a comet visually is more difficult than the pretty pictures make
it appear. Standing next to the photographer, few people would
have noticed the comet above, and binoculars were required for most to
see it at all. This image of comet PANSTARRS was captured by SkyTools user Ernie
Parker on March 14, 2013 at StargateCOlorado Observatory in
You Need is a Small Telescope or Binoculars
45P from the northern hemisphere through January 5th will be
relatively easy. This comet will not be visible to the naked eye,
but if you know where to look, it will be fairly easy to spot in a
small telescope or binoculars.
is visible right after sunset, low in the southwestern sky, so a
location with a relatively clear western horizon is required. The
less light pollution the better. The tricky part is the timing.
The comet is following the setting sun, so it will be highest in
the sky as twilight begins, but very difficult to see because of
the bright sky. As the minutes pass the sky will become darker,
but the comet will move closer to the horizon, making it harder to
see. There are few magic minutes in between when the comet will
be most easily seen.
the exact time depends on your latitude and how bright your sky
is. If I knew exactly where you would be observing from I could
tell you exactly when and where to look. But we can get pretty
close. The chart below shows the position of the comet on the evening
of January 2. Note the position of Venus and Mars and how they
point out where the star Theta Cap is. The comet will be near this
star, so finding this star will be most of the battle.
on the evening of January 2, as seen for New Mexico
chart below shows the approximate position of the comet each night
until the moon begins to interfere too much. It shows the field of
view and stars that you would see from a dark location in typical
7x50 binoculars. The date and best time to view is marked for each
night. The times depend on your latitude. If you are in the south,
say at 24N in Florida, it may be as late as 7PM before you get the
best view. Farther north, at say 50N, the best view may be as
early as 5:50 PM.
than go by the time, It is best to go out as the sun is setting
and start looking for Venus and Mars. As the sky darkens, more
stars will appear. Looking at the naked-eye chart above, try
looking where you think the star Theta Cap is. This is the brighter
star that 45P is moving toward as each night passes. It will pass
close to this star on the nights of the 4th and 5th. Holding your
gaze steady, bring the binoculars up to your eyes. The brightest
star you see will likely be Theta Cap. Use the binocular finder
chart provided below to spot the comet relative to this star on
the night you are looking.
New Year's Eve the moon will be to the right of the comet, which
may help in spotting it. But the moon will be a very thin crescent
and difficult to spot itself. It will also be outside of the comet
field of view in typical binoculars.
comet will appear as a faint round smudge of light. In very dark
skies, or in a small telescope, a faint tail may be apparent,
pointing up and to the left, away from the sun.
the Scenes -- How I Made the Calculations
may notice that the predictions of other web sites and various
software are different from those presented here. Others have
focused on the close pass to the earth in February, but I think
this is a mistake. Unless it brightens dramatically, the best
opportunity to see this comet is in early January.
follow the observations that are reported by observers around the
world. Based on these observations I compute magnitude, coma
diameter, and "degree of concentration" parameters.
These parameters are made available to SkyTools users when they
update their Current Comets observing list, which is always
kept up to date with the latest bright comets. Using these
parameters, SkyTools can accurately predict the magnitude and size
of the comet for a month or two in advance, presuming that the
comet doesn't suddenly change. If the comet does change suddenly,
the parameters are quickly updated.
there is more to being able to detect a comet than its magnitude
alone. In fact, the magnitude of a comet is a poor predictor of
visibility in the eyepiece. This is because comets vary greatly in
size and how concentrated their light is. A large diffuse comet
will be much more difficult to spot than a small one, or one that
has a bright center, even though the magnitudes are the same. To
make things even more interesting, a bright twilight sky will
affect the visibility of the large or diffuse comet to a greater
degree than that of the small or concentrated one. It is at this
point that most people simply throw up their hands.
my SkyTools software, I developed a scientific model for the
detectability of extended objects in the eyepiece, based on the
sky brightness and visual contrast. Given the magnitude, size, and
degree of concentration, this model can be successfully applied to
the altitude of the comet and brightness of the sky changes during
the night, SkyTools samples the visual detectability of the comet,
selecting the time of night when the contrast is at its highest.
When this is done for successive nights, a Nightly Optimum
Viewing Ephemeris can be computed. It is this ephemeris that
was used to make the predictions above, and no other software can
ephemeris can be displayed on a chart, like the binocular finder
chart above, for any location and telescope.
Story of Comet 45P
years ago, in December 1948, Moniru Honda discovered a new comet.
Antonín Mrkos, and Ľudmila Pajdušáková also shared in the
started way out in the Oort cloud, where millions of comets circle
the sun, so distantly that they cannot be detected. Out that far
they are easily deflected, and sometimes they fall toward the sun
and the inner solar system. Most make a pass and then head back
out to where they came from, perhaps never to be seen again. But a
few will pass close enough to the gravity of a planet, usually
Jupiter, such that the orbit is altered. These comets can be deflected
so that they no longer go far away from the sun, but orbit the sun
regularly, and because they periodically appear in our skies, they
are called periodic comets. Each periodic comet is given a number.
The most famous is the first one that was recognized, comet
1P/Halley. The comet discovered by Honda is the 45th numbered
periodic comet. The orbit of 45P stretches out to Jupiter, but
every 5.3 years it passes closer to the sun, between the orbits of
Venus and Mercury. It is at these times that it can be spotted in
backyard telescopes, although some opportunities are better than
others. This is one of the better opportunities.
next time 45P/Honda-Mrkos-Pajdusakova will be close to the earth
and sun will be in early April 2022, when it is predicted to reach
a maximum brightness of magnitude 8.5, more than a magnitude
fainter than now.
Greg Crinklaw —
Astronomer and Developer of
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