Video Notes: The Science of Astronomy (Vocabulary Flashcards)

Vocabulary flashcards covering key terms and concepts from the astronomy video notes.

Astronomy

The study of all matter and energy in the universe, focused on evolving bodies like planets, stars, and galaxies; shows Earth as part of the universe and the starting point for exploration.

Astron

'Star' in Greek; one of the roots in the word astronomy.

Nomos

'Arrangement/order/law' in Greek; combined with astron in astronomy.

Light pollution

Electric lights that interfere with astronomical observations.

Timekeeping (in astronomy)

Astronomy enabled ancient peoples to track time and seasons, crucial for agriculture.

24-hour day

Modern measure derived from the Sun’s apparent circle across the sky.

Month

A time period derived from the Moon’s cycle of phases.

Weekdays origin

Names derived from the Sun, Moon, and five naked-eye planets (Mercury, Venus, Mars, Jupiter, Saturn).

Celestial navigation

Using the Sun and stars to determine one’s position on Earth; examples include Polaris, Alpha Centauri, Beta Centauri, and the Southern Cross.

Polynesian/Micronesian navigators

Historical exemplars of celestial navigation across the Pacific.

Alpha Centauri and Beta Centauri

Stars used as navigational guides because they rise and set at consistent points on the horizon.

Southern Cross

A key constellation used for navigation in the southern sky.

Astrology

A belief system linking heavenly positions to human affairs; astronomy is the science distinct from astrology.

Ancient structures (Stonehenge, Caracol)

Stonehenge and Mayan Caracol show alignments with significant solar and planetary points and reflect early naked-eye astronomy.

Stonehenge

Ancient stone circle with alignments indicating sunrise/sunset at key times.

Caracol (Chichén Itzá)

Mayan tower whose windows align with Sun and Venus rising/setting points.

Telescopes

Primary tool for collecting astronomical data; improve brightness/sharpness and enable observations beyond the naked eye.

Adaptive optics

Technique to reduce twinkling by correcting atmospheric distortion in real time.

Hubble Space Telescope

A space telescope orbiting above Earth’s atmosphere to avoid atmospheric blur.

Electromagnetic spectrum (visibility)

Telescopes observe wavelengths beyond visible light, such as radio and X-ray.

Refracting telescope

Telescope that uses lenses to bend light and focus distant objects.

Yerkes refracting telescope

Largest refracting telescope (40-inch lens, 64-foot tube) at Yerkes Observatory.

Reflecting telescope

Telescope that uses a curved mirror to gather and focus light.

Subaru telescope

Largest single-piece reflecting telescope on Mauna Kea (27.25-foot mirror).

Spacecraft (robotic)

Most spacecraft operate without humans aboard, controlled from Earth.

Flybys

Spacecraft that pass by a world once, e.g., Voyager 2’s flybys of Jupiter, Saturn, Uranus, Neptune.

Orbiters

Spacecraft that go into orbit around a world (e.g., Cassini around Saturn).

Probes and Landers

Spacecraft that probe atmospheres or land on surfaces (e.g., Mars Exploration Rovers).

Celestial Sphere

Ancient model imagining stars/planets fixed on a hollow sphere surrounding Earth.

Celestial Dome

The apparent dome of the sky over an observer; defines the local sky.

Horizon

Boundary between Earth and sky.

Zenith

The point directly overhead from the observer.

Celestial Meridian

Imaginary line from north horizon through zenith to south horizon.

Celestial Poles (NCP/SCP)

Projections of Earth’s North/South Poles onto the celestial sphere.

Precession

Slow conical motion of Earth’s axis caused by Sun/Moon gravity; ~25,725-year cycle changing North/South star positions.

North Pole Stars

Current North Star is Polaris (in Ursa Minor); Thuban (13,000 years ago) and Vega (in ~13,000 years) will be North Star in the future.

One wobble period

One full 360° wobble of Earth’s axis — about 25,725 years.

Celestial Equator

Projection of Earth’s equator onto the celestial sphere.

Ecliptic

Apparent path of the Sun through the sky; corresponds to zodiac and the Moon’s/planets’ paths.

Distances (illusion on the sky)

Objects appear to lie at similar distances due to lack of depth perception in space.

Moon distance

Approximately 238,000 miles from Earth.

Sun distance

Approximately 93,000,000 miles from Earth.

Neptune distance

About 2.8 billion miles from the Sun (and Earth).

Light year

Distance light travels in one year (~6 trillion miles).

Proxima Centauri

Nearest star to Earth at ~4.22 light-years away.

Horizon system (altitude & azimuth)

Coordinate system for locating objects using altitude (above horizon) and azimuth (compass direction).

Altitude

Angular height of an object above the horizon (0° at horizon, 90° at zenith).

Azimuth

Compass direction of an object along the horizon (0° North, 90° East, 180° South, 270° West).

Circumpolar Zone

Region of sky that remains above the horizon; size depends on latitude.

Long Island example (40°N)

Five circumpolar constellations: Ursa Minor, Draco, Cepheus, Cassiopeia, Camelopardalis.

North Pole vs Equator for circumpolarity

At North Pole, the circumpolar zone is the entire sky; at the equator, there is no circumpolar zone.

Diurnal Motion

Daily rising in the east and setting in the west due to Earth’s rotation.

Seasonal Motion

Slower annual cycle of Sun/stars; same constellations appear seasons each year.

Stars

Massive gaseous bodies that emit light; energy produced by nuclear fusion in cores.

Constellations

Patterns of stars identified by names (mythology, animals, etc.); boundaries standardized by IAU in 1930.

Asterisms & example

Prominent star patterns not officially official constellations (e.g., Big Dipper).

Twinkling

Stars appear to twinkle due to atmospheric turbulence.

Magnitude scale

Brightness scale; each step changes brightness by a factor of ~2.512; larger numbers are fainter.

Apparent Magnitude (m)

Brightness of a star as seen from Earth; depends on luminosity and distance (inverse square law).

Albedo

Reflectivity of a planet; higher albedo often indicates atmosphere, water, or ice.

Brightest objects & magnitudes

Sun (around -26.78), Moon (-12.5), Venus (-4.6), Sirius (-1.4); Polaris (+2.0). Faint naked-eye limit ~ +6.5.

Absolute Magnitude (M)

Magnitude a star would have at 32.6 light-years (10 parsecs); used to compare intrinsic brightness.

Circumpolar Zone (continued)

Region of sky always above horizon; dependent on latitude; Long Island example lists five circumpolar constellations.

The Sun’s seasons

Seasons arise from Earth’s 23.5° axial tilt relative to the ecliptic; changing Sun height and day length.

Planets (definition & naked-eye visibility)

Objects in orbit around a star; five easily seen with naked eye: Mercury, Venus, Mars, Jupiter, Saturn; Uranus barely visible; Neptune require telescope.

Planet names & brightness variation

Planets named after Roman gods; brightness changes with distance and, for some, atmospheric/ice properties (albedo).

Non-Uniform Motion

Planets vary in speed as they move along their orbits.

Annual Motion

Planets’ slow west-to-east drift relative to stars due to orbital motion; the Sun and Moon also show west-to-east motion.

Retrograde Motion

Apparent backward motion of planets (east to west) caused by relative positions and motions; often when brightest.

The Moon

Earth’s natural satellite; the term can refer to any planetary moon.

Lunar Phases

Moon’s phases change as sunlight illuminates different portions of the Moon while it orbits Earth.

Eclipse

Blockage of light from one object by another between it and the observer.

Solar Eclipse

Moon passes between Earth and Sun, partially or wholly blocking Sun’s light.

Lunar Eclipse

Earth passes between Sun and Moon, casting Earth's shadow on the Moon.

Red Moon

Moon appears reddish during some eclipses due to atmospheric scattering of sunlight.

Rarity of Eclipses

Eclipses are uncommon because the Moon’s orbital plane is tilted relative to Earth’s orbit around the Sun.