P20160822 Occultation August 22, 2016

(last updated 2016 07 18)

Finder Charts


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 0 degrees below the horizon. The red lines indicate Charon's northern limit, centerline, and southern limit using a radius of 605 km.
Table 1: Prediction Details
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)

2016 August 22 11:15:41± 00:00:571 UT

Pluto Minimum Geocentric Separation 0.015± 0.0431 arcsec
Charon Geocentric Mid-time (yyyy month dd hh:mm:ss)

2016 August 22 11:31:45± 00:00:571 UT

Position Angle (Pluto relative to the star; measured north through east) +166 degrees
Geocentric Velocity 15.62 km/sec
Occultation Star UCAC2 magnitude 16.132
Occultation Star Measured magnitude (SARA-S Bessel R) 16.19

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
P20160822 Catalog 19 04 26.1917± 0.1470 –21 19 07.526± 0.137
P20160822 Measured 19 04 26.1583± 0.0133 –21 19 07.939± 0.025
From 7 USNO 61-inch 1chip frames
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body RA (arcsec) Dec (arcsec)  

+0.0483 ± 0.0360

–0.051 ± 0.036 See Notes 5 and 6

3Measured position corresponds to RA offset of –0.4666'' and Dec. offset of –0.4126''.

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: PLU043; Earth center source file: DE431). 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 USNO 61-inch, Lowell 42-inch telescope, SARA-South 24-inch telescope, and Lowell Astrograph telescopes over the span of 5 years were reduced with respect to stars in the UCAC2 catalog. A model was developed to fit the residuals obtained from our measured positions compared to that of the object's JPL ephemeris. All residuals obtained from the different telescopes were consistent with the model. The model includes the first-order effects of errors in the orbital elements of Pluto: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, (iii) sinusoidal terms with the Earth's orbital period, and (iv) sinusoidal terms with the Pluto-Charon mutual orbit. The model was propagated to obtain the predicted position and error of the Pluto at the time of the occultation. The errors listed for the Pluto are the RMS of the models fitted.


Table 4: Site Information

East Longitude

Site Altitude6


Pluto Distance7


Charon Distance7




–155 28 29
19 49 46
2241 N.
2198 S.
Siding Spring
149 03 44
–31 16 17
773 S.
5060 S.
center of Earth
351 N.
3833 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 ±1029 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: P20160822 Occultation Predictions for Individual Sites

Immersion (UT)9
Mid-Time (UT)


Mid-Time (UT)
Pluto Altitude

18 (Charon)

Siding Spring


9The errors on all times are ±0:57 (2 minutes and 31 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) 2016-07-20 06:02

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