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A galaxy is a huge collection of gas, dust, and billions of starts and their solar system, all held together by gravity.

There are 5 types of galaxies:

Spiral Galaxies

Elliptical Galaxies

Lenticular Galaxies

Irregular Galaxies

Seyfert Galaxies

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A Spiral Galaxy consist many stars, gas, and dust that rotates around a flat disk. The Milky Way is an example of the spiral galaxy which is where the solar system is located.

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Class F stars have a color of yellow-white and they are made out of atomic metals and hydrogen. Their surface temperature is ranged between 6000-7300 K and their luminosity is between 1.5-5 L. These stars are hydrogen-fusing and will eventually grow into a red giant that fuses helium. An example is the Polaris.

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Stars are giant balls of hot gas that is held together by self-gravity. However, they are classified based on their luminosity, spectral, and evolutionary types. Stars are grouped into 7 main categories which was created by astronomer Annie Jump Cannon. The classes are constructed by O, B, A, F, G, K, and M.

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Stars that are classified in O have the hottest and brightest type of star. The surface temperature is typically between 25000-50000 K and their luminosities are between 30000-1000000 L. These type of stars are usually found in the region of active star formation like a spiral galaxy. The spiral arms compress molecular clouds which leads to the formation of stars. One famous example is the Stars of Orion's Belt.

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Class B stars are similar to class O stars because they are both bright and hot. Their surface temperature is ranged between 10000-25000 K and the luminosity is 20000 L. They are formed because of the CNO cycle of thermonuclear fusion which generates the energy for the core. An example of a class B star is the Rigel.

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Class A stars have a color of white or bluish-white that is more common that other stars. Their surface temperature is ranged between 7400-10000 K and their luminosity is between 5-25 L. They are usually a dwarf star that is made out of hydrogen. An famous example is the Sirius.

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A class G star are typically yellow or yellow-white and they are also known as the yellow dwarf. Their surface temperature is about 5200-6000 K and their luminosity is about 0.6-1.5 L. These stars are made out of hydrogen and it fuses energy fro about 10 billion years. An example of a class G star is the Sun.

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Elliptical galaxy can be shaped in many different ways from round to oval. However, they are less common than spiral galaxies which contains little gas and dust that shows little organization and no spiral arms. Cygnus A is one of the most famous elliptical galaxies which is about 600 million light years away from Earth.

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A lenticular galaxy is a combination between spiral and elliptical galaxies. It is similar to a spiral galaxy due to the spiraling disk and it is also similar to the elliptical galaxy because don't have arms of stars that extend out the disk. The Cartwheel Galaxy is a famous example of a elliptical galaxy.

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Irregular galaxy are very different from other types of galaxies because of their unusual shapes. They are the smallest compared to size and they are full of gas and dust. The Large Magellanic Cloud is an example of a irregular galaxy.

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Class K stars is also referred as a orange dwarf and their colors are yellow and orange. Their surface temperature is about 3900-5300 K and their luminosity is about 0.08-0.6 L. Their formation is very similar to class G stars and a famous example is the Arcturus.

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Class M stars is also referred as a red dwarf and their color is red. Their surface temperature is about 2300-3900 K and their luminosity less than 0.08 L. They are formed from the T Tauri pre-main sequence stars and will stay in the main sequence for up to trillions of years. A famous example is the Proxima Centauri.

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Distance to sun 57.909175

Size 2439.7

Orbital period 58.646 day / 87.97 day

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Distance to sun 108.20893

Size 6051.8

Orbital period 243 day / 224.7 day

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Distance to sun 149.59789

Size 6378.14

Orbital period 0.9972 /. 365,24 years

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Distance to sun 227.93664

Size 3397

Orbital period 1.0260 day / 686.93 day

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Distance to sun778.41202

Size 71492

Orbital period 0.41354 day / 11.8565 years

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Distance to sun 2870,9722

Size 25559

Orbital period 0.718 day / 84.02 years

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1 light year =

9.4605284 × 1012 kilometers

=9 trillion km

Sirius 82 megameter / 8.6 light years

Arcturus / 36.71 light years

Polaris 434 light years

Proxima Centauri 4.2 light years

Star of Orion’s belt Rigel /863 light years

Sun The distance between the Earth and the Sun is about 149.6 million kilometers, which is about 1/65700 light years

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Astronomical units are used to measure the distance within our solar system. These units are known as AU, a unit of length that is between Earth and the Sun (92955807.3 miles).

Mercury: 0.39 AU away from the Sun

Venus: 0.72 AU away from the Sun

Earth: 1 AU away from the Sun

Mars: 1.52 AU away from the Sun

Jupiter: 5.20 AU away from the Sun

Saturn: 9.54 AU away from the Sun

Uranus: 19.22 AU away from the Sun

Neptune: 30.06 AU away from the Sun