The Sun as a Star | Physics for GCSE/IGCSE - Year 11 PDF Download

The Sun

• The Sun, a luminous sphere of gas and plasma, constitutes more than 99% of the total mass present in the solar system. Its massive gravitational influence is the primary reason why the comparatively diminutive planets encircle it. The gravitational pull exerted by the Sun plays a crucial role in balancing the orbital motions of the planets.
• The Sun, an immense celestial body primarily composed of hydrogen and helium, dominates the solar system's mass distribution. Its gravitational pull is the fundamental factor dictating the trajectories of the orbiting planets.

Classification of Stars

• Stars exhibit a diverse range of sizes and colors, spanning from yellow stars to red dwarfs, and from blue giants to red supergiants.
• Star classification is based on their color, where warm objects emit infrared light and extremely hot objects emit visible light, determining the color they emit.
• Objects emit different colors based on their temperature.
• A star's color is directly linked to its surface temperature:
  • Red stars are the coolest, at around 3000 K.
  • Blue stars are the hottest, at around 30,000 K.
• Understanding the correlation between a star's color and its temperature is vital.

Nuclear Fusion in Stars

• In the core of a stable star, hydrogen atoms combine through nuclear fusion to create helium. This process generates a substantial amount of energy that sustains the star's stability.
• The fusion reaction equation represents the conversion of hydrogen into helium.

• The energy released during this fusion reaction counteracts the gravitational force, maintaining the star's size and preventing collapse.