Astronomy and Astrophysics Lecture Notes

These flashcards cover fundamental concepts in astronomy, including star classification, telescope functions, and the historical development of astronomical models.

What is parallax in terms of distance?

Parallax is calculated as the reciprocal of distance in parsecs.

How do you calculate parallax in light-years?

Divide the distance by 3.26 first.

What is the relationship between magnitude and brightness of stars?

Stars with lower magnitude are brighter; stars with higher magnitude are dimmer.

What is the surface temperature of red dwarfs?

Red dwarfs have a surface temperature of about 3000 K.

What type of star is the Sun classified as?

The Sun is a main sequence star, also known as luminosity class V.

What does luminosity class V represent?

Luminosity class V represents main sequence stars.

What is proper motion in astronomy?

Motion perpendicular to an observer’s line of sight is called proper motion.

What happens when a star moves toward an observer?

It produces a blueshift.

What does the Hertzsprung-Russell (H-R) diagram show?

It shows the relationship between stellar temperature and luminosity.

What characteristics do stars at the top of the H-R diagram have?

They are extremely luminous.

What characteristics do stars at the bottom-right of the H-R diagram have?

They are cool and dim.

What is the Sun’s surface temperature?

The Sun’s surface temperature is roughly 6000 K.

Why do A-type stars show strong hydrogen lines?

Because electrons are easily excited at ~10,000 K.

What factors are needed to calculate the true space velocity of a star?

Distance, radial velocity, and proper motion.

What effect does transverse motion have on Doppler shifts?

Transverse motion does not produce a Doppler shift.

Who discovered the correlation between temperature and luminosity?

Russell and Hertzsprung.

What are O-type stars known for?

They are the hottest and most luminous, with temperatures between 25,000–50,000 K.

How do spectral lines assist astronomers?

They help astronomers classify stars.

What is radial velocity?

Motion toward or away from an observer.

What effect does motion away from an observer have?

It produces a redshift.

What do Roman numerals indicate in star classification?

A star’s luminosity class.

What are the components of atoms?

Atoms are made of protons, neutrons, and electrons.

What happens when atoms absorb photons?

Electrons jump to higher energy levels.

How do astronomers determine a celestial object's chemical composition?

By using spectra.

What are the three main parts of a telescope?

Light-collecting area, observation instrument, and detector.

How do reflecting telescopes gather light?

By using mirrors.

What can interfere with observations in astronomy?

Infrared radiation from Earth.

What composes the atomic nucleus?

Protons and neutrons.

What occurs when electrons drop to lower energy levels?

They emit photons.

What types of waves are included in electromagnetic waves?

Radio waves, visible light, and infrared; sound is not an electromagnetic wave.

How does infrared compare to visible light?

Infrared has lower energy than visible light.

How does ultraviolet compare to visible light?

Ultraviolet has higher energy than visible light.

How do refracting and reflecting telescopes differ?

Refracting telescopes use lenses; reflecting telescopes use mirrors.

What does Wien's Law relate to?

A star’s temperature to its peak wavelength.

Which waves have the longest wavelength?

Radio waves have the longest wavelength and lowest photon energy.

What is the Earth-Sun distance approximately?

About 150 million kilometers.

What is the diameter of the Milky Way?

Roughly 100,000 light-years.

How do planets' orbits behave according to Kepler?

They are elliptical.

What model did Copernicus propose?

A heliocentric model of the universe.

What significant discovery did Galileo make?

Jupiter’s four moons, proving not all celestial bodies orbit Earth.

What did Babylonia create around 3,000 years ago?

Astrology.

What is the value of an astronomical unit (AU)?

It equals the average Earth-Sun distance.

Who is the closest star to Earth besides the Sun?

Proxima Centauri.

What initiates the scientific method?

Observing trends and creating models.

What is Kepler’s first law?

Planets move in elliptical orbits.

What is perigee?

The closest point in an elliptical orbit around Earth.

What does inertia according to Newton’s first law describe?

An object’s resistance to changes in motion.

What does gravity assist allow?

Spacecraft to gain or lose energy by passing near a planet or moon.

Why do planets orbit the Sun in the same direction?

Due to motion constraints in the solar system.

What occurs during planetary differentiation?

Heavy elements sink when heat from impacts melts rock.

What categories are planets divided into?

Terrestrial or giant.

How does a meteor differ from a meteorite?

A meteor is a streak in the sky; a meteorite reaches the ground.

What is asteroid Vesta?

A surviving planetesimal.

What have impact rates in the solar system been like?

Roughly constant for billions of years.

What do aphelion and perihelion refer to?

Orbits around the Sun; apogee and perigee refer to Earth orbits.

What does Newton's first law state?

Objects in motion stay in motion unless acted upon by an external force.

What do gravity assist maneuvers utilize?

A planet’s mass to change spacecraft speed or direction.

What happened to rocky protoplanets due to impacts?

They melted, allowing differentiation.

When was Pluto discovered?

In 1930, as the first trans-Neptunian object.

What are comets primarily composed of?

Ice and frozen gases.

What is the Moon classified as?

Not a surviving planetesimal.

What can craters on the Moon indicate?

The Moon’s age.

What is aphelion in astronomy?

Mercury’s farthest point from the Sun.

What do the Voyager spacecraft continue to do?

Travel in straight paths unless acted on by a force.

What allows spacecraft to change direction and speed?

Gravity assists.

What does conservation of angular momentum explain?

The Sun’s rotation and planetary orbits.

What is differentiation?

The process of heavier elements sinking in a protoplanet.

What are the five recognized dwarf planets?

Pluto, Makemake, Eris, Ceres, and Haumea.

Where do most asteroids orbit?

Between Mars and Jupiter.