollution, and the Moon is out of the sky, you might be able to go up to 1600 or even 3200.

The camera will need to be set to manual focus rather than autofocus as starlight is generally too dim for most cameras to be able to lock onto it. Turn the lens to infinity (the little squiggle resembling a figure 8 lying on its side). You can achieve even sharper focus if your camera has “live view” and you can see a bright star on your screen while you are focusing.

Use a cable release, if you have one, to avoid shaking the camera. An alternative would be to set the camera’s shutter-delay feature (usually between 2 and 10 seconds) between pushing the button and the photo being taken. Usually this facility is used to allow you to get into your own photo, but it works equally well in allowing the camera to settle down once you’ve fired the shutter!

Using a standard lens, you should be able to open the shutter for 15 seconds or so before the motion of the stars across the sky becomes apparent. This is due to the rotation of the Earth. Longer exposures will record the stars as trails rather than points of light, which is still a pleasing effect if that is what you want! With a telephoto lens, the effect is more noticeable, and your exposures will need to be shorter than 15 seconds.

Take a range of shots, using different exposure times and ISO ratings, and see which gives you the best results. Nowadays, in this digital age, you can find out almost immediately by checking your camera’s screen. Later you can use Photoshop or an alternative piece of software on your computer to adjust brightness and contrast to enhance your photo if you need to.

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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