Lecture Notes on the Universe and Solar System Formation

A set of flashcards covering key concepts, definitions, and important terms related to the origin of the universe, galaxy and star formation, and the solar system.

What is the Big Bang Theory?

The theory that the universe began about 13.8 billion years ago from an extremely hot, dense point and has been expanding ever since.

What is the Cosmic Microwave Background (CMB)?

The leftover heat or 'echo' of the Big Bang, discovered in 1964, uniformly found across space at 2.7 Kelvin.

What does Hubble's Law state?

The farther away a galaxy is, the faster it is moving away from us.

What is redshift?

A phenomenon explained by the Doppler effect where light waves are stretched, increasing the wavelength, indicating galaxies are moving away from Earth.

What are the three main components of the universe's composition?

Ordinary matter (4.9%), dark matter (26.8%), and dark energy (68.3%).

What is the Doppler Effect?

A change in the wavelength of light due to the motion of the source.

What defines a spiral galaxy?

A type of galaxy with a rotating disk of stars and dust, a central bulge, and several arms spiraling outward.

What are the three main types of galaxies?

Spiral, elliptical, and irregular galaxies, classified by their shape and structure.

What is nuclear fusion in stars?

The process where stars produce energy by fusing hydrogen atoms into helium in their cores.

What is a main-sequence star?

A star that is fusing hydrogen into helium in its core, representing the longest stage of a star's life.

What happens during a supernova?

A huge explosion caused by the collapse and rebound of the core of a very large star.

What is a black hole?

A region in spacetime where gravity is so strong that nothing, not even light, can escape.

What is the Nebular Theory?

The theory that describes how the solar system formed from a rotating cloud of gas and dust about 4.6 billion years ago.

What constitutes a terrestrial planet?

Rocky inner planets like Mercury, Venus, Earth, and Mars that have solid, rocky surfaces.

What are Kepler’s Laws of Planetary Motion?

Three laws describing the motion of planets: orbits are elliptical, planets sweep equal areas in equal time, and the square of the orbital period is proportional to the cube of the distance from the Sun.

What is the definition of gravity?

The force of attraction between all masses, dependent on their mass and the distance between them.

What does the term 'electromagnetic spectrum' refer to?

The range of light waves traveling at different wavelengths, including radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray.

Besides the CMB and Hubble's Law, what is another key piece of evidence for the Big Bang?

The observed abundance of light elements like hydrogen and helium, which matches predictions made by the Big Bang model.

What is the current estimated age of the universe?

Approximately 13.8 billion years.

What is cosmic inflation?

A hypothesized period of rapid exponential expansion of the early universe, shortly after the Big Bang.

What is Big Bang Nucleosynthesis (BBN)?

The process during the early universe (first few minutes) where the first light atomic nuclei (hydrogen, helium, lithium) were formed.

What is the ultimate fate of a low-mass star like our Sun?

It will evolve into a red giant, then shed its outer layers to form a planetary nebula, eventually leaving behind a white dwarf.

What is a white dwarf?

The dense, compact remnant of a low-to-medium mass star after it has exhausted its nuclear fuel, primarily composed of degenerate matter.

What is a planetary nebula?

An expanding shell of ionized gas ejected from a red giant star late in its life.

What is a neutron star?

The extremely dense and compact core remnant of a massive star after a supernova, composed almost entirely of neutrons.

What is a pulsar?

A highly magnetized, rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles.

What is the difference between ordinary matter, dark matter, and dark energy?

Ordinary matter interacts with light; dark matter has mass and gravity but does not interact with light; dark energy is a mysterious force causing the accelerated expansion of the universe.

How do astronomers detect dark matter?

Indirectly, through its gravitational effects on visible matter, such as galaxy rotation curves and gravitational lensing.

What is gravitational lensing?

The bending of light from distant galaxies by the gravity of massive objects (like galaxy clusters or dark matter) between the source and the observer.

What defines an elliptical galaxy?

A type of galaxy with an oval shape, very little gas and dust, and typically composed of older stars.

What defines an irregular galaxy?

A galaxy with no distinct regular shape, often rich in gas and dust, and thought to result from galactic collisions or interactions.

What is the Milky Way galaxy?

Our home galaxy, a barred spiral galaxy estimated to contain 100-400 billion stars.

Where is our solar system located within the Milky Way?

In one of the spiral arms (Orion Arm), about two-thirds of the way out from the galactic center.

What is a light-year?

The distance light travels in one Earth year, approximately 9.46 \times 10^{12} kilometers or 5.88 \times 10^{12} miles.

What is parallax in astronomy?

The apparent shift in the position of an object when viewed from different locations, used to measure the distance to nearby stars.

What are Jovian planets (gas giants)?

Large, low-density planets composed primarily of hydrogen and helium, like Jupiter, Saturn, Uranus, and Neptune.

What is a dwarf planet?

A celestial body orbiting the sun that is massive enough to be rounded by its own gravity but has not cleared its orbital neighborhood of other objects (e.g., Pluto).

What is the asteroid belt?

A region between the orbits of Mars and Jupiter containing a large number of irregularly shaped asteroids.

What is the Kuiper Belt?

A region of the solar system beyond Neptune, extending from about 30 to 50 AU from the Sun, consisting mainly of icy bodies and dwarf planets like Pluto.

What is the Oort Cloud?

A theoretical spherical cloud of icy planetesimals believed to surround the Sun at distances far beyond the Kuiper Belt, thought to be the source of long-period comets.

What are comets?

Icy bodies that release gas and dust as they approach the Sun, forming a visible coma and often a tail.

What is the definition of a meteoroid, meteor, and meteorite?

Meteoroid: A small rocky or metallic body in outer space.

Meteor: The streak of light seen when a meteoroid enters Earth's atmosphere and burns up (a "shooting star").

Meteorite: A meteoroid that survives passage through the atmosphere and impacts the Earth's surface.

What are the main layers of the Sun?

Core, Radiative Zone, Convective Zone, Photosphere, Chromosphere, Corona.

What is the core of the Sun responsible for?

Nuclear fusion, converting hydrogen to helium and releasing immense energy.

What is the primary energy source for stars?

Nuclear fusion, specifically the fusion of hydrogen into helium in their cores.

What is the Hertzsprung-Russell (HR) Diagram?

A scatter plot of stars showing the relationship between their absolute magnitudes (luminosities) or spectral types (temperatures) and their evolutionary stages.

What does the main sequence on an HR Diagram represent?

The longest stage of a star's life where it is fusing hydrogen into helium in its core.

What is the concept of general relativity regarding gravity?

Gravity is not a force, but a manifestation of the curvature of spacetime caused by the presence of mass and energy.

What is the relationship between wavelength and frequency for electromagnetic waves?

They are inversely proportional: as wavelength increases, frequency decreases, and vice versa (c = \lambda f).

What is a protostar?

A contracting mass of gas and dust that represents an early stage in the formation of a star, before nuclear fusion begins.

What is the event horizon of a black hole?

The boundary around a black hole beyond which nothing, not even light, can escape.