An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular

Perpendicular

In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

 axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth (compass bearing) of the pointing direction of the instrument. Rotation about the horizontal axis varies the altitude

Altitude

Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

 (angle of elevation) of the pointing direction.

These mounts are used, for example, with telescope

Telescope

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

s, camera

Camera

A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

s, radio antenna

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

s, heliostat mirror

Heliostat

A heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space...

s, solar panel

Solar tracker

A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices....

s, and gun

Weapon mount

A weapon mount is a weapon component used to secure an armament. Weapon mounts can be broken down into two categories: static mounts and non-static mounts.-Static mount:...

s and similar weapons.

Several names are given to this kind of mount, including altitude-azimuth, azimuth-elevation and various abbreviations thereof. A gun turret

Gun turret

A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...

is essentially an alt-azimuth mount for a gun, with some armour to protect the weapon and its operators.

Astronomical telescope altazimuth mounts

When used as an astronomical telescope mount

Telescope mount

A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument...

, the biggest advantage of an alt-azimuth mount is the simplicity of its mechanical design. The primary disadvantage is its inability to follow astronomical objects in the night sky

Night sky

The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight,...

 as the Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 spins on its axis the way that an equatorial mount

Equatorial mount

An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...

 can. Equatorial mounts only need to be rotated about a single axis, at a constant rate, to follow the rotation of the night sky (diurnal motion

Diurnal motion

Diurnal motion is an astronomical term referring to the apparent daily motion of stars around the Earth, or more precisely around the two celestial poles. It is caused by the Earth's rotation on its axis, so every star apparently moves on a circle, that is called the diurnal circle. The time for...

). Altazimuth mounts need to be rotated about both axes at variable rates, achieved via microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 based two-axis drive systems, to track equatorial motion. This imparts an uneven rotation to the field of view that also has to be corrected via a microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 based counter rotation system. On smaller telescopes an equatorial platform

Equatorial platform

An equatorial platform or equatorial table is an equatorial telescope mount in the form of a specially designed platform that allows any device sitting on it to track astronomical objects in the sky on an equatorial axis. They are used to give equatorial tracking to any device sitting on them, from...

 is sometimes used to add a third "polar axis" to overcome these problems, providing an hour or more of motion in the direction of right ascension

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

 to allow for astronomical tracking. The design also does not allow for the use of mechanical setting circles

Setting circles

Setting circles are used on telescopes equipped with an equatorial mount to find astronomical objects in the sky by their equatorial coordinates often used in star charts or ephemeris.-Description:...

 to locate astronomical objects although modern digital setting circles have removed this shortcoming.

Current applications

Typical current applications of altazimuth mounts include:

Research telescopes

• Mounts for very large telescopes. In the largest telescopes the mass and cost of an equatorial mount is prohibitive and they have been superseded by computer controlled Altazimuth mounts. The simple structure of an alt-azimuth mount allows significant cost reductions, in spite of the additional cost associated with the more complex tracking and image-orienting mechanisms. An altazimuth mount also reduces the cost in the dome structure covering the telescope since the simplified motion of the telescope means the structure can be more compact.

Amateur astronomical telescopes

• Beginner telescopes. Altazimuth mounts are cheap and simple to use.
• Dobsonian telescope
  Dobsonian telescope
  A Dobsonian telescope is an alt-azimuth mounted newtonian telescope design popularized by the amateur astronomer John Dobson starting in the 1960s. Dobson's telescopes featured a simplified mechanical design that was easy to manufacture from readily available components to create a large, portable,...
  
  s. John Dobson
  John Dobson (astronomer)
  John Lowry Dobson is a popularizer of amateur astronomy. He is most notable for being the promoter of a design for large, portable, low-cost Newtonian reflecting telescopes that bears his name, the Dobsonian telescope. The design is considered revolutionary since it allowed amateur astronomers to...
  
   popularized a simplified altazimuth mount design for Newtonian reflectors because of its ease of construction; Dobson's innovation was to use non-machined parts for the mount that could be found in any hardware store such as plywood
  Plywood
  Plywood is a type of manufactured timber made from thin sheets of wood veneer. It is one of the most widely used wood products. It is flexible, inexpensive, workable, re-usable, and can usually be locally manufactured...
  
  , formica
  Formica (plastic)
  Formica is a brand of composite materials manufactured by the Formica Corporation now based in Newcastle, Tyne & Wear, a division of the New Zealand company Fletcher Building. In common use, the term refers to the company's classic product, a heat-resistant, wipe-clean, plastic laminate of paper or...
  
  , and plastic plumbing parts combined with modern materials such as nylon
  Nylon
  Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
  
   or teflon.
• "Goto telescopes
  GoTo (telescopes)
  In amateur astronomy, "GoTo" refers to a type of telescope mount and related software which can automatically point a telescope to astronomical objects that the user selects...
  
  ". It has often proved more convenient to build a simple alt-azimuth mount and use a computer
  Computer
  A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
  
   to manipulate both axes to track an object, than to build a more mechanically complex equatorial mount that employs only a single motor. When astrophotography
  Astrophotography
  Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photographs of an astronomical object were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for...
  
   is involved, a further motor has to be used to rotate the camera to match the field of view for long exposure photographs.

See also

• Heliostat
  Heliostat
  A heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space...
  
  
• Horizontal coordinate system
  Horizontal coordinate system
  The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane. This coordinate system divides the sky into the upper hemisphere where objects are visible, and the lower hemisphere where objects cannot be seen since the earth is in...
  
   - a system to locate objects on the celestial sphere via Alt-azimuth coordinates
• Parallactic angle
  Parallactic angle
  In spherical astronomy, the parallactic angle is the angle between the great circle through a celestial object and the zenith, and the hour circle of the object. It is usually denoted q. In the triangle zenith—object—celestial pole, the parallactic angle will be the angle at the celestial object....
  
  
• Solar tracker
  Solar tracker
  A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices....