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(Alternative words: zettahertz.)

Today’s question for Dr. Science is, “What’s the biggest optical telescope in the Empire? How far can it see?”

Over the years, a great many different telescopes have held that particular title: from the Great Eye at the Starspike (Eliéra’s oldest observatory, dating to the pre-Imperial era), through the first orbital telescopes, the large refractor at Farside Observatory, Seléné, and the Deep Orbit Oculus in far Súnáris orbit.

All, however, were rapidly outclassed by the discovery of very-long-baseline interferometry, which uses a technique referred to as aperture synthesis to correlate signals from a set of telescopes to produce images having the same angular resolution as an instrument the diameter of the entire set. Some limited use was made of these techniques with ground-based and orbital instruments, restricted by the difficulty in accurately quantifying optical-range photons for software processing, but once these difficulties were solved, construction began on much larger interferometric telescopes. Three particular examples of these held the title of largest optical telescope in turn, and while the others have been upgraded and remain in use, it is the last of these retains it today.

The first of these, the Barrascán Array, was constructed in the Meryn System, consisting of an array of millions of statites (produced by self-replicating, autoindustrial techniques) 48 light hours in diameter. Intended for general observation, the array possesses an angular resolution of 1.12 x 10^-20 radians, enabling it to resolve objects 20 cm across at 2,250 light-years (i.e., the current fringe of the Associated Worlds, which was then unknown space).

The second, intended to carry out both exploration surveys and long-range observations of the galactic core, was the Very Long Baseline Observer, which made use of smaller arrays of deep-orbit telescopes located in systems across the width of the Empire, each reporting via the interstellar dataweave to the Exploratory Service’s headquarters in Almeä System. This gave it an effective diameter of 164 light-years, and thus an angular resolution of 3.74 x 10^-25 radians, giving it the capability of resolving with micrometer resolution objects throughout the Starfall Arc, should its view be unobstructed. Indeed, if not for intervening objects, planetary rotation, local weather, and other such obstructions, it would be capable of reading a book over the shoulder of a sophont on any world in the galaxy — were one to pass within its view, since as you can imagine, an array of array of telescopes 164 light-years across is somewhat unwieldy to maneuver.

The apex of this technology is the Super-Size Synthetic Aperture, intended for in-depth studies of the deep universe. The SSSA takes the general concept of the VLBO even further by extending the array – by means of various treaty arrangements and leases – across much of the width of the Associated Worlds, reporting data back over tangle channels. Its effective diameter is no less than 1,825 light-years, giving it a theoretical angular resolution of 3.36 x 10^-26 radians – which is to say, it can resolve a 33 m object at the rim of the observable universe.

The SSSA, however, is limited by the larger gaps between its elements, which are themselves limited to a single mobile telescope per system, and thus in turn by the amount of light collectable by each of these individual telescopes. It is also, unfortunately, constrained by the difficulty of maneuvering and recalibrating such a massive device, and by the political difficulties of passing through many different polities during reorientation, which tends to cause lengthy delays, increased costs, and where no permission can be obtained, gaps in array coverage. For most practical purposes, therefore, the VLBO can be considered the largest general-purpose optical telescope available to the Empire.

Dr. Science

– from Children’s Science Corner magazine