Says Robert Vanderbei, chair of Operations Research and Financial Engineering at Princeton, the modern digital world is making it possible, and almost easy, for amateurs to take astrophotos in their own backyards that are as good as or better than those taken at professional observatories only a generation ago. The key enablers are computer controlled mounts for very precise pointing control, CCD cameras, and modern image processing tools.
In his February 27 Lunch ‘n Learn talk, he shared many of the images that he captured with his own equipment from his Montgomery, NJ home, as well as a working methodology to guide amateurs who wish to pursue astrophotography affordably.
Vanderbei became interested in amateur astronomy around 1999 with a small optical telescope and star catalogs. He was largely unsuccessful in seeing many interesting objects owing to New Jersey’s light pollution. And so, after about a year, he purchased a specialized digital camera that allowed long exposures that made faint objects brighter. With digital processing techniques, he found that he could eliminate much of the effect of local light pollution by subtracting a constant from the brightness of every pixel. The result is a picture that appears to have been taken from a mountaintop.
Surprisingly, perhaps, he has never visually seen most of the pictures that he has captured. He showed images of the Crab Nebula, the remnant of a supernova that exploded in 1054, the Lagoon Nebula, a cloud of glowing hydrogen gas, the Hercules Globular Cluster, a cluster of about a million stars within our Milky Way that emulates a beehive of activity, and Vanderbei’s favorite,the Dumbbell Nebula, whose image involved a two and a half hour hour exposure that brought out many subtle details.
Vanderbei recommends a solid, stable, and accurate mount that can compensate precisely for the earth’s rotation during long exposures. His 1.4 megapixel CCD [charge-coupled device] camera has only a USB cable and a port for power. Its quantum efficiency is approximately 65%; in other words, about 65% of the photons that hit its CCD chip generate a signal. That makes for a vast improvement over conventional emulsion photography. Cooling the CCD chip dramatically reduces random noise, and so there is cooling circuitry that lowers the temperature of the CCD chip to 30 degrees Celsius below the ambient temperature. He notesthat the least important part, for deep sky astrophotography at least, is the telescope itself.
His honed set-up methodology requires only about 20 minutes. Key steps include:
· using a finder scope on the mount to site Polaris, the North Star, loading specialized software that controls the camera;
· loading a planetarium program that assists locating items of interest;
· synching on a star to establish good communication between the telescope and planetarium program;
· and centering the target area and calibrating
The real fun, he emphasizes, starts the next day with the required image processing on the computer. The raw data gathered at night might include as many as 50 images that need to be aligned and combined into one final image. Vanderbei limits the length of individual exposures in case airplanes fly though and because the quantitative measures of a star’s brightness cannot exceed certain limits for individual exposures, but the measures can be added arithmetically from the multiple images. There are also interesting opportunities to enhance images with color and to correct pixel values to provide for greater clarity.
A podcast and the presentation are available.
Robert J. Vanderbei is the chair of Operations Research and Financial Engineering. He also has associated faculty status in the departments of Astrophysics, Computer Science, and Mathematics. Originally from Michigan, he has been “out east” for most of his adult life and here at Princeton since 1990. As a researcher, he applies the tools of his training in mathematics to a broad variety of problems ranging from designing the optics for a space telescope capable of imaging Earthlike planets around nearby stars to the portfolio selection problem in finance. He also likes computer graphics and spends some time every November making a new version of his so-called “Purple America” election map.