Date: July 10, 2012

Title: The Advanced Technology Solar Telescope

Podcaster: Rob Sparks

Organization: National Optical Astronomy Observatory (NOAO)


Description: Solar astronomy is about to take a big leap forward. The Advanced Technology Solar Telescope is currently under construction on the island of Maui. ATST Project Manager Joseph McMullin describes the ATST and discusses some of the research questions this new instrument will address.

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

Joseph McMullin is the project manager for the Advanced Technology Solar Telescope.

Today’s Sponsors: This episode of “365 days of Astronomy” 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

Additional sponsorship for this episode of 365 days of astronomy was provided by – Expanding your horizons in astronomy today. The premier on-demand telescope network, at dark sky sites in Spain, New Mexico and Siding Spring, Australia.”


Rob: Hi, this is Rob Sparks of the National Optical Astronomy Observatory and I am here today with Joseph McMullin of the National Solar Observatory. Good morning, Joe.

Joe: Good morning.

Rob: We are here today to talk about the Advanced Technology Solar Telescope but first could you tell us a little bit about your background, where you come from and what you have studied.

Joe: Sure. I am actually new to solar physics. I came to the National Solar Observatory back in November of 2011. Before that I had worked at the National Radio Astronomy Observatory and worked on the ALMA (Atacama Large Millimter Array) telescope and the EVLA (Enhanced Very Large Array) principally.

Rob: We are here to talk about a new telescope, the Advanced Technology Solar Telescope (ATST). What is your position with the ATST?

Joe: I am the Project Manager for the ATST.

Rob: Okay. It will be the largest solar telescope in the world when it is complete. First could you tell us what is currently considered state of the art in solar telescopes so we know where we stand now.

Joe: Sure. Well the reason this is so exciting is that the solar community has not really had a new large facility in over 30 years. So the facilities that are in existence now, the Dunn Solar telescope on Sac Peak…

Rob: In Sunspot.

Joe: In Sunspot, thank you, is a much smaller aperture mirror. However, it has a lot of new technologies the National Solar Observatory (NSO) has been developing to ensure diffraction limited observing even with that facility so instrumentation has been maintained but the ATST is going to be an innovation because it’s a four meter aperture and with that size you have the sensitivity and resolution to really observe the phenomena that the modeling has been predicting that you really haven’t been able to resolve at that point.

Rob: You sort of jumped ahead a little bit, but that’s fine. We now have an idea of where we are. You mentioned that it’s a four meter telescope. Could you give us some of the other specs and where and when it will be built.

Joe: Sure, It’s on the island of Maui in Hawaii and it will be on the summit of Haelakala and there are already other facilities on that site. This is the one, they did a survey to find the best conditions for seeing in particular to make sure that they would be able to optimize the imaging quality that they would be able to cover and that was the best site for them. And we’re hoping to start building on that site this year, later in the year. It’s a seven year construction project so 2019 is what we’re looking for in operations of that. The key aspects are the four meter aperture, that gian aperture is really the key. It’s an off-axis paraboloid and what that does in terms of the optical chain is that it avoids a lot of problems with diffraction around support structures so it allows you to have a very pure path without scattering.

Rob: That is similar to the design of the Green Bank Telescope, an off-axis paraboloid.

Joe: Exactly.

Rob: Even though it has great seeing, it is being outfitted with adaptive optics, is that correct?

Joe: That is correct. The key is you want to get down to the diffraction limit, the theoretical resolving limit of an ideal mirror and with the help of the adaptive optics you are able to correct for problems in the atmospheric seeing, the modulations of the atmosphere and get to that diffraction limit.

Rob: About a year ago, we did a podcast on adaptive optics and we talked about how it is done at night with guide stars and that sort of thing. So how does it work during the day when there are no guide stars to use?

Joe: They basically have what is called a wavefront sensor and there is a camera that breaks up images and because you are looking at the Sun you can use pieces of the Sun basically as your guide. And they break up that picture of the Sun into little sub-apertures, little pictures, and by correcting the focus of each of those, each of those will be slightly in or out of focus depending on the modulation of the atmosphere whatever optical aberrations you have remaining. So you can essentially correct the wavefront in that way. It’s similar to the way they correct problems with the cornea in the eye.

Rob: They are doing some neat stuff with eye surgery these days with that. So what types of scientific instruments will this telescope have and what types of scientific research will they be able to engage in with these instruments?

Joe: There are going to be five facility instruments to star with for the ATST. They span over ultraviolet, the visible and into the infrared which is really the new frontier in solar physics in a sense. Each of the different instruments, the Invisible Broadband Imager, which is being produced in-house at NSO. There is a VISP, Visible Spectral Polarimeter which is being provided by the High Altitude Observatory from UCAR.

Rob: I love all the acronyms.

Joe: Sorry about that. There are two instruments being produced by the University of Hawaii. One is a cryogenically cooled spectral polarimeter, another is a diffraction limited near-infrared spectral polarimeter and the last is what’s called a visible tuner filter bank which is being produced by Kipenhower Institute in Germany. One of those, the cryo near infrared spectral polarimeter is actuall a coronographic instrument, being able to observe on the edge of the Sun and observe a lot of these phenomena that are happening on the edge of the corona.

Rob: So what types of research and research questions are going to be answered by these instruments?

Joe: Fundamentally, the ATST design, everything that has driven the four meter aperture, the initial facility instruments is the fundamental goal of understanding the magnetic field, the magnetic structures, the three dimensional magnetic structure on the Sun. Because this is what’s controlling and what drives the variability of the solar output, it drives the solar wind, the solar flares, the coronal mass ejections. And the Sun is not only our nearest star so its astrophysically interesting in that we can study it with unprecedented resolution, foundationally we can use that to understand stars in other places. But it has a real immediate and tangible impact for us on the Earth because it does influence us. It drives our climate and some of this energetic solar activity can have a dramatic impact on telecommunications.

Rob: Yeah, space weather phenomena.

Joe: Exactly, and even human biology. So one of the things that I used in the talk earlier this week is that there is a good reason to study the Sun. Its interesting from an astrophysical sense it’s a plasma laboratory. But if you don’t want to be in it for that, for self-interest reasons, you could die as a result.
Rob: Especially if you are an astronaut.

Joe: That’s right. But NASA has put out some bulletins as the Sun was going into its solar maximum again that historically there have been some pretty energetic phenomena that have at solar maximum in particular. And one of them happened back in the 1800s, in 1859, called the Carrington Event that was so dramatic. There was so much energy deposited striking the Earth’s atmosphere, the magnetosphere, that it caused telegraph stations to spark and aurora were basically seen around the globe and that was at a relatively primitive time of our electronic and communications grid. Now something of that magnitude could really blow out that stuff so it really is relevant to us.

Rob: Even a much smaller one in ’89 took out the electrical grid in Quebec.

Joe: Exactly.

Rob: One of the engineering aspects I find fascinating about this is that you have a 4.2 meter, 4 meter telescope and it collects a lot of light which has to generate a lot of heat. So how do you deal with all the heat generated by a four meter telescope pointing at the Sun?

Joe: Exactly, that’s really the fundamental issue. As I said, we want to get diffraction limited images and the problem you have in a lot of observing is the seeing conditions. You have differences in temperature that can destruct or distort images that you are seeing. So for a solar telescope, for the ATST is that it’s a Gregorian focus. What that allows you to do, is you are coming to a focus before the secondary and what’s put in place there is a heat stop. What that does is it blocks off all the light other than that sort of 2-5 arc minute beam that you want for the scientific experiments. So that’s all that you are letting propogate past that point. So you have got several kilowatts of power hitting that primary and beaming up toward that secondary but you’ve only got a few hundred watts that pass beyond that. Then you got the whole observatory design. You have got plate coils with cooling structures. Each of the different optical structures has cooling around it. Everything is there to control the heat properties and to make sure we are flushing that out and trying to keep everything as close as possible to the same temperature.

Rob: That’s very interesting. That has to be a big engineering challenge.

Joe: It is, but we have a great crew doing it.

Rob: Well, thanks for joining me this morning, Joe. It’s been great talking to you.

Joe: Great. Thank you.

Rob: This is Rob Sparks for the 365 Days of Astronomy podcast and I hop you will join us for our August edition.

End of podcast:

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