Observing Occultations Primer

Predictions:  The IOTA software creates predictions based on the current orbital data. 

	Click this link http://lunar-occultations.com/iota/asteroids/astrndx.htm to open another browser window with the IOTA site.  Select any of the predictions for reference.
	Click this link http://asteroidoccultation.com/asteroid_help.htm to open another browser window with an explanation of the prediction data.
	http://lunar-occultations.com/iota/occult3.htm is the link for the free software

Path notes:

	Imagine a lumpy potato casting a shadow.
	Move that potato and the shadow follows those movements.
	For the duration of the event, the potato is frozen in place.
	Putting observers in brackets perpendicular to the path (groups of red dots above) will "slice the potato" and define small part of the asteroid's profile.  Combining the data (stacking the slices) gives us a rough shape of the asteroid.
	The more slices, the more detail we can gain.

	Near misses define the outer limits of the asteroid size.
	Grazing occultations define profiles in high detail.
	Full slices define a small section
	The time it occults the star fixes the asteroid in the sky.  Taken with other observations, that helps refine the asteroid's orbit.

Ideally, groups would assign people along the center, out to the edge of the shadow, and just outside the predicted path to give full coverage.

Each person within a group would observe a slightly different profile of the blocking body.  For a 50km-wide path, observers spaced 7-10km apart would give useful profiles.

Look up the finder charts and familiarize yourself with the star and the surroundings.  (See the "equipment required" {below} for location of the predictions.)

If possible, view the star a few nights before the event.

Test your equipment well before the event.

Gather everything you'll need in a kit so you're sure you bring everything along.

Practice with the reaction testing software - http://lunar-occultations.com/iota/aops.htm

Practice observing and finding the star.

Equipment Required:

	Telescope - Motorized helps, but any scope that can see the target star will do.
	Timing Device Normally a radio tuned to WWV (short wave) If coordinated, a local FM radio can substitute
	Voice Recorder with microphone.  Usually a standard cassette or mini voice recorder.
	Occultation info (finder charts, timing info) with recent updates from: Preston - http://asteroidoccultation.com/ IOTA - http://lunar-occultations.com/iota/asteroids/astrndx.htm Mally - http://www.eclipsetours.com/events.html WinOccult generated updates http://lunar-occultations.com/iota/occult3.htm

Process:

	Tune the radio to WWV and set the volume so the tape recorder can record it and your voice.
	Use the finder chart and set the scope to center on the star.
	When the star winks out, call "out".  When the star reappears, call "in". A clicker of some sort would help increase the accuracy of the timing by producing a quicker sound.
	Ensure the timing ticks from WWV are recorded both before and after the event.

At the most basic, the star helps outline the blocking object.  This will define:

	The orbit, size, and shape of the blocking object
	The mountain and valley profile of the moon (during a grazing occultation)
	Small moonlets of asteroids
	Close companion stars that can't be split any other way
	Redefine the star's position

If the dark object is airless, the occultation appears like switching off a light.

If the dark object has an atmosphere, the occultation is likely to dim or change, then wink out, then reappear dim and then come back to the original magnitude.   Sometimes, scientists can read the change in the light spectrum and determine the gasses in the atmosphere.  Most of the time, this can help define the depth of the atmosphere.

Asteroids & airless moons - it will suddenly blink off and back on

Very close, very large stars can sometimes produce a stepped event where the star gradually disappears rather than winking on or off. 

Planets and moons with an atmosphere will also dim gradually.

Occultations happen randomly throughout the surface of the Earth.  Some will happen in your neighborhood and your backyard.

Professional astronomers are collected at large observatories (Hawaii, Chile, the Rockies, & sites in Europe & Japan) or at universities.  They or their equipment are likely to be too busy to observe occultations.  Their equipment may not be suitable for occultation observations.

Amateur astronomers are scattered around the world and have equipment suitable to occultation observation. 

Amateurs are also willing to donate time and effort to the project.

The observations return valuable information to expand our scientific knowledge.

This knowledge may help scientists defend the Earth from encroaching asteriods!