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1. If the sun were to "turn off", the Earth would completely freeze within a week with a temperature of 0 degrees Fahrenheit even in the equator. In a year's time it would dip to -100 degree Fahrenheit, and millions of years later it would be a stable -400 degrees Fahrenheit.

2.The sun is getting hotter, becomming 10% more luminous around every billion years. This could mean that in a billion years, there will be no liquid water on Earth.

3. The sun is comprised of 72% hydrogen, 26% helium and other trace elements. These dense mass of gases makes up 99% of all the mass in our solar system.

4. The sun puts out a huge amount of energy to heat the solar system. Every second around 700 million tons of hydrogen are converted into helium ashes by the sun's fusion process.

5. The sun's surface is comparatively colder than its atmosphere, at around 6000 Kelvin. The atmosphere can reach 10,000K while the core is about 1 million Kelvin.

6. The sun is around 25,000 light years away from the center of the Milky way galaxy. It takes about 240 millions years to orbit once around the galactic center.

7. Different sections of the sun rotate at varied speeds, as it is made of gas. The equator regions rotate around every 25 days, whereas the poles take about 36 days to complete one rotation around the sun.

8. On some planetary bodies and moons, there exists a "peak of eternal light" where the sun never sets. This is due to the angle of rotational axis on relation to the sun.

9. The sun is middle aged. Astronomers believe it formed around 4.59 billions years ago. In 5 billion years time, it will enter the red giant phase of its life time.

10. 100,000,000,000 tons of dynamite would have to be detonated every single second to match the energy that the sun produces.


I thought to write something about the orbital mechanics that I know so far. This would be a revision for me as well as chance to realize new things and come up with new questions to ask for myself.

The celestial mechanics or the orbital mechanics is the study of dynamics of satellites and planets in their orbit around bigger masses. For example, the moon and artificial satellites such as GPS, International Space station, etc. revolve around the earth in their orbit while the planets revolve around the sun in their orbit. The orbit around the sun is called helical orbit while the orbit around the earth is named as geo-orbit.
Nomenclature: It is important to understand the terminologies used to define the characteristics of orbit. In the demonstration figure below a mass is revolving around a bigger mass in its orbit. When the smaller body is at the closest distance with the bigger body (at position 2), its position is called as the periapsis. On the other hand, when the body approaches the farthest point (at position 1), its position is called as the apoapsis.

If the center body is sun, the closest and farthest positions are called perihelion and apohelion position respectively. Similarly, if the center body is earth, the closest and farthest position are called apogee and perigee respectively.See table below for more terms of apogee and perigee.

Body Farthest approach Closest approach
General Apogee Perigee
Sun Apihelion Perihelion
Earth Apogee Perigee
Mercury Apohemion Perihermion
Venus Apocyterian Pericytherian
Mars Apoareion Periareion
Jupiter Apozene Perizene
Saturn Aposaturnium Perisaturnium
Uranus Apouranion Periuranion
Neptune Apoposeidion Periposeidion
Pluto Apohadion Perihadion
Star Apoastron Periastron
Galaxy Apogalacticon Perigalacticon
Black Hole Apobothra Peribothra

Obviously, you must have noted that the periapsis is equal to the apoapsis for a circular orbit. The circular orbits can be seen in case of artificial satellites only. By nature, each and every cellestial body revolves in an elliptical path. The Keplers law define these kind of properties of properties of planets around the sun.

Kepler's law:
1. The orbit of each planet is an ellipse with the sun occupying the focus (center object).
2. The line joining the sun to a planet sweeps out equal areas in equal intervals of time
3. A planets orbital period is proportional to the mean distance between the Sun and the planet raised to the power 3/2.

First law
Picture owned by Gary M. Winter
Second law
Third law


Helical Orbits:

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