Declaration:
I and two friends went to Russian Ride Open Space Preserve on February 17th to watch the sunset. We parked at the Vista Point parking lot at approximately 17:00-17:30.
As we entered the park, we read a sign on the gate that said, "Park closed half hour after sunset". We reasonably interpreted this to mean that that the rules accommodated access to the area to observe the process of the sun setting and give adequate time to safely make egress from the area.
We proceeded to walk up to the hill adjoining Borel Hill - a horizontal distance of 2400 ft, which took approximately 15 minutes. Borel Hill is at 2572 ft elevation above sea level - the highest named point in San Mateo County. The view towards the west was excellent, with clouds / fog below us as far as the horizon, and very little light pollution.
We talked quietly, watched the sun set, and immediately proceeded to walk towards the exit after the sunset, when it was beginning to get dark. It took less than 15 minutes to leave, since the return was downhill. We tried to check the time, but the only timepieces we had were cellphones, which were out of battery.
Had we not been detained by the ranger on our way back, we would have exited the park about 15 minutes before one half hour after sunset, as we expected to do upon entering - well within compliance with the requirement as posted.
We did not drink any alcohol, leave any trace of our presence, make noise, or otherwise cause any disturbance, nor have we ever done so in enjoying the preserves.
According to the US Naval Observatory, sunset for that day began at 17:51; end of civil twilight was at 18:18; end of nautical twilight was at 18:45; and end of astronomical twilight was at 19:15.
Argument:
We obeyed the law as posted, by leaving before one half hour after sunset.
Sunset is an event with duration. Only its onset can be predicted with any accuracy generally, and even that is problematic. According to the USNO at
http://aa.usno.navy.mil/faq/docs/RST_defs.php, the sunset times it gives explicitly do not take into account elevation or atmospheric conditions. Both of these were relevant to our presence at Russian Ridge - with high elevation, low horizon, cloudy conditions, and very low light pollution - and resulted in a true time of the beginning of sunset significantly later than that given in the automatic calculations table used by the Ranger.
The end of sunset is even more dependent on local conditions, which is why astronomers have three different definitions for it - 'civil twilight', 'naval twilight', and 'astronomical twilight', each intending to approximate a certain level of light pollution. The level of light pollution appropriate to our location was between naval and astronomical.
Additionally, the time of 19:03 listed on the complaint is later than the time at which we were stopped by the ranger.
Since we were there to watch the sun set and we left directly after the sun set, and since we reasonably presumed that it would not take us more than 30 minutes to depart, we never anticipated nor reasonably knew we would be in violation of the posted sign. I.e., we fully intended to, and in fact did, comply with the stated requirement to exit the park "[one] half hour after sunset".
Therefore, in the interest of justice, I should be found not guilty.
