Chapter 9 Astronomy Midterm

What do we primarily see when observing the Sun in H-alpha light?

Sunspots, filaments, and chromospheric features.
Sunspots appear dark because they are cooler than the surrounding photosphere.

In which wavelength range do we see “active regions” most clearly?

Extreme Ultraviolet (EUV).

What are “active regions” on the Sun?

Areas with strong magnetic fields, often containing sunspot groups and producing flares and CMEs.

What are the two major types of solar events that originate from active regions?

• Solar flares – release energy, accelerate charged particles (especially protons).

• Coronal Mass Ejections (CMEs) – large ejections of plasma and magnetic fields.

Why are solar flares dangerous?

They accelerate high-energy protons, which can threaten satellites, astronauts, and communications.

What are the main inner zones of the Sun?

• Core – nuclear fusion

• Radiation zone – energy transported by photons

• Convection zone – hot material rises, cool sinks

What are the outer atmospheric layers of the Sun?

• Photosphere (visible surface)

• Chromosphere

  • Corona

What are the approximate temperatures of the core, photosphere, and corona?

• Core: ~15 million K

• Photosphere: ~5800 K

• Corona: ~1–3 million K

How long does it take for radiation to travel across the radiation zone?

100,000+ years (random walk of photons).

How long does light take to get from the photosphere to Earth?

About 8 minutes.

What is hydrostatic equilibrium in the Sun?

Balance between:

• Gravity, pulling inward

• Radiation pressure (Prad) and gas pressure, pushing outward

This keeps the Sun stable.

What is granulation?

A pattern of bright and dark cells from convection:

• Bright = rising hot gas

• Dark = sinking cooler gas

What are spicules?

Short-lived jets of gas in the chromosphere that shoot upward and fade rapidly.

What are coronal loops?

Arched magnetic structures filled with hot plasma; some eventually become CMEs.

What is the primary fusion process in the Sun?

Hydrogen → Helium (H → He) via the proton-proton chain.

What are the main outputs of H→He fusion?

• Helium nucleus

• Positrons

• Neutrinos

• Gamma rays (energy)

How do we determine the elements in the Sun’s atmosphere?

Using absorption spectra (dark lines where atoms absorb specific wavelengths).

What is a coronagraph used for?

To observe the corona by blocking the bright disk of the Sun with an artificial “eclipse disk.”

What is the solar cycle?

The ~11-year cycle of changing sunspot numbers (solar minimum to solar maximum and back).

What is the “butterfly pattern”?

A plot showing sunspot latitudes vs. time—sunspots start at high latitudes and migrate toward the equator.

What are the two main speeds of the solar wind?

• Slow wind: near the equator

• Fast wind: from polar coronal holes

Does the Sun rotate at the same speed everywhere?

No. The Sun has differential rotation:

• Equator ≈ 25 days

• Poles ≈ 35+ days

What is the spectral class of the Sun?

G2V (G-type main sequence star).

What is a sunspot pair?

Two sunspots of opposite magnetic polarity, representing the footprints of a coronal loop when viewed in H-alpha.