PHYS 1025Q Ultimate Review

What is scientific notation used for in astronomy?

To express very large or small numbers simply, e.g., distances, masses, wavelengths.

How do you multiply numbers in scientific notation?

Multiply the coefficients and add the exponents.

What is a light-year?

The distance light travels in one year, about 9.3 x 10^12 km.

What is the formula for surface area of a sphere?

A = 4πr²

What causes the apparent motion of stars across the sky?

Earth's rotation on its axis.

What does Polaris indicate in the Northern Hemisphere?

The direction of true north and your latitude.

What causes the seasons?

Earth's 23.5° axial tilt.

When is the Sun highest in the sky at noon?

Summer solstice (around June 21 in the Northern Hemisphere).

What causes the Moon's phases?

The angle between the Earth, Moon, and Sun, which determines the visible illuminated portion.

What is a solar eclipse?

When the Moon blocks sunlight from reaching Earth.

Why don’t we have eclipses every month?

The Moon's orbit is tilted 5° relative to Earth's orbital plane (the ecliptic).

What is Earthshine?

Sunlight reflected off Earth that dimly lights the dark side of the Moon.

What are retrograde motions of planets?

An apparent backward motion of a planet as Earth passes it in orbit.

What did Kepler discover about planetary orbits?

They are ellipses with the Sun at one focus.

What was Galileo’s major telescope discovery?

Moons orbiting Jupiter, phases of Venus, sunspots, etc.

What does Newton's law of gravity state?

Gravity pulls every object toward every other object, and the force gets stronger with more mass and weaker with more distance.

What did Copernicus propose?

The heliocentric model, with the Sun at the center.

What is Kepler's First Law?

Planets orbit the Sun in ellipses with the Sun at one focus.

What did Galileo’s observations prove?

The heliocentric model and that not all celestial objects orbit Earth.

What is Newton’s Universal Law of Gravitation?

F = G(M1*M2)/r²

What happens to gravity as distance increases?

It decreases by the square of the distance.

What is escape velocity?

The speed needed to break free from a celestial body's gravitational pull.

What is orbital velocity formula?

v = sqrt(GM/r)

What is Newton’s Third Law?

For every action, there is an equal and opposite reaction.

What are characteristics of terrestrial planets?

Small, rocky, with solid surfaces and few moons.

What is differentiation in planetary formation?

Denser materials sink to form a core while lighter materials form the crust.

What causes surface features on planets?

Volcanism, impact cratering, tectonics, and erosion.

Why is Venus hotter than Mercury?

Due to its thick CO₂ atmosphere causing a strong greenhouse effect.

Why is Earth habitable?

Stable climate, magnetic field, liquid water, and atmosphere with oxygen.

What is the Moon’s rotation period relative to its orbit?

It is tidally locked—one rotation per orbit.

What is Venus’ surface temperature and why?

About 860°F (460°C) due to runaway greenhouse effect.

What is the main source of Moon craters?

Impacts from asteroids and meteoroids.

What happens in the Sun's core?

Nuclear fusion of hydrogen into helium at ~15 million K.

What is the Sun’s radiative zone?

A layer where photons undergo a slow 'random walk' outward.

What is the convective zone of the Sun?

Hot gas circulates, transporting energy to the surface.

What is the photosphere?

The Sun's visible surface, emits blackbody radiation (~5800 K).

What is the chromosphere?

A thin layer above the photosphere.

What is the corona?

The Sun's outer atmosphere; very hot and source of the solar wind.

What are sunspots?

Cooler, dark regions following magnetic field lines; part of an 11-year cycle.

What are prominences?

Solar material arcing along magnetic field lines.

What are coronal mass ejections (CMEs)?

Explosions of solar material into space; can disrupt Earth tech.

What is granulation on the Sun?

Boiling pattern from convection cells visible on the surface.

What is helioseismology?

Study of solar oscillations to learn about the Sun’s interior.

What are solar neutrinos?

Byproducts of fusion in the core that escape directly into space.

How does wavelength relate to temperature (Wien’s Law)?

λ = (3 x 10^-3) / T, where λ is in meters and T in Kelvin.

What does shorter wavelength mean?

Higher energy radiation (e.g., UV, X-ray).

What does longer wavelength mean?

Lower energy radiation (e.g., infrared, radio).

What does a redshift indicate about a star's motion?

The star is moving away from us.

What does a blueshift indicate about a star's motion?

The star is moving toward us.

What is the Doppler shift formula?

(λshifted - λrest) / λrest = v / c

How is stellar temperature determined?

By color or peak wavelength using Wien’s Law.

How is luminosity determined?

Using distance and brightness, or from radius and temperature (L = 4πR²σT⁴).

How is stellar radius estimated?

By combining temperature and luminosity to get surface area.

How is mass measured in stars?

Using Kepler's Laws in binary systems.

What is selection bias in observing stars?

Brighter stars are easier to detect at far distances, skewing samples.

What is the end state of a star with < 8 M☉?

White dwarf.

What is the end state of a star with 8–20 M☉?

Neutron star.

What is the end state of a star with > 20 M☉?

Black hole.

What is the relationship between mass and stellar remnant type?

More massive stars leave behind more compact remnants.

What happens when a high-mass star forms an iron core?

Fusion stops, the core collapses, and a supernova explosion occurs.

What is the Chandrasekhar limit?

1.4 M☉ — the maximum mass for a white dwarf.

Ecliptic

The apparent path of the Sun across the sky over the course of a year.

Zenith

The point in the sky directly overhead.

What type of galaxy is the Milky Way?

A barred spiral galaxy.

What is dark energy?

A mysterious force causing the universe’s accelerated expansion.