Seeing the Universe

before 1610 - naked eye astronomy

1608 - Galileo's hand held telescopes

1673 - Hevelius' long telescopes

1780 - Herschel's large reflectors

1845 - Rosse's Leviathian

1890 - Barnard's camera

1923 - The Hooker 100 inch

1948 - The Palomar 200 inch

1990 - The Hubble Space Telescope

1998 - The Keck 10 metre pair

2000 - The VLT array

2015 - Planning for the JWST

2020? - Planning the OWL

How much further?

The distance to the nearby stars is found by measuring their parallax, their movement in relation to distant stars as the Earth moves round its orbit. Astronomers from ancient times had tried to detect stellar parallax without success. Some even claimed that its non-observability was evidence for a geocentric universe.

The demands of positional astronomy, the science of determining positions on the surface of the Earth using the stars as reference points, led to the gradual improvement of telescope mountings. By 1838, instrumention was precise enough for three astronomers to measure parallax simultaenously using three different types of instrument. Bessel succeeded with a heliometer, Struve with a filar micrometer, and Henderson with a meridian circle. Bessel's measurements were the most accurate, but heliometers were difficult to construct and few observatories had them. It was soon realised that Henderson's meridian circle method could produce satisfactory parallaxes. Most observatories already possessed meridian circles for positional astronomy and were thus equipped for participation in the exciting new activity of measuring distances to nearby stars. The sketch shows a wall mounted, single axis, telescope for positional astronomy - a mural circle, a prototype meridian circle.  History of Astrometry