The Sun
The Sun is the star at the centre of the Solar System, a nearly perfect sphere of hot plasma that generates energy through nuclear fusion of hydrogen into helium in its core. It accounts for about 99.86% of the total mass of the Solar System and provides the light and heat essential for life on Earth. The Sun is classified as a G-type main-sequence star (G2V) with a surface temperature of approximately 5,778 K and a diameter of about 1.39 million kilometres.
Key Formula
E = m × c²
LaTeX: E = mc^2
| Symbol | Meaning | Unit |
|---|---|---|
| E | Energy released | Joules (J) |
| m | Mass converted to energy | Kilograms (kg) |
| c | Speed of light in vacuum | m/s (≈ 3 × 10⁸ m/s) |
Worked Example
Problem
The Sun converts approximately 4 × 10⁹ kg of mass into energy every second through nuclear fusion. Calculate the power output of the Sun using E = mc².
Solution
Step 1: Identify mass converted per second: m = 4 × 10⁹ kg/s Step 2: Use c = 3 × 10⁸ m/s Step 3: Power = m × c² = 4 × 10⁹ × (3 × 10⁸)² Step 4: Power = 4 × 10⁹ × 9 × 10¹⁶ Step 5: Power = 36 × 10²⁵ = 3.6 × 10²⁶ W
Answer
Power output ≈ 3.6 × 10²⁶ Watts (actual solar luminosity ≈ 3.83 × 10²⁶ W)
Key Physical Properties of the Sun
| Property | Value | Unit |
|---|---|---|
| Mass | 1.989 × 10³⁰ | kg |
| Radius | 6.96 × 10⁸ | m |
| Surface Temperature | 5,778 | K |
| Core Temperature | 1.5 × 10⁷ | K |
| Luminosity | 3.83 × 10²⁶ | W |
| Age | 4.6 × 10⁹ | Years |
Interactive Tools
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Related Terms
Solar System
The Solar System is the gravitationally bound system comprising the Sun and all the objects that orbit it, including eight planets, their moons, dwarf planets, asteroids, comets, and interplanetary dust. It formed approximately 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The Solar System extends from the Sun to the Oort Cloud, spanning distances of up to 100,000 astronomical units.
Planetary Orbit
A planetary orbit is the curved path followed by a planet as it moves around the Sun (or another star) under the influence of gravitational attraction. According to Kepler's First Law, planetary orbits are ellipses with the Sun at one of the two foci. The shape of an orbit is described by its eccentricity, where 0 represents a perfect circle and values approaching 1 represent highly elongated ellipses.
Kepler's First Law
Kepler's First Law, also called the Law of Ellipses, states that every planet orbits the Sun in an elliptical path, with the Sun located at one of the two foci of the ellipse (not at the centre). This was a revolutionary departure from the previous belief in perfectly circular orbits. The degree of elongation of the ellipse is described by its eccentricity (e), where e = 0 is a circle and e approaching 1 is a highly elongated ellipse.
The English word "Sun" derives from Old English "sunne", from Proto-Germanic "sunnon". The Latin name "Sol" (used in scientific contexts) gave rise to "solar". The symbol for the Sun ☉ has been used since ancient times.