Explanation of Comet Synopses

There are often several comets detectable in even a small telescope on any given night.  The trick is know which ones are likely to be visible to you.  Comet magnitudes alone are a very poor indicator of visibility and the magnitudes from most astronomy software are unreliable.  Comets also vary greatly in size;  you may need to use your widest field eyepiece for one comet or much more magnification for another.  It is hard to reliably spot a comet if you don't know which to use.  For these reasons many fledgling comet chasers give up after not being able to find anything but the brightest comets in their telescopes.  The purpose of the comet synopses is to fill this information void.  

Minimum Telescope Aperture

Perhaps the most useful information provided is the minimum aperture required to observe the comet from a dark site.  This is computed by a sophisticated algorithm that employs recent magnitude and diameter observations.  The telescopes indicated are the minimum aperture required for a relatively experienced observer to spot the comet without difficulty from a fairly dark site (Bortle 3). The minimum aperture required is broken down into the following categories: naked eye, 7x50 binoculars, small scopes (4 inches or smaller), various intermediate apertures, and very large scopes (20-inch or larger).  Note that a highly experienced observer observing from a very dark site will likely be able to detect the comet in a smaller telescope. 

General Visibility by Latitude

To determine the general visibility of a comet, first find the latitude closest to your location in the leftmost column.  Use 40N for the U.S., southern Europe, China and Japan.  Use 55N for Great Britain, northern Europe and Russia.  Use Equator for equatorial regions.  Use 30S for Australia, South Africa and southern South America.  Visibilities and times indicated will be approximate for latitudes that differ significantly from the above.

The visibility of the comet is listed for certain dates throughout the month in the row to the right of your latitude.  "Not Visible" indicates that the comet cannot be observed on that date because it never rises far enough above the horizon in  enough darkness to spot it. 

The Nights Visible column lists for each latitude the nights during the current month that the comet will be visible.  Don't forget that if the comet is indicated as visible in the morning of the night of 3rd, this is technically the morning of the 4th!

All times listed in the synopses are local standard time.  If daylight savings time is in effect at your location add one hour.

All dates listed in the synopses are for the night, which is defined as the date of local evening.  All times before local noon refer to the date of the previous evening.  For example, if the night of the 3rd is indicated this corresponds to the evening of the 3rd and the morning of the 4th.


The following symbols are used: o = degrees, ' = arc-minutes, " = arc-seconds, ~ means approximately, ? means questionable, usually because there are no recent observations.  E.g. a coma of ~4' means that the coma of the comet is approximately 4 arc-minutes in diameter.  

The tilde symbol "~" means "approximately." E.g. ~5th magnitude, means "apprximately 5th magnitude."

Finder Charts

The charts provided always have north up and east to the left like an atlas unless otherwise indicated.  The times and dates indicated are UT.  In some cases you may need to locate  the field on your atlas in order to determine where in the sky the object lies.  Several stars are labeled on each chart to help find the proper location.  These charts are created using our SkyTools observing software.  

Do the charts look poor or grainy?  If so, this is likely because your browser is shrinking the chart to fit the window.  In Windows Explorer an icon will appear with arrows on it when you pass the cursor over the chart.  Click this icon to zoom to full resolution.  

An important note about the comet charts: these charts are provided primarily because people have asked for them and in the hope that they will encourage beginners to go out and have a try at a telescopic comet or two.  But in practice the best charts are those you make yourself using your software of choice.  The advantage of using software is that it can be set for your specific location and for a specific date/time.  Most astronomy programs plot the positions of comets (even those that are free), and most do so accurately as long as you download the latest orbital elements.  Although the magnitudes computed by most software products cannot be relied upon, and few plot an accurate diameter, they do plot accurate positions.  We recommend that you use the Comet Chasing page  to discover which comets are going to be visible in your scope and how large they will appear.  Then use software finder charts that plot the position.  In this way you should be able to happily observe several comets on any given dark night.

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Information regarding our SkyTools software, which has many unique comet observing features, can be found here.