Astronomy (Midterm I)

I'M GOING TO KILL MYSELF

What is a light-year?

Time it takes for light to travel in one year

What does a light-year measure?

Distance, not time

What is the diameter of Earth?

13,000 km

How far is the Moon from the Earth?

384,000 km

What is the diameter of the Earth?

3,476 km

How long does it take for light to travel between the Earth and the Moon?

1.3 seconds

What is the speed of light?

3×10^8 m/s

How far is the Earth away from the Sun?

150 million km

What is an astronomical unit (AU)?

Average Earth-Sun distance

How long does it take light to travel from the Earth to the Sun?

More than eight minutes

What is interstellar dust?

Tiny solid particles that are mixed with sparse distribution of gas; found within the space between stars

What is dark matter?

The material that makes up the Galaxy; cannot be observed; its gravity is exerted on nearby stars and material

What are the Milky Way’s two satellites?

Sagittarius and Magellanic Clouds

What is the nearest galaxy to the Milky Way?

Andromeda (M31); 2 million light years

How many galaxies in a local group?

50

What are quasars?

Brilliant centers of galaxies, with energy produced by gas that is heated to a temperature of millions of degrees as it falls toward a massive black hole and swirls around it

When can an atom of interstellar gas be found in the universe?

Every cubic meter

What is the celestial sphere?

A sphere that early Greeks regarded as the sky

What are the two parts of the celestial sphere?

Zenith and Horizon

What is the zenith?

Point above one’s head

What is the horizon?

The plane in which an individual stands on

What are poles?

Imaginary lines that intersect the celestial sphere that are 90 degrees to the equator

What is the circumpolar zone?

Region in which stars within 38 degrees of the North Pole that never set

What is the ecliptic?

The path in which the Sun appears to take around the celestial sphere each year
- Causes Sun to rise about four minutes earlier each day with respect to the stars

What is the axial tilt of Earth?

23.5 degrees

What are fixed stars?

Maintain their patterns among themselves through many generations

What are wandering stars?

Planets

What is a zodiac?

The narrow 18-degree belt that the planets, Sun, and Moon are found in

What are constellations?

One of 88 sectors in which the sky is divided in

How is the celestial sphere divided?

Into 88 sectors

What is cosmology?

Concept of the cosmos (basic structure and origin)

What is the parallax?

Apparent shift in direction of an object due to motion of the observer

What is the stellar parallax?

Refers to Earth's orbital motion

What did Hipparchus discover?

Apparent magnitude and precession

What is apparent magnitude?

Way of dividing stars based on their brightness

What is precession?

Slow change in the direction in which the Earth's axis points towards to
- Causes Earth to wobble while it spins

How long does it take Earth to complete one precession?

26,000 years

What is retrograde motion?

Temporary westward motion of a planet as Earth swings between it and the Sun

What is an epicycle?

A small orbit

What is the great circle?

Any circle on the surface of Earth whose center is at the center of the sphere

What is each circle from the great circle called?

Meridian

What are the two types of coordinates astronomers use?

Declination and Right Ascension

What does declination measure?

Latitude

What does right ascension measure?

Longitude

What point was chosen for measuring right ascension?

Vernal equinox

What causes seasons?

Earth’s axial tilt

What is the tropic of cancer?

When the Sun at the zenith at noon on the first day of summer

What is the tropic of capricorn?

When the Sun at the zenith at noon on the first day of winter

What is the arctic circle?

Circle of latitude in which the Sun is present all day (North Pole)

What is the antarctic circle?

Circle of latitude in which the Sun is present all day (South Pole)

What is a solar day?

Rotation period of Earth in respect to the Sun

What is sidereal day?

Rotation period of Earth in respect to the stars

What is apparent solar time?

Time determined by the actual position of the Sun

What does AM stand for?

Anti meridiem

What does PM stand for?

Post meridiem

What is mean solar time?

Average value of a solar day over the course of a year (exactly 24 hours)

How long is a Moon’s sidereal month?

27.3217 days

How does the Moon rotates?

Rotates on its axis in exactly the same time that it takes to revolve about Earth

What is synchronous rotation?

Rotation of an object that always shows the same face to an object that it is orbiting because its rotation period and orbital period are equal

How far is 1 AU?

149,598,000 km

How far is 1 light-year?

9.46 trillion km

What zone is Earth part of?

Goldilocks Zone

What is the universe mostly made of?

Hydrogen and Helium
- 2% is everything else

What is the cosmic calendar?

Cosmic chronological calendar invented by Carl Sagan

The stars that we see are based on what?

Our location

Is brightness related to closeness?

No

What do you call the brightest star?

Alpha

What is apparent brightness?

Brightness from view on Earth; unrelated to luminosity

What is the ecliptic plane?

Plane where all planets fall along in our solar system (Earth, Sun, Moon)

What are circumpolar stars?

Stars that never set below the horizon

In what direction does Earth rotate?

Counterclockwise

What is the equivalent of Southern hemisphere’s North Star?

Southern cross

What is the current North Star?

Polaris

How does the Sun rise and set?

Rises directly East, and directly sets in the West

How does sunrise and sunset differ in Summer and Winter in the Northern Hemisphere?

Summer = North East to North West

Winter = South East to South West

How many objects did the Ancient Greeks saw?

Sun, Moon, Five other planets

How many degrees does the Moon move per hour?

12 degrees

What are the three candidates for the North star?

Polaris, Vega, Thuban

What happens to the parallax when the object is closer?

Parallax angle increases

How long is one complete rotation of the Earth?

23 hrs 56 mins 4.1 secs

How long is a sidereal day?

23 hrs 56 mins 4.1 secs

What is the calendar based on?

Solar time

Is the Moon always half-lit by the Sun?

Yes

What is a synodic/solar month for a Moon?

29.53 days relative to the Sun

Which phase of the Moon rises at sunrise and sets at sunset?

New

How many kilometers does the Moon travel per hour?

3,682 km

What does tidally locked mean?

Rotating in sync with how Earth rotates; causes same face to face dark side

What is tidal stretch?

Causes Moon to synch with Earth's rotation

What is another term for lunar eclipses?

Syzygies

How do lunar eclipses occur?

When the Moon passes Earth’s umbra; turns blood red

What is an umbra?

Darkest shadow on Earth

How many degrees is Earth’s orbit off center?

5 degrees; can cause partial eclipses

What causes the reddish colour of lunar eclipses?

Content of the atmosphere may scatter the red light

How do solar eclipses occur?

Moon passes between Earth and the Sun; casts a shadow on Earth

How large is the umbra for solar eclipses?

160 km

What can you see during a total solar eclipse?

Can see the corona of the Sun (halo)

What is an annular eclipse?

When the Moon is too small to cover the Sun

What causes a partial solar eclipse?

When the Moon is moving past the penumbra

What is perigee?

Reaches surface of the Earth; full eclipse; closest to Earth

What is apogee?

Causes annular eclipse; furthest from Earth