Earth and Space Science: Seasons, Moon Phases, and Light Spectrum

What causes the seasons on Earth?

The tilt (23.5°) of Earth's axis relative to its orbit causes sunlight angles and day length to change through the year.

When is the Sun directly overhead at the Tropic of Cancer?

At the summer solstice (around June 21) when the northern hemisphere is tilted toward the Sun.

What happens at the equinoxes?

Day and night are equal length; the Sun is directly over the equator.

Latitude of the Tropic of Capricorn?

23.5° South.

What causes the Moon's phases?

The changing relative positions of the Moon, Earth, and Sun.

List the 8 main Moon phases in order.

New → Waxing Crescent → First Quarter → Waxing Gibbous → Full → Waning Gibbous → Third Quarter → Waning Crescent → New.

How long is one full lunar cycle?

About 29.5 days.

What causes a solar eclipse?

The Moon passes between Earth and the Sun during a new moon.

What causes a lunar eclipse?

Earth passes between the Sun and Moon during a full moon.

Kepler's 1st Law states:

Planets move in elliptical orbits with the Sun at one focus.

Kepler's 2nd Law states:

Planets sweep out equal areas in equal times—move faster near perihelion and slower near aphelion.

Kepler's 3rd Law formula:

P² = a³ (P in years, a in AU).

What does eccentricity measure?

How oval an orbit is (0 = circle, closer to 1 = more stretched).

Newton's 1st Law (Inertia):

Objects remain at rest or in motion unless acted on by a force.

Newton's 2nd Law:

F = ma — acceleration depends on force and inversely on mass.

Newton's 3rd Law:

Every action has an equal and opposite reaction.

Newton's Law of Universal Gravitation:

F = (G M₁ M₂) / r²

What does the inverse-square law mean for gravity?

Doubling the distance makes gravity ¼ as strong.

Why do astronauts feel "weightless" in orbit?

They are in freefall, falling at the same rate as their spacecraft.

What causes ocean tides on Earth?

The Moon's gravitational pull (and to a lesser extent, the Sun's).

Why are there two high tides each day?

The Earth spins through two bulges—one facing the Moon and one opposite.

What are Spring Tides?

Strongest tides—when Sun, Moon, and Earth are aligned (new or full moon).

What are Neap Tides?

Weakest tides—when Sun and Moon pull at right angles (first or third quarter).

What does "tidally locked" mean?

The Moon's rotation matches its orbit—same side always faces Earth.

What two properties define a light wave?

Wavelength (λ) and frequency (f).

Relation between wavelength and frequency:

They're inversely related—shorter wavelength = higher frequency.

Order of electromagnetic spectrum (shortest → longest):

Gamma → X-ray → Ultraviolet → Visible → Infrared → Microwave → Radio.

Which color of visible light has the shortest wavelength?

Blue/violet.

Which color of visible light has the longest wavelength?

Red.

How does brightness change with distance?

Brightness ∝ 1/r² (inverse-square law).

What is a blackbody?

A perfect absorber and emitter of all wavelengths.

As temperature increases, how does blackbody radiation change?

Gets brighter and bluer (shorter λ_peak).

What does Wien's Law describe?

The hotter the object, the shorter its peak wavelength.

Which is hotter—Betelgeuse (red) or Rigel (blue)?

Rigel—blue means higher temperature.

Three types of spectra:

Continuous (full rainbow), Absorption (dark lines), Emission (bright lines).

What causes absorption lines?

Atoms/molecules in a cooler gas absorb specific wavelengths of light.

Why do elements make different spectral lines?

Each element has unique atomic energy levels—its "fingerprint."

Which wavelengths reach Earth's surface easily?

Visible and radio light.

Why do we need space telescopes?

Earth's atmosphere blocks most infrared, UV, X-ray, and gamma rays.

What causes the greenhouse effect?

Earth absorbs visible light, re-emits infrared; atmosphere traps some IR, warming the planet.

What is redshift?

Light waves stretched (longer wavelength) when a source moves away.

What is blueshift?

Light waves compressed (shorter wavelength) when a source moves toward you.

How do astronomers detect exoplanets using Doppler shift?

They observe periodic red/blueshifts in a star's spectrum as planets pull it back and forth.