Liquid mirror

From Wikipedia, the free encyclopedia

It has been suggested that this article or section be merged with Mercury mirror. (Discuss)

Liquid mirrors are mirrors made with reflective liquids. The most common liquid used is mercury, but other liquids will work as well (for example, low melting alloys of gallium). Liquid mirrors can be a low cost alternative to conventional large telescopes.

Isaac Newton noted that the free surface of a rotating liquid forms a circular paraboloid and can therefore be used as a telescope, but he could not actually build one because he had no way to stabilize the speed of rotation (the electric motor did not exist yet). The concept was further developed by Ernesto Capocci of the Naples Observatory (1850), but it was not until 1872 that Henry Skey of the Dunedin Observatory in New Zealand constructed the first working laboratory LMT.

1 Conventional land-based liquid mirror telescopes
2 Moon-based liquid mirror telescopes
3 Space-based ring liquid mirror telescopes
4 Advantages and disadvantages
5 Sources
6 External links

[edit] Conventional land-based liquid mirror telescopes

These are made of liquid stored in a cylindrical container made of a composite material, such as Kevlar. The cylinder is spun until it reaches a few revolutions per minute. The liquid gradually forms a paraboloid, the shape of a conventional telescopic mirror. The mirror's surface is very precise and small imperfections in the cylinder's shape do not affect it. The amount of mercury used is small, less than a millimeter in thickness.

[edit] Moon-based liquid mirror telescopes

Low temperature ionic liquids (below 130 kelvins) have been proposed[1] as the fluid base for an extremely large diameter spinning liquid mirror telescope to be based on the earth's moon. Low temperature is advantageous in imaging long wave infrared light which is the form of light (extremely red-shifted) that arrives from the most distant parts of the visible universe. Such a liquid base would be covered by a thin metallic film that forms the reflective surface.

[edit] Space-based ring liquid mirror telescopes

It has been suggested that this article or section be merged with Mercury mirror space telescope. (Discuss)

The Rice liquid mirror telescope design is similar to conventional liquid mirror telescopes. However, it will only work in space, where gravity will not distort the mirror's shape into a parabola. The design features a liquid stored in a flat-bottomed ring-shaped container with raised interior edges. The central focal area would be rectangular, but a secondary rectangular-parabolic mirror would gather the light to a focal point. Otherwise the optics are similar to other optical telescopes. The light gathering power of a Rice telescope is equivalent to approximately the width times the diameter of the ring, minus a percentage based on optics, superstructure design, etc.

[edit] Advantages and disadvantages

The greatest advantage of a liquid mirror telescopic is its small cost, about 1% of a conventional mirror. This cuts down the cost of the entire telescope at least 95%. The University of British Columbia's 6-meter liquid mirror telescope cost about a fiftieth as much as a conventional telescope with a glass mirror.[2] Unfortunately, the mirror can only be pointed straight up. If it tilts from the zenith, it loses its shape. The mirror's view changes as the Earth rotates and objects cannot be physically tracked. An object can be briefly electronically tracked while in the field of view by applying a voltage to the CCD to shift electrons across it at the same speed as the image moves; this tactic is called "drift scanning." However, some types of astronomical research are unaffected by these limitations, such as long-term sky surveys and supernova searches. Since the Universe is isotropic and homogeneous, the investigation of its structure by cosmologists can also use liquid mirror telescopes. However, research is underway to develop telescopes that can be tilted.