Louis Daguerre pointed a telescope at the Moon in 1839, exposed a plate, and got a fuzzy spot. The telescope had drifted as the Earth turned. It was the first known attempt to photograph an astronomical object, and it failed.
A year later, on March 23, 1840, John William Draper, a chemistry professor at New York University, managed the first successful Moon photograph. He took a 20-minute daguerreotype through a 5-inch reflecting telescope.
The early records
Progress came slowly because the problems were physical. Early processes were poor fits for the sky. The daguerreotype was too slow to catch anything but the brightest objects, and the wet collodion plate limited exposures to however long it stayed wet. Telescopes had to be stiff enough not to sag out of focus, and clock drives had to turn the mount at a steady rate. Many of the pioneers were amateur astronomers and experimenters, the “gentleman scientists” of the mid-19th century.
The Sun came next. Léon Foucault and Hippolyte Fizeau may have photographed it in 1845. The solar corona was first captured during the eclipse of July 28, 1851, when a local daguerreotypist named Johann Julius Friedrich Berkowski exposed a plate for 84 seconds at the Königsberg Observatory. On July 16 and 17, 1850, William Cranch Bond and John Adams Whipple photographed Vega with Harvard’s 15-inch Great refractor, the first picture of a star other than the Sun.
In 1880 Henry Draper, John’s son, used dry plates to take a 51-minute exposure of the Orion Nebula, the first photograph of any nebula. Three years later Andrew Ainslie Common made exposures of up to 60 minutes with a 36-inch reflector he built in his backyard in Ealing, outside London. The images showed stars too faint for the human eye.
Catching light
The principle has not changed since. Film and digital sensors both add up photons over long exposures, so they record dim stars, nebulae and galaxies that eyes cannot see. Filters that pass a narrow band of wavelengths pull out further detail. Bigger lenses and mirrors gather more light, and remote sites help because urban light pollution swamps the detector.
Because the Earth rotates, the telescope has to turn the other way to keep up. Equatorial or computer-controlled mounts handle this, but motor drives are imperfect, tubes sag and the atmosphere bends light. Photographers correct for it by keeping a guide star centred during the exposure, using a second guide scope or an off-axis guider with a prism or beam splitter. Observers once did this by hand, even riding inside the telescope. Automated systems now do it in professional and amateur kit alike.
From the 1970s, the CCD began replacing photographic plates. It is far more sensitive, records across a wider range of light, and does not lose sensitivity during long exposures the way film does. The Hubble Space Telescope, working above the atmosphere’s turbulence with a 2.4-metre mirror, can record stars down to the 31st magnitude, roughly 1,000 times dimmer than the Hale Telescope could reach in 1949.
A hobby with many branches
Almost all observational astronomy now relies on photography, so the word “astrophotography” usually means the amateur kind, chasing attractive pictures rather than data. Setups run from an ordinary film or digital camera on a tripod to advanced gear, and some amateurs build or modify their own equipment.
The field split early into specialities: star mapping, astrometry, stellar classification, photometry, spectroscopy, polarimetry, and the discovery of asteroids, meteors, comets, variable stars, novae and planets.
