252P LINEAR

Closest to Sun on 15 March 2016 at 0.99AU
Closest to Earth on 21 March 2016 at 0.03AU
Maximum magnitude 4 in March 2016
Period = 5.3 yrs

2 periodic comets, probably related, had near record close approaches to the Earth in March 2016.
252P LINEAR passed 13.9 lunar distances (5 million kms) on March 21 and reached a naked eye visibility of magnitude 4
P/2016 BA14 PANSTARRS at 9.2 lunar distances (3.5 million kms) on March 22 reached telescopic magnitude 12.

The remarkable performance of comet 252P LINEAR.

252P LINEAR is a short period comet (5.3 year orbit) which had an exceptionally close passage to the Earth, only 13.9 Lunar distances on 2016 March 21.
This is one of the closest approaches of a comet to the Earth on record. (5th closest)
Back in early March 2016, I found the comet a difficult object in an 8" telescope and was questioning whether it would reach its predicted peak of magnitude 10.  
Never had I expected it to reach naked eye brightness!

On the evening of March 7, I estimated the comet at magnitude 9.8 through 25x100mm binoculars.
I was very fortunate with the weather and, over the next 14 nights, made a further 11 visual observations using a combination of 25x100mm and 8x40mm binoculars.
The comet seemed to be brightening at a rate of 0.5 magnitudes per day and, by the morning of March 19, was visible to the unaided eye.
It appeared as a large circular haze nearly 2x moon diameters wide, with a surface intensity slightly lower than that of the Magellanic clouds, and situated near the south celestial pole.
The coma size expanded rapidly during March. I estimated it at 10' wide through 25x100mm binoculars on March 7th, to over 1 degree wide with the naked eye on the 19th.
In linear terms, this equates to a diameter of over 100,000 kms, similar in size to Saturn. The coma is very tenuous however. 
The extremely low surface gravity of a comet allows the gas to escape off the surface quite easily. The intense green colour is due to the emission from diatomic Carbon.

The degree of condensation started out highly diffuse, but increased as March progressed, since the comet was approaching perihelion.

The extraordinary rate of brightening cannot be explained by changes in Delta (distance to Earth) and r (distance to Sun) alone.
The comet obviously underwent a surge in intrinsic brightness, probably caused by a new active region on the surface. There is no evidence of fragmentation at this point.
The predicted peak was magnitude 10, but the observed peak was magnitude 4. That is 6 orders of magnitude brighter than predicted.
The absolute magnitude at previous appearances was in the order of 17.5 (extremely faint for a comet). Now it is 11.5, more typical of its short period cousins.

252P LINEAR on 2016 March 8 taken remotely from Siding Spring.
My visual observation at the time through giant binoculars (25x100mm) indicated a very large coma,
at least 15' across (18' in this image) and a total integrated magnitude of approximately 9.5.
Comet's distance to Earth at the time of this image (13 million kms).
Despite the comets brightness, the coma is very diffuse. Wide field instruments and dark skies are required to see it.

Below Comet 252P LINEAR on 2016 March 13

Below: The Large Magellanic Cloud and comet 252P LINEAR on 2016 March 14.
I estimated comet LINEAR at magnitude 6.5 with 35' coma through 8x40mm binoculars

Below: 2016 Mar 18.75 UT; m1= 4.8 ; Dia= 50’; DC= 3...Naked eye [Michael Mattiazzo, Swan Hill, Vic, Australia]
[My first naked eye observation of this comet, made after moonset. Comet appears as a large circular haze nearly 2x moon diameters wide,
with a surface intensity slightly lower than that of the Magellanic clouds. Distance to Earth was 5.9 million kms]

Below: 252P LINEAR on the morning of March 20 near closest approach. Visible to the unaided eye at magnitude 4.5 near the south celestial pole.
Small Magellanic Cloud is at lower left. Part of Milky way in Carinae at upper right.

Below: the naked eye comet was situated near Alpha Trianulum Australae.
Milky way stretches from Scorpius (left) to Alpha and Beta Centauri (top right)
3 minute photo using a Canon 60Da + Canon 35-70mm EF US ISM lens at f/4

Below. Spot the green comet. 252P LINEAR in Ophiuchus. 2016 April 2 at 15:00UT. Comet appeared magnitude 5.5 with 40' coma in 8x40mm binoculars.
Scorpius is at top with Mars top left and Saturn above centre left. Sagittarius is at lower right. A beautiful scene looking towards the galactic centre.
Image details 3 minutes using Canon 60Da + Canon EF US ISM lens at 35mm

Comet was magnitude 5.8 on April 7th when this image below was captured, next to globular cluster M14.

My last observation of 252P occurred on May 5 when the comet was estimated at magnitude 7.5

FINDER CHARTS

March 2016 finder charts

April 2016

May 2016.

Night mode finder chart May-July 2016


June-July 2016 finder chart Hercules-Ophiuchus.

Comet C/2016 BA14 PANSTARRS
In late January, the PANSTARRS survey team in Hawaii discovered an asteroid, 2016 BA14, the orbit of which has been shown to be remarkably similar to 252P.
On closer inspection, the asteroid had a small hint of a tail and was rebadged comet P/2016 BA14 PANSTARRS.
In fact, 2016 BA14 passed the Earth even closer than 252P, 9.2 lunar distances on March 22.
The two comets are probably related, with 2016 BA14 a small fragment breaking off the larger 252P centuries ago.
Radar observations of 2016 BA14 in late May indicated that the nucleus is in the order of 1km.
It is quite puzzling how a comet of this size can be so inactive. 

Meteor Shower?
The potential meteor shower associated with both comets during March, didn't appear to eventuate as there were no reported observations to date.
The expected peaks were March 20 and 28 for 2016 BA14 and 252P respectively.
Only scant observations were reported mid march and the night before the peak of the 28th. Most of Australia was blanketed in cloud during the peak.
On February 10th, NASA's "fireball" network detected a cluster of very slow, low inclination meteors that appeared to be linked to the comets.
Southern Meteor observers were on the lookout for any potential activity, arising from the constellation of Columba or thereabouts, during evening skies.
The meteors would be recognizable by their very slow speed.
The shower was predicted to last for quite some time, February through to May, due to the low inclination of the shower orbit.

P/2016 BA14 is the intrinsically much fainter object and still appears asteroid like.

http://www.astro.umd.edu/~msk/blog/articles/comet-p2016ba14-feb16

Southern observers should be on the lookout for a potential meteor shower during March, emanating from the Columba/Lepus region.
http://www.cbat.eps.harvard.edu/iau/cbet/004200/CBET004259.txt

the meteor shower associated to P/2016 BA14 should have its radiant located at (RA = 05h 05' ; Dec. = -39°), around March 20 (prediction Quan-Zhi Ye)
the meteor shower associated to 252P/LINEAR should have its radiant located at (RA = 05h 15' ; Dec. = -16°), around March 28 (prediction Mikhail Maslov).