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Altazimuth mount

technology Maturity 11-13 Next article →

An altazimuth mount is a mechanical system used to support and rotate instruments.

Dobson class
Dobson class

It works by rotating an object around two perpendicular axes. These axes are one vertical and one horizontal. This design allows an instrument to point in many different directions. Many different tools use this system for movement. A standard camera tripod is a common example of an altazimuth mount. Gun turrets also function as altazimuth mounts for weaponry. Other uses include radio antennas, solar panels, and heliostat mirrors.

To understand how it moves, you must look at its two specific motions. The first motion occurs around the vertical axis. This movement changes the azimuth, which is the compass bearing of the instrument. The second motion occurs around the horizontal axis. This movement changes the altitude, which is the angle of elevation. By combining these two movements, the device can scan the sky or the horizon. This two-axis system is also called an altitude-azimuth or azimuth-elevation mount.

Using these mounts for astronomy presents unique mechanical challenges. The Earth rotates on its axis, which causes stars to move across the sky. This movement is known as diurnal motion. An equatorial mount handles this by rotating on only one axis at a constant rate. An altazimuth mount cannot do this easily. It must rotate both axes at variable rates to track a star. Modern systems use a microprocessor-based two-axis drive to manage this. This system must also include a microprocessor-based counter rotation system. This corrects the uneven rotation in the field of view.

There is a specific technical problem called gimbal lock at the zenith. The zenith is the point directly overhead. When a telescope points at elevations close to 90 degrees, the azimuth axis must move very quickly. If the altitude is exactly 90 degrees, the required speed becomes infinite. Because of this, altazimuth telescopes have a "zenith blind spot." This blind spot is usually between 0.5 and 0.75 degrees from the zenith. This means they cannot track smoothly at elevations greater than 89.5 or 89.25 degrees.

History shows how different designs have solved these tracking problems. John Dobson popularized a specific version for Newtonian reflector telescopes. He created what is now called a Dobsonian mount. His innovation was using non-machined parts for the mount. He used materials found in any hardware store, such as plywood and formica. He also used plastic plumbing parts alongside modern materials like nylon or teflon. This made building telescopes much simpler and more affordable for many people.

Dobson class
Dobson class

Today, altazimuth mounts are essential in professional research. The largest telescopes in the world often use computer-controlled altazimuth mounts. In these massive projects, the mass and cost of an equatorial mount are prohibitive. The simple structure of an altazimuth mount provides significant cost reductions. It also reduces the cost of the telescope dome. Because the motion is simplified, the dome structure can be more compact. This efficiency is vital for large-scale astronomical research.

Amateur astronomers also find many ways to use these mounts. Many beginners start with cheap and simple altazimuth mounts. Some users prefer "GoTo" telescopes for their convenience. These telescopes use a motion controller to manipulate both axes simultaneously. This allows the telescope to track an object automatically. While equatorial mounts use a single motor, the GoTo system manages the complex two-axis movement. This provides a modern way to explore the night sky with ease.

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