Introduction to Observing Occultations of stars by the Moon or Asteroids
also my : Quick Start Guide
A star will
disappear behind the Moons limb during
a Lunar occultation reappearing up to an
hour later. But for an asteroid (
a much smaller object ) the star will reappear
within seconds (1 to 30s) after the asteroid has passed.
use a 30cm F/4 Newtonian allowing observation of 10-11th magnitude stars
with the eye, or 13 -14th magnitude stars by video. Here is the "Once
in a life time" occultation of a naked eye star by asteroid
Roma recorded by Jan Manek (cz)
OccultWatcher is the planning tool ( for Windows) used by occultation enthusiasts, and is recommended to anyone wishing to take asteroid occultation a bit further. Many additional predictions are listed, and what is displayed can be customised to local conditions.
Radio code analogue clocks with accurate 1 sec ticks are guaranteed to be accurate, and can be used to check other time sources the observer may be using. Some clocks with liquid crystal displays howver have a display time lag of 50 to 100ms, or more if used in cold conditions (eg outside in Winter)
Accuracy and certainty is improved when recording events by video camera with a GPS video time inserter (VTI). The WATEC 120N+ ( and similar MINTRON cameras) can record at 25fps for Lunar events or set to integrate (stack) frames for asteroid events. The VTI overlays the exact UT ( to 1ms ) on each field of the recording which can then be replayed to get the event time and its duration. Here is an example of one frame taken from a video of an asteroid occultation (41-Daphne). The drop brightness between "Occulted and uot occulted" may look small on the insert, but is very clear when measured in the image on the right.
video frame above using a GPSBOXSPRITE2
time inserter was recorded on: 2012 Feb 23 at 2045hr
22.5799 sec. Times are reported (rounded) to the nearest 10 ms
web cams are usable for bright objects but not for occultations generally.
BUT this will change as developments (http://www.kuriwaobservatory.com/ADVS.html)
in timing and analysis hardware+software allow the use of digital web
cams (planetary imagers) which operate in 12, or 14 bit.
A Image Source planet webcam can also be controlerd with FireCapture, and the most recent version has a time stamp facility.
web page (http://www.hristopavlov.net/Observations/Positives/index.html)
is particularly helpful, because the analysis software is used
by me and many others.
observations are typical for asteroids, because their orbits
and dimensions are uncertain (hence a reason for observing them) and
the occultation shadow is not where its predicted in most instances.
The star positon also has errors. The errors all add up,so its alwat
a good idea to observe it.
Other observers using video prefer a USB video digitiser and recording to a PC directly using Virtual Dub (Open source). Everyone has there own preferences. There is a purpose build VTI designed by IOTA (http://www.occultations.org/) and made by Videotimers (http://videotimers.com/home.html)
video digitisers: (added Dec 2014)
Here is a mobile camera for bright star asteroid occultations down to magnitude 10, consisting of a 200mm F3.5 telephoto lens (Pentax screw thread) adapter (M42 to C-mount) and a Watec 120N+ integrating video camera. Video is recorded on a Sony TRV22E DV camcorder (video/in)
The predictions and observing opportunities are obtained from Steve Preston (http://www.asteroidoccultation.com/) or by using OccultWatcher software ( http://www.hristopavlov.net/OccultWatcher/OccultWatcher.html)
on Jan 17, 2014:
The British Astronomical Association Handbook contains predictions a year in advance calculated by E.Goffin. These are used for medium term planning of bright events, and OccultWatcher is used day-to-day. A new UK-occultation feed UKOCL for OccultWatcher, provides low probability events for the keen observer to monitor.
The BAA web pages are http://britastro.org/asteroids/Occultations.htm
Lunar occultation predictions are available in the Lunar Section Circular downloadable from the BAA web site, or predicted using free software. These programs are the result of continuous development by the author/programmer:
Occultation WorkBench http://www.softpedia.com/get/Others/Home-Education/Lunar-Occultation-Workbench.shtml