Horizontal and Equatorial coordinates

Horizontal: the view from your horizon

Horizontal coordinates use altitude, the angle above the horizon, and azimuth, the direction around it. They are recomputed for your selected place and time. This is the mode to reach for when you are using naked eye, binoculars or an alt-azimuth mount.

An altitude near 0° sits on the geometric horizon; 90° is directly overhead. Azimuth is measured around the horizon from north. The compass control and the horizon layer help you connect this view to the ground around you.

Equatorial: the atlas reference

Equatorial coordinates use right ascension and declination, projected from Earth’s equator and poles onto the celestial sphere. They are a stable way to identify an object in catalogues and printed atlases, and they map onto equatorial telescope mounts. The Equatorial view is no less real; it simply does not put your local horizon at the centre of the reading experience.

Which mode should you choose?

• Horizontal when asking where to look from a specific place and time.
• Equatorial when reading right ascension and declination or using the map as a reference atlas.
• Switch deliberately when the sky looks unfamiliar. The coordinate system changes the frame, not the objects.