P20121018 Occultation October 18, 2012

(last updated 2012 09 19)



Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of Pluto's shadow. The northern and southern limits correspond to a radius of 1400 km. The upper and lower dashed lines indicate 3-sigma errors. The shaded area represents where the sun is more than 12 degrees below the horizon.
Table 1: Prediction Details
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)

2012 October 18 04:38:54± 00:01:331 UT

Pluto Minimum Geocentric Separation 0.060± 0.0331 arcsec
Position Angle (Pluto relative to the star; measured north through east) 9.37 degrees
Geocentric Velocity 15.49 km/sec
Occultation Star USNOB-Rmagnitude 15.42

1One standard deviation of random error.
2The UCAC bandpass (579-642nm) is between V and R.

Table 2: Reference Star Position
Reference star position:
(UCAC2, at epoch of event)
RA (h:m:s; J2000) Dec (d:m:s; J2000) Notes
P20121018 Catalog 18 29 43.3447± 0.112 -19 44 12.3500± 0.706
P20121018 Measured3 18 29 43.3840± 0.0604 -19 44 12.778± 0.021
From 65 Lowell 42-inch Telescope frames. See note 4; See Note 6
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body RA (arcsec) Dec (arcsec)  

–0.0931± 0.0138

+0.169± 0.024 From 65 Lowell 42-inch Telescope frames. See note 4; See Notes 5 and 6

3Measured position corresponds to RA offset of +0.5549'' and Dec. offset of –0.428''.

4All "offsets" are defined in the ("corrected" – "reference") or ("observed" – "calculated") sense. The offsets should be added to reference positions to get the measured positions, which we use to calculate the prediction.

4Data analyzed using UCAC2 reference network. A weighted average of the data from the two telescopes was used to calculate the RA and DEC. The errors given are 1 standard deviation.

5The reference positions for Pluto and Charon are those given by JPL Horizon's ephemeris (Pluto source file: PLU017; Earth center source file: DE405). Our residual model is based on the assumption that the same offsets in RA and Dec apply to both Pluto and Charon.

6Data from the Lowell 42-inch telescopes taken when both Pluto and PC20121002 were both in the same image.


Table 4: Site Information

East Longitude

Site Altitude6


Pluto Distance7




–156 15 24
20 42 24
2870 N.
center of Earth
1423 S.

6Altitude of each observatory is measured in kilometers above sea level.

7"Distance" refers to the closest approach distance of the "Site" to the center of Pluto's shadow in the shadow plane. The errors on all closest approach distances are ±787 km (one standard deviation). "S." means the site is south of the center of Pluto's shadow. "N." means the site is north of the center of Pluto's shadow.

Table 5: P20121018 Occultation Predictions for Individual Sites

Immersion (UT)9
Mid-Time (UT)


Pluto Altitude


9The errors on all times are ±1:33 (1 minutes and 33 seconds; one standard deviation). The solar altitude is given for locations where it is relevant (solar altitude greater than -18°). No entry in the immersion and emersion columns indicates that the occultation is not predicted to be visible at that site.


Last updated by Carlos Zuluaga (czuluaga@mit.edu) 2012-09-19 2:20

Please direct all inquiries to PAL (planetary-astronomy@mit.edu)