Timing Occultations

[JamesF]

I've been exchanging emails for quite some time with someone in the US who is interested in timing of occultations and it only struck me this afternoon to wonder if anyone on SGL is into that particular branch of astronomy.  I assume there must be specific objects that are targeted to obtain more information about the motion of celestial bodies, but if that's your bag do tell.  I'd be interested to hear more.

James

[Bizibilder]

Maybe someone like the BAA still has an occultation timing programme.  The data would need to be collected and collated to be of scientific use.

[Astrobits]

I have successfully made occultation observations ( both Lunar grazes and asteroidal ) many years ago. At that time there were many short wave transmitters sending out the second beeps. Unfortunately most of these have apparently been closed down in favour of some other methods.

I have been considering  getting back into asteroidal occultations for some time but the problem of timing has arisen. There are obviously stopwatch based methods but these are not necessarily as accurate as one might hope.

There are now several long wave transmissions that are used for radio clocks but they fall below the limits of reception of common LW radios. The exception ( the only one I have found so far ) seems to be in France transmitting at 162khz which most LW radios should be able to pick up providing the signal strength is sufficient.

An alternative approach advocated by IOTA is to use a video camera and a Video Time Inserter which imprints the time from GPS onto each frame of the video. The only problem that I can see with this method is the short exposure of each frame limits the faintest star that can be seen when compared to a visual approach. Also the cost of the IOTA VTI unit is around $300+ with shipping, which added to the video camera cost makes it quite expensive for the few times that an occultation has covered my position on a cloud free night.

It would be nice if an app for smart phones was available that produced the beeps at one second intervals from the GPS signals for the visual observers.

I would be interested in other ideas for the accurate timing of occultations.

Nigel

[JamesF]

Was this purely for your own interest Nigel, or were you submitting data to "somewhere" for collation with data from other observers and further research?

James

[Phil Fargaze]

Hi James, I have been actively pursuing occultations for  about four years now and submit my observations. Primarily, I concentrate on asteroidal occultations and my results get emailed in to the planoccult mailing list, details of which are here  http://www.euraster.net/. On this page you will notice there is a link for the results page which is located centre top. For example if you go to `2015 complete year` and in December, the 4th line down there are the results for (589) Croatia. click on that and there are the results, my name is in there too. From our times, the shape of the asteroid can be determined, which can be seen if you click on `chords` or see here http://www.euraster.net/results/2015/20151220-Croatia_crd.gif 

Tim Haymes of the BAA is the UK coordinator for occultations and he has been a great help to me with what can be a very technical subject. his web page is here http://www.stargazer.me.uk/ 

My equipment is a C9.25 on a HEQ5 mount in an observatory. To that I use a watec 120n+ camera with a video time inserter which uses GPS time, and it is then recorded onto laptop. The results are then analysed by other software after the event to extract times. A positive result is what we all seek but a negative result is just as valuable so they are always reported too. I find this aspect of astronomy very exciting and rewarding and can be done from a light polluted location such as mine ( London Suburb).

[JamesF]

That's really fascinating.  I guess it's one of those areas where amateur astronomers can really contribute to "proper" science because for attempting to map the shape of an asteroid for instance, the more data available (especially from different locations) the better the potential result?

James

[Astrobits]

My data, along with others, was co-ordinated by Danie Overbeek and submitted to-- I'm not sure where, IOTA I suspect. I seem to remember the predictions were from David Dunham? so I guess that is where the data was sent. All my observations were during the 80's in South Africa where it seems to have always been clear unlike here in the Somerset

Nigel

[JamesF]

I remember it being clear here in Somerset once.  One Saturday last October, I think it was...

James

[Phil Fargaze]

Occultations are extra frustrating because it has to be clear at a certain time on a certain day! I get my predictions from a freeware called http://www.occultwatcher.net/ which helps to coordinate observations by letting the users see who else is attempting the observation. And yes, the more observers there are the better the results. Sometimes (rarely) even the moons of asteroids can be detected by this method. Another prediction stream is here http://www.asteroidoccultation.com/ 

For lunar occultations the BAA publish a monthly lunar circular with details contained within that. Also the Society for Popular Astronomy have an occultation section of which I have submitted many observations. They also provide lunar predictions. 

 

[ChrisLX200]

If you have an internet connection the simplest way to achieve millisecond accuracy is to install an NTP daemon on your computer. I have to do that anyway for my mount to achieve the accuracy that it does, and the one I use is Meinberg ( https://www.meinbergglobal.com/english/sw/ntp.htm ) and if you need better accuracy then you can install your own server. Mine keeps my mount's clock accuracy to around 3msec which is good enough. I also search my data for asteroids and the FITS header will include an accurate Time of Observation which is a necessary parameter when reporting to the MPC. If I take video with an embedded timestamp (I do for my allsky cam on a different PC also with Meinberg installed) then any events like meteors I record also have that kind of accuracy, so again it's useful for reporting purposes.

ChrisH

[JamesF]

I'm really pleased I asked about this now.  There's a whole load of stuff going on that I was completely unaware of

James

[Astrobits]

Thanks for that info and link ChrisH.

None of the Asteroid occultation web sites that I have looked at ( IOTA, BAA which refers to EAON ) mention the latest timing possibilities.

Nigel

[laudropb]

Asteroid occultations are only visible along a small track. Many serious observers work in teams who position themselves at different places along the predicted track, then if someone misses the occultation hopefully others will have caught it. Of course a miss also provides useful information. Timing of the occultation is the most difficult aspect.

lunar occultations are very interesting too. If the dark limb occults often the star does not just disappear but flickers out. This is usually a result of the topology of the lunar surface, eg mountains. Many close double stars were also first detected by this method. Try this. It can be great fun.

 

[DaveGee]

On 28/01/2016 at 02:52, Astrobits said:

It would be nice if an app for smart phones was available that produced the beeps at one second intervals from the GPS signals for the visual observers. I would be interested in other ideas for the accurate timing of occultations. Nigel

Hi Nigel,

I found an app for android smartphones that is very useful for visual timing of occultation events.  It's called Time The Sat.  It is designed for visual timing of artificial satellites in their orbit but many of it's features make it a very useful tool.  It's available here...

https://play.google.com/store/apps/details?id=com.satflare.timesat&hl=en

I have tested it and have a write up here...

http://www.kuriwaobservatory.com/pdf_files/TimeTheSat.pdf

It relies on a good data connection to access accurate NTP servers.

If you wish for a GPS-time solution for a visual observer somewhat akin to IOTA-VTI then perhaps GPS-ABC is the answer.  See...

http://www.kuriwaobservatory.com/GPS-ABC.html

Clear skies!

HooRoo

DaveGee

[Astrobits]

Thanks for that Dave. Will have to check this out, could be very useful.

Nigel

[LeoLion]

Have a look at Tim Haymes website  http://www.stargazer.me.uk/asteroids/asteroids.htm .Use the menu on the LH of the screen to view the tools that can be used for occultation work. Follow through the BAA website to the Asteroid and Remote  section and eventually you will find an occultation link on the external website.

The UK hosts an international meeting occultation meeting  http://www.esop35.uk/  in Guilford this August. It should be possible to attend as a day registrant.

Here is a sample of the international JOA  http://www.occultations.org/on/JOA/Vol01/JOAvol1num1.pdf

Hope this helps a bit in updating folks,