BETTER ASTRONOMY STUDY SET

smaklin is so cooked

What three observations did ancient scientists use to prove Earth is a sphere?

Ships vanish bottom to top over horizon; Constellations change with latitude; Earth's shadow on Moon is round

Who first calculated Earth's circumference and how?

Eratosthenes, using shadows in 3rd century BCE

When did the first circumnavigation of Earth occur?

1519-1522 CE

What five "wandering stars" (planets) did ancient astronomers know?

Mercury; Venus; Mars; Jupiter; Saturn

Why did Ptolemy believe Earth was the center of the universe?

No stellar parallax was observed

How did Ptolemy explain retrograde motion?

Epicycles (small orbits within orbits)

What did Copernicus's heliocentric model explain without epicycles?

Retrograde motion of planets

What were Galileo's two major observations that supported heliocentrism?

Phases of Venus → orbit around Sun; Moons of Jupiter → objects orbit bodies other than Earth

What is the tilt of Earth's axis relative to the ecliptic plane?

23.4°

What are three main effects of Earth's tilt?

Different day/night length; Different Sun path; Opposite seasons

What are solstices, when do they occur, and what do they mean?

Hemisphere tilted most toward/away from Sun; occur June and December

What are equinoxes, when do they occur, and what do they mean?

Sun perpendicular to axis → equal day/night; occur March and September

Why do seasonal changes lag behind solstices and equinoxes?

Thermal inertia (oceans/land store and release heat slowly)

What do lines of latitude measure?

North/south position on Earth

What are the latitude values of the equator and the poles?

Equator = 0°; Poles = ±90°

What do lines of longitude measure?

East/west position on Earth

What longitude is the prime meridian?

0°

What is the maximum longitude?

±180°

What is elevation?

Angle of an object above horizon

What is declination?

Angle above/below celestial equator

How does latitude relate to the celestial pole at your location?

Latitude = elevation of celestial pole

Where does the Sun rise and set?

Rises in east, sets in west

What is the formula for longitude?

Longitude = 15° × (tPrime - tLocal)

What is the formula for latitude?

Latitude = 90 - [tan⁻¹(Object length/Shadow length) - declination]

Which galaxy is found in Andromeda?

Andromeda Galaxy (M31)

What is the brightest star in Canis Major?

Sirius

What shape does Cassiopeia make, and how does it help locate other stars?

"W" shape; points to North Star and Andromeda

Why is Orion important for navigation?

Easy to identify; head points to North Star; left arm to Big Dipper

What is the Great Square of Pegasus, and what branches off of it?

Large square; Andromeda branches off

What constellation contains the Big Dipper?

Ursa Major

How can Ursa Major help you find the North Star?

Line through two Big Dipper stars points to Polaris

What important star is in Ursa Minor?

Polaris (North Star)

Which constellation is called the "Southern Cross" and what is it used for?

Crux; used to find South Celestial Pole

What constellation contains Rigel Kentaurus and is used with Crux to find the South Celestial Pole?

Centaurus

How long does it take the Moon to orbit Earth and rotate once?

About 28 days

Why do we always see the same side of the Moon?

Tidally locked (rotates once per orbit)

What does waxing mean?

Lighted portion growing (east to west)

What does waning mean?

Lighted portion shrinking

What causes the Moon's apparent size to change (libration)?

Elliptical orbit

Is the Moon moving closer to or farther from Earth?

Farther away

When do solar eclipses occur?

New Moon; Moon's shadow falls on Earth

When do lunar eclipses occur?

Full Moon; Earth's shadow falls on Moon

What is the difference between the penumbra and umbra?

Penumbra = partial shadow; Umbra = total shadow

Why are lunar eclipses visible over a larger area than solar eclipses?

Earth's shadow covers entire night side; Moon's shadow covers small area

Why don't eclipses happen every month?

Moon's orbit is tilted; alignment needed at nodes