The Baxter Garden Observatory, Salisbury - IAU Observatory I74

On clear evenings I'm often to be found in my small home observatory tracking asteroids. In 2011 my observations were deemed good enough by the International Astronomical Union's Minor Planet Center that my home site received the designation I74, meaning I was all set to do proper minor planet and comet astrometry (position measuring). You can find a record of all my published observations on the MPC's website. My telescope (f/3.9 0.25 m diameter) and photographic equipment limit me to observing objects down to a visual magnitude of 20 or thereabouts (which anywhere outside the world of minor planets would be considered really quite faint!) but within this limitation my main activities are:
  • Attempting to confirm possible Near-Earth Objects (NEOs), i.e., asteroids and comets, shortly after they are first discovered
  • Follow-up measurements of recently discovered asteroids so their orbits can be improved as much as possible before they disappear from sight. This increases the chances of being able to find these objects on their second oppositions
  • Providing data to improve the orbits of objects on the MPC's Critical List or unusual minor planets list that are flagged as needing further data, especially for those objects not observed recently
  • Providing up-to-date data on asteroids that might be visited by probes, examined by radar or that might interact with other solar system bodies
Of course, like all amateur minor planet trackers, I quietly dream of one day finding a minor planet that nobody has spotted before. But in my case, with a poor view to the East thanks to the tree you can see behind the observatory, I know that's very unlikely. Alas, alas.

Through a friend, I was approached in 2011 to take part in a two-part interview on amateur astronomy; Guy Consolmagno, author of Turn Left at Orion, provided the first interview and I did the second - talk about going from the sublime to the ridiculous! Anyway, it's worth a quick read if you want to know how the Baxter Garden Observatory got its name (edited version: Baxter is my dog).

Asteroids and comets

I have been named in Minor Planet Electronic Circulars (MPECs) as having helped confirm the following discoveries: 2013 OG, 2012 K74 [second confirmation], 2012 VF82, comet C/2012 S3 PANSTARRS, and 2012 SW20. I was also in an MPEC for the rediscovery of 2005 BW1

The subsections below get updated with news and images about interesting events over time.

Comet C/2012 S3 (PANSTARRS)
This comet was was seen on 27 September 2012 and announced on the Near Earth Object Confirmation page on 28 September. I found it on 29 September, being the fifth observer to measure it. I found it again on 1 October. On this second occasion, there were definite signs of a core with a nebulous surround, which you might just be able to make out in the photo on the left (click to embiggen). Given this, and early estimates of a highly eliptical orbit, I suspected we were looking at a comet, and sure enough when the MPEC annnouncement came out this was listed as a parabolic comet. It won't be one of the most spectacular, as unlike the recently discovered C/2012 S1 it won't get too close to the Sun (perihelion will be over 2 AUs away from the Sun), but it was still a delight to have helped confirm its orbit early on.

OBS I. Walker
MEA I. Walker
TEL 0.25-m f/3.9 reflector + CCD
ACK MPCReport file updated 2012.09.30 01:16:05
P104hnV KC2012 09 29.96217 19 52 21.85 +66 17 00.3 18.7 V I74
P104hnV KC2012 09 29.98174 19 52 20.66 +66 16 33.3 19.6 V I74
P104hnV KC2012 09 30.00126 19 52 19.58 +66 16 08.5 19.3 V I74
----- end -----

OBS I. Walker
MEA I. Walker
TEL 0.25-m f/3.9 reflector + CCD
ACK MPCReport file updated 2012.10.01 22:12:21
COM I think I can see signs of nebulosity. Is this a comet?
P104hnV KC2012 10 01.81016 19 50 42.85 +65 36 59.2 19.8 V I74
P104hnV KC2012 10 01.83728 19 50 41.67 +65 36 24.5 20.3 V I74
P104hnV KC2012 10 01.85529 19 50 40.77 +65 36 00.6 19.2 V I74
P104hnV KC2012 10 01.86367 19 50 40.14 +65 35 50.6 19.5 V I74
P104hnV KC2012 10 01.87074 19 50 39.97 +65 35 40.0 19.9 V I74
----- end -----

Minor planet 2012 SW20
This was a very proud moment. The minor planet with the temporary designation 2012 SW20 was the first newly discovered asteroid where I was named in the Minor Planet Electronic Circular that announced its discovery as one of the first observers. I was particularly pleased to see that the residuals (errors) in my measurements were comparable with, and in some cases lower than, those from many of the more established (indeed, professional) surveys. Mine was the smallest telescope used of all the early observers; some were using scopes with mirrors up to 2.4 metres in diameter, as opposed to my mirror of 20 cm.

The image on the left is cropped from a composite photograph made up of many short exposures, stacked together so that the background stars seem to move and the asteroid stays still. The asteroid is marked with two black lines in this picture to make it easy to find. This is totally representative of the kind of images used to measure the positions of asteroids.
This night I seemed to get an unusually high number of satellites crossing my field of view, which really messes up the images, as you can see on the left

Minor planet 2012 QG42
The asteroid with the provisional name 2012 QG42 was flagged shortly after its discovery as a priority target for astrometry. A "Potentially Hazardous Asteroid" (PHA), a call went out on the Minor Planet Mailing List for people to help with observations as soon as possible so the asteroid's orbit could be better calculated.

My first two attempts to track the asteroid failed. On 7 September 2012 I managed to get a series of images, but I had some internet connectivity problems which, apparently, left my computer's clock slightly out of sync. My observations of 2012 QG42 were sent back by the very diligent workers of the MPC with the subject line "Bad obs" and the comment "Off by ~ 3" in R.A. (time problem?)" [This kind of careful checking is why getting observations accepted by the MPC is seen as equivalent to a peer-reviewed academic publication]. I switched my computer's timekeeping from Dimension4 to Meinberg's NTP software. I went out again the next night and this change in the software made all the difference. My observations of 2012 QG42 were not only accepted, but those - and the observations of several other asteroids I made that night - were amongst the most accurate I'd produced. The NTP software was definitely the right move.
This composite of around 240 8-second exposures shows the path of 2012 QG42 as it moved across the sky. It's off-centre because, this early after the asteroid's discovery, the predicted orbit wasn't that accurate; my software expected it to be closer to the centre of this frame. Click the image for bigger.
Here you can see an animation of the same data. Stacks of 32 images were created using Astrometrica with each stack centred on the asteroid (which is why the stars trail and the asteroid remains a dot). Again, click for full size.

Equipment and Software

Although I'm trying to do relatively serious stuff at the BGO, the equipment is all available to the amateur.


The following equipment is housed in a 2.2m Pulsar dome.

  • Skywatcher Quattro 254 mm telescope (nominally f/4, but really f/3.9)
  • Skywatcher HEQ5 Pro German equatorial mount
  • Brightstar Mammut Lyuba CCD camera. Affordable, and pretty sensitive. The only downside is its interlaced chip, but this limitation disappears, really, as I almost always work with stacked images
  • Finderscope guider with QHY5-II CMOS camera


Astronomy can involve a surprising amount of specialized software. I use the following programs in the observatory, running on a fairly ordinary laptop.

  • Planetarium, telescope control and observation planning: SkyTools. I've tried various other programs that offer similar functions but none match SkyTools for me. Perhaps the killer function, which more than anything stopped me jumping ship to TheSkyX, is the highly accurate display of what I should be seeing on the CCD image. Knowing exactly what I should be seeing through the scope, accounting for temperature, light pollution and so on, makes getting the scope exactly on target up so much easier.
  • Telescope guiding: PHD Guiding. It just works. It's great. It's free. Guiding uses a second telescope and camera attached to the main scope. No mount can follow the stars' movement perfectly. PHD scans the image from this guide camera for movement and, if it detects the stars moving, issues commands to the mount which compensate for this undesirable motion.
  • Image capture and camera control: Nebulosity. From the same author as PHD (who shares with me the unusual situation of being a professional psychologist with a serious interest in astronomy). Like PHD, it's easy to use and just works.
  • Astrometric and photometric analysis: Astrometrica. Superb. Takes some learning, but then it's a serious tool. And once you've understood it, it makes astrometry a breeze.
  • Clock synchronization: NTP. I found it more successful than alternatives like Dimension4 and Tardis. I regularly check whether it's working by visiting
  • Low-level communication between computer and hardware: ASCOM drivers. This system is the de facto standard for letting PCs talk to astronomical hardware
  • Mid-level telescope control: EQMOD. Provides a really powerful tool to control and calibrate the telescope's pointing when you have a Synta mount such as a Skywatcher.
  • Plate solving and fine tuning of telescope pointing: AstroTortilla. This is a very new piece of free software which is really quite amazing. It takes quite a bit of learning and tweaking to get the best out of it, but once set up it does amazing things. It can take a photo of the iew through the scope, calculate from the patterns of the stars where the telescope is actually pointing and using this, move the scope to exactly where it should be. Also does other clever things like automatic polar alignment. Highly recommended.

Other images - click any for larger versions

The 2013 nova in the constellation Delphinus
The Double Cluster in Perseus
Part of the the Veil Nebula in Cygnus. This bit is often called the Witches Broom. Not a great photo - this was more an experiment that an attempt at a proper photo and doesn't have too many data in it
The moon Io just begins to cross the face of Jupiter (the light "bump" on the bottom-left). The dark circle near the centre is Io's shadow. This picture was taken with a simple, cheap webcam. It was a period when Jupiter's Southern Equitorial Belt had disappeared, as it tends to from time to time, which is why there is only one broad red stripe across the planet.
Yes, the moon! Worth clicking this for the full-size, as it's a big, 2000x2000 pixel image made as a mosaic of several high-res images. Look down the terminator (the shadow line) and about two-thirds of the way down you can see the Lunar X: a chance arrangement of crater-edges which, when the light is just right, form an X shape