The following describes the format of the planetary occultation predictions which are available for download from:

• Planetary Occultations for Australia and New Zealand

Planetary occultation predictions generally consist of one sheet containing header information, a world map showing the predicted occultation path across the Earth, and two charts showing the occultation starfield.

HEADER INFORMATION

This gives the (usually, minor) planet's number and name, and the name of the star to be occulted. The star's name is usually the catalogue name (e.g. PPM for the Positions and Proper Motions Catalogue) followed by its number within the catalogue. Immediately following the planet and star name are the date of the event (NOTE: Universal Time) together with the time of closest geocentric approach. (i.e. closest approach to the centre of the Earth). However, this time is NOT usually the time of occultation for your location - see below.

Under the heading "Planet" the following data are given:

• V.mag : Visual magnitude of the planet
• Diam : Expected actual diameter of the planet in kilometres, and apparent diameter in seconds of arc
• Greek Mu : Motion at closest approach, in seconds of arc per hour
• Greek Pi : Horizontal equatorial parallax in seconds of arc
• Ref. : Source for the orbital elements used. (MPC = Minor Planet Circular)

Under the heading "Star" are given:

• Source cat : Source catalogue used for the star position
• Greek Alpha : Right Ascension (J2000.00) at the epoch of occultation
• Greek Delta : Declination (J2000.00) at the epoch of occultation
• V. mag : Visual magnitude of the star
• Ph. mag : Photographic magnitude

The last line of the header contains information about the occultation:

• (Greek Delta)m : Drop in magnitude if an occultation occurs
• Max. Dur. : Maximum duration for an observer on the central line (in seconds)
• Sun : Distance of the Sun (in degrees) from the star
• Moon : Distance of the Moon (in degrees) from the star, and illuminated fraction (in %) of the Moon

NOTE: For bright stars and faint minor planets the magnitude drop may be such that an observer with a small telescope will see the star disappear completely.

THE WORLD MAP

This shows the Earth as seen from the star, i.e. the centre of the disk is the point on the Earth's surface where the star is directly overhead. The night side is the part within the heavy lines and is shaded slightly.

The shadow path is indicated by the dark central line; tick marks appear at regular intervals. For large diameter minor planets (e.g. Pallas) you can sometimes see separate lines for the northern and southern edge of the central line track. The direction of motion is shown by an arrow on the end of the track. The dashed lines show the position of the central line if there were a shift of one arcsecond perpendicular to the predicted shadow path. i.e. the dashed lines show what would be the path should there be a combined error of one arcsecond in the star's position and/or minor planet's ephemeris.

The times written at the bottom of the chart give the first and last tick marks on the path, plus the interval between tick marks.

REALLY IMPORTANT NOTE!:

The time given at the head of the prediction is not usually the time at which you should expect the occultation to occur. This time is in fact the predicted time for a person in the centre of the Earth's hemisphere facing the star. If you are much distant from the centre of the disk, the predicted occultation time will also be different. Here's how to work out the time for your location:

• Note the text printed below the chart. It might say something like: "13h24m00s - 13h48m00s; int. 2m"
• In this, the first time (e.g. "13h24m00s") is the time of the start point of the track.
• The second time (e.g. "13h48m00s") is the time of the end point of the track.
• The third figure (e.g. "int. 2m") is the interval between tick marks along the track. This is usually in minutes, but can sometimes be 30 seconds.
• Now, note the direction in which the occultation shadow is travelling and count tick marks from the start of the track until you get to the part of the occultation band closest to your location. So now your predicted occultation time will be the (number of ticks) x (tick interval) + (start time).
  
  For example, using the figues above, say you counted five tick intervals along until you came to the part of the track closest to your location. Your predicted time would then be (5) x (2 minutes) + 13h24m00s = 13h34m.

THE SMALL STAR CHART

This shows a portion of sky 15 degrees x 15 degrees. Only stars of visual magnitude 7.0 and brighter are plotted. The dashed rectangle indicates the part shown by the larger chart.

THE LARGE STAR CHART

This shows the star to be occulted encircled in the middle of the chart. A visual magnitude scale is shown at right. The star chart also shows the path of the minor planet with crosses indicating its daily positions at zero hours U.T. over the days preceding the event.

NOTE: be aware when using the star charts that Edwin Goffin's computer-drawn charts do not allow for the convergence of RA lines towards the pole. Although this has little noticeable effect within 30 degrees of the equator, it becomes quite noticeable by 45 degrees and very noticeable by 60 degrees. This can cause problems in attempting to recognise areas on the charts.

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