An arcminute (symbol: ' or arcmin) is a fundamental unit of angular measurement in astronomy, representing 1/60th of a degree. Just as we divide an hour into 60 minutes, astronomers divide each degree of the celestial sphere into 60 arcminutes. This unit is perfectly suited for measuring medium-scale celestial objects and separations—too large for arcseconds, yet requiring more precision than whole degrees.</p><p>The arcminute proves invaluable when describing the apparent sizes of familiar astronomical objects. The full Moon spans approximately 30 arcminutes across our sky, making it an excellent reference point for visualizing this angular scale. Deep-sky objects like galaxies, nebulae, and star clusters are commonly measured in arcminutes, with the spectacular Orion Nebula extending roughly 66 by 60 arcminutes. Modern digital astronomy has made arcminute measurements increasingly precise, allowing astronomers to track subtle changes in object positions and sizes over time, crucial for studying stellar proper motion, asteroid trajectories, and the expansion of supernova remnants.
Examples
**Examples:**<br>- Full Moon: ~30' (0.5°)<br>- Venus at maximum: ~1'<br>- Orion Nebula (M42): ~66' × 60'<br>- Typical binocular field of view: 5-7°<br>- Typical telescope eyepiece field: 30-60'
Practical Applications
Arcminutes are essential for telescope field-of-view calculations, helping astronomers select appropriate eyepieces and plan observations. They're crucial for measuring double star separations, tracking asteroid positions, and determining the angular sizes of planets, comets, and deep-sky objects. Observatory pointing systems and astronomical catalogs universally employ arcminute precision for accurate celestial navigation and object identification.