Calling the Night

This is my first post on this blog, and it's a bit of a shame because tonight will not be a good night for astronomy from Las Campanas.  Exhibit A, the sunset this evening:

Last night was my first night "observing" on this run. I am the PI for three nights on Baade, hoping to find some unique high-redshift galaxies to study. I put "observing" in quotes because in reality we did not open the dome. There was a brief moment of hope. The clouds looked like they were parting! But then the wind picked up. (If the wind speed is higher than 35 miles per hour, we can't open the dome because the wind could damage the telescope.) So the telescope remained shuttered and no data was collected. Well, unless you count this lovely photo of the Belles of Campanas standing on the Nasmyth platform of the Baade Telescope. 

From the left: myself, Johanna, Angelica, and Cindy

Since there is no observing going on again tonight, I thought I'd write a post about Calling the Night... This is one of the most agonizing decisions a PI at the telescope must make. At one point during a terribly hopeless bought of bad weather you say to yourself and those with you at the telescope: "Ok, we are done. I call the night. We can all go to sleep." For most of us, we stay up all night hoping and hoping that the skies will clear, that the wind will die down, or that the humidity will drop. Observers all care very deeply for the telescopes they use, and so we remain patient and understanding about the fact that the telescope remains closed - but many of us still hold out hope. You see, we plan - sometimes for weeks - for a few nights on the telescope. We make target lists, calculate optimal observing strategies and exposure times. But in the end, Nature decides. 

Last night, I called it at 5AM. The wind was above 35 mph, and one must wait for the wind to stay below that mark for a full 30 minutes before the telescope can be opened. Twilight begins around 6AM, and while I can observe for a while after twilight begins, obtaining less than an hour of data is unfortunately not very useful for my current project. But trust me, it's an agonizing decision. Last night, I made the right call. There was no way we could have opened. 

Sadly, it's a decision I expect to make again tonight. The weather does not look good. 

We are currently suffering from an extreme winter storm that is expected to last well past the end of my run and drop a tremendous amount of snow in the Andes south of here. Right now, as you can see we have 50 mph winds. You can feel the wind shake the telescope building from time to time. It's kind of gloomy. 

I've called nights before. Last year, I was at Magellan for the 4th of July. It snowed. 

When there is snow on the dome, you call the night. Even if it stops snowing, the snow on the dome can melt and drip onto the telescope - or blow off the dome and onto the telescope. That's an easier decision - there is no chance for the night once there is snow on the dome. 

I'm here until Tuesday - I'm hoping before I leave we get to collect some interesting photons. But you never know - Nature decides.