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BAA Observing Sections Comet

Comet 21P approaches the North America Nebula

It will be a challenging observation due to midsummer skies and a First Quarter Moon but the periodic comet 21P/Giacobini-Zinner will be passing the bright emission nebula NGC7000 (the North America Nebula) in Cygnus between June 19 and June 21. The comet is currently around 13th magnitude but will brighten over the summer to become a potentially 6th magnitude object by September. At present the comet is a small fuzzy spot with a short tail to the south west and it will be completely overwhelmed by the large nebula but it will be interesting to compare the two objects. A chart showing the encounter is here. Please send any observations to the Comet Section.

The image at left shows the comet on the morning of 2018 June 13. The field of view is around 11 arcmin square. More images of this comet are available in the Section's archive here.

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BAA Tutorials Starting out

Noctilucent Clouds – a beginners guide

Noctilucent clouds (popularly referred to by the abbreviation “NLC”) are high atmosphere clouds which occur over summertime at mid latitude locations. They form at very high altitudes – around 82 km above sea level – and are, thus, a quite separate phenomena from normal weather or tropospheric cloud. They appear as thin streaks of “cloud”, often a pearly-blue colour, reminiscent of “mares-tail” cirrus cloud formations.

NLCs can be seen from around mid May to early August during the darkest part of a summer’s night when the Sun is between 6 – 16 degrees below the horizon. Typically, they will occupy the northern horizon, along the twilight arch, extending to an altitude of 10 – 15 degrees. Over the NLC “season” the bright star Capella dominates this part of the sky and serves as a good marker for the NLC observer. They used to be associated with northern UK but have been seen as far south as central France and they seem to be spreading further south with each season.

Observations of NLC remain of great value to professional scientists studying upper-atmosphere phenomena. Useful observations are very easy to make and require no special equipment.

The following information lists the important details you should include in your report:

LOCATION: Give the latitude and longitude of the place observations were made. Alternatively, give the name of the nearest town or city.
DATE: Use the “double-date” convention as used in reporting aurorae. That is, “June 21-22″ would refer to the night of the 21st and the early hours of the 22nd.
TIME: Try to use universal time (UT) even though British Summer Time (BST) will be in civil use for UK observers. Remember, UT = GMT = (BST – 1 hour).

Observations
The following features and details should be recorded at 15 minute intervals (i.e. on the hour, quarter past, half past and so on):

AZIMUTHS If you see NLC measure the left (western) and right hand (eastern) extent of the display. This is measured in degrees with west = 270, north = 000, east = 90 and south = 180. Polaris defines the northern point of your horizon. Azimuths can be gauged by using a clenched fist, held at arms length, as a measure of 10 degrees.
ELEVATION If possible, measure the angle subtended by the uppermost part of the display. A simple alidade can be made from a protractor and plumb line for this purpose.
BRIGHTNESS NLC brightness is measured on a three point scale with 1 = faint; 2 = moderate; 3 = very bright.

Structure
NLC forms are classified into 5 easily identified structures. Any combination of the following is possible:

Type 1: Veil – A simple structureless sheet, sometimes as background to other forms.
Type 2: Bands – Lines or streaks, parallel or crossing at small angles.
Type 3: Waves – Fine herring-bone structure like the sand ripples on a beach at low tide. Very characteristic of NLC.
Type 4: Whirls – Large-scale looped or twisted structures.
Type 5: Amorphous – Isolated patches of NLC with no definite structure.

Drawings
Simple sketches of the NLC can be very useful. These are best made in negative form with the darker parts of the sketch corresponding to the brighter NLC.

Photography
Photographs of NLC can easily be taken with a digital camera firmly fixed to a tripod; using 400 ISO gives good results. An exposure of 3-6 seconds with a lens aperture setting of f3.4 will normally suffice. However, it is always best to take several shots of different exposures, and pick the best exposure. Once this is done you can try a panorama by taking several overlapping photos. Make sure the camera is level, then move it about 20 degrees after each shot, starting just beyond one end. This makes sure that you will get it all, because the camera will see more than you can.

Sandra Brantingham

Sandra is the Director of the Aurora and Noctilucent Cloud Section of the BAA.

A selection of observatorions of noctilucent clouds which BAA members have uploaded to their Member pages can be found here.

[Thumbnail image by Gordon Mackie]

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BAA Articles

Observer's Challenge - Observing Saturn

Saturn reveals its loveliness even in a small telescope and observers will always remember their first view of the planet and its ring system.

Saturn is always a fine sight for any observer but this year it is located at -25 latitude and -26 from the first of July. Opposition is 2018 June 27. Being at such a low altitude in Sagittarius makes observing any fine detail very difficult in the UK. The rings are around 25° but it will be a challenge to see Encke’s Division. This division is situated in Ring A which is the outer ring beyond Cassini’s Division. Cassini’s can be seen with a 3-inch refractor under favourable conditions but Encke’s is much more elusive.

The satellites will be a challenge too and light pollution and low altitude will make Iapetus, Rhea, Tethys and Dione difficult. The BAA Handbook gives position data for these satellites on pages 83 and 84; Iapetus is brighter at Western Elongation and is much further out but mid-June and later August will be the best time to look for it.

There are two challengers therefore, these being to see if you can see Encke’s Division and also any satellite fainter than Titan. If you do not manage to meet either challenges, Saturn will always be a magnificent sight anyway.

As well as observing, why not make a sketch of Saturn and its rings and any visible moons; here is a sketch by Paul G. Abel made 2018 May 08 from the University of Leicester's Observatory. Or maybe you prefer to take images. Please do submit any sketches, images or observing notes to Mike Foulkes at the BAA's Saturn, Uranus and Neptune Section and upload them to your member page.

For more information on Saturn read this article by Mike Foulkes, or check out the BAA Handbook.

Alan Heath
Long Eaton, Nottinghamshire


Alan is a former BAA Saturn Section Director, 1964-1994, and continues to submit regular observations to the BAA. Alan is pictured here giving a talk to Nottingham Astronomical Society on the use of filters for planetary observation, 17th August 2017; Alan's article, The 'Great Filter Debate', which was published in the Journal in 2017 can be found here.

[Thumbnail image: Saturn, June 18th 2017, John Sussenbach, NL]

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BAA Observing Sections Jupiter

All about Juno and Jupiter at a pro-am workshop, 2018 May

EuroPlanet Workshop in London, 10-11 May 2018:  ‘New Views of Jupiter: Pro-Am Collaborations during and beyond the NASA Juno Mission’

 

This workshop, hosted by the Royal Astronomical Society at Burlington House, London, brought together 50 amateur and professional observers and researchers from Europe and across the world, to discuss collaborative studies of Jupiter while Juno is in orbit around ithe planet.  There were 17 professionals (including 3 senior Juno team members who came specially from the USA) and 33 amateurs (some who take images, some who analyse and interpret them, and some who develop software tools).  There were 26 talks, 10 from professionals and 16 from amateurs.

The talks are now posted on the workshop web page, along with a 5-page introduction/summary of the talks, and a large collection of photographs.  This is all at:

https://www2.le.ac.uk/departments/physics/people/leighfletcher/ras-juno-europlanet-meeting-2018

 

Also online are a Europlanet press release about the meeting, short interviews with some of the participants, and (for people in the UK) a new episode of the BBC’s ‘Sky at Night’: 

  http://www.europlanet-eu.org/new-views-of-jupiter-showcases-swirling-clouds-on-giant-planet/

  https://www.youtube.com/channel/UCUZJ5FO9ayrmepOM4FHAASw

  https://www.bbc.co.uk/programmes/b0b6tpsn

 

The workshop was funded mainly by EuroPlanet with a grant from the European Union, with a contribution from the European Research Council, and the Royal Astronomical Society provided the venue and staff free of charge.

 

Suggestions and recommendations for amateur imaging:

The workshop included informative talks from several observers about optimising procedures for image acquisition and analysis. There was also a discussion about optimising procedures for amateur imaging and for pro-am collaboration, which is summarised in the introduction to the talks on the above web page (direct link:)

https://drive.google.com/file/d/1nBwVLpWtJgVefZpLRvi7hZkoB5eoxgw1/view

This included the following:

--Should images be produced with north or south up?  A general recommendation that observers should submit images with north up (as professionals want) seemed to be widely accepted. 

--It is also desirable that everyone use the standard PVOL filename format:

   j2018-05-08_12-00_RGB_ABC  (for 2018 May 8, 12:00 UTC, RGB image, observer ABC).

--It is not necessary to provide individual color layers when a RGB image is provided.

 

NASA updates on the Juno mission:

 

1.  NASA have now approved the mission’s continuation for the full 34 orbits, culminating in a fatal plunge into Jupiter’s atmosphere at the end of the 35th orbit on 2021 July 30.  Press release at:

https://www.missionjuno.swri.edu/news/nasa-replans-junos-jupiter-mission

 

2.  Juno’s Microwave Radiometer picks up microwave bursts from jovian lightning flashes, and has mapped the thunderstorms across the planet.  It confirms that lightning flashes are most frequent in the mid/high northern latitudes (probably in cyclonic stormy regions as mapped by previous spacecraft), but they are also common all the way up to the north pole, and also occur in high southern latitudes though less frequently than in the north. The lightning bursts are also detected by Juno’s plasma waves instrument. They appear to be similar to lightning on Earth, and may be in similar water-driven thunderstorms.  Press release at:

https://www.missionjuno.swri.edu/news/juno-solves-39-year-old-mystery

 

BELOW:  Dr Scott Bolton (Principal investigator of the Juno project) and Dr Candy Hansen (PI of JunoCam) explaining Juno's results.

 

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Aspects of Mars

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About this observation
Observer
Alexei Pace
Time of observation
10/06/2018 - 02:40
Object
Mars
Observing location
Malta
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Alexei reports that this is his first Mars image for this apparition.  The planet is unfortunately not very high from his location (Malta) at 32°.  The Leftmost image is in RGB (true colour), the centre one is through an IR filter and the last image is in false colour IRRGB, which is not his favourite but he says it gives a different perspective.

Copyright of all images and other observations submitted to the BAA remains with the owner of the work. Reproduction of the work by third-parties is expressly forbidden without the consent of the copyright holder. For more information, please contact the webmaster.
BAA Tutorials Intermediate

The visual observation of comets

Electronic imaging is now the mainstream of amateur observing however visual observations are still valuable and with practice are easy to carry out.  There are usually several comets visible in simple equipment every year and observing them is a rewarding pastime.  This description of techniques for the visual observation of comets is updated from an article published in the Journal in 2004. 

Preamble

Figure 1 This series of images by David Strange of comet 2002 C1 shows what you might see with a telescope (top), binoculars (middle) and naked eye (bottom).Electronic imaging has taken over in many areas of amateur observation, where it clearly does a better job than the human eyeball.  Planetary observation is one clear example and I know that I could not even see the detail presented in the majority of electronic images.  Supernova searching is another area, where, at least in the UK, the patrollers are beating visual hunters hands down.  Electronic imaging is also without doubt best for the precise astrometry of stars, asteroids and comets. 

There are however some areas where the visual observer is more productive, does a better job, or provides continuity with the past.  Variable star observation is one such area, where a visual observer can produce far more, though not necessarily as accurate, observations.  For many variable stars the precise magnitude is not so important, but what is important is the general shape and amplitude of the light curve and a visual observer can easily provide this.

With comets there is a need for both electronic and visual observations (Figure 1) in order to provide continuity with historic observations.  Periodic comets in particular evolve from apparition to apparition, and so to link them comparable observations are required.  Nick James has developed a technique to reduce electronic observations to their visual equivalent, but this does need comparison with visual observations to ensure consistency. 

The perception that visual observation is a thing of the past is apparent in the decreasing number of visual observations that are coming in, particularly from UK observers.  In part this may be due to increasing light pollution, and it will certainly make a big difference to your observations if you can get to a dark sky site, however observation is still possible from a suburban back-garden and I have made observations of many comets from my home in central Cambridge.

Whilst a good site is one key aspect for visual observation, another is to match the equipment to the comet.  As an example take comet 2P/Encke, which was very diffuse.  I made an observation of the comet with the 0.3-m Northumberland refractor at the Cambridge University Observatory, estimating it at magnitude 12.4.  The following morning I saw a report on the Internet saying that it was visible in binoculars.  This seemed a bit unlikely given my observation, however the Cambridge site does suffer from light pollution, so the next evening I drove out to a dark sky site and was astounded to see the comet in 20x80 binoculars at an estimated magnitude of 9.9. 

Features of a comet

Figure 2 The various features that may be visible in a comet.Through a telescope or binoculars there are several features to see in a comet (Figure 2). 

The majority of comets show a diffuse coma, some arc minutes in diameter, with perhaps a nearly stellar nuclear condensation.  This is not the true solid nucleus as seen from spacecraft, as this is far too small to be seen from any earth-based telescope. 

The comet may show a tail, either composed of dust that is reflecting sunlight, or of ionised gas that is fluorescing in its own right.  This tail normally, but not always, points away from the Sun.  Under high power observers may see features such as jets or hoods in the inner coma, particularly if it is a bright comet relatively close to the Sun.

Visual observation is always subjective to a greater or lesser extent, because it is a synthesis of how the brain interprets what the eye sees.  Everyone’s eyes see differently, indeed no two eyes are the same.  Their spectral sensitivity may be different and the optical defects of each eye will also be different, with some more defective than others.  Once the image has formed on the retina it has to be interpreted and this will depend on our background and preconceptions.  Despite all these handicaps, visual observers still produce the goods and make valuable observations.

There are many reasons for making an observation.  For amateur observers, personal satisfaction plays a large part and so an observation need not satisfy any scientific goal.  It can be simply to tick on object off on a list, or the satisfaction gained in making an artistic drawing. 

Amateur observers can however make significant contributions to science and the visual observation of comets is no exception.  Visual magnitude estimates go towards making up a light curve, which allows the determination of the absolute magnitude of a comet.  This gives a measure of the size of the nucleus and professional astronomers then draw up a statistical picture of the size distribution.  This can tell us much about the evolutionary history of comets. 

With periodic comets that have been observed over many returns it is possible to investigate if the absolute magnitude is changing with time and it is therefore essential to use consistent methods over a long period of time.  Whilst electronic observation might give a precise magnitude, there are many problems in the reduction of electronic images.  For example when visual observers were reporting 2P/Encke as being easily visible in binoculars, some reports on the Internet gave magnitudes fainter than 13.

The Comet Section

The Comet Section was formed in 1891, the year after the BAA was founded.  Since 1945, 990 observers have contributed some 101,000 visual observations of 1200 comets, including returns of 80 periodic comets .  Sadly the raw records prior to 1945 were lost during the Second World War, though there are some reports and analyses in the Journal.  There are a number of Section publications, including Journal papers covering past comets, predictions on comets for the coming year, an observing guide, a Section newsletter and frequently updated web pages.

The first Director of the Section was W F Denning, who discovered five comets.  The third Director, Dr A C D Crommelin, didn’t discover a comet, but did compute the true orbit of what is now known as 27P/Crommelin.  Jonathan Shanklin was the 12th Director and although no comets were named after him, he discovered seven SOHO comets. 

Today visual discovery is unlikely, thanks to professional search programmes such as LINEAR (Lincoln Laboratory Near Earth Asteroid Research) and PanSTARRS (Panoramic Survey Telescope and Rapid Response System), however Southern Hemisphere observers still stand a chance and since 2007 Terry Lovejoy has discovered no less than six comets.   There is also a chance of discovery in what might be termed the twilight zone, which is too close to the Sun for the surveys and too far from the Sun for the SOHO (Solar and Heliospheric Observatory) LASCO (Large Angle Spectroscopic Coronagraph) coronagraphs, although even this area is covered by its SWAN (Solar Wind Anisotropies) camera and some professional survey programmes.

Observing equipment

Observing comets is rarely a naked eye pastime, so some visual aid is desirable.  Binoculars are a good starting point and I have over half a dozen pairs ranging through 10x25, 3x40, 7x50, 10x50, 20x80 and 25x100.  Of these the most frequently used are the 20x80B as the higher magnification and light grasp are good in light polluted conditions as well as in dark sky conditions.  Telescopically I mostly use the old long focus refractors of the University Observatory – the Northumberland 0.30-m f20 and the Thorrowgood 0.20-m f14.  One important reason for continuing to use these telescopes is to provide continuity with the past, but to provide comparison I also use a 0.15-m f8 Newtonian, a 0.20-m LX200 and a 0.33-m f4.5 Dobsonian.  The Dobsonian mounting is a great benefit when comets are overhead!

The location of the observing site is important and ideally there should be no light pollution, but these days this is rarely possible.  It is however worth making the effort to get to the best site that is readily accessible, particularly if you have portable equipment.  As a guide you should be able to see a 7th magnitude comet in 7x50 binoculars for a comet above 45° altitude.

You will also need some accessories such as an observing log book, a dim red torch and finder charts.  Good preparation prior to observing is very important as you can waste a lot of time looking in the wrong place for a faint comet. GOTO telescopes are a big help as are digital setting circles, but very often the comet is not immediately visible and then detailed charts are essential.  Even then it is still not always obvious which star is which and I often use the traditional method of star hopping so that I am certain of the field.  Using a planetarium style programme such as Megastar or Guide I prepare a wide field finder chart showing the track of the comet with respect to stars down to around 9th magnitude.  For fainter comets I then have a narrow field view showing stars down to around 14th magnitude. The Computing Section also produces interactive charts for current comets.

Simple observations

The first step in observing a comet is simply to find it and confirm that it is (or is not) visible.  This by itself can be a useful observation as a large number of comets are known to outburst, and so may be much brighter than the ephemeris prediction would suggest.  Alerting other observers to such an outburst can allow detailed scientific study of the processes taking place.

The next stage in observing is to try making a drawing.  Drawings are a good way of training the eye to see more detail and also provide a lasting record of what you saw.  They can also be true works of art and perhaps the first of these was the drawing of a comet (which might be Halley’s) by Giotto.  Guidance on drawing techniques is given in many books on observing and the styles most commonly used in comet drawings are the ‘smudged finger’, white on black or isophote methods. Section 4.8 of the Comet Observing Guide has further details and observing forms while the tutorial by Stewart Moore on sketching Deep Sky objects may also be of benefit.

Detailed observations

Visual observers should concentrate on the visual magnitude of the comet, with some associated description of the coma.  Tail observation is better left to electronic observation as this is best suited to measuring lengths, angles and features in the tail.  One point to remember when measuring the position angle of the tail (or other features) is to do so with respect to the celestial co-ordinate system and not with respect to the terrestrial one.

The diameter of the coma can most easily be measured with respect to pairs of stars in the field.  The separation of these can then be measured later using one of the many planetarium programmes on the market.  Another important aspect of the coma is its degree of condensation.  An uncondensed coma is virtually the same brightness from centre to edge and is rated 0, a well condensed comet might be DC5 and a comet approaching close to the Sun often assumes a nearly starlike appearance of DC9.  Comets that undergo outbursts, such as 29P/Schwassmann-Wachmann, often change from nearly stellar to very diffuse in the space of a week or two.  There are illustrations of the scale in the section observing guide.

Figure 3 The light curve of comet 2014 Q2The standard method that the Comet Section use for estimating the total magnitude of a comet is the in-out or Sidgwick method.  This technique was first described by J B Sidgwick in Observational Astronomy for Amateurs, which was the pre-eminent manual for observers when I was at school.  The method is broadly similar to that used by variable star observers, however the hard part is that the in focus comet has to be compared with out of focus stars.  The stars have to be sufficiently out of focus to match the apparent diameter of the coma.  With practice the method becomes straightforward, however it does take a while getting used to.  One important point is to choose the smallest aperture and magnification that clearly shows the comet as this gives the most consistent results.  In general a larger aperture gives a fainter magnitude, however it is possible to correct for this in the analysis.

With comet observing we don’t usually stick to a standard field, as the comet’s position changes throughout the apparition as does its elevation, though some observers use the North Polar Sequence.  The widespread availability of the Tycho and APASS catalogues for comparison star magnitudes has improved the consistency of estimates across widely separated fields for most comets. 

No observer is perfect and we all tend to make small random errors in our estimates, superimposed on a bias from the mean, which give a significant scatter in the light curve.  When all observations are taken together the mean curve is usually very consistent and this allows a good measurement of the magnitude parameters (Figure 3).

Figure 4 Comet 45P imaged by Denis Buczynski on 2017 February 6thDo not worry if your observations are different to those reported on the Internet by other observers.  An experiment during a Section workshop using an image of a comet showed that simultaneous estimates of DC were mostly spread over DC5 to 7, but with a range from 2 to 8; the estimates of coma diameter were very scattered, ranging from 0.3 to 2.4 minutes with a mean of 1.0 and the magnitudes ranged from 10.5 to 13.0 with most between 10.4 and 12.0 giving a mean of 11.7.  On this date visual observers were actually estimating the comet’s magnitude at 8.8, a coma diameter of 5’ and DC of 4, quite different to the experimental values, exemplifying the difference between electronic and visual observers.  Although these differences seem large, most observers are fairly consistent in their reporting, so it is possible to apply corrections to even out the differences between individual observers.  Do go out and give visual observation a try the next time a comet comes within range of your equipment, and send your observations to the visual coordinator.

----------------------------------
Jonathan Shanklin was Director of the Comet Section for 25 years and is now the visual observations co-ordinator.  His first comet was the infamous comet Kohoutek in 1973 and this stimulated a long term interest in visual observations.  Professionally he was a meteorologist with the British Antarctic Survey and discovered the Antarctic Ozone Hole.  After retirement he was recalled to service to make his 20th visit to the Antarctic in 2017/18.

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AA2_20180614_0002

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Observer
Monty Leventhal
Time of observation
13/06/2018 - 22:55
Object
Sun
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AA2_20180613_0001

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Observer
Monty Leventhal
Time of observation
12/06/2018 - 22:35
Object
Sun
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AA2_20180611_0001

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About this observation
Observer
Monty Leventhal
Time of observation
10/06/2018 - 23:00
Object
Sun
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Copyright of all images and other observations submitted to the BAA remains with the owner of the work. Reproduction of the work by third-parties is expressly forbidden without the consent of the copyright holder. For more information, please contact the webmaster.

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