Equatorial mount

A type of mount for an astronomical telescope. As a reflection of the Earth's rotation, celestial objects rotate from east to west around the celestial poles. The simplest way to track these celestial objects is to rotate the telescope around the polar axis, which is parallel to the Earth's axis. To point it in any direction, a declination axis is set perpendicular to the polar axis, and the telescope is attached at a right angle to this. Once the telescope is pointed at the celestial object by rotating both axes, it is only necessary to drive it at a constant speed around the polar axis. Many of them use a synchronous motor driven by a commercial power source.

Equatorial mounts are divided into various types depending on how the polar axis is supported and the arrangement of the declination axis. There are the German type, which has the declination axis at the end of the polar axis, the British type, which supports the polar axis at both ends and places the declination axis in the middle, the yoke type, which splits the polar axis in two and places the telescope between them, the fork type, which cantilevers the polar axis, and the type in which the upper bearing of the yoke type is horseshoe shaped so that observations can be made around the poles. The German type is used for relatively small telescopes, while the horseshoe shaped bearing is used for large telescopes. Equatorial mounts are widely used for small to large telescopes because they make it easy to track celestial bodies. However, there is a trend toward using altazimuth mounts, which are more symmetrical with respect to gravity, for large optical and radio telescopes.

[Shiro Nishimura]

"How to Make a Portable Equatorial Mount" edited by the Astronomical Guide Editorial Department (1979, Seibundo Shinkosha)" ▽ "Fujii Akira's Astronomical Telescope Guide" by Fujii Akira (1990, Seibundo Shinkosha)" ▽ "How to Make a Telescope 2: From Tuning Up Equipment to Portable Equatorial Mounts" edited by the Astronomical Guide Editorial Department (1999, Seibundo Shinkosha)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

天体望遠鏡の架台の一形式。地球の自転の反映として、天体は天の南北極を中心として東から西へ回転する。この天体を追尾するには、地軸と平行に設けた極軸の周りに望遠鏡を回転させることが、もっとも簡単な方法である。任意の方向に向けるために、極軸と直交する赤緯軸を設け、さらにこれに直角に望遠鏡を取り付ける。両軸を回していったん天体に望遠鏡を向けると、あとは極軸の周りに等速度で駆動するだけでよい。商用電源で同期電動機を回すものが多い。

　赤道儀は、極軸の支え方と赤緯軸の配置によっていろいろな形式に分かれる。極軸の端に赤緯軸をもつドイツ式、極軸を両端で支え、中間に赤緯軸を置くイギリス式、その極軸を中間で二つに分け、その間に望遠鏡を置くヨーク式、これを片持ちにしたフォーク式、極のまわりも観測できるようにヨーク式の上側軸受を馬蹄(ばてい)形にした形式のものなどがある。ドイツ式は比較的小型のものに、馬蹄形軸受は大型望遠鏡に用いられる。赤道儀は天体の追尾が容易に行えるので、小型望遠鏡から大型望遠鏡まで広く用いられている。しかし大型光学望遠鏡や電波望遠鏡では、重力に対して対称性のよい経緯台式架台が採用される方向にある。

［西村史朗］

『天文ガイド編集部編『ポータブル赤道儀の作り方』（1979・誠文堂新光社）』▽『藤井旭著『藤井旭の天体望遠鏡ガイド』（1990・誠文堂新光社）』▽『天文ガイド編集部編『天体望遠鏡の作り方2　機材のチューンナップからポータブル赤道儀まで』（1999・誠文堂新光社）』

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