Re: Modeling Starlink magnitudes in a simulation

From: Brad Young via Seesat-l <>
Date: Tue, 2 Jun 2020 17:13:52 +0000 (UTC)
Just a few subjective comments. I am not an analyst, but these may impact how the public perceives the effect of the satellites.

1. Flat brightness - most of the passes I've seen that were at operational altitude tended to maintain similar brightness across a long arc of the pass. I.e. phase angle is not as critical as with some satellites.

2. Flaring behavior - especially in the early stages of the earlier launches, there were often flares when the objects were in the W-NW at the same azimuth as the sun, but within a phase angle of 60-90 degrees. This behavior reminds me very much of the Terra / Tandem SAR-X pair. Since recent launches have not presented passes with this aspect, and/or the "shark fin" orientation has been implemented, there have not been many examples lately. And curiously, I never saw a complementary behavior in dawn passes, as might be expected.

3. Other flares - there have been a few "normal" flares when the objects have been at culmination opposite the sun, although these have been much shorter and not as bright. But, in line with point 1, the phase angle window for flares has been very tight, with even the next satellite in the train passing 90-120 seconds later not flaring.

4. First passes - ranged from a "gossamer spider web" to a "line of Valkyries" but as beautiful as those passes are, my opinion is that we must not give much weight to the initial passes in final analysis as they are temporary.

5. Darksat - unique object - has been invisible on many passes but nearly (within 1 magnitude) as bright as its sisters on others. Can't wait to see VisorSat.

There have also been a lot of passes of normal Starlinks that should have been visible but weren't. However, I haven't determined a pattern to that behavior.

6. Summer - has not resulted in the constant parade of bright satellites feared. In fact, since all the previous launches have raised to near or at operational altitudes, they've been just a few more in the normal plethora of LEO satellites in the summer sky.

I know these thoughts are not numerical, but you have seen my observations in the archives. It might be useful, depending on the audience, to also include some idea of the look and feel of what these objects are like.

Brad Young PE
Oberwerk 8 x 40 Mariner binoculars
Meade ETX-125 
22" f/4.2 UC Obsession
COSPAR 8336 =TULSA1 +36.139208,-95.983429 660ft, 201m
COSPAR 8335 =TULSA2 +35.8311  -96.1411 1083ft, 330m
Remote Imaging:
MPC I89 COSPAR 7777 38.165653 -2.326735 5150ft, 1650m Nerpio, Spain
MPC Q62 COSPAR 7778 -31.2733 149.0644 3400ft, 1122m Siding Spring, NSW, Australia 
MPC H06 COSPAR 7779 32.92 -105.528 7298ft, 2225m Mayhill, New Mexico USA 
MPC 323 COSPAR 7782 -32.008 116.135 984ft, 300m Perth, WA, Australia

On Tuesday, June 2, 2020, 11:12:37 AM CDT, Ted Molczan via Seesat-l <> wrote: 

Max Hartshorn Wrote:

> What I'd like to do is create a *responsible* and *non alarmist*
> visualization of what the night sky *could* look like when 12,000 Starlink
> satellites are up and running. As far as I know such a simulation does not
> exist.

I vaguely recall seeing or hearing about something similar, but I could be wrong.

> I've been looking through the archives here and I've seen a range of
> apparent magnitude observations, anywhere from 2 to 9. Additionally
> Starlink is iterating the design of their satellites to minimize
> reflectivity.
> The threshold that's most interesting to me is the 6.5 threshold for naked
> eye observation. If the satellites (particularly those in the lower orbital
> shells) are below that threshold, they could potentially impact how the
> general public views the night sky.
> Is there any agreed upon estimate for the apparent magnitude of the
> Starlink satellites currently in orbit? Do we just not know yet? Are there
> any responsible methods for modeling / estimating the magnitude of the
> remaining satellites?

SeeSat-L subscribers have reported hundreds of Starlink magnitude observations. In April, I posted a preliminary
analysis of a subset of this data:

The graph on page 2 of the pdf in the above post gives a good idea of the magnitude of regular Starlinks at the
operational altitude. The magnitudes have been normalized to 1000 km range based on the inverse-square law, which is the
convention for analysis of LEO satellites. 

Eyeballing the graph, it is evident that the mean 1000 km magnitude was around 6, but with some variation, which is
typical of satellites. Most of the observations were within +/- 1 magnitude of the mean. This means that actual
brightness can be expected to be up to 1 magnitude brighter or fainter than predicted. For a realistic simulation, it
would desirable to show this variation, if practical. 

I have been working on statistical analyses that might be helpful in that regard once completed. I can imagine using a
random number generator to approximate the variation in magnitude, based on the mean and variance. The devil will be in
the details. Does the +/- x mag variation tend to occur primarily within a pass, or between different passes? Do
satellites in a given plane tend experience the same variation at the same time?

Ted Molczan


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