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Io

Io Moon Gemini Visible Level 3 Medium telescope (6-8") - Timing dependent
Credit: NASA / JPL / University of Arizona. License: Public domain. (Wikimedia Commons)
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Properties

Magnitude 5.0
Angular Size 1.2 arcmin
Type: Moon
Distance: 0.003 AU
Orbital Period: 1.8 days
Diameter: 1,822 km
Atmosphere: Sulfur dioxide
Features: Volcanoes, lava flows
Most volcanically active body.

Position & Identifiers

RA 07h 05m 45.7s
Dec +22° 56' 34.3"
Constellation Gemini
Catalog Io
Io — NASA/JPL
Image: NASA/JPL · PIA00715

Physical Properties

Diameter 1,822 km (0.14× Earth)
Mass 8.93e22 kg
Albedo 0.62 (62% reflected)
Temperature -183°C to -130°C
Rotation 42.5 hours
Atmosphere Sulfur dioxide
Surface Volcanoes, lava flows
Angular Size 0.5″ (current)

Orbital Properties

Semi-major Axis 0.0028 AU (421,567 km)
Eccentricity 0.0040
Inclination 0.00°
Orbital Period 1.8 days
Distance 4.987 AU (41.5 light-min)
Elongation 99.2° Good

Observing Tips

Best Months May , June , July
Visibility Binoculars
Where to Look Near Jupiter
Notes Most volcanically active body.

Parent Body

Orbits Jupiter
Orbital Period 1.76 days
Distance 421,567 km

Discovery

Discovered by Galileo Galilei
Date 1610

Current Ephemeris

4.987
AU from Earth
746.1M
km
0.5″
Angular Size
99°
Elongation

Visibility

Set a location in User Settings to see visibility data.

Community Photos (1)

Credit: NASA / JPL / University of Arizona. License: Public domain. (Wikimedia Commons)

Credit: NASA / JPL / University of Arizona. License: Public domain. (Wikimedia Commons)

Skybred Feb 28, 2026