Observations of Visorsats from Starlink launch L1.9

As noted by Anthony Mallama, the first wave of visorsats from the 
Starlink L1.9 reached 550km early on 2020-08-31. Below are my 
observations of this wave over two nights.

Notes:
1. I estimate the measurement accuracy to be no better than +/-0.2mag.

2. The adjusted magnitude is to a standard range of 1000km and for 
Lambertian cosine angle from the Earth-facing flat base panel. The 
latter will only be significant for lower altitude observations.

3. Strong moonlight effected visibility after 21UTC on each might and 
prevented observations at lower altitudes. This may be suppressing 
fainter objects from the observation set.

The graphs at the link show some analysis, with these very initial comments.

http://recole.org.uk/starlink/2020-09-02-graphs-v1.jpg

1. The adjusted magnitude plot show no significant trend with altitude. 
Average magnitude is 7.3 for adjusted 1000km range, 6.0 for adjusted 
550km range.

2. There are small trends to lower brightness at higher Sun to satellite 
azimuth angles and lower Sun altitudes.

Conclusions:

a. The observed brightnesses are higher than might be expected from a 
few observations of the prototype Visorsat

b. There are variable results between Starlinks and between the same 
Starlink on the two nights.

c. There is no indication yet that the L1.9 visorsats are systematically 
fainter than the single Darksat launched earlier in 2020.

regards

Richard Cole


Pass  SL #   Az  Alt   Az  Alt  Mag  Off   Range Corre- Adj-    Notes
UTC          Sun Sun                 base  (km)  ection usted
                                      angle       (mag)  mag
2020-08-31

19:55  1555  298  -10  297  50  4.5  36    699   0.54       Bright
19:55  1555  298  -10  330  71  3.2  17    579   1.14       Bright
20:03  1582  299  -11  324  70  6.1  18    582   1.12  7.2
20:03  1582  299  -11  355  75  6.1  14    568   1.20  7.3
20:08  1522  300  -12  354  80  6.0   9    558   1.25  7.3
20:23  1584  304  -14  301  78  6.1  11    561   1.23  7.3
20:32  1576  306  -15           N/S                         Not at 550km
20:42  1591  308  -16  256  74  5.7  15    570              Not at 550km
20:47  1534  309  -17  224  76  6.6  13    565   1.21  7.8
20:53  1544  310  -18  192  74  6.3  15    570   1.18  7.5
20:58  1565  311  -18  250  63  6.1  25    611   0.97  7.1
20:58  1565  311  -18  178  68  6.5  20    589   1.08  7.6
21:02  1560  312  -19  217  67  6.4  21    593   1.06  7.5
21:12  1556  315  -20  247  52  7.1  35    682   0.62  7.7
21:17  1557  316  -20           N/S                         Moonlight
21:23  1567  317  -21           N/S                         Moonlight

2020-09-01
20:04  1522  299  -12  288  76  5.7  13    565   1.21  6.9
20:12  1526  301  -13  119  72  2.2
20:17  1584  302  -13  128  67  6.5  21    593   1.06  7.6

20:28  1576  304  -15  262  65  6.3  23    602   1.01  7.3
20:33  1580  305  -15  275  47  4.3                      bright to W
20:33  1580  305  -15  251  66  5.9  22    597   1.04  6.9
20:42  1534  307  -17  223  64  6.4  24    606   0.99  7.4
20:47  1544  308  -17  268  40  3.7                         Bright
20:47  1544  308  -17  254  52  2.8                         Bright
20:51  1565  309  -18           N/S                  sky limiting mag 7
20:56  1560  310  -18  246  51  6.2  35    690   0.58  6.8
21:05  1556  312  -19           N/S                  sky limiting mag 7

N/S = not seen
Off-base-angle = angle between the observation direction and the 
pointing direction of the base panel
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