Luke Keller

Luke Keller

Dana Professor, Department of Physics and Astronomy

Specialty:Astrophysics, airborne astronomy, spectroscopy, optical instrumentation, natural science general education
Phone:(607) 274-3966
Office:264 Ctr for Natural Sciences
Ithaca, NY 14850


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Preparing for astronomy with NASA's newest airborne observatory

Posted by Luke Keller at 11:40PM   |  Add a comment
Looking out the window of SOFIA as we taxi across the DAOF runway prior to takeoff on November 18, 2010.

On Thursday, November 18, we took off for the last of the observatory characterization flights. We tested several techniques that we will use to get the first science results in early December. The next time we fly we'll be conducting observations for new astronomical research.

The tests went very well. Follow this link to a short movie of an infrared image of a star taken with FORCAST while in flight. You will notice that the image of the star is two or three pixels across and moves around very quickly. The movie is actually five copies of a two-second clip for a total of ten seconds. The movie was recorded with FORCAST at a frame rate of 400 Hz (Hertz, or frames per second, see my previous post for a few more details). The purpose of this test was to understand telescope vibrations (and how they affect image motion) so that they can eventually be removed or at least minimized. Minimizing vibrations will improve the image quality since most objects we observe with SOFIA will be very faint so we will use long exposure times, which combined with the motion of the telescope will produce fuzzier images.

This and other tests went very well. Our final test included observations of the Orion Nebula (M42 for you astronomers), a region where stars are forming about 1500 light years from Earth. The data look so good that we expect to be able to use them for new astrophysics studies. In other words, SOFIA is ready for astronomy! [Images to come in a future post.]



Posted by Luke Keller at 8:40AM   |  4 comments
Self portrait as we take off on SOFIA

Today we took off on SOFIA for its second flight devoted 100% to measuring and characterizing the performance of the telescope and camera systems. It was very exciting for me to finally fly after working so long on the project. I was in charge of data quality control during the flight. We spent last week conducting line operations (we call them "line-ops"), using the observatory as if we were in flight but actually sitting on the ground. During the line-ops we practiced controlling the movement of the telescope with computer commands issued from the FORCAST camera. Juergen Wolf and his team from DSI and NASA/Ames also tested their new fine diagnostic camera (FDC), which can take visible light images at several hundred frames per second. For comparison, a movie or video camera usually records images 60 times per second. Why so fast? We wan't to "freeze" the star images, which move around in the telescope and camera viewers due to vibrations of the telescope and aircraft. Taking very fast movies in both visible (FDC) and infrared light (FORCAST) will allow the telescope team to understand in detail how the optical and telescope control systems are working. All of our testing so far indicates that the telescope and cameras are ready to go after a few small adjustments. Our first flight devoted to new astronomy (no more testing!) are scheduled for the week after Thanksgiving. 

Take-off time was 5:00 PM (Pacific Time) on Wednesday, November 10. The flight was scheduled to be 10 hours long, enough time for us to fly from LA to London, but instead we flew a back-and-forth flight plan as they did for the first light flight in May. Here's the flight plan from from last night's flight:

SOFIA flight plan

The flight began and ended at DAOF in Palmdale, CA (the white dot at the top of the map). The faint dotted outline in the upper right corner is the coast of southern California and Baja, Mexico. The light blue/green lines are the flight "legs" that add up to the full 10-hour flight plan. Each flight leg is plotted so that SOFIA can observe a particular object in the sky. For this flight the targets were bright stars that we used to test the cameras.

The flight crew including FORCAST team worked hard during the flight. This photo shows the FORCAST team working at the "PI Rack" that contains our camera control computer and the communication system that we use to communicate with one-another during the flight. Everyone wears headphones to reduce noise and enable efficient communication.

FORCAST team working on SOFIA

Our flight was about an hour longer than planned due to a minor problem: the telescope cavity door was stuck open (!!) due to a software glitch. Not a problem for the aircraft or pilots, but they had to slow our descent to allow the telescope mirrors to warm up from -37 C (at our cruising altitude of 42,000 feet) to 1 C on the ground. Landing with a cold telescope would have condensed ice on the mirrors, bad news for a $100,000,000 telescope! As soon as we landed, the aircraft operations engineers fixed the problem and closed the door.
All in a night's work on SOFIA.

Posted by Luke Keller at 11:05AM   |  Add a comment
Three FORCAST infrared images of Jupiter

It's been a few months since we took the first infrared images with SOFIA and FORCAST. I promised some more detail on how we produced the "first light" images so here it is. Since people can't see infrared light we need a way to display the images from the camera using colors we can see. FORCAST records raw images through filters that pass infrared light of different wavelengths. These filters work just like red, green, or blue filters do in visibile light. When a computer displays a digital image it can be with any color map. A color map is a list of the colors the computer uses when it displays pixels of different brightness in an image. One of the simplest looking color maps is "gray scale"; shades of gray indicate brightness usually with white being brightest and black indicating faintest. But a color map can display brightness variations in an image in any color you like. Here's and image of Jupiter in visible light (color image at right) and in infrared light displayed with a blue color map:

SOFIA/FORCAST and visible light images of Jupiter

For the first light image of Jupiter we used a red color map to represent infrared light recorded through a 37 micron filter, green to represent infrared light recorded through a 24 micron filter, and blue to represent 5.4 micron light. Here's the result:

Three SOFIA/FORCAST infrared light images of Jupiter

Now we add the three images together to get a "false color" image of what Jupiter might look like if humans could see infrared (see for more details on interpreting false color images). Note that false color images can represent any measurable quantity. Perhaps the most common false color image you have likely seen is a radar weather map of precipitation, which uses visible colors to represent reflectivity of radar waves (also a form of light that humans can't see) off of rain droplets. Our false color image displays infrared brightness at three different wavelengths. Here's the final result that USRA/FORCAST team member Jim De Buizer created:

SOFIA/FORCAST image of Jupiter adding the three infrared

The smaller dots in this image are three of Jupiter's moons. Note that we usually measure wavelength in microns (thousandths of a millimeter). We use the symbol 'µm' for microns so 5.4 µm is 0.0054 millimeters. For comparison, the average human hair diameter is about 50 µm.

We're back in Palmdale preparing for more SOFIA flights. We'll do two flights of telescope tests followed by three flights doing new astronomical observations! More updates coming soon.



Posted by Luke Keller at 12:13PM   |  Add a comment
SOFIA first light image of Jupiter

SOFIA has flown with FORCAST running and returned its very first astronomical images!

I just returned to Ithaca after nearly two weeks helping prepare FORCAST and SOFIA for these first light images. I literally had goose bumps as I watched the airplane land early Thursday morning and then downloaded the data from our infrared camera on-board. I worked at DAOF with SOFIA scientists Jim De Buizer, Bill Vacca, and FORCAST lead Terry Herter all day Thursday to process the data and produce the first light images. After 11 years of work on theSOFIA project (and I'm one of the more "recent" additions to the team!) it was a true thrill to see these images take shape on our computers. My next post will include details of how we processed the data to make the color images. SOFIA's next flights will be devoted 100% to new astronomy research and I'll be flying!

NASA press release

Note on viewing infrared images: Infrared light has colors just as there are colors in visible light, but since infrared light is invisible to humans, astronomers use “false color” images to display infrared views of the universe. In false color images, like those presented here, visible light colors (blue, green, and red) are used as proxies for the brightness in three infrared colors captured by the SOFIA/FORCAST camera system. So the color image you see is a representation of how the object might look if you could see in infrared light. Different physical processes cause emission of infrared light in different infrared colors so the three colors presented in these images indicate differences in physical characteristics like temperature, density, and chemical composition. Finally, it is important to note that in astronomy visible light images often only show us the details on the surfaces of objects while viewing infrared light allows us to look deep into the objects. Using infrared images like those enabled by SOFIA and the FORCAST camera are the only way to remotely look deep into the atmosphere of Jupiter or into the very center of the M82 galaxy. Visible light shows us the tip of the iceberg while infrared light images show us what lies beneath.

SOFIA/FORCAST image of the planet Jupiter

Jupiter: Composite (false color) infrared image of Jupiter from SOFIA’s first light. Observations were at infrared wavelengths of 5.4 (blue), 24 (green) and 37 microns (red), made by Cornell University’s FORCAST camera. A recent visible-wavelength picture of approximately the same side of Jupiter is shown for comparison.  The white stripe in the infrared image is a region of relatively transparent clouds through which the warm interior of Jupiter can be seen. (Visible light image credit:  Anthony Wesley)

MORE DETAILS: Composite (false color) infrared image of Jupiter from SOFIA’s first light flight taken at infrared wavelengths of 5.4 (blue), 24 (green) and 37 microns (red), with Cornell University’s FORCAST camera. A recent visual-wavelength picture of approximately the same side of Jupiter is shown for comparison.  The white stripe in the infrared image is a region of relatively transparent clouds through which the warm interior of Jupiter can be seen. Visible light shows us the detailed structure of the surfaces (tops) of the clouds on Jupiter while the infrared image shows us the distribution of different atmospheric components and physical characteristics of material deep under the cloud surfaces. (Visible light image credit: Anthony Wesley)

SOFIA/FORCAST image of the galaxy M82

Galaxy, M82: Composite (false color) infrared image of the central portion of galaxy M82, from SOFIA’s first light flight, taken at wavelengths of 19 (blue), 31 (green) and 37 microns (red). The middle inset image shows the same portion of the galaxy at visual wavelengths.  The infrared image views past the stars and dust clouds apparent in the visible-wavelength image into the star-forming heart of the galaxy. The long dimension of the inset boxes is about 5400 light years. (Visible light image credit:  N. A. Sharp/ NOAO/AURA/NSF)

MORE DETAILS: Composite (false color) infrared image of the central portion of galaxy M82, from SOFIA’s first light flight, taken at [infrared] wavelengths of 19 (blue), 31 (green) and 37 microns (red). The middle inset image shows the same portion of the galaxy at visible wavelengths.  The infrared image views through the stars and dust clouds apparent in the visible-wavelength image deep into the star-forming heart of the galaxy, which is totally invisible when viewed only in visible light.  Where the visible light images show features like stars and dust in the outer regions of the M82 galaxy, the infrared image reveals  the central regions of the galaxy where stars are forming much faster than they do in our own Milky Way galaxy. The long dimension of the inset boxes is equivalent to about 5400 light years at the distance of M82. (Visible light image credit:  N. A. Sharp/ NOAO/AURA/NSF)


Posted by Luke Keller at 1:39PM   |  1 comment
FORCAST team leader, Terry Herter, operating FORCAST just after its first installation on the SOFIA telescope. (Photo: George Gull)

I spent last Friday teaching sixth grade classes in McLean, VA, at Spring Hill Elementary School where my nephew is a student. We discussed infrared astronomy and SOFIA. Kids ask some of the best questions, many that adults are curious about but bashful to ask. These kids had great questions about what it's like to work on the aircraft so I decided to post those here with answers in case anyone else is wondering:

How long are the flights and where do you go?
Flights will be about 8 hours long, of which about 6 hours will be spent conducting astronomical observations. It takes about 1 hour from takeoff to reach the cruising altitude and start observations, and another hour at the end of the flight to descend and land. SOFIA currently takes off and lands at NASA's Dryden Aircraft Operations Facility (DAOF), located in Palmdale, CA. So after an 8 hour flight we end up exactly where we started! The actual route of our flights depends on what objects in the sky we are observing. Since the SOFIA telescope only points our of the port (left) side of the aircraft, we fly from east to west when looking into the southern part of the sky, west to east when looking north, etc. Flight plans for SOFIA look very chaotic since the aircraft must change direction every time we point the telescope towards a new object for observations, typically every hour or so.
How many people fly on a SOFIA flight?
There are three pilots in the flight crew, 10 seats in the First Class section in the nose of the aircraft, and 17 seats in the science operations section farther back. Not all seats will be occupied on a given flight, though. The average crew for science operations, not including the pilots, includes the mission director, one person operating the science instrument (camera or spectrograph), at least one telescope operator, and at least one astronomer from the team conducting the astronomical observations. So a total of three in the cockpit and at least four in the science operations section of the aircraft. 
Why does SOFIA have First Class seats?
These seats will often be unoccupied, but when SOFIA missions become more routine over the next few years these seats will be available for science teachers who work with astronomers to gain experience participating in astronomical observations first hand. These teachers will be part of the Airborne Astronomy Ambassador program. Other guests of the SOFIA project may occasionally use these seats. Finally, SOFIA will eventually spend part of the year flying from a base in the southern hemisphere. This will allow observations of objects in the southern sky, which are not possible from locations in the northern hemisphere. During the southern deployments of SOFIA it may be necessary to fly maintenance and other personnel from DAOF and Ames to the southern site and back. Currently the site planned for southern deployments is Christchurch, New Zealand.
What do you eat and drink while flying on SOFIA?
That depends on the person. There is no "galley" (or kitchen) on SOFIA like on commercial aircraft so we have to bring our own snacks and drinks and they can't require cooking. Most astronomers I know, including me, will just bring snacks. We have to be very careful not to spill food or drinks on the electronics and computers, though, we don't want sticky fingers to ruin our observations. Work on airborne astronomy flights is often so busy that there is very little time for even thinking about eating.
What happens if there is an emergency while the plane is flying?
On a commercial jetliner the flight crew, including flight attendants, assist passengers in the event of an emergency. SOFIA has a crew of three or four pilots, but no flight attendants, so anyone who flies on SOFIA must take safety training classes at NASA prior to flying. In those classes, which last a few hours each, we learn how to open and close the aircraft door and how to deploy the emergency slides if we have to evacuate the aircraft quickly. We also learn where all of the on-board fire extinguishers are, where the oxygen masks are, where the first aid kits are, and how to use them. The modifications left SOFIA with not as many places for the emergency oxygen masks that pop out of the ceilings of commercial jets if the cabin looses pressure. If SOFIA losses cabin pressure, we'll put on oxygen masks located near our work spaces and then wait for the pilots to fly to a lower altitude where the air is thick enough for us to breath.
Why do you wear headphones?
SOFIA only has a few seats and the floors are not carpeted all over like in a commercial jet. Seats and carpeting, not to mention all of the other passengers, absorb a lot of sound. That means that SOFIA is very loud even inside the pressurized cabin. Since we need to be able to talk with people sitting all over the aircraft during flights and observations, we all wear headphones with microphones on them. These help us talk to and hear everyone with out having to yell or get up and walk around the aircraft. We can also get updates and instructions from the flight crew if necessary.
How high does SOFIA fly?
SOFIA can fly to a maximum altitude of 13.7 km (about 45,000 feet), but most astronomical observations with be conducted at altitudes of about 12.5 km (41,000 feet). Under normal operating conditions, the telescope cavity will never be opened below 10.7 km (35,000 feet). This is to keep the telescope optics clean since most of the dust, moisture, and pollution in our atmosphere are located below 10.7 km. For comparison, most commercial aircraft cruise at 10.7 to 11.9 km.
Is it scary on SOFIA?
No, it's very exciting. The people who made the aircraft modifications and the people in charge of aircraft testing safety at NASA have worked very hard to insure the safety of people flying on SOFIA. It is just as safe as a regular commercial flight on a 747. However, when you first walk onto SOFIA it can be startling to see all of guts of the cabin exposed. Most of the white plastic molding and fixtures (like walls, overhead bins for carryon luggage, and even the low ceiling) have been removed on SOFIA to access the wiring and instruments that are normally hidden in a commercial jet aircraft. Here's a picture of what it looks like inside SOFIA. There are more at my Frequent Flyer photo gallery.
Do you have parachutes? 
Nope. Neither do the pilots. But I'm not worried.
Is there a bathroom?
Yes, the aircraft lavatory in the front of the airplane is available for all on board. The rest of the lavatories were removed to make room for the telescope. With only 10 or so people on board, though, I don't expect lines for the potty.
Got a question of your own? Leave a comment and I'll do my best to answer.

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