Observing near Ear ving near Ear ving near Earth asteroids by etssetcf


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									                      THE BAA OBSERVERS’ WORKSHOPS
               Cambridge                                       Winchester                                             York
             2003 February 15                                   2003 April 26                                 2003 September 6
                                     Milton Keynes                                    Nottingham
                                      2004 February 28                                  2004 April 24

   Observing near Earth asteroids
   Observing      Earth asteroids
   by Roger Dymock                                                                                       Workshop No. 5:
                                                                                                Nottingham 2004 April 24

I explain to potential asteroid observers                                    (114mm) reflector. A     clear when there is a full Moon?’ Some of
how they might progress from visual                                          good telescope but       this at least may soon change as I am in the
observing to CCD astrometry and                                              rather heavy, and it     process of setting up my study PC and
photometry. The presentation covers my            had to be stored in a corner of the lounge so       observatory laptop for remote control of
own experiences observing main belt               that I could lift it out into the garden            the telescope and CCD camera. While on
asteroids and imaging near Earth asteroids.       through the patio doors. The TAL was                the subject of cold nights it is worth
This presentation can be viewed in its            followed a year later by an Orion 10-inch           mentioning that all my equipment is mains
entirety on my Near Earth Asteroid (NEA)          (250mm) reflector. The difficulty of moving         powered, since batteries are expensive and
website.1 Links to the sites mentioned in         this fairly large telescope and other               quickly die in the cold.
this article and a fuller explanation of the      observing paraphernalia in and out of the
methods described here can also be found          house tended to limit my observing to
on this website.                                  evenings of absolutely certain clear skies,
                                                  and thus a permanent outside location
                                                  became a necessity. The ‘Observapod’ was            Observing main belt
                                                  constructed in 1999.2 At this time I also
                                                  made the move from visual to CCD                    asteroids
What, when and why?                               observing (using a Starlight Express MX516
                                                  camera) and the observatory became even             Magnitude estimates
                                                  more necessary in order to be able to leave
Beginning                                         all the electronics permanently connected.          This is probably the easiest way to start
                                                  The pod, telescope and associated equip-            observing asteroids visually. To find them
After completing a basic astronomy course         ment are shown in Figure 1.
at the Hampshire Astronomical Group’s                                                                 you need a star charting program such as
                                                     Hardware requires software and my                Megastar and the latest orbital elements.
observatory, a small group of attendees           current packages are
decided to continue observing on the                                                                  These can be found on the Minor Planet
evening previously set aside for the course.         Megastar for plotting asteroid tracks            Center (MPC)3 or the Lowell Observa-
We would observe any objects of interest             Astroart for imaging and tracking                tory4 websites. The asteroid’s magnitude
as described in magazines such as Sky and            Astrometrica for astrometry                      can be estimated by comparing its
Telescope.                                           AIP4WIN for
   The first asteroid we observed was (4)               photometry
Vesta – not terribly impressive, just another        Guide for plotting
‘star’, and we weren’t even sure we were               astrometric
looking at the right object. A few nights later        measurements
I received a phone call from one of the              TAC32 for updating
group to say that he had observed the                  the PC clock from
asteroid again and it had moved, so we were            a GPS receiver.
observing the correct object after all. This      The ‘why’ in the
was about the time asteroids were in the          section title is ‘Why in
news due to the possibility of impacts            the name of sanity am
wiping out large proportions of life on           I out here freezing my
Earth, and I was hooked.                          crown jewels off when
                                                  I should be in a nice
                                                  warm bed?’ or ‘Why
Equipment                                         does it always cloud
                                                  over just as I have got
My first telescope proper, purchased in           everything set up?’ or
1996, was a Russian TAL 4.5-inch                  ‘Why is it always                          Figure   1. MPC observatory code 940.

J. Br. Astron. Assoc. 115, 1, 2005                                                                                                              39
Dymock: Observing near Earth asteroids
                                                                  system. Moving                  asteroid was imaged for a period of one
                                                                  outwards from the               hour on two different nights, approxi-
                                                                  Sun we have near                mately twelve images being obtained
                                                                  Earth asteroids, the            each hour.
                                                                  main belt between            4. Three images, approximately fifteen/
                                                                  Mars and Jupiter,               twenty minutes apart, were selected
                                                                  Centaurs amongst the            from each hour’s results and processed
                                                                  gas giant planets, the          using COAA FITSX (I now use
                                                                  Edgeworth−Kuiper                Astrometrica) to determine the positions
                                                                  belt beyond Pluto and           of the asteroids.
                                                                  the far distant Oort
                                                                  Cloud, most of which         5. The results were submitted by email to
                                                                  are actually comets.            the MPC, and after a nail-biting few days
                                                                     Near Earth                   I was assigned the observatory code 940.
                                                                  asteroids inhabit a             An observatory code is specific to an
 Figure 2. Light curve for the main belt asteroid (250) Bettina. variety of orbits:               observer and location. Changes to either
                                                                  Arjunas, always                 will require a new code.
brightness with some or all of the stars in  closer to the Sun than the Earth; Atens,
the field of view. Slightly defocusing helps Earth crossers but spending most of their
with the comparison of stars which are       time inside the Earth’s orbit; Apollos, ditto     Imaging tips
almost the same magnitude as the asteroid.   but mostly outside; and Amors which are
The Asteroids and Remote Planets Section     found between Earth and Mars.                     Correct setup is all-important for accurate
(ARPS) Director, Andy Hollis, will be                                                          astrometry.
pleased to receive your estimates.
                                                 Obtaining an observatory code                 PC clock set to correct time
                                                                                               Good polar alignment accurate tracking
Occultations                                     Why do you need one?                               sharp images
                                                 The MPC issues an observatory code in         Good focus sharp images
Occultations of stars by asteroids can also      recognition of the accuracy of your           Correct exposure times avoid saturation
be observed, predictions being available         astrometry. Once you have such a code         Application of dark frames and flat fields
from the International Occultation Timing        your observations of asteroids (or comets)         sharp images
Association.5 If several observers time the      may be submitted to the MPC.                  Do remember to autosave your images – it
same event the approximate shape of the             Astrometry is the measurement of the       is no fun having nothing to show for an
asteroid can be determined.                      position of an asteroid or any other          evening’s work.
                                                 astronomical object.6 Accurate astrometry
                                                 enables the orbit of an asteroid to be
Light curves                                     defined and subsequently refined. The         Processing tips
                                                 longer the period of observation the better
Asteroids rotate, many in just a few hours.      defined will be the orbit. (Initial orbit     Image calibration, the application of dark
By obtaining CCD images over such a              calculations, which by definition are not     frames and flat fields, will much improve
period and measuring the magnitude of the        well defined, are often the source of media   the quality of the images and thus
asteroid on each image a light curve can be      speculation as to possible impacts with       astrometric accuracy. It is worthwhile
obtained (Figure 2). Such data assist            newly-discovered NEAs.)                       checking your results against the track
professional astronomers in determining                                                        predicted by Megastar or by the MPC
the rotational period, pole orientation and      How do you get one ?
                                                 There are three steps to obtaining an         Ephemeris Service before sending them to
shape of the asteroid.                                                                         the MPC.
                                                 observatory code: imaging a number of
                                                 suitable asteroids, measuring their posi-
                                                 tions on the images obtained and submit-
                                                 ting those measurements to the MPC. I         Submission tips
Imaging near Earth                               went about it as follows.
                                                                                              The MPC now handles incoming reports
asteroids                                        1. A planisphere was used to determine
                                                    which constellations
                                                                                              automatically so it is very important to get

                                                    were best placed, i.e.
What and where?                                     in the SE to allow
                                                    the maximum
I use the term ‘imaging’ because it is              number of nights’
unusual to be able to observe these objects         observation of a
visually. One exception to this rule was            particular asteroid.
2002 NY40, but if you do see one the
dinosaurs in Jurassic Park might well be         2. Six mid-numbered
running for cover again!                            asteroids between
   Asteroids are the leftovers from the             magnitudes 14 and
creation of the solar system – the builders’        16 were selected,
rubble − and come in three flavours, iron,          using Megastar to
stony and stony-iron. If you have                   plot their positions.
purchased a new house you will know that         3. Imaging was
builders leave all their rubbish in one place,      spread over
namely your garden. However the builders            approximately six
of the solar system were much more even-            weeks during Oct/
handed and spread the rubble all over the           Nov 2000. Each          Figure 3. An Astrometrica Track and Stack composite image.

40                                                                                                           J. Br. Astron. Assoc. 115, 1, 2005
                                                                                                    Dymock: Observing near Earth asteroids
the format right. Details can be found on      5. Calibrate and analyse the images. After      appears to be a new object you may
the MPC website.7 I submit my observa-            the application of dark frames and flat      have discovered a supernova, or even an
tions as an email attachment generated            fields Herbert Raab’s superb Astromet-       asteroid which is heading straight for
using Microsoft Notepad. That email and           rica software makes the next stage           Earth!
attachment are then used as a template for        simple. NEAs move quite quickly and
future observations. Don’t worry unduly           it is thus necessary to stack a number
about making a mistake − the MPC will             of short exposure images, taking the         And finally...
put you right if needed.                          motion into consideration. Astrometri-
                                                  ca’s Track and Stack feature allows this     Do make a start and share your observa-
                                                  to be done with ease. The stars appear       tions with others, and don’t be too worried
                                                  as lines of images and the asteroid as a     about submitting them to the relevant
                                                  single point (Figure 3).                     organisation. There is a lot to learn (and
Follow-up,confirmation                         6. Verify measurements. A useful check of
                                                                                               money to spend) so take things a step at a
                                                                                               time and don’t be afraid to ask for help.
and discovery of near                            your measurements can be made by load-
                                                 ing them in to Guide. Assuming that the
                                                                                               And when you finally know it all, please
                                                                                               do be prepared to help those who don’t.
Earth asteroids                                  images have been obtained at regular inter-
                                                 vals the plot should show equally spaced
                                                 positions more or less in a straight line     Address: 67 Haslar Crescent,Waterlooville, Hants
These three aspects of NEA observation                                                         PO7 6DD. [roger.dymock@ntlworld.com]
                                                 (Figure 4). The gaps are due to some im-
have increasing degrees of difficulty. Only
                                                 ages being discarded.
the first will be described in detail since
this is the most straightforward and my        7. Submit results to the MPC. Results are
setup is not really suitable for the others.     submitted as previously described. Later      References and websites
                                                 you can check the Minor Planet Electronic
                                                 Circulars (MPECs) and the Near Earth           1 NEA        homepage:      http://homepage.
Follow-up observations                           Dynamics website10 to see if the meas-         2 Dymock R., ‘Observapod, a GRP
                                                 urements have been accepted.                      observatory’, J. Brit. Astron. Assoc.,
The procedure for making such observa-                                                             111(4), 199 (2001)
tions is:                                                                                       3 Minor Planet Center: http://cfa-www.
                                               Confirmation and discovery                          harvard.edu/iau/mpc.html
1. Select a target. Suitable targets depend-                                                    4 Lowell Observatory: http://asteroid.
   ing on the limiting magnitude of your                                                           lowell.edu/asteroid/loneos/loneos_disc.
                                                Details of recent discoveries can be found
   setup and the region of the night sky                                                           html
                                                on the NEO Confirmation page.11
   available can be selected from the                                                           5 IOTA, European section: http://mpocc.
                                                   Although I have tried a couple of times
   Spaceguard Priority List which can be                                                           astro.cz
                                                to image asteroids listed on this page I
   accessed via the NEO Coordination                                                            6 James N. D., ‘An introduction to astro-
                                                have not been successful. The asteroids            metry’, J. Brit. Astron. Assoc., 114(1), 29
                                                have either been too faint or too far from         (2004)
2. Obtain orbital elements and an               their predicted track. UK amateur Peter         7 MPC submission details: http://cfa-www.
   ephemeris from the MPC.9 It is               Birtwhistle has been very successful in            harvard.edu/iau/info/OpticalObs.html
   necessary to do this as orbital elements     this field and is highly regarded world-        8 NEO Coordination System: http://space
   are continually being updated as the         wide by both amateur and professional              guard.esa.int/SSystem/SSystem.html
   orbit becomes better defined. Choose the astronomers. To see how it is done visit            9 Orbital elements: http://cfa-www.harvard.
   ‘MPC-8’ line option on the web page to       his website.12                                     edu/iau/MPEph/MPEph.html
                                                                                               1 0 Near Earth Dynamics: http://newton.dm.
   obtain both elements and ephemeris.             There are two other lists of potential          unipi.it/cgi-bin/neodys/neoibo
                                                targets on the NEO website, ‘NEOs not          1 1 NEO Confirmation Page: http://cfa-www.
3. Load the elements into Megastar and
                                                seen recently’ and ‘Bright recovery                harvard.edu/iau/NEO/ToConfirm.html
   plot the predicted track. Any star
                                                opportunities’ which are worth a visit by      1 2 Peter Birtwhistle: http://www.birtwhi.
   charting program will suffice but I find
                                                those who can image faint objects.                 demon.co.uk/index.htm
   Megastar easy to use.
                                                   It is always worth checking your            1 3 Minor Planet Checker: http://scully.
4. Take the images. Image along the line of     images to see if there are any moving              harvard.edu/~cgi/checkmp
   the predicted track as described under       objects other than the one you are
   ‘Obtaining an observatory code’ above.       looking for. This can be done by blinking
                                                                       the images – a series
                                                                       of four is preferable
                                                                       as this considerably
                                                                                                GREEN WITCH
                                                                       lessens the chance
                                                                       of hot pixels or
                                                                                                Cambridge Astronomy Centre
                                                                       blemishes being           Telescopes & Binoculars
                                                                       mistaken for an           Unit 6 Dry Drayton Industries,
                                                                       asteroid. Peter                Cambridge CB3 8AT
                                                                       Birtwhistle discov-
                                                                       ered 2004 DN25 in
                                                                                                A well-stocked showroom,
                                                                       this way when            warm welcome & Less10%
                                                                       imaging 2004 CK3.                           to B
                                                                       The MPC’s
                                                                                                friendly advice.
                                                                       MPChecker                     FREE PARKING       es
                                                                       facility13 can be
                                                                       used to eliminate            01954 211288
                                                                       known objects.           Also mail order and on-line sales
                                                                       However if it             www.green-witch.com
       Figure 4. A plot of asteroid positions made by Guide.
                                                                       doesn’t move and
J. Br. Astron. Assoc. 115, 1, 2005                                                                                                          41

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