365DaysDate: February 1st, 2009


Title: The Stratospheric Observatory for Infrared Astronomy (SOFIA)

Podcaster: Martin Ratcliffe

Description: SOFIA is the Stratospheric Observatory for Infrared Astronomy, and it’s ready to fly. SOFIA houses a 2.5-meter telescope in the tail of a 747-SP Jumbo Jet. Flying higher than 41,000 feet, a huge sliding door will uncover the cavity where the telescope lies, and expose the telescope to low temperatures, perfect for infrared viewing. Above 99% of atmospheric water vapor, the telescope will study a wide range of astronomical objects over its expected 20-year lifetime. Come on board and tour this amazing aircraft and learn about some of the astronomical targets as the aircraft approaches its first open door flights this spring, followed by its first science observations this summer.

Bio: Martin Ratcliffe received his BSc in Astronomy from the University College London, England. Although his final year research project was published, he pursued a career in Planetariums, working at theaters in Armagh, Northern Ireland, Buhl Planetarium in Pittsburgh and the CyberDome Theater in Wichita, Kansas. A former President of the International Planetarium Society, Martin is a contributing Editor for Astronomy magazine, co-writing the Sky Show monthly column for the past 13 years. For the past three years as Director of Professional Development, Martin travels the country and occasionally around the world training planetarium staff in the use of “DigitalSky” for Sky-Skan, a leading digital planetarium manufacturer. Martin has published 4 books, including The Night Sky Revealed (Barnes and Noble) and State of the Universe 2008 (Praxis-Springer).

Today’s Sponsor: This episode of “365 Days of Astronomy” is sponsored by the American Association of Variable Star Observers, the world’s leader in variable star data and information, bringing professional and amateur astronomers together to observe and analyze variable stars, and promoting research and education using variable star data. Visit the AAVSO on the web at


Hello, my name is Martin Ratcliffe. You can read my regular Sky Show column each month in Astronomy magazine. I teach astronomy part time at Wichita State University, and work full time for Sky-Skan, a leading international digital planetarium company.

Today I’ll talk about an amazing airborne telescope, matching the size of the Hubble Space Telescope, called SOFIA. Just imagine for a moment flying above 41,000 feet in a 747 jumbo jet and one quarter of the rear fuselage slides open to reveal a giant 2.5 meter wide telescope. You’re above 99 percent of water vapor and nearly half way to space. SOFIA stands for the Stratospheric Observatory for Infrared Astronomy. And it’s almost ready for its first observing flights.

You may have heard of this project. It’s been going on for years. At one point it was even cancelled by NASA, even though the airborne observatory was almost complete. Many wondered if SOFIA would ever fly. It now has more than 50 hours in the air, and coming in spring of this year, the first flights with the door open are planned. Now that’s exciting.

I visited the aircraft in early January 2009 at the Dryden Aircraft Operations Facility in Palmdale California. Housed in a giant hanger used as the film set for Pirates of the Caribbean, this airborne vessel of the skies is not looking for gold, but for precious photons of infrared light emitted, for example, from regions of star and planet formation. It’ll search for extrasolar planets, and explore the left-over debris disks from planet formation. SOFIA will trace complex molecules buried deep inside cold clouds of gas and dust – molecules like glycines, the simplest amino acids which are the building blocks of life. The atmospheric structure of planets and the sizes of Kuiper Belt objects that wander the cold dark reaches of the outer solar system will be probed in unprecedented detail. And SOFIA is expected to last 20 years, providing the opportunity for long-term monitoring of astronomical objects in the infrared.

So let’s tour the aircraft first. Entering the hanger, I’m immediately overwhelmed by the gleaming white 747, it’s tail practically touching a roof – an illusion I am assured – there’s a substantial clearance. SOFIA is ready to fly. Climbing aboard, I recall my first visit some years ago at the WACO facility in Texas where the aircraft was refitted. Its unpainted external body expressed the years of preparation still underway. The giant cavity at the rear of the aircraft had no door on it – the engineering challenges caused significant delay – no plane has ever flown with such a large hole in the side, and the door *had* to close prior to landing. Now the door was complete, the plane ready, and the telescope was fully functional.

The previous empty shell in the main cabin is now full of positions for computer consoles for controlling the telescope and its instruments. It’s here that scientists will sit to control the observations. Toward the rear is a large white bulkhead and a blue-colored ring – it’s a huge bearing with a giant counterweight – the telescope lies on the other side of the bulkhead, balanced like a dumbbell. It’s also the optical axis – light is directed from telescope into giant instruments located in the main cabin.

The 2.5 meter telescope itself lies behind this new bulkhead to separate the telescope cavity that will be open to the stratosphere from the shirtsleeve comfort of the main cabin. The bulkhead supports a half an atmosphere of pressure, or a load of half a million pounds of force!

So let’s go aft and enter the tail section. Now we’re behind the bulkhead. This tail section will be open to the low stratospheric pressure and -40 degree temperatures. A small door leads to the telescope cavity. Later this year the dust protecting black material will be removed and the telescope will be ready for the crowning moment for any new telescope, “First Light”.

Advanced instruments being built for SOFIA can be changed out far easier than a space-borne telescope – and can take advantage of heavier, more complex instruments.

Nothing about this aircraft is small. 177 feet long and a wingspan of 196 feet, SOFIA is designed to fly in the stratosphere, high above 99.9% of atmospheric water vapor. The scope was built in Germany and the telescope was fabricated in France. Germany is a key partner in operation of the observatory as well as in construction. With a similar aperture to HST, the SOFIA telescope weighs 44,100 lbs and points out of a giant 3,150 pound sliding door that leaves one quarter of the fuselage gaping open to the thin air of 41,000 feet.

The aircraft is a retired 747SP used by Pan-Am, but never reached service. However, it was originally christened Clipper Lindberg by Charles Lindbergh’s wife. With a new life as an astronomical observatory, Lindberg’s son Eric and last year was rechristened the plane.

Dr. Eric Becklin, long-time project manager of SOFIA and iconic IR astronomer is excited to see the first science – he has looked forward to this moment for at least the past ten years, and now he really believes it.

So why infrared? The main reason is that many of the most interesting objects astronomers want to look at emit a lot of light in the infrared. Infrared light is really heat radiation. Where visible light is blocked by the dark dust clouds that fill our galaxy, and shroud the central black holes of many galaxies, infrared light can pass straight out of these regions, allowing astronomers to investigate the details of how stars form inside dusty cocoons, what complex molecules are present.

But that only covers part of the story. Stars and galaxies in the early universe produced copious amounts of ultraviolet light. Because of the sheer size of our universe, light from these objects still reaches us from billions of light years away. However, as this light traveled to us over billions of light years, taking billions of years for the journey, the space between galaxies stretched, and so did the wavelength of light in transit. The glow from these distant objects now lies in the infrared, and is the target of many major new telescopes, from Europe’s Herschel Space Telescope being launched later this year to NASA’s James Webb Space Telescope due to be completed in the middle of the next decade, just a few years from now. SOFIA will provide a 20 year lifetime of observations against the backdrop of these shorter lifetime instruments, allowing in some case detailed follow-up that might otherwise be unavailable.

That’s really soon folks. The waiting is almost over. SOFIA plan to ramp up to 100 flights a year, each at least 8 hours long. If events such as special occultations of stars by solar system objects occur anywhere in the world, SOFIA will be able to fly into the path to make detailed observations.

And if you’re a teacher, you could get to fly. At the front of the aircraft cabin are a dozen or so seats for teachers and science writers – these individuals will carry the news and experiments far beyond the university research lab’s and into the classrooms of America and into the magazines, blogs, and future podcasts for the public to read, and hear. SOFIA has an extensive and involved Education and Public Outreach program.

You can discover more at the SOFIA web site at

Thanks for listening, this is Martin Ratcliffe, a member of the 365days of astronomy subcommittee.

End of podcast:

365 Days of Astronomy
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