by Kate Grier
My name is Kate Grier and I’m part postdoc and part Planetarium Director in the Department of Astronomy at OSU. That means I get to play two different roles in the department: In my role as a postdoctoral researcher, I spend my time measuring the masses of black holes at the centers of galaxies, and in my role as the planetarium director, I oversee all of the activity of our awesome, newly-renovated planetarium on campus. This week, I am putting on my research hat and escaping the cold Columbus weather with OSU graduate student Jamie Tayar to the sunny desert mountains of Arizona to collect data.
Desert mountains, like those found in Arizona, are perfect places for astronomers to put telescopes for a number of reasons: First, there aren’t many people around, so the skies are very dark. Second, deserts are known for being very dry, and we like dry climates because water molecules in the air interfere with our observations. Third, desert mountains are at high elevations, which means there is less atmosphere between us and outer space, which also helps us to get more accurate information about the stars and galaxies we’re looking at!
This brings me to the top of Kitt Peak, a mountain in Arizona that has a large number of telescopes at its top. OSU co-owns two telescopes on Kitt Peak at an observatory called MDM, which stands for “Michigan-Dartmouth-MIT” — the original owners of the observatory. One of these telescopes has a mirror that is 1.3m in diameter, and the other has a mirror that is 2.4m in diameter. Even the 1.3m, which is fairly small when compared with the largest telescopes in the world, weighs over 1000 pounds, and the entire telescope structure dwarfs us humans!
Now, follow me as I take you through a night of observing at the 1.3m telescope at MDM in March, on a beautiful, clear (but cold), early-spring night.
The Night Begins
5:oo PM — Before it even gets dark out, we must start taking “calibration data” in the afternoon. Astronomers don’t look through telescopes by eye anymore—we use CCD cameras (basically really expensive digital cameras) to take pictures of galaxies and stars and then save the pictures to analyze later. Because these CCD cameras are not perfect, we take many calibration images before the observing even starts so that we can account for any imperfections in the cameras.
6:oo PM — The first thing we have to do is to make sure the CCD camera that we’re using stays cool. Warm cameras radiate their own light that interferes with the light coming down from the sky, so we cool the cameras down to about -165°F with liquid nitrogen (using liquid nitrogen as a coolant is also a really, really fun way to make ice cream). The liquid nitrogen itself is actually much colder than this—liquid nitrogen is about -321°F, but the insulation of the camera isn’t perfect, so it’s generally warmer than the liquid nitrogen itself. We have to make sure the camera never warms up much more than this, or we could have problems with our observations.
6:45 PM — It’s sunset time! Watching the sun set from a beautiful desert mountain in Arizona is one of my favorite parts of observing. Sunsets in Arizona are spectacular, and sunsets at MDM observatory never disappoint.
It takes nearly an hour after sunset before it is dark enough for us to take data, but after watching the sunset, we start getting the telescope ready to observe. We call this period after the sun sets “evening twilight,” when there’s still some ambient light in the sky.
7:45 PM — It is now dark enough for us to observe! We start with a star to use for calibrations—we use a star that has had very detailed brightness measurements taken previously. Since we know how bright it should be, we can see how bright it looks to us, and use that to calibrate the brightness of all of our data.
8:15 PM — It’s time to observe our first galaxy! Tonight, we are looking at galaxies that are hundreds of millions of light-years away—specifically, we are looking at the centers of these galaxies. Each galaxy has a supermassive black hole that is millions or billions of times as massive as our sun. We watch the gas and other material falling into the black holes in these galaxies to learn about the black holes—specifically, by watching the gas move around the black hole, we can calculate how strong the gravity of the black hole is, which gives us a measurement of the black hole’s mass. Because these galaxies are so far away, they are faint and we have to take really long exposures to collect enough light, so we take three 20-minute-long exposures on each target. Throughout the night, we move to a new galaxy every hour.
10:00 PM — Time for some star gazing. It’s important that we go outside and look at the sky often to make sure there are no clouds interfering with our observations, and on a beautiful, clear night like this, I am happy to go out and check out the sky! Out here, we can see the Milky Way up in the sky, and so many stars! It’s a beautiful night.
12:30 AM — Dinnertime! Since we’re on an observing schedule, our mealtimes are a bit mixed up. I woke up and had breakfast at about 3:00PM and had lunch right after sunset, so now it’s time for dinner! The dorm at the telescope has a mini kitchen that we use to cook food in, so we bring groceries up with us when we come up the mountain. We have to eat quickly, though—we can go eat food while the telescope is taking a 20-minute long exposure, but we can’t leave it for longer than that.
3:00 AM — It’s time for a 3AM dance party! This time of night, even after I’ve been observing for a few days, I tend to get pretty tired—it’s hard work staying up all night long. What better way to wake myself back up then by staging my own dance party inside the control room?
5:15 AM — It’s about an hour before the sun rises this morning, which means it will start getting light out soon. Sunlight will start interfering with our observations, so it’s about time for us to stop observing and pack up for the night. We return the telescope to its home position (pointing straight up), close the dome, cover up the mirrors, and once again, refill the container of liquid nitrogen so the camera doesn’t warm up during the day. Time to head in and go to sleep – successful night of observing!
About Kate Grier
My name is Kate Grier and I am a recent PhD graduate from The Ohio State University (OSU). I grew up in the suburbs of Chicago and received my undergraduate degrees in both physics and astronomy from the University of Illinois at Urbana-Champaign. Having completed my PhD in Astronomy last summer, I am currently serving as the Director of the OSU Planetarium as well as carrying out postdoctoral research on supermassive black holes. I also love teaching and public outreach, and in my spare time I like to read, hike, and travel the world!