This page gives beginner-oriented explanations of common terms used throughout the TRITON GOTO documentation.

TIP

Some definitions are intentionally simplified for first-time users. Consult dedicated astronomy references when more precision is required.

Equipment

Equatorial Mount

A mechanical mount that carries a telescope and rotates it to track celestial objects. Its two perpendicular axes are arranged specifically for following the apparent motion of the sky. TRITON GOTO controls equatorial mounts that use ONSTEP.

German Equatorial Mount

A common design with the telescope on one side and counterweights on the other. After a target crosses the meridian, the mount may need a meridian flip to place the telescope on the opposite side and continue observing.

Polar Axis

The mount axis aligned parallel to Earth's rotational axis, also called the right-ascension axis. When it points toward the corresponding celestial pole, the mount can track the sky primarily by rotating this one axis.

Polar Alignment

The process of adjusting the polar axis to point at the celestial pole during setup. Better alignment produces steadier tracking and reduces star trails in long exposures. In the Northern Hemisphere, roughly pointing toward Polaris provides an initial alignment.

Celestial Pole / North Celestial Pole / South Celestial Pole

Earth's rotation axis extended indefinitely meets the celestial sphere at two celestial poles. Stars appear to rotate around them.

Polaris

A bright star close to the north celestial pole, used in the Northern Hemisphere to locate the pole and assist polar alignment. Polaris is not exactly at the pole; it is offset by slightly more than one degree.

Polar Scope

A small reticle-equipped sight installed along a mount's polar axis. The position of Polaris in its field helps align the axis more accurately. Polar Scope Simulation provides a Polaris position reference.

Coordinates and Direction

Right Ascension (RA) / Declination (DEC)

The equatorial coordinate system identifies positions in the sky similarly to longitude and latitude on Earth:

• Right Ascension (RA) is analogous to celestial longitude and is expressed in hours, minutes, and seconds.
• Declination (DEC) is analogous to celestial latitude and is expressed in degrees.

A celestial object's RA and DEC are approximately fixed, and the mount uses these coordinates for GOTO.

Azimuth / Altitude

The horizontal coordinate system describes where an object is in the local sky at a particular time:

• Azimuth is its compass direction along the horizon.
• Altitude is its angle above the horizon: 0° at the horizon and 90° at the zenith.

Azimuth and altitude for the same object change continuously with time.

Meridian / Transit

The meridian is an imaginary great circle running from north through the zenith to south. When an object crosses it, the object transits and is generally at its highest altitude of the day.

Meridian Flip

If a German equatorial mount continues tracking after transit, the telescope can approach the tripod. A meridian flip moves the mount to the opposite side while keeping the same target, allowing tracking to continue with safer geometry. See Slewing and Meridian Flips.

Hour Angle

An angular measure of how far an object is from the meridian. It can be understood as how long remains before transit, or how long has elapsed since transit. Polar Scope Simulation uses hour angle to calculate the current Polaris position.

Sidereal Time / Local Zone Time

• Local Zone Time is ordinary civil clock time.
• Sidereal Time is an astronomical time scale tied to the apparent rotation of the stars and is used to calculate their positions.

The two progress at slightly different rates. The App performs the conversion automatically.

Clock Position

A convenient description that treats the field of view as a clock face, using directions such as 3 o'clock or 9 o'clock to describe an object's position.

Operation and Control

GOTO

A command that rotates the mount automatically to point the telescope at a selected celestial object. Select a target, then ONSTEP moves to its calculated coordinates.

Sync

A command that tells the mount which known object the telescope is currently pointing at, thereby correcting pointing coordinates. After accurately centering a known bright star, Sync can improve subsequent GOTO accuracy.

Tracking

Celestial objects appear to move because Earth rotates. Tracking moves the mount at a corresponding rate to keep an object in the field without continuous manual correction.

Sidereal / Lunar / Solar Rate

Tracking rates for different targets. Use Sidereal for stars and deep-sky objects, Lunar for the Moon, and Solar for the Sun—only with proper solar protection.

Guide Rate / Slew Rate / GOTO Speed

• Guide Rate is a slow direction-correction rate used for precise centering, such as 0.25X.
• Slew Rate controls manual movement through the direction controls, while GOTO Speed sets the maximum speed for automatic GOTO slews. Both are available in multiple levels.

Home

The mount's mechanical reference position, with both axes in an agreed starting orientation. Alignment and coordinate calculations use Home as their reference, so the mount should be at the correct home position at startup.

Park

A configured fixed position and state intended for shutdown, storage, and easier recovery at the next startup. Home is primarily a calculation reference; Park is primarily for operational storage and safety.

Limits

Configured movement boundaries intended to reduce the risk of the telescope or counterweight bar colliding with the tripod or other equipment. ONSTEP stops movement in the affected direction when a limit is reached. See Limit Settings.

Three-Star Alignment

A process of centering and confirming three known bright stars so the mount can calculate pointing error and improve GOTO accuracy. See Three-Star Alignment.

Smart Polar Alignment

After Three-Star Alignment, the software calculates polar error and guides adjustment of the base to improve polar alignment without an optical polar scope. See Smart Polar Alignment.

Celestial Objects and Observing

Magnitude

A measure of an object's brightness. The scale is inverse: a smaller number is brighter. A first-magnitude star is much brighter than a sixth-magnitude star; under a dark sky, the unaided eye can see stars around magnitude 6.

Deep-Sky Object

A general term for objects beyond the Solar System, primarily galaxies, nebulae, and star clusters. Most are faint and are best observed under dark skies away from urban light pollution.

Messier / NGC / IC / Caldwell Catalogs

Astronomical object lists. The Messier catalog contains 110 classic, relatively bright deep-sky targets popular with amateur observers, such as the Andromeda Galaxy M31. NGC and IC contain many more objects. The App includes these catalogs for target selection; see Tonight and Catalogs.

Light Pollution / Bortle Scale / SQM

• Light pollution is artificial illumination that brightens the night sky and obscures faint objects.
• The Bortle scale classifies sky darkness from 1–9: class 1 is darkest and class 9 represents a bright inner city.
• SQM is a measured sky-brightness value; a larger value generally represents a darker sky.

Twilight: Civil / Nautical / Astronomical

After sunset, the sky passes through civil, nautical, and astronomical twilight before becoming fully dark. Faint deep-sky observing is generally best after astronomical twilight ends.

Moon Phase / Terminator

• Moon phase is the changing shape of the Moon's illuminated portion, such as new, first quarter, full, and last quarter.
• The terminator is the day/night boundary on the Moon or a planet. Shadows near it make surface relief especially visible; near full Moon, high brightness and limited shadows reduce apparent detail.