We open around twilight and close around dawn. Of course, the timing varies throughout the year due to seasonal sunlight. In most cases this is when the sun has set to -10º below the horizon for opening and when the sun has risen to -10º below the horizon for closing, but can vary by location and time of year slightly.
Generally, we open the domes if the skies are clear and the weather is deemed SAFE. Each site uses it's own weather monitoring systems that will automatically open and close the domes based on the current conditions. As a fail-safe, and to ensure our members are getting the highest quality of images, we also have a staff member or members monitoring the weather as well.
There are times when staff members will override the automated weather systems if they see problems that automated systems cannot measure well (like occasional, but consistent high wind gusts that would lead to guiding failures). This means that sometimes the domes will show open on the Web Cameras, but the systems will still show closed.
We close our domes under the following conditions: Mostly Cloudy, Rain, High Sustained Winds (generally around 20km/h), High Wind Gusts (any gusts over 25km/h), Ice, Snow, High Humidity (88%+), Approaching Dew Point, and Frost.
We will also opt to close if we see more than one of the above, even if each is not severe. Meaning that if it is partly cloudy (which we would usually remain open for as long as the clouds were not directly overhead), but we were also seeing winds of 15 km/h and humidity at 85%, we will likely close. This is simply because of the combination of the above, while likely not dangerous to equipment, will lead to extremely poor imaging.
Please keep in mind that if we choose to keep an observatory closed, it is with our members' best interests in mind.
You can check the current conditions at the observatories via the following links:
Siding Spring Australia Weather
For current closure information, please check the Network Messages Bar at the top of the Launchpad.
You can also get instant updates via Our iTelescope.Net twitter alerts service.