COMETS

Comet. C/2011 L4 ( PanSTARRS )

2013 April 02: A temporary PanSTARRS page has been opened.

Important: The comet passes within less than 2 arc-degrees of the Great Andromeda Galaxy  M31 April 2/3. Do not confuse one with the other!

There is a location diagram on the SKY VIEW page showing the path of the comet up to April 19 2013.

Update March 31.

Comet PanSTARRS preparing to “bypass” the Andromeda Galaxy (M31) top left.

2013 March 31, 20h 37m UT.  A 20 sec. exposure: Nikkor 135mm f/2.8 D300 ISO 800. (Left click to enlarge.)

Comet in twilight: 

Comet C/2011 L4 (PanSTARRS ) imaged 2013 March 31, 20h 50m. A 20 sec. exposure Nikkor 500mm f/4, D300 ISO 800. Compare with image below noting improved colour correction for stars using this high quality lens. (Left click to enlarge.)

A number of high quality images were obtained with lenses ranging from 135mm f/2.8 to 600mm f/4. A selection will be featured on site shortly.

Update March 30. Extensive observations were made from 20h 15m to 21h 30m

Comet C/2011 L4 ( PanSTARRS ) imaged 2013 March 30, 20h 50m UT. 150mm f/5 achromatic refractor: exp. 45 sec. D300 ISO 800.

The star to the left of the comet is TYC 2270-570-1 mag. 6.74. Stars to magnitude 13 are visible. (Field: 75' x 55' approx.) Left click to enlarge.

Update March 29. The comet is now circumpolar from the latitude of Orkney. This image was secured at 21h 04m UT between short breaks in cloud and before moonrise. A 4 sec. static camera, exposure; Nikkor 105mm f/1.8 D300: ISO 800. (The comet is presently out of reach from the observing station.)

The star to the left of the comet is pi And. (mag. 4.33). The brightest star in the field (far left) is beta And. (mag. 2.07). Stars to magnitude 11.5 are visible in the frame. The fan-like tail is a little under 2 arc-degrees in this image. Estimated integrated magnitude of comet is 4.0 and a little brighter than predicted. (Left click to enlarge.)

2013 March 29, 21h 12m UT. A 4 sec. static camera, exposure; Nikkor 180 mm f/2.8 D300: ISO 800. (Left click to enlarge.)

The appearance of the comet on March 29 was impressive in binoculars (7x50s) but far less so to the unaided eye, naturally.

Update March 27. We have yet to observe the comet from Rousay. Observers elsewhere in the UK have been facing similar problems with weather and so forth.

I have to reiterate my view that this comet was unlikely to be a spectacular event from the northern hemisphere. Unfortunately, the national and international media go hold of it and in their “ignorance” (word used politely but advisedly)  raised expectations unnecessarily . 

Hopefully, with the Moon soon leaving the scene and with the comet’s increased declination, we should be able to achieve some images within the next week. BUT, we are now approaching the period of long twilight hours in the north and this, coupled with the appalling weather, would substantiate the view that one has to be something of a fanatic to do this job!

UPDATE  march 15: All attempts to observe the comet from Rousay have so far been foiled by cloud. As remarked previously, the comet is not an easy object from the northern hemisphere and reports from observer in this neck of the woods have been sketchy to say the least. We had the following from Telescope House earlier today:

Comet Panstarrs is now visible from the UK and the entire Northern Hemisphere. It's still a fairly challenging object in the early evening (or morning) twilight because of its relative position to the Sun, but is putting on a fine show for those with a good westerly horizon. Telescope House Sales Manager, Peter Gallon, witnessed the Comet on the evening of Thursday 14th March at about 6.45PM and gave the following report:

"Comet Panstarrs had a bright nucleus, which I'd estimate to have been mag +0. It would definitely be a really easy object if it were a bit higher in the sky. The tail was reasonably prominent - I'd estimate it to be about a degree in length. A really nice comet!"

 

UPDATE March 11. We have the following communication from the British Astronomical Association's Comet Section:

Comet C/2011 L4 (PanSTARRS) is now setting after the Sun as seen from UK latitudes. It has put on a good show in the southern hemisphere and,although its brightness has been difficult to estimate in a bright sky, it may have reached zero magnitude. It certainly has a nice tail as can be seen in this image taken from Perth, Australia:

http://www.dpreview.com/galleries/6455983989/photos/2452791/comet-panstarrs

This comet is not well placed for northern observers.

Maximum brilliance will occur around March 09 – 11, 2013 when the integrated magnitude may be in the order of  0.8 to 0.6. (We have yet to receive reliable estimates of magnitude from southern observers.)

From about 11 March the comet will start to fade, halving in apparent brightness approximately every five days. It will likely drop below naked eye visibility within the first week of April.

 

Comet C2012 K5 (LINEAR)

The first clear night (dusk to dawn) for over six weeks and the first “usable” night in 2013. As a result we have missed the best of this comet, which is heading south at a prodigious rate.

 

C2012 K5 (LINEAR) Imaged 2013 January 16, 19h 43m UT. 132mm f/7 apochromatic refractor, D300 SLR, a 50 sec. exposure at ISO800. Brightest star in field (dia. 50 arc-min) is TYC 4727-2098-1 mag. 5.86. Stars to magnitude 15 are visible despite Moon (phase 29%) separation 65°, altitude 22° 39'. The comet was at altitude 29° 44'. (Left click to enlarge.)

 
Comet C2012 K5 (LINEAR) approaching TYC 75-546-1 (mag.7.63). The comet now below mag. 11, and retrograding at around 115 arc-seconds per hour, was imaged against a background of light from the Moon limiting exposures to around 50 seconds.

A 50 sec. exposure 150mm aperture f/5 achromatic refractor ISO1200.

(Left click to enlarge.)

 

Introduction

In astronomy one can divide subjects between the predictable and the un-predictable. For example, tables are issued many years in advance giving the positions for planets and other objects in the Solar System to a high degree of precision. (Unlike planets, comets with, few exceptions, move in highly elliptical and sometimes highly inclined – to the ecliptic – orbits*.)  Also within the category of the predictable events are eclipses of the Sun and Moon, the occultation of stars by the Moon and other bodies in the Solar system.

Amongst non-predictable events we have the appearance of the aurora, sunspots, visitations by comets hitherto unknown, the flare-up of stars – novae and super nova – transient phenomena on other planets and so on.

Moreover, in the case of comets, although we may calculate their position as they approach the inner Solar System with some order of accuracy, their physical appearance is impossible to predict. Even our assumptions as to their orbits (or pathways) can sometimes come adrift, as was dramatically demonstrated in 2006 when Comet 73P/Schwassmann–Wachmann broke up into several fragments. Two of the larger portions were indeed recorded by us on Rousay (see fig. 6).

Fig. 1 Comet Hale-bopp  1997 March 28.842: Takumar135mm focal length f/3.5. MJH East Bergholt (film). Exposure: 10 minutes.

Fig. 2 Comet Hale-bopp  1997 April 04.864: 150mm aperture f/4.5 Cooke triplet MJH East Bergholt (film B&W). Exposure: 20 minutes.

It would be difficult for me to position in order of priority and achievement my many and varied interests in the field of astronomy. Fortunately, I learned the hard way. That is to say, with little financial backing (few of us knew much in the way of luxury in the immediate post-WW2 period) I quickly learned economy of effort.

Professionally my work in theoretical physics, celestial mechanics and binary stars in particular, was sufficiently academic for me to turn down an invitation from my old friend Patrick Moore (long before he had become an celebrity, of course) to appear on one of the early Sky at Night programmes. At various stages of my career has Patrick tempted me with exposure to the wider media all of which, for some strange reason, I have not followed up!

But I digress. When I first joined the British Astronomical Association (BAA) as a schoolboy in 1951, I offered my services to the Computing Section. I quickly became involved in the calculation of cometary ephemeredes and the reduction of meteor observations, two related topics in many respects. (Remember in those days there were no electronic computers; all calculations involved many hours fingering through large tomes of mathematical tables to six figures of decimals or more; tedious to some but a worthwhile challenge to others, including myself.)

A few years later I commenced, still as an amateur, the serious observation of comets and this activity has followed me through life to the present day. (As the composer Edward Elgar once said, the finest professionals are amateurs.) Some of my closest friends and associates have been, and are still, comet people. This included three BAA Comet Section Directors one of whom is Michael J Hendrie (retired) now in his early eighties but still very active as an observer. (fig.8) In addition to his tireless efforts for the Comet Section, Michael was also for over twenty years The Times Astronomy Correspondent. To Michael I am indebted for the fine images of Comet Hale Bopp (figs 1 & 2). (I should also wish to pay tribute to another good friend and colleague, Michael P Candy, formerly of the RGO, Sussex, and later active in Australia where he died in his prime, sadly.)

Going back some fifty years I would have to give a very different picture for the comet observer compared to today. To record on film some of the fainter comets would require patient manual guiding at the eye-end of the telescope, sometimes spanning two or three hours. Our equipment comprised two Aldis 4 inch aperture f/4.5 cameras attached to the 5.2 inch Cooke refractor. The total weight of this outfit would have been in the region of 150 kilos, excluding the iron column upon which the massive equatorial head was bolted. Such things were only possible with the protection of an observatory (in this case 11ft diameter), revolvable dome.

Contrast the above to our current range of equipment, most of which is portable, albeit at some expenditure of effort. For example, the fast 400mm f/2.8 Nikkor lens coupled to a D300 SLR is useful for a wide range of comets offering 2.3˚ x 3.4˚ field. This may be attached to an EQ6 equatorial mount offering adequate stability and may be set up within two to three minutes. The even faster 200mm f/2 lens is ideal for comets with tails up to 6˚ long.

We have been fortunate in acquiring these fine S/H lenses at a fraction of their original cost since most photographic professionals these days upgrade to the latest automatic versions. Most of our recent comet work has been done with these lenses (fig. 4, also see Comet Garradd page).

Fig. 3 Comet Ikeya-Zhang; Date 2002 March  21. JCV (film), 400mm f/5.6 lens using Fujicolour 400 ASA, Pentax Super “A” SLR attached to the tube of a Meade 178mm Maksutov (cradle, fork mounting); exposure 4.5, minutes manual guiding; The length of the comet's tail is 4.5 arc degrees. Site: Braes, Sourin Valley, Rousay, Orkney. Note: there was a 7-day-old Moon contributing to sky glow.)

Digital techniques have revolutionised astro-photography in all areas not least where comets are concerned when images that would have taken hours to secure on film may now be secured in a few minutes. With the advantage of repeated imaging, where time and conditions permit, the so-called stacking of images using specialist software can reveal detail that would have been unimaginable fifty years back.

Fig. 4 Comet Hartley 2010 October 15 at 22h 03m UT. a 50 sec. exposure 400mm f/2.8. D300 SLR, ISO1200.

Fig 5 Comet Swan 2006 September 30 at 20h 22m UT. Nikkor 105mm f/1.8 D100 SLR. (Looking NW from Springfield, Rousay, with house chimney stack to left.)

However, there are drawbacks to the modern era mainly in the form of pollution from artificial light sources and aircraft condensation trails, Today it is impossible to image most regions of the night sky without encountering trails from artificial Earth satellites. There are literally thousands of bits and pieces up there constituting an inner cosmic dustbin that in the opinion of some is unjustified and irresponsible. For example, commercial space enterprises including a plethora of communications satellites for civilian and military use. The so-called sat-nav systems are superfluous to a good navigator, and I rather resent having our sky images disfigured by streaks of light in order to enable folk to chat by mobile phone from one end of a bus to the other!

Fig. 6 73PSchwassmann-Wachmann 3. 2006 April 27. Nikkor 105mm f/1.8 D100 SLR. A composite image pair showing the two major fragmented portions of the comet: Note: the trail of an artificial Earth satellite passing through the coma of the “fragment” (right). Left click to enlarge.

Number of personally observed comets.

My personal tally of observed comets is in excess of fifty, or a little under one for every year since I commenced serious observational work on these objects in 1957. Most of these have been faint objects well below naked eye visibility, but a few have ranked amongst the finest ever to grace our skies of the many-recorded comets spanning hundreds of years. In fact, that very next year, in 1957, we were blessed with the very fine C/1956 R1 (Arend-Roland).

My log for 1957 April 24 reads verbatim: Observed first with the naked eye the comet Arend-Roland from London at 20h 15m GMT. (37  Lloyd Baker Street, WC1, from where the comet lay almost over St. Pancras Railway Station.) A tail of about 3˚ long was easily seen. With 2 inch binoculars (7x50 Bar & Stroud) the tail was evidently longer but diffuse beyond 4˚ due to heavy artificial illumination of the sky.

Three days later, observing from Brentwood, Essex, in a darker sky, I estimated the magnitude of the coma at 2.0 and the tail 6˚ in length. Movement against the stellar background was evident to the unaided eye over a period of an hour or so.

A notable feature of Arend-Roland was its continually changing appearance. For many days it developed a down-pointing spike, which resulted from debris in its wake.

I am sometimes asked to name the most impressive comet I have ever observed. One has to qualify their choice carefully. There have been some brilliant comets that have put on a grand display over a short period of a few days; recently comets C/2011 W3 (Lovejoy) and McNaught 2007 (C/2006 P1) for example. Others have hung around for several weeks dominating that portion of the sky such as Hale-Bopp C/1995 O1; but the one I would give full-marks to would be Comet C/1996 B2 (Hyakutake).

From the JBAA 1998.108..157: “Unfortunately it was almost totally overcast in the UK at the time of closest approach. One of the few observers to see the comet from Britain was Vetterlein in Orkney. He had clear skies on the early morning of March 25 (1996) and reported a 35˚ tail visible to the naked eye.” Unfortunately, my own image was on film and does not do justice to the comet.

The comet’s coma (or “head”) passed almost through the zenith with the tail stretching away towards the southern horizon. Watching this spectacle alone in the early hours of a clear, late-March morning before twilight, gave me an understanding for how comets earned the reputation as portenders of catastrophe.

Of course there have been a number of much brighter comets such as the famous Halley’s Comet in 1910 (the 1986 apparition was by no means favourable for Earth dwellers). C/1969 Y1 (Bennett), and Comet West in 1976. (I would recommend readers go to the Google image pages for illustrations of these comets.)

As readers will have gathered, comets are very individual “creatures” in appearance, few if any replicate each other nor do those that return (and most do at some time or another) necessarily repeat their previous performances.

One possible exception is Comet 17P/Holmes discovered in 1892 and extensively observed from Rousay 2007/8. (fig. 7a and 7b). Looking like a snowball with no perceptible tail, the comet’s appearance in this latest apparition resembled closely descriptions of its showing in the year of its discovery.

Fig. 7a Comet Holmes 2007 November 20 at 05h 33m UT. Tokina 300mm f/2.8 D100 SLR. A 50 sec. exposure at ISO 600. The bright star is Mirfak (alpha Persei mag. 1.82)

Fig. 7b Comet Holmes showing apparent size compared to the Moon (superimposed top left) 2007 November 26 at 17h 27m UT.

Looking to the future we have the prospect of a brilliant “sun-grazer” comet when in November 2013 Comet C/2012 S1 (ISON) approaches perihelion; some are even predicting that for a few hours the comet may be visible with the unaided eye in broad daylight. Unfortunately for we northern observers those in the southern hemisphere should have the best opportunity of seeing this one!

Fig. 8 Michael J Hendrie (right - closest to telescope) and John C Vetterlein at Michael’s Observatory East Bergholt, Essex: 1993 August 25.

All imkages JCV excepting figs. 1 & 2 (MJH) & 8 (Pat Hendrie). 

* See Basics page: “Orbits etc.” coming soon.

 

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