astrophysics and cosmology Flashcards
(29 cards)
What defines a planet?
A spherical object with sufficient mass, no nuclear fusion, and a cleared orbit.
What is a dwarf planet?
A planet that has not cleared its orbit of other objects.
What is the difference between asteroids and comets?
Asteroids are small rocky objects with circular orbits, while comets are irregularly shaped and have eccentric elliptical orbits.
What is a galaxy?
A collection of stars, gas, and dust, containing around 100 billion stars.
What is a nebula?
A large cloud of gas and dust where stars are born.
What is the main sequence phase of a star?
The stable phase where gravitational forces and radiation pressure balance each other.
What happens when a low-mass star (0.5M☉ - 10M☉) runs out of hydrogen?
It becomes a red giant, then a white dwarf, and finally cools over time.
What is the Chandrasekhar limit?
1.44M☉—the maximum mass a white dwarf can have before collapsing.
How does a massive star (>10M☉) evolve?
t becomes a red supergiant, undergoes a supernova, and may become a neutron star or black hole.
How do black holes form?
f a collapsing core exceeds 3M☉, gravity overcomes all forces, preventing even light from escaping.
What happens when an electron absorbs energy?
It moves to a higher energy level
What is an emission spectrum?
Bright spectral lines on a black background, unique to each element.
What is an absorption spectrum?
Dark spectral lines on a continuous spectrum where light is absorbed by a cooler gas.
What is Wein’s Law?
Peak wavelength of a star’s radiation is inversely proportional to its temperature.
What is Stefan’s Law?
A star’s luminosity is proportional to the fourth power of its temperature.
What is an Astronomical Unit (AU)?
he average distance from Earth to the Sun (1.5 × 10¹¹ m).
What is a parsec (pc)?
The distance at which 1 AU subtends an angle of 1 arcsecond (3.1 × 10¹⁶ m).
What is stellar parallax?
The apparent shift in a star’s position due to Earth’s orbit, used to measure distances up to 100pc.
What is the Doppler Effect?
The change in wavelength when a source moves relative to an observer.
What does redshift indicate?
A star or galaxy is moving away from us.
What is Hubble’s Law?
he farther a galaxy is, the faster it moves away (V = H₀d).
hat is the Big Bang Theory?
The idea that the universe started as a singularity and has been expanding ever since.
What is cosmic microwave background radiation?
Remnant radiation from the early universe, supporting the Big Bang theory.
What is dark matter?
A mysterious substance making up 27% of the universe, detectable only by its gravitational effects.
