Aperture

How it is used

The most important specification when choosing a telescope, given in millimetres or inches. Experienced observers like to say 'aperture is king'. Photographers use the same word for the opening of a camera lens.

Example sentences

1. For galaxies and nebulae, aperture matters much more than magnification.

2. On a dark night, a telescope with a 200 mm aperture can show the spiral arms of bright galaxies.

Common collocations

• large aperture
• an aperture of 200 mm
• aperture size
• small-aperture telescope

Related terms

• telescopeAn instrument that collects light or other radiation from distant objects with lenses, mirrors or antennas, so that faint and far-away things can be seen and studied.
• eyepieceThe small lens at the end of a telescope that you look through. Changing the eyepiece changes the magnification and the field of view.
• magnitudeA number that measures how bright a star or other object looks. The scale runs backwards: the lower the number, the brighter the object, and very bright objects have negative values.
• observatoryA building or site with telescopes and instruments for observing the sky. Many large observatories are built on high, dry mountains far from city lights.

This word in other fields

The same English word can have a different meaning in another field:

• aperture · Photography

More terms: Telescopes & Observation

• astronomer
• light pollution
• space telescope
• radio telescope
• spectroscopy