Double telescope
A double telescope is used in astronomy to describe two telescopes of approximately the same size , which are arranged parallel to one another, so that they enable simultaneous observations on the same star or in the same star field. Mechanically, this can be done on the same mount , but recently also in neighboring observatory domes , if the telescopes have a common electronic control.
Public observatories
During star tours at public observatories, there are often longer waiting times when looking through the telescope, which a suitable double telescope can cut in half. In addition, the astronomer can help if anything is unclear or if the telescope is unintentionally adjusted.
Astrophotography
The first large double telescopes were constructed in the second half of the 19th century for the purposes of astrophotography - e.g. B. for the Astrophysical Observatory in Potsdam. While the sky image is exposed on one telescope , the other can serve as a precise guide telescope . Using a guide star, it monitors the correct tracking of the celestial rotation in order to depict the photographed stars precisely as a point. Simultaneous astrophotography and spectrography is also possible .
The Bruce refractor is a rare special form , which was built around 1890 for the Heidelberg observatory and named after the sponsor from the USA. It is even a triple telescope , consisting of a double astrograph for photo plates , mounted on a long guide scope with a 25 cm aperture and 400 cm focal length. With the photographic lenses of 40 cm aperture and 200 cm focal length each, thousands of plates were recorded and over 100 asteroids were discovered. Today the Bruce refractor is still used for guided tours.
Double astrographs were then to a common design, adjacent to simultaneous recordings star fields - such as for accelerating a sky screenable - perform. Around 1965, in just a few months at the Black Forest private observatory Vehrenberg (observatory), the Falkau photographic star atlas was created, which with its 300 map sheets (10 × 10 ° each) was widely distributed and later led to further celestial atlases with an even larger map scale . For the search for asteroids or comets , simultaneous recordings of the same star field are carried out in order to be able to distinguish small bodies from plate defects or "hot" CCD pixels. In the case of time-shifted recordings, an approximate determination of the path speed is possible.
Parallel control of large telescopes
A modern special form of the double telescope was implemented in the Large Binocular Telescope (LBT), where two independently usable giant telescopes with two 8 m mirrors can be connected in parallel for purposes of interferometry .
Similar, even larger projects are being planned, e.g. B. the Large-Aperture Mirror Array (LAMA). This should then be used to couple four or more large telescopes.
Double telescopes for amateur astronomy
For amateur astronomers , the market also offers double telescopes that
- are either constructed according to the construction of large binoculars , but have objectives twice as large (aperture 60, 80 or 100 mm),
- or in the form of a double observation telescope with a common tube for both optics. These instruments can - if they have a stable mount - be equipped with apertures over 100 mm and about 20 to 100 times magnification.