PURPOSE
We established this Sky Quality Monitoring Program to monitor the darkness of the night sky over Ivins Utah. This will allow us to assess the effectiveness of future light pollution mitigation efforts in the city. The monitoring program may also be used to support an application to International Dark Sky Association for certification as a “Dark Sky Community.”
EQUIPMENT
The monitoring program utilizes a Unihedron Sky Quality Meter (SQ-L). This meter measures the darkness of the sky in magnitudes per square arcsecond (mag/arcsec). This is a logarithmic measurement which means that large changes in sky brightness correspond to relatively small numerical changes. The meter’s range is roughly 16 to 23. Lower numbers indicate more light pollution. Higher numbers indicate darker skies. Readings over about 20.00 indicate “dark skies.” The SQ-L is not affected by temperature and is typically accurate to ±0.10. The SQ-L has a field of view of 20°.
MEASUREMENT LOCATIONS
Nine locations have been identified in Ivins to take regular sky quality measurements. These locations are shown on the map below and identified on the Sky Survey Data sheets surveyors will use to report survey results. The locations were chosen to contain a mix between sites on the edge of the City likely to have darker skies and sites in the middle of the City likely to have brighter skies. Over time, review the readings at each location to see if any locations are redundant.
TIMING
The initial base line sky quality measurements at the 9 locations took place on December 30, 2018. Thereafter, measurements will normally be taken at least twice a year, ideally quarterly.
HOW TO TAKE MEASUREMENTS
- Observations should be taken at least one hour after evening astronomical twilight ends or before morning astronomical twilight begins, and at least one hour before moonrise or after moonset.
- Leave the meter outside for at least 5 minutes to reach ambient temperature before taking any measurements. Avoid using the meter near lights like streetlights and in areas that are shaded by trees or buildings. A rule of thumb is to be as far from the object as it is high. For streetlights, 25 feet away, if possible.
- Point the meter directly overhead (at the zenith). The meter should be held above head level so that shadows or reflections from your body do not interfere with the reading. Keep it steady.
- Press the start button once to take a reading. Under urban skies, a reading will be displayed almost immediately. Under the very darkest skies, the meter may take up to a minute to complete its measurement.
- (Optional:) Press the start button a second time. The temperature in C° and then F° is displayed.
- Take 3 consecutive readings at each site and record the numbers.
- The mean for each site will be calculated once the survey data is added to the spreadsheet. The mean will be the final reading for the site.
- Complete the Survey Data Sheet and take readings for all sites on the same night if at all possible.
- We will only report the mean when we post summaries of the results of each sky survey. However, we will report the complete survey, listing all three readings at each site along with the mean for each site in this section of the website.
FUTURE
After several quarterly sky quality measurements have been made, we will be able to track the changes in tables and graphs and analyze why changes are taking place. (Note: We expect some variation from survey to survey, so we will need a number of completed surveys before we will have meaningful trend data.)
SKY CONDITIONS
Sky quality surveys require dark, clear or mostly clear skies. The Clear Sky Chart below forecasts a number of factors that are important for these surveys. This forecast is for Ivins, Utah. If you plan to conduct a sky quality survey in Ivins, check this chart first. Also click the link below to check additional information, including times for sunset, civil twilight, moonrise, and moonset daily for the next 12 months.
