50 AUSTRALIAN SKY & TELESCOPE May | June 2017
COMETS by David Seargent
Close comet coming south
Comet 41P moves into the southern skies. Will it have another outburst?
A
s I remarked in the previous issue,
the short-period comet 41P/
Tuttle-Giacobini-Kresak will
arrive in the constellation Hercules as
April closes and May begins, becoming
accessible to observers at mid-southern
latitudes in the northern predawn sky at
an expected magnitude of around 7.5–8.
41P will move quickly southward
as it pulls away from its April 14
perihelion passage at 1.05 a.u. from
the Sun and its passage by Earth at
just 0.15 a.u. on April 5. It will traverse
Hercules and Ophiuchus during May
and June, ending the latter month in
Serpens Cauda. During this period, it
is expected to fade as it moves away
from both Sun and Earth, declining in
brightness to around magnitude 10 by
early June and to around 12–13 by the
end of that month.
Unless, that is, an outburst occurs!
As noted in earlier issues, this comet has
experienced some spectacular brightness
outbursts at several past apparitions
and there is a chance — albeit far from
certain — that something similar may
happen this year as well. A careful watch
on this object is advised... and might
prove to be very interesting indeed!
May and June will also see twocomets of long period reaching their
respective perihelia. The first of these
is the dynamically evolved, long-period
object C/2015 ER61 (PANSTARRS)
which will reach its closest point to the
Sun (at 1.05 a.u.) on May 9. As noted in
the previous issue, this body was initially
catalogued as an asteroid, but with
the eventual appearance of cometary
activity, was re-listed as a comet.
Throughout May, C/2015 ER61 will
drift through Pisces, arriving at Aries in
the middle of June and remaining within
the boundaries of that constellation
for the rest of the month. Predicting
this comet’s brightness is not easy as
it seems to be in a state of low activity
as these words are being written, and
may yet ‘switch on’ to something more
vigorous just prior to, or even following,
perihelion passage. Assuming that the
early activity is, however, typical of what
we might continue to expect, the comet
should be around magnitude 8 through
most of May, slowly fading to 9–9.5 by
the final days of June.
June 12 will see the dynamically new
comet C/2015 V2 (Johnson) arrive at its
perihelion passage at 1.64 a.u. from the
Sun. Beginning the previous month in
the constellation of Hercules, close tothe meeting point of this constellation
and two of its neighbours, Bootes and
Corona Borealis, this comet will become
progressively better placed for southern
observers as it moves through Bootes
and into Virgo around the middle
of June. It will pass close to the very
conspicuous star Arcturus in early June.
Images obtained by moderate
telescopes fitted with CCD cameras
early this year revealed Johnson to be a
very impressive object with a strongly
condensed coma and sporting an
intense tail. If it continues to develop
in this manner, we can look forward
to some spectacular images during the
period covered here. Visually, however,
the comet is likely to be a good deal
less impressive, although still a very
interesting object for large binoculars
and small telescopes. If it maintains
its early brightness trend, it should be
around magnitude 8 or 9 during early
May, brightening to perhaps 7.5 or
thereabouts in early June before fading
by around half a magnitude before that
month’s end.■ David Seargent’s latest book on
comets, Snowballs in the Furnace, is
available from Amazon.comG. RHEMANN X 2Comet 41P/Tuttle-Giacobini-Kresak will be well-placed
in the southern sky during May and June, beginning the
period at around magnitude 7.5–8.Comet C/2015 V2 (Johnson) will be
a great target for astrophotographers.