PS_Unit 5: The Universe

Observation

in astronomy refers to the process of gathering data about celestial objects and phenomena through various methods, including telescopes and space missions.

Inference

is the logical conclusion drawn from observations, helping astronomers interpret data about the universe.

Scientific Theory

is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence and repeatedly tested hypotheses.

Scientific Law

is a statement that describes an observable occurrence or phenomenon in nature, usually expressed mathematically and universally accepted as true.

Universe

refers to the totality of existence, encompassing all space, time, matter, and energy.

Big Bang

is the leading explanation for the origin of the universe, suggesting it began from an extremely hot and dense state and has been expanding ever since.

Electromagnetic Spectrum

is the range of all types of electromagnetic radiation, including visible light, radio waves, X-rays, and gamma rays, differentiated by wavelength and frequency.

Hubble’s Law

describes the observation that the farther away a galaxy is, the faster it is moving away from us, indicating the expansion of the universe.

Red Shift

is the phenomenon where light from an object moving away from the observer is shifted to longer wavelengths, providing evidence for the universe's expansion.

Blue Shift

is the phenomenon where light from an object moving towards the observer is shifted to shorter wavelengths, indicating its approach.

Doppler Shift

is the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave, commonly observed in sound and light waves.

Frequency

is the number of occurrences of a repeating event per unit of time, measured in hertz (Hz) for both sound and electromagnetic waves.

Wavelength

is the distance between successive crests or troughs of a wave, determining its color in light waves and pitch in sound waves.

Cosmic Background Radiation

is the afterglow radiation from the Big Bang, filling the universe and providing evidence for the origin of the cosmos.

Galaxy

is a vast system of stars, stellar remnants, interstellar gas, dust, and dark matter, bound together by gravity, and can contain millions to trillions of stars.

Milky Way

is the galaxy that contains our Solar System, characterized by its spiral shape and millions of stars.

Spiral Galaxy

is a type of galaxy characterized by its distinctive spiral shape, with arms that extend outward from the center, often containing younger stars and star-forming regions.

Elliptical Galaxy

is a type of galaxy that has an ellipsoidal shape, ranging from nearly spherical to more elongated forms, and generally contains older stars with very little new star formation.

Irregular Galaxy

is a type of galaxy that does not have a defined shape or structure, often resulting from gravitational interactions and typically containing older stars and active star formation.

Star

is a luminous celestial body made up of plasma, undergoing nuclear fusion to produce light and heat, forming the basic unit of galaxies.

Nuclear Fusion

is the process by which two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy, and is the fundamental mechanism powering stars.

Hertzsprung Russel Diagram

is a graphical representation of stars plotted according to their absolute magnitudes versus their stellar classifications or temperatures, illustrating the relationships between different types of stars.

Luminosity

is a measure of the total amount of energy emitted by a star per unit of time, usually expressed in watts, and indicates the brightness of the star as seen from a standard distance.

Temperature

is a measure of the average kinetic energy of particles in a substance, influencing a star's color, spectral classification, and overall characteristics.

Diameter

is the distance across a star, typically measured at its equator. It influences both the star's luminosity and its evolutionary stage.