The nearest star and the source of life for organisms on Earth.
In the vast universe, there are billions of stars and trillions of different planets. We’ve heard a lot about stars and planets, but the definitions of what a star is, what a planet is, and how they differ might still be unclear to many readers.
What is a Star? A star, or a celestial body capable of emitting light, is a massive spherical plasma entity, often much larger than Earth, ranging from tens to hundreds of thousands of times Earth’s mass. Stars can have orbits or no orbits at all.
Why Can Stars Shine on Their Own? Every object has a gravitational force that acts toward itself, whether it’s a small object like a table, a chair, a human, or large objects like planets, stars, and more. This force depends on the object’s mass. Therefore, for small objects, the gravitational force is too weak to be noticed and doesn’t have any significant effect. However, for large celestial bodies like stars, which are many times larger than Earth, this force creates extreme pressure at their cores. It’s so intense that it pulls atomic particles, especially hydrogen atoms, towards it at tremendous speeds. These atomic particles collide at high velocities, breaking each other’s structures and turning into a chaotic mixture of electrons and photons, known as plasma. Consequently, the core of a star is made up of plasma.
In this plasma state, hydrogen nuclei continue to collide at high velocities, recombining to form heavy hydrogen, and ultimately, helium nuclei. This process is known as nuclear fusion. Nuclear fusion releases an enormous amount of energy in the form of radiation, which moves to the star’s surface and makes it shine.
To become a self-emitting star, an entity must have a sufficiently large mass. According to calculations, the minimum mass for an object to become a star is about 70 times the mass of Jupiter, approximately 7% of the mass of our Sun.
What is a Planet? A planet is a celestial body that orbits around a star, a solar system, or a stellar remnant (also called a mother star or host star). It must have enough mass to overcome its material strength, resulting in a state of hydrostatic equilibrium, often resembling a nearly spherical shape. Additionally, a planet should not have a mass large enough to initiate nuclear fusion and emit light like a star.
How Are Stars and Planets Different? From these definitions, we can distinguish stars from planets in the following ways:
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Mass: Stars are typically much more massive than planets. The minimum mass for a star is around 7% of our Sun’s mass, while planets have significantly less mass.
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Orbit: Planets orbit a star or a stellar remnant, while stars can have fixed or non-fixed orbits.
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Temperature: The temperature of a star is determined by its nuclear fusion reactions. The surface temperature of a star ranges from approximately 2,800 to 50,000 degrees Celsius (2,727 – 49,727 degrees Celsius), with the core temperature reaching several million degrees Celsius. In contrast, a planet’s temperature depends on the thermal radiation it receives from its host star. The hottest observed exoplanet has a temperature of around 4,300 degrees Celsius.
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Luminosity: Stars emit light due to their internal nuclear fusion, while planets do not produce their own light but instead reflect the light of their host star. Without the light from stars, planets would be dark and not visible to the naked eye.
It’s important to note that terms like “Mars,” “Venus,” “Mercury,” etc., are not used to designate these celestial bodies as stars but rather as the individual names of planets within our Solar System.