Not unlike Lawrence-of-Arabia crossing the broiling Sahara Desert on a camel, an astronomer riding herd on a CCD astrocamera, can see-with the aid of this time-exposure digital photographic technology-the weird optical effects of mirages, too. What an astronomer sees in deep space are mirages caused by a phenomena known as gravitational lensing.
Gravitational lensing is a result of a heavy gravity object, such as a galaxy, bending light waves coming from a more distant object (or objects) located far behind it. This effect can create duplicate, triplicate, or even more "copies" of the distant object or objects.
So, where one distant quasi-stellar object-QSO or quasar for short-exists, gravitational lensing produces two quasars in the observer's eyepiece. Such lensing phenomena was predicted by Einstein's General Theory of Relativity.
According to astronomer Bill Keel of the University of Alabama, "If gravity can be properly viewed as a bending of space produced by mass, then light rays should change their direction upon passing a massive object. In extreme cases, we might expect to see multiple images of the same object, formed by light that has gone around opposite sides of the intervening mass."
Keel notes that the world's first example of gravitational lensing involved the odd double quasar known as QSO 0957+561 located in the constellation Ursa Major.
At the time of its discovery in 1979, 0957+561 was a major deep-space find-two identical quasars just a few arcseconds apart appeared in the telescope eyepiece. Indeed, while finding such a literal "twin quasar" would have been a sweet scientific discovery (sadly, none have been found to date), it turned out that the 0957+561 duo was, in fact, the same quasi-stellar object-optically "Xeroxed", so to speak.
I guess you could say finding "Xeroxed" quasars may be stranger than finding a real-life twin quasar. At the very least, the discovery verified Einstein's prediction about gravity affecting space.
Astronomers Dennis Walsh, Bob Carswell, and Ray Weymann showed that 0957+561 has identical redshifts and electromagnetic spectra; a gravitational lens, they said, created by an unseen giant galaxy (between the quasar and the astronomers) cuased the optical illusion of two quasars from one.
"A luminous (unseen) galaxy almost in front of one quasar image, and a surrounding cluster contributes to the lensing," said Keel. "This system has given us more to work with, in analyzing its properties and the mass of the lensing galaxies, than any other lensed QSO."
Viewing a gravitational lens is easily within the realm of an amateur astronomer, if the observer is patient and has, at least, a 10" telescope. Before you attempt this deep-space feat, you should be somewhat skilled at CCD astrophotography. (I am not an astrophotographer, so I will defer to the experts.)
A CCD or charge-coupled device is the major electronic component of digital-imaging technology. CCD cameras used in astrophotography require sturdy mounts to deal with wind and other sources of vibrations. Also, long exposures are required to photograph distant objects such as quasars.
A few years ago, amateur astronomer Michael Purcell successfully took a CCD astrophoto of QSO 0957+561 using a Meade 10" LX200 (f/6.3) off-the-shelf telescope.
"I normally take a quick 30-second picture of an object to ensure that its positioning is correct," Purcell said. "In this case, although the background starfield was what I expected, there was no sign of the quasar! It was only when I had taken the 15-minute exposure that I actually saw the quasar... I took the picture from my driveway."
What's in the Sky: Get ready for a total eclipse of the Moon on the day of the winter solstice, Tuesday, Dec. 21, at 3 a.m. It will be visible throughout the United States. There's an extra bonus this time: the Moon will be full during the eclipse. In December, the southernmost Moon of the month occurs Dec. 6. On that day, our nearest neighbor is lowest in the south around noon.
Lou Varricchio, M.Sc., was a senior science writer at the NASA Ames Research Center in California. He is a member of the NASA-JPL Solar System Ambassador program in Vermont. He is the author of the book, "Inconstant Moon: Discovery and Controversy on the Way to the Moon" and has produced and hosted several science programs for public radio and television.