Comets, quasi-comets and the Comet Section

Comets, quasi-comets and
the Comet Section

Jonathan Shanklin
Director, BAA Comet Section

• BAA founded 1890
• Comet Section formed 1891
• Around 40,000 observations
• Virtually all extant observations are post WW2
• Visual observations of nearly 500 different comets,
including returns of over 100 periodic comets, over 60 years

Jonathan Shanklin, 12th Director

Comet Section Publications

• Comet Section web page at
http://www.ast.cam.ac.uk/~jds

• Yearly Comet Section newsletter (available on the internet)
• Papers in Journal of the British Astronomical

Association

– Reports on the comets of each calendar year (includes
magnitude parameters)

– Predictions on comets for the coming year
– Predictions in the BAA Handbook

• BAA Observing Guide to Comets

– New edition in preparation

Comets



Amateur visual observations of 67P

1. The comet was discovered in 1969 following a very close encounter
with Jupiter (0.05 AU) in 1959 that reduced the perihelion distance
from 2.7 AU to 1.3 AU.

2. There were no visual observations at the discovery return and the
photographic magnitudes are a little inconsistent.

3. The comet was poorly placed in 1976; when within visual range it
was at a small elongation from the Sun

4. There was a well observed return in 1982 when the comet had a
perihelic opposition

5. The comet was again poorly placed in 1989
6. There have been observations at the last three returns.









Amateur visual observations of 67P

1. The comet is intrinsically brightest about 40 days after perihelion
2. The comet may show a secular brightening or it may change its

absolute magnitude from return to return
3. There is little evidence for significant outbursts

Amateur visual observations of 67P

If the perihelion distance is the critical factor in the absolute magnitude:

• The comet should become a binocular object in 2015
• The activity of the comet will be similar to that of 2009
• The observing circumstances will be similar to those of 2002, when

the comet was a morning object.

• At 1.21 AU the perihelion distance in 2021 is the closest for the next
100 years and the comet will be at opposition when near perihelion.
If my prediction for 2015 is correct the comet may reach naked eye
visibility in 2021.





Solar halo over the new Halley station, Antarctica



Comet 2011 W3 (Lovejoy),
Australia, 2011 December 24



















Quasi-comets









Image of 2010 G2 by Nick James, showing its slightly non-stellar profile

2012 BJ98 (Lemmon)

An object reported as asteroidal in images obtained in the second half of January, was
identified as cometary in images taken by the Mt Lemmon Survey on March 1, and then
linked to images obtained by the Steward Observatory, Pan-STARRS and the Catalina
Sky Survey. The comet has perihelion at 2.2 AU in September and has a period of
around 70 years.

2012 CH17 (MOSS)

The Morocco Oukaimeden Sky Survey (MOSS) discovered this comet on February
7.12, though it had earlier been flagged as an asteroid. It is due to reach perihelion at
1.3 AU in September. It could reach 13th magnitude, but is not well placed for
observation from the UK.

2012 NJ (P/La Sagra)

The La Sagra team reported an asteroid found on images taken on July 13.03, and their
positions combined with those from several other observatories lead to the automatic
determination of an orbit, which had a high inclination and a period of around 50 years.
This was published on July 14. Further observations and indications that the object had
a tail lead Gareth Williams to compute a manual orbit for the comet, which was
published on July 18. The comet was around a month past perihelion at 1.3 AU and the
period is around 25 years.

A/2012 DG61 [PanSTARRS]

This unusual asteroid was discovered by the Pan-STARRS 1 1.8m Ritchey-Chretien
reflector on February 28.33. [MPEC 2012-E10, 2012 March 1, 3-day orbit]. It has an
orbit with a period of around 5.2 years and perihelion is at 0.8 AU in 2012 July. It can
approach Jupiter within 0.25 AU and the Earth to 0.16 AU. The orbit has a Tisserand
criterion of 2.75 with respect to Jupiter.

A/2012 GS5 [PanSTARRS]

This unusual asteroid was discovered by the Pan-STARRS 1 1.8m Ritchey-Chretien
reflector on April 11.39. [MPEC 2012-G46, 2012 April 14, 3-day orbit]. It has an orbit
with a period of around 6.2 years and perihelion is at 0.5 AU in 2012 June. It can
approach Jupiter within 0.5 AU and the Earth to 0.29 AU. The orbit has a Tisserand
criterion of 2.35 with respect to Jupiter.

A/2012 HD2 [Spacewatch]

This unusual asteroid was discovered at the Steward Observatory, Kitt Peak by Jim
Scotti with the 0.9m Spacewatch reflector on April 18.28. It has a period of around 28
years and perihelion is at 2.5 AU in 2012 September. It has a retrograde orbit, with
aphelion at 16 AU. [MPEC 2012-H32, 2012 April 20, 2-day orbit]. The orbit has a
Tisserand criterion of -0.94 with respect to Jupiter.