Sky
library.

Right ascension is measured eastward in hours, while declination is measured north or south of the celestial equator. Astro Arena uses epoch J2000.0.

The scale is logarithmic: five magnitudes represent a hundredfold difference in received flux. Negative magnitudes are very bright.

Letters often roughly follow brightness, but not always. The designation is a stable way to connect a star with its constellation.

For a quick estimate, use a fist at arm’s length as about 10°, three middle fingers as 5°, and a little finger as 1°.

A wide field helps orientation; a narrow field confirms detail. During star hopping, move through overlapping fields.

Clusters resolve into stars, nebulae are diffuse, and galaxies often show a brighter core. Appearance depends strongly on sky darkness and magnification.