SCI Earth+Space T2 26

What is a star

giant ball of hot glowing gases, mostly hydrogen and helium, produces energy through nuclear fusion in core —> released as light, heat, other electromagnetic radiation.

Characteristics of stars

• Mass – greater mass, stronger gravitational force which compresses core, increasing rate of nuclear fusion.

• Size – Stars vary greatly in size, from small stars to enormous supergiants.

• Temperature –

• Brightness

Nuclear Fusion

Nuclear fusion is the process that powers stars.

• ¾ of a star is hydrogen.

• core to 15 million°C.

• atoms become plasma, where electrons separate from nuclei.

• Gravity forces positively charged hydrogen nuclei together- overcome repulsion.

• fuse together, forming helium.

• some mass is converted into energy

• pushes outward against gravity, keeping the star stable during the Main Sequence stage.

difference between absolute and apparent magnitude

Apparent Magnitude

• Measures how bright a star appears from Earth.

• Depends on the star's distance from Earth.

• The more negative the magnitude, the brighter the star appears.

Absolute Magnitude

• Measures a star's true brightness (luminosity).

• Compares all stars if they were 10 parsecs from Earth.

• Allows astronomers to compare stars fairly regardless of distance.

A star may have a high absolute brightness but appear dim because it is very far away.