Separation

Also called: sep.

The angle between two objects — for a double star, the distance between its stars in arcseconds.

Separation decides how easy a double star is: Albireo's 34″ splits at 20×; Epsilon Lyrae's pairs, about 2.3″ apart, need 100–150× and steady air. Your telescope's resolution sets the limit.

Examples in the sky

• Albireo (β Cyg)
• Epsilon Lyrae (Double Double)
• Mizar and Alcor

Related terms

• Double star
• Position angle
• Resolution
• Angular size