Bryan McAllister’s personal reference notebook
July 30, 2026Short & citedBlog
Civic Viewpoint.
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Kept by Bryan McAllister — short guides, clear facts, and the Canadian angle when it matters.
Field Notes • Astronomy

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet in the Solar System.

Updated July 30, 20261 min readCited sources

Jupiter is the fifth planet from the Sun and the largest in the Solar System — a gas giant visible to the naked eye from Earth.

What it is

Jupiter is a gas giant planet made mostly of hydrogen and helium, with no solid surface. Its diameter is about 143,000 km, and it has a mass roughly 318 times Earth’s — more than twice the mass of all other planets combined.

Key details

Jupiter has 95 officially recognized moons, including the four Galilean moons (Io, Europa, Ganymede, and Callisto). It also has faint rings and a strong magnetic field. Its day lasts about 9.9 hours, and its year is about 11.86 Earth years.

Why it matters

Jupiter is the Solar System’s dominant planet by size and mass, with a powerful magnetosphere. It formed about 4.6 billion years ago and is a common target for amateur astronomy across Canada, visible with the naked eye in the night sky.

In short

  • Largest planet in the Solar System, a gas giant with no solid surface.
  • Made mostly of hydrogen and helium; diameter about 143,000 km.
  • Has 95 known moons and faint rings.
  • Visible from Earth without a telescope, including from Canada.
Canadian angle

Jupiter is visible from Canada’s night sky and is a common target for amateur astronomy across the country.

Quick questions

How big is Jupiter?
Jupiter’s diameter is about 143,000 km, or about 11 times Earth’s diameter.
How many moons does Jupiter have?
Jupiter has 95 officially recognized moons.
Can you see Jupiter from Earth?
Yes. Jupiter can be seen with the naked eye and is one of the brightest objects in the night sky.

Sources

  1. NASA — https://www.nasa.gov/jupiter/
    Supports: Largest planet, composition, day length, moons, and general Jupiter facts.
  2. NASA — https://science.nasa.gov/jupiter/jupiter-facts/
    Supports: Diameter, composition, orbital distance, and official moon count.
  3. Encyclopaedia Britannica — https://www.britannica.com/place/Jupiter-planet/Basic-astronomical-data
    Supports: Diameter and mean distance from the Sun.
  4. Universe Today — https://www.universetoday.com/articles/jupiter
    Supports: Gas giant composition and atmospheric structure.
  5. European Space Agency — https://www.esa.int/Science_Exploration/Space_Science/Juice/Facts_about_Jupiter
    Supports: Diameter, mass, atmosphere, moons, rings, and day length.
  6. Las Cumbres Observatory — https://www.lco.global/spacebook/solar-system/jupiter/
    Supports: Visibility from Earth and basic planetary facts.