9/3/26 astromony and earth study

Astronomy

The scientific study of celestial objects, space, and the physical universe.

Observational Astronomy

Branch studying objects via telescopes and instruments.

Theoretical Astronomy

Branch modeling physics to explain celestial observations.

Planetary Science

Branch focused on planets, moons, and solar systems.

Astrophysics

Physics of stars, galaxies, and the universe.

Milky Way Star Count

100-400 billion stars.

Observable Galaxies

~2 trillion galaxies.

AU (Definition)

Average distance from Earth to the Sun.

AU (Distance)

~93 million miles (150 million km).

Light-Year

Distance light travels in one year (~5.88 trillion miles).

Ground Telescopes (Limitation)

Distortion from atmosphere and light pollution.

Space Telescopes (Advantage)

Observes invisible wavelengths without atmospheric interference.

Spectroscopy

Analyzing light spectrum and reflectivity to determine composition.

Sun (Stellar Type)

G-type main-sequence star.

Sun (Comp)

~74% Hydrogen, ~24% Helium, ~2% trace elements.

Sun (Core Temp)

~15 million °C.

Sun (Light Travel)

~8 minutes to Earth.

Spectral Order

O B A F G K M (Hottest to Coolest).

Class O (T&C)

30,000°C; Blue-white.

Class O (Traits)

Most massive, very bright, short-lived.

Class B (T&C)

10,000–30,000°C; Blue-white.

Class B (Traits)

Very hot, massive, bright.

Class A (T&C)

7,500–10,000°C; White.

Class A (Traits)

Strong Hydrogen absorption lines.

Class F (T&C)

6,000–7,500°C; Yellow-white.

Class G (T&C)

5,300–6,000°C; Yellow.

Class G (Traits)

Moderate size/lifespan, stable energy output (e.g., Sun).

Class K (T&C)

3,900–5,300°C; Orange.

Class K (Traits)

Long lifespans.

Class M (T&C)

Red, St <3,900°C,

Class M (Traits)

Coolest, most common (red dwarfs, giants, supergiants).

Main Sequence

Fusing H to He in core (~90% of stars).

Red Giants

Exhausted core hydrogen.

White Dwarfs

Hot, dense, Earth-sized leftover stellar core.

Neutron Stars

Dense core remnant left after a supernova.

Black Holes

Core collapse where gravity prevents light from escaping.