Vatican Observatory Night Sky Brightness Project Status August 2006

1. Vatican Observatory Night Sky Brightness Project Status August 2006 Dan McKenna University of Arizona Steward Observatory Engineering and Technical Services Vatican Advanced Technology Telescope Project

2. Project GoalsNetworked Sky Brightness Monitor (NSBM) • Stable performance over decades of time • Referenced to a method of primary and secondary standards. 1% RMS target • Network based • Flexible configuration (mobile,articulated) • Wireless data transmission (single/multihead) • Lowest cost and as many as possible

3. People • Vatican/Steward Observatory • IDA Tucson • Students • Supporters • Outside contractors • Volunteer NSBM operators

5. History • Original Inspiration: sci.astro.amateur “Toward a cost effective night sky meter” • TSL 230R promise of 10% measurement In dark skies. • TSL 237S at least a factor of ten better i.e. 1% in dark skies.

7. Development of Prototype • project funded (2005) • Barr management contracted for first prototypes • Assembled NSBM project lab • Delivered GENI, wired, and GenII Wireless NSBM • GENIII developed by Matrix Product Development • GENIII now in first stages of testing

8. Detector Performance • TSL 237S TAOS • Light to Frequency Converter 2.5 e -12Amp/Hz • Silicon based detector .3-1 micron • Easy to use 3 terminal part (2.7 to 5.5 v.dc) • Frequency linear to 10,000 Hz @ 1% • 21.9 Mag / Arc Second 2= .06Hz@, F/D=0.65 + 1mm thickness Hoya CM500 mfgs. spec nominal 2.3kHz/uw @524 nm • Noise .001 Hz rms= 0.13 picowatts rms

9. Dark Temp Coefficient

11. Delta T= +15 C

13. VATT SBM Detector Head

15. Detector Head • CM500 Glass Si+CM500 photometry • 18 mm F.L. F 0.65 glass asphere lens • F.O.V. 5-6 deg • Front window • Detector temperature measured

21. Mounted detector

22. Electronics • Self calibrated real time clock (network) • Two channel period based frequency measurement with 1millisecond resolution and max frequency of 1 Khz • Wireless communication between sensors and base unit • Solar powered temperature compensated lead acid charger in head unit with low voltage cut off. • Base unit has 128 MB data buffer • Provides “housekeeping data” temperature, system current, and battery voltage • Accessible by web browser • Calibration of window transparency

24. Gen I Rabbit board

25. GENII Base

26. GENII Head

27. GENIII prototype electronics

30. Two channel GENII Wireless prototype and handsome garden Candelabra

31. GENIII NSBM Remote Unit

32. Sensor with window removed

33. Calibration of window transmission

36. The output data format sent as an E-mail GENII format Date time serial# ch1 ch2 color Bat V current Temp GEN III format Date time cal status serial# ch1 ch2 cal Bat V current Temp Signal Strength 08/17/06 04:51:03 0 00 C726B3 18.873 0.000 0.000 6.31 -023 31.9 57

37. Examples of Data

45. Next steps • Better repeatability needed with cal cap • Primary and secondary standards • First test in Tucson region. • Refine calibration and link to standard star • Calibrator sent to NIST for calibration.

46. The term “magnitude per square arc second” is not commonly used outside of astronomy. Linear measurement facilitates direct communication of the impact of sky brightness. A unit of brightness based on a natural dark sky and expressed in a linear form, “1 sky,” as well as the standard expression in magnitudes, will be displayed on our web interface. We anticipate that the use of these two reporting units will optimize cross-disciplinary communication.

47. An example of this reporting system would be: Sky brightness: 16.90 magnitudes per square arc second (i.e. 5 magnitudes brighter than the natural 21.9 sky) Or 100 “sky” We assume 21.9mag per square arc second (solar minimum)as 1 sky. This value maybe subject to revision.

48. GPS + NSBM diameter scale: min= 2 max displayed= 33 sky