Outdoor Lighting and Crime - Amper

For 1977-07-04:
End of Civil Twilight 2103 EDT
End of Astronomical Twilight 2235 EDT
Start of Astronomical Twilight 0325 EDT
Start of Civil Twilight 0457 EDT
Sunrise 0530 EDT
Moonset 0935 EDT
Sunset 2030 EDT
Moonrise 2252 EDT
End of Civil Twilight 2103 EDT
End of Astronomical Twilight 2234 EDT
Shutdown was therefore 66 minutes after sunset and 33 minutes after the end of civil twilight.
The moon rose 41 minutes after shutdown. There was still some faint trace of twilight left at
moonrise because astronomical twilight still had 18 minutes to run.
An amateur astronomer (Rao 2002) took the opportunity of a lifetime to spend the night
observing stars and galaxies with his telescope from The Bronx. He saw the Great Nebula in
Andromeda and stars down to magnitude 5.4 with unaided vision. These observations are
mutually consistent, and correspond to a moonless sky with about 2500 stars visible unaided
and traces of the Milky Way overhead (Moore 2001). As it happens, this implies skyglow of
about 1.6 mcd/m 2 , a little fainter than the value shown (coincidentally) for 1977 in Figure 3.
If the sky were uniformly this bright, the minimum illuminance at the ground would have
been about 5 millilux (0.005 lux), or roughly one-fiftieth of maximum moonlight. This is
consistent with the difficulty that people experienced in moving about New York on the
evening of the blackout, before moonrise. This rather dim period lasted for less than an hour.
Ambient light from road vehicle lights, emergency generator lights, flashlights, candles (about
1 lux at 1 metre distance) and even the flames from the gettoes would have supplemented this
substantially in parts. After the moon rose, moonlight would have added about 0.1 lux at
normal incidence or at most, 0.05 lux horizontal illuminance (Hollan 2003). This amount of
direct moonlight is sufficient to walk about in. A slow further increase in illumination would
have started at the beginning of morning astronomical twilight, about two hours before
sunrise.
One indication of indifference to the amount of ambient light is that the looting and burning
continued unabated for 25 hours, ie throughout the moonlit later part of the night and the
whole of the daylight hours of the next day (Newsweek 1997, pp 22, 25). When it stopped
next night, it was around the time that:
a. goods for looting and things for smashing ran out in the areas affected,
b. the power came on again, and
c. the last trace of twilight disappeared at the end of astronomical twilight.
It was also before the moon rose. At present there is insufficient information to decide which
of these, if any, stopped the riots. (Doubtless, the police would have prevailed eventually, if
not at this time.)
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