Sun's Structure & Nuclear Fusion: Key Concepts for Astronomy

What maintains the Sun's stability?

Gravity pulling inward is balanced by pressure from hot gas pushing outward from nuclear reactions.

What happens if fusion in the Sun's core suddenly increases?

Pressure outpaces gravity, causing the Sun to expand.

What is the temperature and density of the Sun's core?

Temperature is approximately 15 million K, and density is roughly 150 times that of water.

What nuclear reaction occurs in the Sun's core?

The proton-proton chain fuses 4 protons into 1 helium nucleus, releasing energy.

What is the radiative zone of the Sun?

The layer extending from the core to about 70% of the Sun's radius where energy escapes slowly by photon diffusion.

Describe the convective zone of the Sun.

The layer from 70% to 100% of the Sun's radius where energy is transported by convection.

What is the photosphere?

The visible surface of the Sun, with a temperature of about 5,800 K, where sunlight is emitted.

What is the chromosphere?

The layer above the photosphere, visible as a reddish rim during eclipses, with a temperature of around 10,000 K.

What is the corona?

The outermost layer of the Sun, with temperatures above 1 million K, and the source of solar wind.

What are sunspots?

Cool, dark regions on the Sun's surface caused by intense magnetic fields.

What is the solar cycle?

An 11-year cycle in which the number of sunspots rises and falls.

What is the primary energy source of the Sun?

Nuclear fusion of hydrogen into helium via the proton-proton chain.

How does energy escape from the Sun?

Energy moves from the core to the radiative zone by photon scattering, then to the convective zone by hot gas motion, and finally escapes at the photosphere.

What is the Hertzsprung-Russell (HR) diagram?

A plot of luminosity versus surface temperature of stars, with the main sequence representing long-lived hydrogen burning stars.

What characterizes main sequence stars?

They are in a long-lived phase of hydrogen burning, making up about 90% of stars.

What is the difference between low-mass and high-mass star evolution?

Low-mass stars evolve through stages like red giant and white dwarf, while high-mass stars undergo supernova and can become neutron stars or black holes.

What is a protostar?

A collapsing, heating object that is not yet fusing hydrogen, surrounded by a dust and gas disk.

What defines a brown dwarf?

A substellar object with mass less than 0.08 solar masses that never reaches the temperature for sustained hydrogen fusion.

What is the interstellar medium (ISM)?

Gas and dust between stars, serving as sites for new star formation.

What is the difference between a protostar and a star?

A protostar is powered by gravitational collapse and not yet on the main sequence, while a star is in hydrostatic equilibrium with ongoing hydrogen fusion.

What are the two main types of supernovae?

Type II supernovae result from core collapse of massive stars, while Type Ia supernovae occur from the explosion of a white dwarf in a binary system.

What is the significance of the Initial Mass Function (IMF)?

It describes the distribution of stellar masses at birth, indicating that many stars are low-mass and few are high-mass.

What is the role of parallax in astronomy?

Parallax is used to measure the distances to the nearest stars directly.

What are standard candles in astronomy?

Objects of known luminosity used to determine distances based on their apparent brightness.

What is the equation for calculating distance using standard candles?

b = L / (4πd²), where b is apparent brightness, L is true luminosity, and d is distance.

What is the concept of time dilation in special relativity?

Time runs slower for objects moving at high speeds relative to an observer.

What is the event horizon of a black hole?

The boundary beyond which nothing can escape the gravitational pull, where escape velocity exceeds the speed of light.