Visual Comet observing and hunting

Bangalore Astronomical Society (BAS) (www.bas.org.in)

Amar A. Sharma

Outline of my talk

History of visual comet hunting How to become a comet hunter? Tools and Techniques Some examples of successful hunters India’s only Comet discovery!

Questions

HISTORY OF COMET HUNTING Comet hunters-on-paper like Halley, Encke, Lexell and Cromellin calculated, and

predicted the next return of comets. Visual observers used to then track and hunt for them.

Halley’s comet was predicted to return at end of 1758 (after apparitions of 1531, 1607 & 1682). Johann Georg Palitzch, a German farmer from Dresden actually spotted it on Christmas eve of 1758 in Pisces, first with un-aided eye and then telescope.

The comet race was formally begun by Charles Messier. This was to avenge for not being able to spot Halley’s Comet Christmas return of 1758! He compiled Messier’s Catalog in due course of hunting.

The 17th, 18th and 19th centuries gave birth to many accomplished comet hunters, who built their own telescopes for hunting.

Some historic comet hunters with highest number of discoveries are – Pons (26 / 37), Brooks (21), Barnard (16), Messier (13 / 20), Swift (13), Peltier (10).

How to become a comet hunter

Step 1: Become a better observer

Step 2: Observe as many comets as possible

Step 3: Acquire the tools and techniques

Step 1 : Become a better observer If you have observed the Messier Catalog and good

share of the NGC catalog, then you are a good observer. It means you can identify various types of celestial objects.

The key to observing is – practice, practice, practice!

Make it a point to get acquainted to sketch DSO’s and comets, if unable to image them.

A small telescope or binocular most used can discover comets and DSO’s, and not the one gathering dust !

Step 2 : Observe as many comets as possible

Firstly, love comets. Comets are wonderful and important celestial bodies to be studied.

Several internet resources like Aerith.net, Skyhound, BAA Comet section, Astrosite Gronigen provide weekly updates on comets.

Yahoo groups like CometObs and Comets-ml have the world’s best and active amateur and professional comet researchers providing daily (!) updates on many comets.

Take your telescope or an imaging setup to a dark place atleast once a month to observe them. If you take it out twice, you could see changing features in these comets, and even new comets.

Once you have selected your visual target (which could be either in the all-night sky, or dawn or dusk sky) use all possible magnifications, studying the comet closely. Try to record it for future reference, by either sketching or imaging it.

Observations to make Comets are like the DSO’s – faint face-on galaxies, or bright condensed globulars (depends on

their inner composition, angle and distance from Earth and Sun, and other factors) not always having tails.

COMA DIAMETER - Observe the entire shape and texture. Use averted vision to enhance faint viewing, since the boundary will not be well defined. Estimate the coma diameter using two field stars. Tails are generally tapering away from one part of the coma.

DEGREE OF CONDENSATION – How ‘soft’ the coma is, on a scale of 0-9.

0 - Diffuse coma of uniform brightness

5 - Condensation appears as a diffuse spot at centre of coma – described as moderately condensed

9 - Stellar or disk like in appearance

ESTIMATE MAGNITUDE – Use nearby field stars of known magnitude, one brighter and one fainter, to estimate brightness, by defocusing them. There are different methods.

MOVEMENT – Many comets do exhibit slight movement even within an hour.

ADDITIONAL FEATURES – Large apertures can show jets, features in tails, and even splitting of nuclei. Anti-tails are some phenomena contemporary to tails of comets.

SKETCH IT – Sketching helps train the eye to see the smallest detail. Builds eye-hand-mind cordination.

Degree of Condensation (DC)Credit : British Astronomical Association (BAA)

http://www.ast.cam.ac.uk/~jds/

Some of my observations…

4/P Faye4/P Faye Date/Time : 17 October 2006 @ ~19:30 UT (1:00 am

LT)

Observing Location : Hosahalli, 70 km North of

Bangalore

Instrument : 10" f/5.1 Dobsonian telescope. 32 mm

Ramsden eyepiece.

Magnification : 40xFOV : 1.25 degree

Constellation : Aries

Magnitude : 9

Sky condition : Sky was dark and good in that

direction. Object was close to zenith. Transparency and

seeing were good.

Description : This object was a very beautiful one. It was reminiscent of a small comet painting, with a small coma and

a small tail. The tail was distinct as a protrusion from the coma. The comet was pretty bright for it's size. This comet, one of the most beautiful ones I've observed till now, was a Birthday's Gift to me, when I observed it on 17th October

after the stroke of midnight!!

C/2006 A1 (Pojmanski)C/2006 A1 (Pojmanski)Date/Time : 25 Feb 2006 @

~ 23:30 UT (5:00 am LT)

Observing Location : Hosahalli, 70 km North of

Bangalore

Instrument : 8" f/8 telescope. 32mm Ramsden

eyepiece

Magnification : 50xFOV : 1 degree

Constellation : Capricornus

Magnitude : ~6

Sky condition : Light polluted in this East direction with reddish color. The object was some distance above the horizon. Transparency and seeing were average

Description : It looked just like a bright globular cluster in appearance and small in size, highly condensed. After few

seconds of staring a thin extension of haze pointing towards the west was revealed. This tail was approximately around half degree in length, very diffuse and thin. A star

appeared in the tail of the comet

Step 3 : Acquire the tools and techniques

A Telescope or Binocular?Ofcourse the preferred choice would be a reflective telescope

because of-Large aperture, Ease of availability, Available short-focal length hence wide fields, Higher

magnifications, change-able magnifications

A binocular loses out because of – small aperture, fixed magnification. It gains on wider field, and portability.

Aperture (mm) Faintest Magnitude

50 8

80 9.5

150 11

200 12

300 13.5

400 14.5

But, finally, select an equipment you will be most comfortable with, during your long, enduring and arduous comet hunting task.

My setup

I decided and purchased a large 25x100 astronomical binocular for comet hunting, simply for choices of – personal preference, comfort and ‘intuitive’ trust on their power.

Binocular discoveries were famous with the Japanese and Australian comet hunters of the yester-years.

I particularly selected Oberwerk IF 25x100, for it’s good repute as a low cost large astronomy binocular, and good optics.

Custom built a parallelogram mount, which is meant for such large heavy (5 kilo!) binocs, and allows free movement in any part of the sky at any height.

My setup

Comparative sizes of 25x100 binocs

Prepare with : Equipment and accessories, Proper star-charts (Norton’s Star Atlas, Cambridge Star Atlas, Uranometria, Sky Atlas 2000.0) or any desktop planetarium software (Cartes du Ciel, The Sky, MegaStar, Sky Map)

Ideal Observing location : Clear horizons, away from Light-Pollution. Safe, not far but accessible.

Others include : Eyepatch, Observing log book, pencils, dim red flash-lights, eyepieces, and winter wear !

Know which comets are where in the sky, to avoid going over them. Watch out for outbursts of previously unknown comets!

Step 3 : Acquire the tools and techniques

Scanning techniqueScanning technique• Searches of the prime sky areas, like near the eastern and western horizons, before sunrise and

after sunset, and polar regions, along with Milky Way should be intensively made. Utilize all New Moon periods. Stay in the Comet Haystack region (upto 60* from the Sun). Preferred is an alt-azimuth mount.

• Previous studies of discovered comets show that more comets have been discovered in the morning sky than in the evening sky. Ensure that morning activity receives as much as, if not more attention than evening effort.

• Scan in horizontal or vertical strips of the sky, as per your convenience. Spend between 3 and 5 seconds on each field. At the end of each strip, reverse back, overlapping the f.o.v by atleast a quarter. Continue till you have reached 40* to 60* in altitude.

• You would come across lots of galaxies, clusters, nebulae, and telescopic meteors and satellites while the scans. Watch out for the misleading ‘asterisms’ – close groupings of stars whose collective fuzz looks like the glow of a DSO.

Some successful comet hunters

Don Machholz (10)David Levy (22)

William Bradfield (18)

George Alcock (5)

India’s only comet discovery

• Prof. M.K.Vainu Bappu – only Indian to have discovered a comet, but from outside the country.

• Discovered in 1949 on photographic plate, when on a scholarship at Harvard University.

• Co-discovery with colleagues Bart Bok and Gordon Newkirk.

• C/1949 N1 (Bappu-Newkirk-Bok)• Long period comet. Perihelion distance – 2.05 AU,

Aphelion distance – 3033.60 AU

• Accidental discovery. Received a reprisal from Indian Govt. instead of congratulations!

• More in blog ‘A treatise on Vainu Bappu's Comet ’ in BAS website – compiled by Amar.

http://www.bas.org.in/Home/blog/amaruniverse/2009/23/03/treatise-vainu-bappus-comet

QUESTIONS?

THANK YOU.