Visual Comet Hunting by Martin McKenna


Visual comet hunting is the systematic search for undiscovered comets by the visual amateur observer using the naked eye, binoculars or telescope. It is a way of exploring the entire sky on a one to one basis, where the searcher checks each moving field of view (FOV) of his or her instrument in the hope of discovering that faint misty patch of light of an unknown comet first beginning to shine. Comet hunting is a discipline, a way of observing like no other as the sky is in charge of what you might find during a session compared to the conventional method of observing. This is what makes it an exciting past time. It will teach you the sky in a way you will never forget. During the search you will be in for at least several treats….

  1. You will be reacquainted with many of the Messier objects on a regular basis.
  2. You will find more objects from the NGC catalogue than you ever thought your telescope could detect.
  3. You will see countless telescopic satellites passing through the FOV, sometimes even 3 in the same field.
  4. You will be treated to the sudden appearance of telescopic meteors which often do not coincide with the major meteor showers.
  5. You will be astounded by the amazing telescopic fields within the milky way that will astound every time you see sweep these areas.
  6. You may even be lucky enough to sweep up a known comet which will give you an unforgettable thrill and prove to yourself that your technique is good.
  7. You could sweep up a known comet which has gone into an unexpected outburst in magnitude that had been previously faint which is important and needs to be reported promptly!



Although any kind of telescope can be used for comet hunting I would heartily recommend an instrument of a short focal length (or short focal ratio). These telescopes will give you a much larger field of view for a given eyepiece hence increasing the contrast between nebulous objects and the sky background. They will also decrease the time spent searching as you are seeing more sky in one field. Alta – azimuth mounts are more favourable as they let you scan the sky more comfortably and around the pole where equatorial mounts tend to block. Reflectors are the favoured choice of many comet hunters as they provide very contrasty fields. The Small to moderate aperture reflectors tend to be more successful at bagging the bright twilight comets and the larger light buckets have a tendency to find the fainter comets located further from the sun. I would suggest using at least a 6-inch reflector with a FOV of at least ¾ of a degree although 1 degree or more would be desirable. I use an 8-inch F/6.3 SCT and a 16-inch F/4.5 reflector for my own sweeps. However more important than anything else is the dedication of its user. A scope sitting in a room gathering dust is not going to find any comets!


Since comets brighten as they near the sun the best place to find a bright newcomer is in the region of sky within the suns vicinity. The region of sky within 90 degrees elongation of the sun is the visual hunting ground and is known as the ‘comet haystack region’. Searching beyond this zone is undesirable as comets located further from the sun tend to be very faint and are unlikely to be picked up by the visual sweeper. Also this is the territory of the professional surveys like LINEAR, NEAT, LONEOS, SPACEWATCH, CSS etc. To avoid these prolific NEO surveys concentrate your search to within 90° solar elongation, below the pole and near the horizon, if your location lets you hunt below -30° in declination then you will have an increased chance of success.

Searching the twilight regions as the sky darkens with the naked eye or binoculars can be rewarding as you may pick out a bright comet that was hidden in the solar glare. A telescopic search can begin when the sky is still bright beginning with those twilight areas that are about to drop below the horizon, as long as you can see stars to mag 4.0 with the naked eye. Then as the sky darkens you can work your way into the higher sky regions and into less fertile hunting grounds. I recommend 2 hours of sweeping in the evening sky and 1 to 2 hours again in the morning sky before dawn. The eastern sky before dawn should be your main area of interest. Statistically 4 times as many comets are found in the morning sky compared to the corresponding dusk regions. Also keep in mind that fewer observers are active at these times especially during the week when many find it very difficult to rise from a snug bed on a freezing cold winters morning so by regular sweeping of this region you will be at an increased advantage though many find it difficult due to there daily routines and work load. If you really want to find a new comet then search the morning sky as much if not more than the evening sector.


You should search for comets only under a dark sky. This means becoming familiar with the moons cycle and phases. If the moon is bright and in the sky then the chances of making a discovery become so small that your observing time is better spent in doing other things. Finding the moon rise/set times can be obtained from a variety of websites or desktop software like Starry Night Pro. In the evening sky the best time to stalk comets is when the moon is just after full and disappearing from view for a short time before it rises again. This time takes place when the moon is around 2 days after full and so the sky is thrust into darkness for an hour or so. With each night in turn the waning moon will be rising later and later leaving a longer dark window for searching. This is a very important and competitive time. A bright new comet could have appeared in the sky and has been hidden from view by lunar glare but as the sky is suddenly plunged into darkness the comet is sitting there waiting to be found by anyone looking so it needs to be swept!

The next prime search time is just before new moon in the morning sky when the waning crescent moon is not bright enough to interfere with dark sky work. This is the prime area for reasons I have previously mentioned.


Searching can be done in a horizontal or vertical manner depending on the individuals taste and setup. I use a horizontal sweep with the 8° because it is easier and more comfortable to use however I use the vertical pattern with the 16-inch as the telescope moves more easily in altitude and its less stressful on my back. Research completed by the Japanese has shown that the human eye is better at finding faint objects with the vertical motion.

I typically search a block of sky 30° in height and 20° or more in length and spend between 1 and 3 seconds on each field depending on my mood, sky conditions or moon phase. I spend much longer in areas of the sky with many galaxies like Virgo, Coma Berenices, Leo, Draco, Ursa Major and Canes Venatici. Spend long enough on each field to scan it for suspects but not too long because the Earths rotation and the skies apparent motion will create gaps in your search. It’s also a good policy to over lap fields and repeat your search regions throughout the monthly dark period. Some comets maybe too faint for even professional scopes but can suddenly flare up in brightness as they approach the sun, repeating your search will increase your chances of bagging one of these ‘outburst’ comets!


Sooner or later you will come across a fuzzy object in your moving FOV that will get your heart rate pumping out of the blue, could that be a comet? Probably not but it will be a comet suspect until you can identify its true nature. These fuzzy deep sky objects are hidden all over the sky waiting to catch inexperienced observers, and most of your time and for many years you will be stopped by these objects. When I first started I sketched the object in the eyepiece and its location in the sky then checked it according to a good star atlas. Then I recorded the sketch and visual description in my log book. Eventually when you spend years doing this you begin to learn the whole sky of by heart and don’t really need to refer to an atlas anymore…only for objects you are unsure about.

In addition to a good 8X50 finder you should also consider one of the popular 1x type finders currently in the market like a Telrad, Rigel quickfinder etc. These devices project a red dot or bulls eye onto the naked eye view of the sky and once aligned with the OTA will tell you instantly where your scope is pointing so you can tell where you are searching and the location of any suspects you find. When I find a suspect I just have a quick look at that lovely red bulls eye projected onto the night sky and can tell immediately by its appearance and location if I have seen it before and thus saving lots of time with identification. I use the sky atlas 2000 field addition which serves me well. It contains all the suspects that an 8” scope would find under a dark sky. Other sky atlases like Uanometria go even deeper and desk top software like starry night or the internet can be invaluable. But if in doubt….watch the suspect, if it doesn’t move within 24hrs then its not comet as all comets do show motion eventually. It really helps if you become a deep sky observer.
Observe all of the different type of DSOs there are and get familiar with them so you can identify them on sight. As a general rule galaxies have sharp boundaries and are symmetrical, globular clusters are mottled with bright cores while the light of a comet is very soft often difficult to tell where the comet ends and the sky begins. On the whole it is recommended that you do not begin a serious comet search until you have located and described as many of the Messier objects as you can. In addition to becoming ‘a fuzzy’ observer you also need to become a comet observer. Observe all the comets that come within range of your telescope as watching them from night to night and locating them in various weather/sky conditions builds the discipline that is needed for a proper comet search. This time and effort is well spent as it will teach you the subtle difference between comets and deep sky objects. But what if it does not appear in any atlas?…………then what?


If you search long enough eventually you will find something that is not in a star atlas. Several years ago while sweeping the eastern sky before dawn through Triangulum I found a fuzzy object very close to M33 which did not turn up in my star atlas. I got very excited. I checked a book by Stephen James O’ Meara called ‘The Messier Objects’ and I found out what it was…..a bright HII region within the outer spiral arms of that galaxy. It was a good job I did some further checking!

But what happens if you find an object and you are convinced it is a comet?? First of all make a sketch of the object in relation to nearby field stars in the eyepiece at low and high magnification. Make another series of sketches showing its location through the finder and/or Telrad. Then watch for motion…..sometimes comet motion can be detected within 15mins but if the suspect has shown no motion by then…….wait longer. All comets show motion eventually so you should wait to confirm motion even if that means you must wait another night. David Levy waited 3 nights before confirming a comet find before he reported it. Its good policy indeed, be patient and don’t report it anyway just so you can be first to get credit for it as it could very well end up embarrassing you. There is one observer who reported the Andromeda galaxy as a comet….imagine the aftermath! A comet can show motion quickly if it is close to the earth or sun or its motion maybe detected easily if its location is close to a field star. Very slow motion is an indication that the comet is far away or if its in the east that it is heading towards the Earth. If you do detect motion and can confirm using the internet that it is not a known comet then you need to obtain the following information…..

  1. The date and time in UT
  2. Comets magnitude
  3. The coma diameter
  4. The comas D.C value
  5. A physical description in words including the length and P.A of any tail.
  6. The comets RA and DEC (2000) and its direction of motion + rate of speed or simply 2 positions separated by time.
  7. Name and Address of the observer
  8. Sent your discovery report to the CBAT via email then send a second for back up.
  9. Make sure you know it’s a real unknown comet before reporting. Daniel Green from the CBAT as said that 90% of the reports he receives from unknown observers turn out to be false.


Hunting for comets is part sport and part science. I personally believe that it can be taken up in a serious way by the type of person who is very passionate about the night sky. It’s a passion for me and it requires a lot of dedication, commitment, patience and it helps to have an addictive personality as well. It gives you a reason to observe on a regular basis (not that you should need one) however you do have to be prepared for knockbacks as it is the worse feeling in the world when a comet is discovered that you missed, being able to take these blows is very important.

You need to be a very motivated individual and be prepared to sacrifice many other things to get the proper sky coverage that is required during each monthly dark period but it is a great journey with the possibility of finding the holy grail of astronomy on any night. But it takes patience, you have to be in for the long run if you want to have a chance of discovery. There is an interesting statistic that says you must search for an average of 400 hours for a 1st find and 200 hours for each find after that. I don’t think that number applies anymore because of the treat of the surveys. I would realistically place it at well over 1000 hours however do not be discouraged.

Mark Whitaker aged 14 began comet hunting as a summer project with his 4-inch reflector, and on his second night he discovered a new comet! George Alcock found 2 within 5 days, one of which was found using binoculars from inside his upstairs window in his pyjamas! I have heard of another observer who found 2 on the same night within 50mins of each other. On the other end of the scale David Levy bagged his first after 917 hours of searching and Don Machholz found his first after 1700 hours and found his second after another 1700 hours!!! – WOW this is what I like about comets and the search for comets, they are unpredictable objects that can appear at any time from anywhere in the sky and I firmly believe that a relative new comer to the field still has a chance of discovering a comet.

Until the surveys can scan ALL of the sky tight around the sun, then there will still be more amateur finds to come in the future. So, if anyone has been thinking about it then do it because now is the time…I have been comet hunting for over 750 hours and I don’t intend to stop! Good luck, stay vigilant and happy hunting!!!

Martin McKenna