Astronomy Lecture Notes Flashcards

Flashcards for reviewing Astronomy lecture notes.

Universe

everything; the entirety of space and time.

Galaxy

A gravitationally-bound system that consists of stars, gas, dust, and dark matter.

Solar system

A gravitationally-bound system made up of a star and all the planets, moons, comets, asteroids, dwarf planets, gas, and dust that orbit it.

Massive

Contains lots of stuff (matter), but not necessarily bigger in size (radius).

Milky Way Galaxy

Our galaxy, a spiral galaxy containing over 100 billion stars.

Local Group

A group of about fifty galaxies, including the Milky Way.

Virgo Supercluster

A supercluster of galaxies that contains the Local Group.

Laniakea Supercluster

A huge supercluster of galaxies that contains the Virgo Supercluster.

Light-year

The distance light travels in one year, used to measure vast distances in the Universe.

Cosmological principle

The assumption that the physical laws that apply here on Earth apply everywhere else in the Universe.

Hypothesis

An idea that can explain a phenomenon.

Theory

A hypothesis that tests have failed to disprove.

Physical law

A theory that has been very well tested and is of fundamental importance.

Occam’s razor

When faced with competing hypotheses that explain observations equally well, use the one that requires the fewest assumptions.

Zenith

The point directly overhead of an observer.

Meridian

An imaginary line from the north horizon point through the zenith to the south horizon point.

Celestial sphere

A projection of Earth’s poles and equator into space.

Celestial equator

A circle on the celestial sphere midway between the two celestial poles.

Ecliptic

The apparent path of the Sun over the year, inclined 23.5 degrees to the celestial equator.

Circumpolar

Stars that do not rise or set but appear to move about the north celestial pole counterclockwise.

Zodiac

The constellations through which the Sun appears to pass as Earth revolves around the Sun.

Retrograde motion

The apparent backward looping motion of the planets over the course of several nights.

Geocentric

Earth-centered.

Heliocentric

Sun-centered.

Ellipse

The shape of planetary orbits around the Sun, according to Kepler's first law.

Semimajor axis

Half of the longest diameter of an ellipse.

Eccentricity

A value that describes the shape of an ellipse; 0 is a circle, and higher values are more elongated.

Force

A push or pull.

Net force

The sum of all the forces acting upon an object.

Frame of reference

A system where an observer measures positions or movement using coordinates such as distance and time.

Inertial frame of reference

A reference frame moving in a straight line at a constant speed.

Newton’s first law of motion

A moving object will stay in constant motion, and an object at rest stays at rest, unless acted upon by a net force.

Newton’s second law

The acceleration of an object is directly proportional to the magnitude of the net force acting on it and inversely proportional to the object’s mass.

Acceleration

Measures how quickly a change in velocity (speed and/or direction) of an object takes place.

Newton’s third law

Forces occur in action-reaction pairs; for every action in nature, there is an equal and opposite reaction.

Weight

The product of mass and acceleration due to gravity.

Gravity

A mutually attractive force between any two objects with mass.

Electromagnetic wave

Light (does not require a medium through which to travel).

Wavelength

The length between crests of a wave.

Amplitude

Height from the undisturbed position (of a wave).

Frequency

Number of waves that pass by each second.

Spectrum

Light sorted by frequency and wavelength.

Photon

A particle of light.

Absorption

When light hits matter, the light energy can be absorbed.

Emission

Matter can emit energy.

Digital detectors

Charge-coupled devices (CCDs), are far more efficient than film.

Refraction

Occurs when light enters or leaves a material.

Reflection

Occurs as light hits a mirror and bounces off.

Refracting telescopes

Use lenses to collect and focus light.

Focal length

The distance from the lens to where the light focuses. The longer the focal length, the larger the image.

Aperture

The diameter of the primary lens. The larger the aperture, the more light can be collected.

Reflecting telescopes

Use mirrors to collect and focus light.

Radio telescopes

Typically tens of meters in diameter and used to collect radio waves.

Interferometric arrays

Combine the signals from many telescopes. The combined signal allows the array to act as one large telescope to improve the angular resolution.

Adaptive optics

Can help correct for atmospheric distortion.

New Moon

Moon is between Earth and the Sun.

Waxing Crescent Moon

Less than half the Moon is lit up from Earth’s point of view.

First Quarter

Moon is at right angles with Earth and the Sun. Half the Moon is lit up from Earth’s point of view.

Full Moon

Moon is on the opposite side of Earth from the Sun. The side facing the Earth is fully illuminated.

Solar eclipses

Occur only at new moon.

Lunar eclipses

Occur only at full moon.