Telescope
A telescope is an optical or multi-wavelength instrument that collects and focuses electromagnetic radiation — including visible light, radio waves, X-rays, and infrared — from distant astronomical objects, enabling detailed study of their properties. The resolving power and light-gathering ability of a telescope depend principally on the diameter of its primary aperture, with larger apertures resolving finer detail and detecting fainter objects. Modern astronomical telescopes range from ground-based optical giants such as the Extremely Large Telescope (ELT, 39 m primary mirror) to space-based observatories like the James Webb Space Telescope, which operates in the infrared to study the early universe.
Key Formula
R = 1.22 × (λ / D)
LaTeX: R = 1.22 \frac{\lambda}{D}
| Symbol | Meaning | Unit |
|---|---|---|
| R | Angular resolving power (Rayleigh criterion) | radians |
| λ | Wavelength of observed light | meters (m) |
| D | Diameter of the telescope aperture | meters (m) |
Worked Example
Problem
What is the angular resolution of the Hubble Space Telescope (primary mirror diameter D = 2.4 m) observing visible light at wavelength λ = 550 nm?
Solution
Step 1: Convert wavelength to meters: λ = 550 nm = 550 × 10⁻⁹ m = 5.50 × 10⁻⁷ m. Step 2: Apply the Rayleigh criterion: R = 1.22 × (λ / D) = 1.22 × (5.50 × 10⁻⁷ / 2.4). Step 3: R = 1.22 × 2.292 × 10⁻⁷ = 2.796 × 10⁻⁷ radians. Step 4: Convert to arcseconds: 2.796 × 10⁻⁷ rad × (180/π) × 3600 = 0.0577 arcseconds.
Answer
Angular resolution ≈ 0.058 arcseconds (approximately 58 milliarcseconds)
Comparison of Major Telescopes by Type and Aperture
| Telescope | Type | Aperture | Wavelength | Location |
|---|---|---|---|---|
| Hubble Space Telescope | Optical/UV/IR | 2.4 m | UV–near IR | Low Earth orbit |
| James Webb Space Telescope | Infrared | 6.5 m | Near to mid IR | L2 point |
| Atacama Large Millimeter Array | Radio | 12 m (each dish) | Millimetre | Chile (4500 m altitude) |
| Chandra X-ray Observatory | X-ray | 1.2 m (grazing) | X-ray | Elliptical Earth orbit |
| Very Large Telescope (VLT) | Optical | 4 × 8.2 m | Optical/IR | Paranal, Chile |
| Extremely Large Telescope | Optical | 39 m | Optical/IR | Cerro Armazones, Chile |
Interactive Tools
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Related Terms
From Greek tele (far) and skopein (to look or observe), meaning "to see far." The word was coined by the Greek mathematician Giovanni Demisiani in 1611 to describe the instrument invented by Hans Lippershey in 1608 and famously improved by Galileo Galilei for astronomical observations.