Starlink brightness observations by Russell Eberst

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Tue, 25 Feb 2020 13:40:41 -0500
Russell Eberst reported 63 brightness observations of Starlink satellites as of 2020 Jan 27 UTC, which I have compiled
into the following file:

http://satobs.org/seesat_ref/misc/Starlink.br.txt

The data format is the one I use to archive Russell's observations. The data consists of international designation, site
code, observation date and time (UTC), RA and Dec (HHMMSS+DDMMSS, epoch 1950), minimum and maximum magnitude, and
optical characteristics code (most commonly used: S=steady, I=irregular variation, R=regular variation, F=flashing with
constant period).

A plot of the derived visual magnitude normalized to 1000 km range vs. phase angle is available here:

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

The data has been segregated according to mean motion. 

Shown in blue are observations with mean motion between 15.04 and 15.12 rev/day, which correspond to the operational
altitude. 
Shown in red are observations with mean motion between 15.22 and 15.73 rev/day, which correspond to lower than
operational altitude.

Objects at the operational altitude tend to have lower intrinsic brightness than those at lower altitudes, but there is
some overlap. More data is required to draw firm conclusions.

Eyeballing the plot, it appears that the standard magnitude at the operational altitude may be around 7.2 (1000 km, PI/2
phase angle). More data is required for a confident estimate.

A single observation of "Darksat" (2020-001U / 44392) is shown. It was at below operational altitude, so of limited
interest.

The underlying spreadsheet is here:

http://satobs.org/seesat_ref/misc/Starlink.xlsx

Columns 5-7 of the data sheet display the difference between a TLE near in epoch to the observation, in terms of total
position, cross-track separation, and time. The TLEs are not necessarily those closest to the time of observation, so
the differences are not necessarily reliable indicators of observational accuracy.

I have the ability to similarly process observations in IOD and UK format (Russell reports his observations in an
abbreviated form of the latter).

Ted Molczan


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Received on Tue Feb 25 2020 - 12:41:39 UTC

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