Visual Starlink brightness observations to 2020 Apr 6

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Sat, 18 Apr 2020 13:28:03 -0400
Here is a brief report on visual observations of Starlink satellites at the operational altitude, to 2020 Apr 6 UTC.
Nearly all were reported via SeeSat-L.

I have compiled 143 observations of standard Starlink satellites, by Russell Eberst, Jay Respler, and Brad Young; and 6
observations of Darksat (2020-001U / 44932), by Richard Cole, Tristan Cools, Thierry Legault, myself, and Brad Young.
Richard Cole kindly provided information which assisted in computing the range and phase angle of his observations.

The following file contains two plots of visual magnitude normalized to 1000 km range versus phase angle. Standard
Starlink satellites are in blue; Darksat is in yellow.

http://satobs.org/seesat_ref/misc/Visual_obs_of_Starlink_satellites_to_2020_Apr_6.pdf

Page 1 plots all of the data.

Most of the brightest observations occurred very soon after arrival at the operational altitude, which I defined as the
epoch of the first TLE with mean motion less than 15.06 rev/d. It has been suggested to me that a Starlink satellite
might take a "couple of days" after reaching operational altitude to assume the operational orientation, including that
of the solar array. I took this as speculative, but it seemed reasonable for there to be some delay. 

To get an indication of the possible validity of this idea, the plot on page 2 includes only those satellites that had
been at the operational altitude at least 2 days at the time of observation. This eliminated nearly all of the brightest
observations, but relatively few of the fainter ones. So there may be something to this idea.

As is typical of artificial satellites, there is considerable randomness in the brightness. The data on page 2 spans a
total range of about 4 magnitudes, most of it within a 2 magnitude range, which is still pretty wide. Therefore, to
confidently draw conclusions about brightness will require many more observations, especially of Darksat, of which we
have just a handful of obs.

The spreadsheets used to generate both plots are here:

http://satobs.org/seesat_ref/misc/Visual_obs_of_Starlink-all_data_at_operational_altitude.xlsm

http://satobs.org/seesat_ref/misc/Visual_obs_of_Starlink-min_two_days_operational_altitude.xlsm

Ted Molczan


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Received on Sat Apr 18 2020 - 12:28:55 UTC

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