Observing Asteroid Occultations

You’ve probably seen me wittering on about asteroid occultations at some point or other, or you’ve seen the links to my results page on the left. Maybe you’ve even read my Asteroid Occultation 101 page and still have no idea how it’s done or why.

It’s rather complicated but the idea of this post is to try and explain how I observe asteroid occultations.

Let’s have a look at a schematic of my setup. Click to see the full size version.

Schematic of Asteroid Occultation Equipment

I told you it was complicated! Basically what we have here is a computer controlled telescope. The laptop controls the pointing of the telescope mount via software (Cartes du Ciel). This allows me to find and point the telescope at the star I want to observe. The gamepad is used as a remote control for fine movements to align and centre the star in the field of view.

Another piece of software (FocusPal) controls a motorised focuser on the telescope so I can keep the star in focus without having to touch the telescope which would cause it to move and vibrate.

The third bit of the jigsaw concerns the video recording aspect. A very sensitive video camera (Watec 910HX) records what it sees through the telescope, it’s sitting where I would put an eyepiece if I was observing visually. The camera is clever in that it can do internal frame integrations. It can take exposures of up to five seconds allowing fainter stars to be observed. Typically exposures of 0.16s or 0.08s are used.

The video signal passes through a Video Time Inserter (VTI) which adds a GPS accurate time stamp onto the signal. I want to record the video on the laptop so the analogue video signal passes via an Analogue to Digital (A/D) converter to the laptop. VirtualDub software is used to record the digital video signal and because the raw video would result in huge files a non-lossy compression codec is used to reduce the file size somewhat (Huffyuv codec).

Once this is all setup and working and I’ve found the star I want to observe I get a 728×576 25fps video recording of the event. I usually take a four minute recording centred on the predicted time. This allows for time errors and/or the possible discovery of asteroid satellites.

A still image from a typical recording looks like this.

I usually put the target star right in the centre of the frame, as I have done above. It needs to be visible but not saturated. Using the camera controls I can adjust the exposure, gain and gamma settings to get a good signal to noise ratio. The timestamp from the VTI can be seen lower left. The time this frame was recorded was 18:23:02.0866 on the 17th February 2015. Accurate timing is essential for asteroid occultation observations. It can be done with radio signals or even a synced PC clock but a 1 pulse per second VTI makes it a whole lot easier.

A few years ago if the observation was positive (the asteroid passes in front of the star) I would have to bother myself with complicated calculations of internal camera delays (see video exposure time analysis). Thankfully it’s a lot easier now with software which automates a lot of the processes.

Firstly I run the video through Tangra 3. This piece of software measures the light output of the target and comparison stars. If the result is negative the light output of the target star (flux) will essentially be a flat line (with random noise) and that’s the end of the processing. The result is reported to the PlanOccult mailing list as negative.

If the result is positive the light output of the star will drop to zero or to that of the asteroid alone. A light curve of a positive result is shown here.

The cyan line shows the light output of the target star. As the asteroid moved in front of the star the light output dropped to that of the asteroid alone. The yellow, green and pink light curves are for nearby comparison stars which are also visible in the video recording.

As this is a positive result I needed to take the data from Tangra 3 (basically a text file of light output values) and import it into the Asteroidal Occultation Time Analyser (AOTA) module of Occult 4 software. After setting some parameters this very clever piece of code automatically looks for occultations in the data, finds them and works out the time of disappearance and reappearance of the target star. It can then correct the times taking into account the internal time delays of the video camera.

The output from AOTA looks like this.

Hey presto, the times are calculated and all that’s left to do is fill in a report form with the observation details and result and send it off to the PlanOccult mailing list. A few days later the result will appear on the European Asteroidal Occultation Results page (euraster.net). Every so often the results are compiled and appear in a peer reviewed journal with my name in the contributers list for use by professionals and future observers.

Easy innit!

Well it is easy once you’ve got the hardware and workflow sorted. It typically takes me less than 20 minutes from the predicted time of occultation to be up and and running and ready to record. Having a permanent setup helps enormously. It means I have been observing many more low probability events that I wouldn’t have bothered setting up for before. I’m still waiting for my first <10% probability positive result though! In fact positive results are rare, about 1 in 20 of my observations have been positive. But the next one could herald a major discovery. The first set of rings around an asteroid were discovered in 2013 using pretty much exactly the same methodology as described above. Maybe I’ll discover the second…

Sport Is Bad For You

I suppose it had to happen at some time. I have a sports injury. I fully expected to get injured running at some point, everyone seems to suffer injuries running. Cycling less likely, unless I crashed or got knocked off. But injured at table tennis? Wasn’t expecting that. I’ve played league table tennis for 30 years and I’ve never missed a match through injury. I suppose I’ve had a good run so should be grateful for that.

Hearing your calf muscle audibly pop, feeling the pop and instant searing pain is not a good sign. I wasn’t doing anything different to what I’ve done thousands of times before, reaching for the ball to return my opponent’s shot. Maybe I wasn’t properly warmed up and the room was cold. Maybe the 10 mile run the day before and left me vulnerable to injury.

It’s very frustrating as it’s totally ruined by preparation for my first half marathon at the end of March. And it’s quite likely that I won’t be able to run it now. I’m just going to have to see how the injury goes in the next couple of weeks, hopefully I’ll be able to do some gentle exercise quite soon. I might need to get some specialist therapy, e.g. ultrasound, to help the recovery.

Meanwhile I’m hobbling around on a crutch.

2014 Cycling Summary

Time to look back at my 2014 cycling stats.

The major achievement of the year was completing Randonneur Round the Year which is an award for completing a 200km or longer audax in each of twelve consecutive months.

In total I cycled 5,080 miles (8,176 km) which easily surpassed my previous best in 2014 of 4,516 miles. The cumulative monthly mileage is shown in the graph below.

2014 Cumulative Mileage

Other than May 2009 which includes my LEJOG I was ahead of every previous year. I cycled 847 miles in June, my highest monthly total since May 2009.

A heatmap of my cycling in the UK for 2014 shows where I cycled. Areas of yellow and orange show where I cycled most frequently. Purples are roads I cycled once or twice.

2014 UK Cycling Heatmap

As is usual the ‘hottest’ part of the map is close to home including my commuting routes. Several audax rides can be picked out in the Midlands and away rides with CTC Wantage can be seen scattered around the country.

I also went to France with CTC Wantage where we cycled near to Carcassonne with one memorable ride on the French and Spanish coast. One ride in central France isn’t shown in this map of the rides from that trip.

2014 France Cycling Heatmap

In summary my stats for 2014 were as follows.

Rides 172
Days Ridden 120
Total Distance 8,176 km (5,080 miles)
Total Climb 68,274 m (223,996 ft)
Total Time 359h 29m 50s
Longest Ride 276 km (171 miles)

My plans for 2015 took a blow when my brother died suddenly in December, we rode together and had planned to ride the National 400 audax together in July. However I’ve kept my run of 200km audax going and I might attempt back to back RRtY. I also want to try and ride a 300km audax to complete Randonneur 1000 for the season.

Longest Cycle Ride

Yesterday saw me complete my longest cycle ride to date, 222.2km (138.1 miles). I’m trying to do Randonneur Round the Year (RRtY) which is an achievement in audaxing for completing a 200km event every month for twelve consecutive months. I did start in November and then couldn’t do one in December, so I’ve started again in January. I find 200km rides tough, mentally and physically. It’s a long time to be on a bike (around 9-10hrs cycling) and most of it on your own so your mind starts thinking thoughts you don’t need, like ‘why am I doing this?’ and ‘am I enjoying this?’.

This was a normal and pretty easy 100km Audax I’ve done several times before but I made it into an Extended Calendar Event (ECE) by cycling to and from the start (57km each way). This is one way of making recognised 200km routes and rides that count towards the RRtY achievement. I was right on my limit, physically and mentally for the last hour back home. Knowing exactly how much further I needed to go on very familiar roads made the distance seem to stretch out forever!

Next up will be a London-Oxford-London (LOL) ride in March. Wonder if I’ll be LOL at the end of it!

2013 Cycling Summary

With the start of 2014, it’s time to look back on the previous year’s cycling. I’ve been keeping accurate records since September 2008.

Last year was my best ever in terms of distance with 4,516 miles cycled (7,267km). Easily beating my previous record of 3,432 miles in 2011. Despite a poor spring (especially March) we had an excellent summer and I beat my previous mileage records in Apr, Jun, Aug, Sep, Oct and Nov. The graph below shows the cumulative mileage for the last five complete years.

cumulative mileage
Cumulative Cycling Mileage

In 2009 I cycled from Land’s End to John O’Groats and you can see that in the abrupt rise in May of that year. However, a consistent mileage through the late spring and summer in 2013 saw me overtake that line in July. Monthly mileage fell in the autumn with fewer opportunities to get out cycling, but I was pleased to beat my previous best November and had my second best December. I also completed my personal goal of completing at least one 100km or longer audax each calendar month in 2013 although I’m still waiting for my December one to be validated.

A heat map of my UK cycling shows where I cycled in 2013.

Heat Map of UK cycling 2013
Heat Map of UK cycling 2013

Yellows show where I cycled repeatedly. Dull purple is where I only cycled once. Clearly the ‘hottest’ part of the map centers around my commute from home to work in South Oxfordshire. The heat bump to the west of this is club rides with CTC Wantage which usually start from Grove. You can see some away rides, e.g. a 160km audax in the Midlands and rides in the New Forest, Isle of Wight and Mendips. The cluster towards Cambridge was during the family summer holiday. The other obvious route was May’s cycle tour with my brother-in-law along the Welsh Border from Chester to Chepstow.

In addition to the UK miles, I joined the CTC Wantage club trip to Uzes in France. Here we did several rides out from the town. We also did an away day to climb Mont Ventoux.

France Cycling Heat Map 2013
France Cycling Heat Map 2013

In numbers my stats for 2013 were as follows.

Days Ridden123
Total Distance7,267 km (4,516 miles)
Total Climb56,504 m (185,301 feet)
Total Time14 days 5 hrs 34 mins
Longest Ride214 km (133 miles)

It’s going to be a tough mileage record to beat especially if we have bad weather in the spring and summer when most of the cycling gets done!

Table Tennis – Mid-season Review

Most people know I play league table tennis. I’ve been playing the sport since I was about 8-years old. My father played in the Oxford league for many years and my siblings and I were all encouraged to play and we all played league table tennis at some point. I’m the only one still playing and I’ve played in the league since the mid 80s. Originally in the Oxford league for Kidlington Forum and since the early 90s I’ve played in the Didcot league without missing a season. I also played in the Newbury league for several seasons (most recently in Division 1).

As a player I would be classed as a “defender”, i.e. I very rarely attack first in a rally and rely on blocking and chopping my opponents until I force them to make a mistake or lift the ball for me to smash. A match between two defenders can be a very long and tactical affair and might appear “boring” for a spectator but there’s a lot of spin and counter-play involved! I’m often referred to as frustrating to play as I will often get everything my opponent can throw at me back, if you’re an attacking player that can be quite annoying!

Just to explain some of the nomenclature you will see below. A fixture (or tie) of table tennis is played by two teams of three players, there are a total of ten matches per tie. Every player plays each other in singles, i.e. nine matches, and there is one match of doubles. Each match is the best of five games (or sets) to 11pts. In the Oxford league teams play for a share of 4pts depending upon the scoreline. In the Didcot league teams play for a share of 6pts per tie. Promotion and relegation in local league table tennis is not automatic but it is normally expected that the top two teams in each division will get promoted and the bottom two teams relegated. It is fairly unusual for players to play in more than one league, but not uncommon.

The sport is played in the winter between September and April, we’re currently halfway through the 2013/14 season and we now take a break for a few weeks for Christmas. Below is a summary of how it’s going so far.

Oxford League

This is my second season playing for the Viking Sports Club in Headington. After a long hiatus of not playing in the Oxford league I was asked to join by a colleague and ex-Didcot team mate. The clubs are rather spread out geographically and involve quite a bit of travelling to away matches, e.g. to Haddenham, Bicester and Begbroke. We are Vikings B this season and play in Division 2 of 4. We have four regular players so we rotate the squad, by the end of the season we will all have played roughly the same number of matches. Co-incidentally my father played for Vikings B in the late 60s and early 70s and the Viking Club is where I first remember playing as a child.

Last season we finished 3rd and I had a rather tough introduction midway through the season as Division 2 is a strong division. This season I have settled in much better and am currently meeting my personal goal of winning at least 50% of my matches. I’ve won 11 of 21 (52%) and not scored a duck yet which I’m very pleased with. I’ve scored one maximum (winning all three matches in a tie).

The team is top of the division at the midway stage, 7pts clear of 2nd but having played one more tie. Our greatest rivals are probably Forum D who are 8pts behind us but have three ties in hand. We have an excellent chance of finishing in the top two positions and getting promoted to Division 1. The playing standard jumps enormously between the divisions in local league table tennis so although it would be great to go up we will struggle to stay up!

Oxford League Division 2
Oxford League Division 2

Didcot League

Didcot is my “first league”, i.e. if I have fixture clashes Didcot matches always take precedence. After many years playing for Howbery Park in Crowmarsh Gifford, and being secretary for the club, we had to fold when we lost our playing premises and couldn’t find an alternative. I played one season for Moreton but it didn’t work out so when I was asked to join Upton Village Table Tennis Club before the start of last season I jumped at the chance. So this is my second season playing for Upton and I play for Upton A in Division 2 of 5. Last year we had four playing members and rotated the squad. I much prefer playing every tie in Didcot and I sometimes found it hard when I was “dropped” from the team. We finished 5th which was a highest ever league position for the Upton club. We had a rather dodgy home venue last season so it was kind of good news when we were forced to move to better premises this season due to the closure of our old venue. This season we have only three players so we have a regular team and we have built an excellent team spirit and I’m enjoying playing more than ever. I hope it’s a threesome that we can keep together for many years.

Last season I finished with a 64% average (won 25 from 39) which was my best ever season and I set myself a personal goal of 66% for this season. That’s not been going well as so far I’ve won 11 from 24 (46%) including one maximum but I have scored two ducks which I hate doing. I’ve been playing with more confidence recently and I should improve that average before the end of the season but I might have to revise my personal goal down a bit.

Despite my lowly average as a team we have been performing excellently and we had a brilliant start to the season. We currently lie in 2nd place and have played one fewer fixture than the teams in 1st and 3rd. It’s an extremely tight division though, everyone is capable of beating everyone else and it’s far too early to tell whether we’ll hold onto a top two position. We have lost a couple of ties we shouldn’t have so hopefully we can reverse them in the second half of the season. The team currently top will be very hard to overtake, they are clearly the strongest team in the division. We’ve all played more than 20 seasons in the Didcot league and none of us have ever played in Division 1, it would be great to get promoted on merit at least once even if we get hammered every week next season!

Didcot League Division 2
Didcot League Division 2


We were a bit late booking anything for holidays this year and were considering Scotland. We couldn’t face the long drive for 10 days so we hit upon the brainwave of going to Camping de la Bien Assise in Guînes just south of Calais in northeast France. We’d stayed there a couple of times before for one night whilst heading further afield in Europe and had said we should try a longer stay. The drive around the M25 to Dover is hideous of course but 3 hours is better than 6 and with the added excitement of a ferry journey to a foreign country too!

We had a fab time, decent weather (couple of beasty storms as well), nice beaches, good countryside, great campsite, excellent historic sites. Here is a cheesy video which sums it up (thanks to iMovies trailers).

Barbury Bash 110km Audax

This was my third Audax for the 2011 season and the first I’ve entered without my brother. The start is only a few kilometres from my front door so it is a very convenient event for me to enter. There are 110km and 200km events but I’m not quite ready for the step up to 200km so entered the 110km event. The route heads westwards from Milton in Oxfordshire across the Vale of White Horse to Barbury Castle in Wiltshire on the North Wessex Downs.

I was lucky to have a fellow CTC Wantage member to tag along with. He’s ridden the event several times so knew the route well. This meant I didn’t have to refer to the route description sheet at all. He’s also a very strong rider so we held a quick pace.

The route westwards to Wantage along the A417 is a familiar one and also beyond on the B4507 past White Horse Hill, Ashbury and Bishopstone. This is an undulating road but you can keep a good steady pace.

The weather was pretty grim along here, strong headwind and rain but nothing really terrible.

After Bishopstone I was in new territory so I’m glad I had company so I didn’t miss any turns. After several picturesque villages we arrived at the foot of the climb to Barbury Castle. A narrow and straight road means you can see it from a long way away. This is the first time I had climbed the hill so I wasn’t sure what to expect, or how long it was. It’s steep (about 15%) but not all that long so it wasn’t too tricky. At the top was the control point, cakes and refreshments (the café is currently closed).

After a brief stop we took the descent rather steady due to the wet road and loose gravel and stones. After retracing our steps to Chiseldon, quickly now the wind was behind us, we headed to the next challenge of Snap Hill. I found this one quite a bit harder, it’s longer and steeper (17%) than Barbury Castle but once over the top you are rewarded by a very long and fast descent, we kept a constant 30+ mph for quite a distance to Aldbourne.

The third major hill on the route is Marridge Hill. This one is barely worth a mention, much shallower than the other two, quite long but not a severe test other than the legs are pretty tired by this stage.

Big black clouds threatened to drench us as we headed to Eastbury and Great Shefford where we arrived just before the shop shut to grab a sandwich and provisions. We were pretty lucky and missed the worst of the downpours which effected some of the riders behind us on the event.

The final stretch home via Farnborough and West Ilsley is again familiar territory for me. We passed one of my table tennis venues on the way. The A34 was new to me though, a road I have always avoided cycling along as it is extremely busy and basically a motorway in all but name.

The short link between Chilton and West Ilsley is the only way across the Berkshire Downs at this point though (until a new cycle route is hopefully opened nearby). We cycled fast and hard in the rain to get it done quickly. It’s only about 1km and we encountered no lorries.

I put a spurt on for the last few kilometres but rather annoyingly suffered a puncture on Milton Hill with the finish almost in sight. After cursing my rotten luck I stopped and quickly replaced the innertube hoping no other riders would pass me.

The delay was about 10 minutes and I arrived back at Milton as the 3rd finisher in a total time of around 5h15m (I’ll know what time I’ve been given when I get my card back). It was also my quickest 100km cycled in 4h5m37s.

A really good route and an Audax I’ll be doing again. Hopefully the weather will be a bit nicer next time. Not that rain bothers me too much to be honest, once you are wet you are wet. Battling against a headwind is worse.

I’ll be trying to do another two 100km Audaxes this season for the Brevet 500 award.

Cotswolds Cycling

Snowshill Lavender
Snowshill Lavender

Great ride with CTC Wantage today. The Cotswolds (if you don’t know) are an area of outstanding natural beauty which straddles Oxfordshire and Gloucestershire. The landscape is rolling and peppered with picturesque villages with houses built from the golden oolitic limestone which the hills are made from. Oxfordshire is not well known as being a hilly county but the Cotswolds offer some tough climbs, especially on the escarpment side. Even on the dip slope side you will rarely find a road that isn’t going up or down, sometimes steeply.

We started in Burford, one of the larger towns in the Cotswolds and a popular tourist destination. Its iconic feature is the steep high street leading down to the River Windrush. It also has a large free car park. We followed the river to Bourton-on-the-Water, which is hugely popular with day trippers and tourists. On a sunny summer weekend afternoon it can be heaving with visitors. It is very picturesque but pick a quiet day to visit.

The rolling terrain led us past the Snowshill lavender fields to Broadway Tower which stands over 300m above sea level, the second highest point in the Cotswolds. The tower itself is a folly tower built so that Lady Coventry could answer the question whether she could see it from her house in Worcester! She could.

From the tower we took more rolling and quiet lanes to Bibury, another village popular with tourists, before heading back to Burford.

We were just shy of 100km for the day and over 1100m of ascent. I found it quite tough today as I hadn’t got my climbing legs with me but had a 2nd wind at around 55miles and could have kept going for a bit longer. It’s another ride towards my target of E50!

If you’ve not cycled the Cotswolds before it’s well worth doing. The route we chose offers a good tour of some busy and quiet villages sticking to minor roads. A good sample of what the Cotswolds offer without tackling any of the really tough climbs.

Eddington Number

Sir Arthur Stanley EddingtonSir Arthur Stanley Eddington is well known as a British astrophysicist of the early 20th century. The Eddington limit, the natural limit to the luminosity of stars, or the radiation generated by accretion onto a compact object, is named in his honour. He is famous for his work regarding the Theory of Relativity. He was also a keen cyclist.



The Eddington Number is defined as E, the number of days a cyclist has cycled more than E miles

For example an Eddington Number of 70 would imply that a cyclist has cycled more than 70 miles in a day on 70 occasions. Achieving a high Eddington number is difficult since moving from, say, 70 to 75 will probably require more than five new long distance rides since any rides shorter than 75 miles will no longer be included in the reckoning.

I stumbled upon his interesting cycling statistic the other day and was curious as to what my Eddington number might be. I only have accurate distance stats from 2008 but I rarely if ever did long distance rides before then so I’ll just discount anything earlier.

Interestingly it works out that my current Eddington number is 49 (E49) and I’m only 5 rides of greater than 50 miles to achieve a milestone E50.

Not sure whether discovering this little statistic was such a good idea, I’m now motivated to do those 5 rides but then when will it stop? I’m not that far off E60 either!!

P.S. Eddington himself died at E87.

UPDATE – On 25th September 2011 I completed a 171km Audax ride which was my 50th ride over 50 miles. I’m now officially an E50 cyclist!!

UPDATE – On 9th June 2013 I reached E60! It’s going to be tough from here, E65 is probably achievable fairly soon, E70 will take much longer.

UPDATE – On 20th July 2014 I reached E65! It’s still a long while before I achieve E70.

UPDATE – As of 9th November 2015 I am E67. It will still take me a while to get to E70!