Date: October 9th, 2012

Title: The Dark Energy Camera

Podcaster: Rob Sparks

Organization: NOAO


Description: One of the biggest puzzles in astronomy and physics is the mysterious substance called dark energy which is causing the expansion of the universe to accelerate. In this podcast, CTIO’s Andrea Kunder described the Dark Energy Camera (DECam) which recently saw first light on the Blanco 4 meter telescope in Chile. DECam is the most advanced astronomical camera in the world and will image millions of galaxies as it studies dark energy.

Bio: Rob Sparks is a science education specialist in the EPO group at NOAO and works on the Galileoscope project (, providing design, dissemination and professional development. He also pens a great blog at

Andrea Kunder is a Postdoctoroal Research Associate at CTIO. Her research interests include Milky Way Galaxy Formation, Galactic Bulge, stellar populations, RR Lyrae stars, and distance indicators.

Today’s Sponsor:  This episode of the 365 Days of Astronomy podcast is sponsored by the National Optical Astronomy Observatory. NOAO is a US national research and development center for ground-based nighttime astronomy. We provide astronomers access to world-class observing facilities on a peer-reviewed basis. Our mission is to engage in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe. For information on observing proposals or our public programs, please visit for more information.


Rob: Hi, this is Rob Sparks of the National Optical Astronomy Observatory and I would like to welcome you to this episode of the 365 Days of Astronomy podcast. I am talking this afternoon to Andrea Kunder of CTIO, the Cerro Tolollo InterAmerican Observatory in Chile. Good afternoon, Andrea.

Andrea: Good afternoon. Thank you for having me.

Rob: Oh, you’re welcome. How are things down south?

Andrea: Pretty nice. It’s spring here now so we are having some nice blooming trees at the moment.

Rob: I would love to get down there and see it some time. First I would like to offer my congratulations to you and everyone down there for your spectacular first light images from the Dark Energy Camera a couple of weeks ago. They are absolutely wonderful.

Andrea: Thank you. That was very exciting for us at CTIO. It was very exciting for the whole DECam team.

Rob: Yes, and that’s what we will mainly be talking about today. But first I was wondering if you could just tell us a little bit about your background and what you do at CTIO.

Andrea: I am a senior post-doctoral fellow at CTIO. I have been here for three years. I moved here fresh out of my PHD program at Dartmouth College and became the instrument scientist for the wide field camera MOSAIC on the Blanco Telescope. That is the largest telescope we have on Cerro Tolollo. For my work, I spend 50% of my time doing my own personal research and 50% of my time is spent doing support work for the observatory.

Rob: So now let’s get to the science. We are going to talk about the Dark Energy Camera or DECam, is that how you say it?

Andrea: Yes, DECam.

Rob: DECam for short. This camera is exploring the mystery of dark energy. We have talked about dark energy before on this podcast, but for those who might have missed those episodes, could you tell us what is dark energy and why are we interested in it?

Andrea: Yeah, I want to say first that I am a stellar astronomy, so I study stars in the Milky Way galaxy and neighboring galaxies so I am not an expert on dark energy. One of the main goals of DECam will be to explore dark energy, but with DECam you can look at whatever you want. You can look at nebula, you can look at planets and space debris. But for one third of the year, for the next five year, DECam will be taking images exclusively to understand what dark energy is. This is a big question: What is dark energy? It seem that there is actually more unknown about dark energy than is known. So we know that the universe is expanding, but the question is how is the universe expanding. This year a Nobel Prize was awarded to astronomers who helped discover that the expansion of the universe is accelerating and the force driving this acceleration is called dark energy. We are interested in dark energy because it is thought to constitute about three quarters of the universe and yet what it is remains still unknown to science.

Rob: Yes it is quite a mystery. I think it was the October, 2011 podcast I interviewed Tom Matheson who did some of the data collection at CTIO that led to that Nobel Prize. So can you tell us a little about what the Dark Energy Camera is and how it is going to help solve this problem.

Andrea: So the Dark Energy Camera is the widest field optical imager in astronomy right now. And this imager is currently on the Blanco Four Meter Telescope, which is a good sized telescope. It’s not the largest telescope in the world. The largest telescopes are about eight meters in size, but a four meter telescope is definitely big. So here we havea large, wide-field imager on a pretty large telescope so this is a good combination to do some pretty good science. DECam is also in a strategic geographic location. It is on one of the best sites in the world to take pictures of the night sky. This is because CTIO is right on the border of the Atacama Desert, which is the driest place on Earth so cloudless skies occur quite frequently here, especially in the summer months and we are approaching summer right now. The DECam imager is made up of sixty two science CCDs and each of them have 2048 by 4096 pixels so this means DECam has a grand total of 528 megapixels.

Rob: Wow! That’ s half a gigapixel!

Andrea: Yes half a gigapixel. So DECam will solve the mystery of dark energy in a systematic manner. The idea is to observe four different probes of dark energy. You can’t see dark energy so there are four different probes of dark energy that DECam will be observing. First, DECam will observe type Ia supernova and baryon acoustic oscillations and this will be to constrain the expansion of the universe. And then galaxy clusters and weak lensing will also be observed to measure both the expansion of the universe and the growth of large scale structures. Then we can compare the results from these first two probes and the last two probes and this can reveal our understanding of gravity and intercomparisons of the results will provide cross checks and bolster confidence in the findings.

Rob: So could you give us a few more details of the camera. You said it was half a gigapixel, what is the field of view? I know it is a pretty wide field of view.

Andrea: Yeah, so DECam has a three degree field of view which means it can fit about four full Moon across its diameter and so in just one image, astronomers can capture a pretty sizeable chunk of the sky. And then it takes about 20 seconds to read out an image so after 20 seconds after you take an image, the telescope can be pointed to another part of the sky and you can take another image.

Rob: One of the things that is unique about this camera is that there will be open access for the astronomical community for DECam. Can you tell us a little bit about the open access program that they will be running.

Andrea: Yes, the DECam imagers is on the Blanco four meter telescope which is an NOAO telescope. And this means it is one of the U.S. National Observatory Telescopes. Astronomers from any country in the world may apply to use the NOAO telescopes. Every year, twice a year, telescope proposals are solicited. So you can go to the NOAO website, download one of the telescope proposal forms and fill it out. This is where you make your case for why you need telescope time and what you want to observe. Then a committee evaluates the submitted proposals and ranks them. There are always quite a few more proposals than there are available nights so it is important to establish which proposals are the strongest and those are the ones that are awarded time. If you are awarded time, then you must come here to Chile to CTIO to take the observations yourself. Of course the instrument scientists and the staff at CTIO will make sure you are well trained and give you all the inside tricks and information to be sure that your observations will be very nice.

Rob: And as you said these other observations could be for almost any type of research since this is such a powerful camera, right?

Andrea: Yes, these proposals can be to observe anything. Now the Dark Enegy Survey is allocated one third of the time every year on the Blanco Telescope, wants to observe away from the galactic plane, the anti-center of our galaxy. Now this part of the sky is visible between the months of October to February, so if you have an interesting target that is up outside the months of October to February, there will be a higher likelihood that your proposal will be accepted.

Rob: Well, thank you very much for joining me today, Adrea.

Andrea: Yeah, thank you, Rob.

Rob: I look forward to seeing more images from the Dark Energy Camera as they come out because those first light images were spectacular.

Andrea: Thanks

Rob: We will put a link to those images in our show notes. Thanks for listening. This is Rob Sparks for the 365 Days of Astronomy podcast and I hope you will join us for the November edition.

End of podcast:

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