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Are stars considered planets or not?

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Are stars considered planets or not? How does a planet differ from a star?-These are one of the common questions in astronomy. You should know the appropriate answer to it. Here you will also get to know about some interesting facts about stars & planets. So stay till the end.

In the clear night sky, we can see so many pinpoint dots shining bright like a pearl. Most of them are stars while some of them are planets. Our whole universe is full of stars and planets that we do not even know. So, start with the basic information of stars & planets.

What is Star:

Talking about stars, it is the only celestial object that emits its own light. We can see stars like tiny dots from the earth. It’s more like a glowing ball in outer space if we see through the telescope.

To be more scientific in the definition of a star, we can say that star can be understood as a glowing ball consisting of plasma clashed together by its gravity. Plasma is an intensely heated state of matter. The main matter of stars is mainly some gaseous elements like hydrogen, helium, and similar others.

In the star’s core, there is producing Thermonuclear Fusion Reaction which causes hydrogen to turn into helium. This is why an immense amount of energy emits in the form of heat and light. The light ends up reaching in our eyes through a radio telescope.

One of the characteristics of stars is that they twinkled. Because of the earth’s atmospheric reflection. The stars move from east to west when observed. The distance of stars is expressed in light-years.

What is Planet?

A planet is also a celestial object which usually spins around a certain star according to its own path also known as orbit. The size of a planet is quite huge and the shape is like a sphere. It is maybe huge but not huge enough to compete with stars.

The planet’s surface may be solid, gaseous, or liquid depending on the distance from its mother star. It does not emit energy which means there is no nuclear reaction as much as a star.

There are two types of planets found in our solar system. They are-

  1. Inner planet: Inner planets are those planets which orbit is found inside the asteroid belt. (Asteroid belt is actually a torus-shaped zone and occupied by many disorderly-shaped solid bodies that are smaller than planets.
    In our solar system the belt is located roughly between the orbit of Jupiter and the orbit of Mars). Inner planets are smaller in size and mostly consist of solid materials. Generally, these planet’s temperatures are high due to relatively closer to the star. The inner planets in our solar system are including Mercury, Venus, Earth, and Mars.
  2. Outer planets: Oppositely outer planets are those which orbit lies outside of the asteroid belt. These planets are much larger than inner planets and have more mass. They are made up of gases and solid mixtures. The temperature is comparatively lower than on other planets. In our solar system, outer planets encompass Jupiter, Saturn, Uranus, and Neptune.
    That’s a total basic idea about stars and planets this information fully indicates that they are not nearly the same but of a huge difference.


Are stars considered planets


How does a planet differ from a star:

To specifically distinguish between stars and planets we need some key factors. Let’s talk about some of them-

  • Light:

Stars have their own light. It’s because star emits light as energy. To be more specific, there is a lot of thermonuclear fusion reaction generating in a star’s core. That tends to produce the energy as light.
But planets have no lights of their own. But in our night sky, we can see some plants shining bright like a star. Actually, the planet reflects the Sun’s light to us which seems like a perfect star.

  • Position:

We know that there is not a single matter, that is still. Everything is move in a direction. The sun is in the center of our solar system but it’s moving along a path centering the milky way galaxy just like the other 200 billion stars.
Similarly, planets are also changing their positions as they move around their own star.

  • Shape:

Stars are mostly spherical. They are quite perfect spheres. Planets are also round or sphere. But they are not a perfect sphere. The reason will be discussed briefly below.

  • Size:

Obviously, the size of stars is much huge compare to a planet. If we look into our solar system, we can find that the radius of the sun is around 696,340 km where the radius of our planet, Earth is approximately 6400 km. About 1.3 million Earth-size planets could fit into the Sun and 333,000 times more mass than planet earth.

  • Temperature:

The temperature of the star is always very high. As there is having a thermonuclear fusion in its core. The hottest star has a temperature of around 40,000 K. And the coldest star has around 2000 K. Sun which is our center star in the solar system has around 6000 K.

On the other plants are relatively low on temperature. It’s because there is no nuclear reaction happening. But not all the planet have same temperatures since it depends on how much closer the plant is to the star.

For example, if we look in our solar system we can see the closest to the sun is Venus which has an average temperature of approximately 430°c (703K). The longest distanced planet is Pluto. And it has around -233°c (40K). Our Earth has a temperature of around 16°c (289K). It’s the perfect place for living with both animals and plants.

  • Twinkle:

In our night sky even with the telescopes, we can see the stars from million miles away as tiny dots. They sometimes twinkle. The reason is that the light of the stars travels millions of miles to reach our eyes.

When the lights come to the earth’s atmosphere, the lights are refracted, and instead of going according to a straight line, it chooses a zig-zag path to travel and finally reaches our eyes. That’s why we see stars flickering in the sky.

Planets usually do not twinkle. Because first of all plants do not have their own lights they reflect the sunlight. And it’s closer to Earth than a star for these reasons it doesn’t seem a tiny dot rather it seems like a little disk.

So when the light travels to Earth’s atmosphere, one edge of the disk forces the light to go a zig way and another edge to the opposite zag way. These two opposite and same refracted light cancel each other out. That’s why the planet shines more brightly and does not twinkle.

  •  Matter:

We discussed earlier that the body of a star is made of gas like hydrogen, helium, and other light elements.
On the other hand, the planet’s surface is made of solids or liquids, or gases or combining these three elements.

  • Period of revolution:

In the universe, nothing is fixed everything is moving. Stars also move in their orbit along with all the planets. This can be identified after a long time.
The planets are also moving in their own orbit centering their mother star. We can spot it very often that our earth is moving. The orbit of planets is elliptical.

  • Number:

In our Milky Way galaxy, there are around 200 billion stars. In our solar system, there is one star that is the sun.
There are eight planets in our solar system but throughout the galaxy, we live in the number of planets is still uncountable.

Why do stars have planets:

We know that planets spin around a star in a fixed path. But how come the star gets the planet in the first place? To find the answer we need to know how to do planet forms.

Mainly the dust around a star is crucial to form a planet. The dust mostly contains carbon, iron alike elements. When a star is in the T-Tauri phase (forming disk), it is extracting immensely hot winds controlling by positively charged particles (mainly protons and neutral helium atoms).

Most of the materials of the disk fall on stars due to gravitational force but some lucky and small dust particles of the disk are crushed into one another and create larger objects like pebbles. Thus from dust to pebbles and then pebbles to larger rocks that demolish together to extend.

Here the gas particles are one of the main catalysts for solid particles to stick together. Sometimes the rocks break apart. But the parts holding on are the building block of planets also known as “planetesimals“. The planetesimals start to spin around the star in a fixed direction and path which becomes its orbit.

When planetesimals spin around the star, it clear the dust, pebble materials in its path gobbling up nearby gaseous, solid particle. After billions of years, the dust totally transforms into a huge planet. So there must need a star to create a planet. That’s why stars have planets.

Do all planets have stars:

Most stars have planets but the proportion of star has planets is still uncertain. But in recent years, scientists have discovered orphan planets. These planets do not have any stars. Orphan planets are also called Rouge planets.

In a solar system, there are quite a few planets that are created but all the planets can not survive. Some planets collide with each other ended up forming a larger one. While in some cases larger planets migrate into a stable configuration of space which causes a cosmic battle for planetary permanence. Due to which some planets get kicked out of that solar system. They finish up reaching interstellar space.

According to simulations, there are 200 billion stars in the Milky Way galaxy and every star has ejected approximately 5 to 10 planets into the interstellar space its lifetime. The planets wander homelessly in space.

How do planets become round:

Planets may have differences in size and mass but they have one thing in common their shapes. They all are three-dimensional spheres. We know previously that the planet forms with dust and clumped materials in space.

Firstly, it was in an irregular shape but when it gains a good amount of gravity, it attracts all the materials and elements while traveling in its orbit. We know that gravity pulls equally from all the side. The gravity is more like the spokes of a bicycle wheel. It causes all the elements to hold still. Overall this is the reason for the planet’s being round or sphere shape.

But if we talk more detail about the shape we will find out that the planets are not perfectly pureed, especially big planets like Jupiter, Saturn. They are thicker in the middle and bulge out along the equator. It is because of the rotation of the planet.

When a huge sphere-like sphere spins the outer edge side of the planet has to move faster to keep up with the middle side which causes the polar diameter to be shortened and the equatorial diameter to be lengthened. It looks just like a football squished down when someone sits on it.

What happens if a star explodes:

When a star reaches its end two possibilities can happen. It can either die or explode. If the star dies it will emit its outer layer into space, leaving the core to cool. Let’s talk about the explosion since it is more interesting.

When the star dies with a massive cosmic explosion, it is called “Supernovae“. Supernovae can shine bright like a normal star and the explosion leads to the destruction of the star while in some cases it creates a black hole which is a powerful gravity from where even light cannot escape.

The supernovae have some significance. It produces new materials in the universe like iron, carbon. So it ends up enriching with dust, gas, and other particles in space. Which later will be the fundamental substance to form a planet. But only a few stars turn into supernovae. Most of the falling star turns cool to end their existence.


Though there is more topic to discuss stars and planets. There are so many mysteries as well. We know only about 4 percent of the universe. So there is 96 percent we did not even aware of. The science in this criteria has been developing in recent decades.

So all the discoveries came in recent decades. So there is plenty more to discover about galaxies, stars, and planets. Even though science has unfolded many mysteries about stars and planets, there is plenty more to be revealed just like Sir Isaac Newton foretold, “What we know is a drop, what we do not know is an ocean.”

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Rayhan Sarwar

I am a glass and ceramic engineering student at the Rajshahi University of Engineering & Technology (RUET). I enjoy exploring science and technology, which is why I chose to study engineering!

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