I arrived at the Apache Point Observatory – two hours north of El Paso – with a head cold, which did not help my adjustment to the 9,000 foot altitude. After a night of nausea and headaches, I (somehow) awoke feeling perfectly fine. Walking out of the small dormitory, I was greeted by the immense cube of the 3.5-m telescope I would be using that night. To the left were two smaller domes and a large building that houses the 2.5-m Sloan Digital Sky Survey telescope, the instrument which has revealed the large-scale structure of our universe. The observatory sits on a peak overlooking the Tularosa Basin, an area of desert larger than the state of Connecticut.
Once Ryan arrived, we took a tour of the 3.5-m telescope with Candace Grey, a graduate student at New Mexico State University who would be collaborating with our research and helping us operate the telescope. Candace showed us the camera we would be using, a person-sized, liquid nitrogen-cooled CCD called ARCTIC. Because of the immense light-collecting power of the telescope’s 3.5-m mirror and the extreme brightness of Venus, Candace had to affix a neutral density filter on the front of the telescope with duct tape to avoid saturating the camera.
Around 5:00PM we geared up for our Venus observations. Because Venus is closer to the sun than the earth, it is always relatively low in the sky. The lower an object is in the sky, the more atmosphere you have to look through to see it. The atmosphere is turbulent and can severely distort and blur images, so the less atmosphere you have to look through the better. Our observing session would be a race against time: we could start as soon as the sun set, but each passing minute after that Venus would sink lower and lower in the sky.
Another complication was that we needed specific stars to calibrate our images. Because Venus shines by light reflected from the sun, we needed to observe a similar star (a G2V star) at a similar time and altitude above the horizon. It also had to be bright so that it would be visible through the neutral density filter.
The hour and a half observing session was frantic. Controlling the telescope and camera from our laptops, Ryan and I changed filters, slewed between Venus and several candidate calibration stars, and hurriedly completely a log of all the images we took. The images did not look spectacular, but we would be able to combine several images afterward in a process called stacking, which would allow us to extract finer details.
We got a second night of observing, but the next two nights were cloudy. The poor weather allowed us to take calibration images and experiment with the camera to optimize our next observing run. There are three major types of calibration images in astronomy: bias, dark, and flat. Bias frames are zero-length exposures, which show only the noise generated by reading the image off the sensor. Dark frames are long exposures with the camera’s shuttle closed, which allow us to quantify the noise inherent in the camera while we take actual photos. Flat frames are taken by uniformly illuminating the mirror to show vignetting and dust in the camera. Flat frames in particular were annoying to take because the neutral density filter increased the exposure time to several minutes (the usual exposure time is at most 60 seconds).
By the final night, we had optimized the camera’s settings, found good calibration stars, and gotten into the rhythm of high-tempo observing. Unfortunately, high humidity and low temperatures (which could create frost on the mirrors) prevent us from using the full observing time, but we got several good images. Ryan went back to Apache Point in early January, and the photos we have taken will be included in our paper, which Dr. Sayanagi will present to the Japan Geoscience Union meeting in May.
The five days at Apache Point were the most exciting of my undergraduate career. It was thrilling to work on such an impressive instrument and be involved with interesting research with dedicated people. I hope that in the future I will be able to do more work with observatories like Apache Point.