Short answer
A star generates much of its light through nuclear fusion; the Sun is our star. A planet is a different kind of body that orbits a star, such as Earth orbiting the Sun. Planets can be bright in the night sky because they reflect sunlight, not because they are stars. 1 2
Planets orbit stars in many systems; stars generate light through fusion while planets mainly reflect stellar light.
On this page
At a glance
Scroll to compare all columns →
| Question | Star | Planet |
|---|---|---|
| Energy and light | Fusion-powered and self-luminous | Mainly reflects starlight |
| Example | Sun | Earth |
| Typical role | Central body of a planetary system | Body orbiting a star |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Star. A self-luminous astronomical body whose energy comes chiefly from nuclear fusion during most of its lifetime. 1
Planet. A large body orbiting a star or stellar remnant; in the Solar System, a planet meets the IAU orbital and shape criteria. 2
Key differences
Mass and internal physics matter more than apparent brightness. A star’s sustained fusion makes it a source of energy for its surroundings. A planet may have internal heat or emit infrared radiation, but that does not turn it into a fusion-powered star. 1 2
A main-sequence star’s core fuses hydrogen into helium, releasing energy that travels outward as light and heat. A planet’s visible light usually comes from illumination by its star. This explains why the Sun is the energy source for Earth even though both bodies can appear as bright disks from some vantage points. 1 2
How to tell them apart
In our Solar System, the Sun is the star and Earth, Mars and Jupiter are planets. In a night-sky image, brightness alone is not reliable; orbital motion against background stars is a more useful clue for Solar System planets. 1 2
Where they overlap
Both are gravitationally bound astronomical bodies and can be nearly round. Both can belong to the same planetary system. 1 2
Edge cases
Brown dwarfs sit between common planets and stars in some properties and complicate a simple mass cutoff. Exoplanets can orbit multiple stars or stellar remnants; the Solar System’s formal planet definition is not automatically a universal exoplanet rule. 1 2
The distinction is not “stars twinkle, planets do not.” Atmospheric conditions and viewing geometry can affect appearances. Nor does a planet have to be cold: planets can retain internal heat and radiate infrared energy. The classification depends on formation and physical behavior, not just a night-sky impression. 1 2
Why the distinction exists
The names distinguish the energy-producing bodies from orbiting companions and help describe how systems form and evolve. 1 2
Common misconceptions
“Planet” does not mean a faint star. Venus looks strikingly bright from Earth because it reflects sunlight. 1 2
Examples
The Sun produces energy by fusion. Earth receives that light and reflects a small portion of it, yet Earth remains a planet. 1 2
Sources
Sources checked October 3, 2026.
- NASA Science — Stars. Stars overview.
- NASA Science — What Is a Planet?. The IAU definition of a planet; Pluto.