Astronomy depends upon observing and interpreting more or less subtle properties in the electromagnetic radiation (‘light’) reaching us from celestial bodies. The usual instruments are imaging cameras and spectrometers, which measure aspects of the first-order spatial and/or temporal coherence of light. Quantum optics potentially offers additional information channels beyond these established ones of imaging and spectroscopy. Further degrees of freedom exist in the statistics of photon arrival times, or in the amount of photon orbital angular momentum. Such quantum-optical measures may carry information on how the light was created at the source, and whether it reaches the observer directly or via some intermediate process. Astronomical quantum optics may help to clarify emission processes in natural laser sources and in the environments of compact objects, while high-speed photon-counting with digital signal handling enables multi-element and very-long-baseline versions of the optical intensity interferometer. In particular, flux collectors built for observing gamma rays through atmospheric Cherenkov light can be used as interferometer elements. A first experiment in electronically connecting telescopes as a digital intensity interferometer was made in October 2007, using 12-meter diameter flux collectors of the VERITAS array in Arizona. In all this, time resolutions of nanoseconds are required, as are large photon fluxes, making photonic astronomy very timely in an era of large Cherenkov flux collectors, and of future extremely large telescopes.