[PeterAnderson (Peter)]

Just as a footnote - I wanted to check out how temperatures drop in the evening. Now let us assume - and this is a big ask - that the telescope is close to ambient temperature at dusk. What happens then? Below is a rambing explanation of my investigations:
TAYLOR RANGE OBSERVATORY – Night time cooling – Peter Anderson

Taylor Range Observatory is situated on a 171 metre high ridge just over 1km to the WNW of the summit of Mt Coot-tha and nearly 100 metres lower. Its position is: -27° 27’ 42.3” S 152° 55’ 57.9” E Alt 171 metres.

As part of my lunar occultation observations I record the temperature at the time the observations are made. By tracking a number of days where I made observations from early to late evening, I was able to establish the pattern of cooling. Two of these records also show a mid-evening increase (notable in spring) as the inversion layer settles over the ridge.

My records from this same site stretch back over 40 years and I use the same two thermometers, mounted on the observatory wall at around 1.5 metres high. The observatory is of the double roll off roof variety and the temperatures would effectively be the ambient outside temperatures.

Whilst I have decades of records, for this exercise I have merely selected those evenings that were appropriate over the last five years, 2012 to 2017. I consider the results produced to be sufficient, as there were17 evenings in all, tending to group at the time of year when clear skies are more prevalent. I did not ‘cherry pick’, selecting all evenings that met the criteria of having observations over a number of hours.

For each of these selected dates, there were many more temperature observations than those shown on the table and for each selected date I did not restate except when there was no change in temperature for a considerable period including the final observation.

I use Universal Time (UT) in the table since the observations are recorded in UT. 8 hours UT is 6pm local time and 13 hours UT is 11pm.

Analysis of the results:
(1) For my site the maximum drop (one result only), is 4 degrees centigrade in a little under 5 hours.
(2) Three drops of 3.5 degrees are recorded in three to four hours and
(3) Six drops of three degrees over the same timespan.
(4) The remaining seven show drops from 1.5 to 2.5 degrees.

Conclusion
Without over-analysing these statistics, it is reasonable to assert that the ambient temperature drops at an average rate of around one degree centigrade per hour, perhaps slightly faster in the early part of the evening and certainly less towards 10pm and 11pm. However it appears that if the temperature starts slightly higher the overall drop will be greater, and less if the start temperature is lower. (I suppose this is pretty obvious.)
None of the selected evenings were during extremes of temperature.

The rate of drop will vary with the local conditions at the time – for example, there are differences in the drop rate in otherwise similar observations, but I do not have humidity or other records to compare/factor in.

Further, since I usually limit my observations to no later than 11pm, I have absolutely no reliable records later than this time in the evening.

Observation
Sites that are well away from the coast, or with different local topography, will undoubtedly experience a different cooling profile.