Astro 120 Test #1

What type of eclipse is visible if the observer is located in the penumbra of the moon's shadow?

A partial solar eclipse.

How could a spacecraft be used to measure the mass of a planet?

You could place the spacecraft in orbit around the planet then measure its average distance and its orbital period. Newton's version of Kepler's 3rd law then allows you to calculate the planet's mass.

The Earth rotates around its axis

once every day

Constellations

pattern or grouping of stars

celestial sphere

representation of the sky around the entire Earth

Tycho Brahe

was the best observer of his time and made detailed, accurate observations of the position of planets all without the aid of a telescope. observations of a supernova and a comet went against the view that the heavens were perfect and unchanging

The Earth orbits around the sun

in 1 year

Galileo's

observations of Venus and Jupiter supported the heliocentric model of the solar system.

DEC of the Sun varies between

-23.5 and +23.5

Properties of planet motion

1. Motion is close to the ecliptic 2. General eastward motion 3. Occasional "retrograde" westward loops 4. Venus & Mercury always near sun

Keplers three laws

1. The orbits of the planets are ellipses with the Sun at one focus 2. A line connecting the planet to the Sun sweeps out equal areas in equal intervals of time, 3. The ratio of the square of the orbital period (P) of a planet to the cube of the semi-major axis (a) of its orbit is the same for all planets: P2/a3 = constant

How old is the universe

13.7 billion years

RA of the Sun increases

2 hours per month

The Earth's axis is tilted

23.5 degrees

How old is the solar system

4.56 billion years old

Sun never sets/rises at least once per year above

66.5 n and s

What is the name given to the average Earth-Sun distance?

AU

Parallax Angle

Apparent shift of a star's position due to the Earth orbiting the Sun

Ptolemy

Center of epicycle moves at a variable speed so that it appears to be moving uniformly as seen from the equant.

Apollonius

Developed the epicycle

Why did Ptolemy and other Greek astronomers need to use epicycles in their models?

Epicycles accounted for retrograde motion.

Approximately when does the 3rd quarter moon rise and when does it set for an observer in Ames?

It rises around midnight and sets around noon.

Which of Kepler's three laws describes the fact planets move at different speeds in their orbit?

Kepler's second law. In order for a planet-Sun line to sweep out equal areas in equal amounts of time the planet must vary its velocity as it travels along its orbit.

why do we only see one side of the moon from earth

Moon rotates exactly once with each orbit

Newton's 3rd laws

Newton #1: bodies move at constant velocity unless acted upon by an unbalanced force Newton #2: Force = mass x acceleration (F = ma) Newton #3 For every force on a body, there is an equal force acting in the opposite direction on another body

You see a newspaper article that says our solar system is 100,000 light-years in diameter - is this approximately correct?

No, that's distance Galaxy.

You go out one evening for a walk around Ames and see a bright object low on your northern horizon; could this object be a planet?

No. All planets are found near the ecliptic, which from Ames will never be found near the northern horizon.

Can you ever see Venus in the sky far away from the position of the Sun?

No. Venus is always found close to the Sun because its orbit around the Sun is entirely within the Earth's orbit.

If a star has a RA = 0h it lies on a line of right ascension that passes through what three main reference points on the celestial sphere?

North Celestial Pole, the Vernal (Spring) Equinox, and the South Celestial Pole.

What makes a planet different?

Planets have a motion relative to the fixed stars

Nicolaus Copernicus

Proposed a Sun-centered model of the Solar System

How did Copernicus' model explain retrograde motion?

Retrograde motion is observed when the Earth passes a planet travelling on an orbit larger than the Earth's.

circumpolar

Some stars never set

Why doesn't the Moon crash into the Earth even though it is attracted to the Earth by the force of gravity?

The Moon also has a "sideways" component to its motion. This combined with the gravitational pull between the Earth and the Moon leads to an orbit around the Earth.

If the Earth was not tilted on its rotational axis how would you describe the variation of the sun's right ascension and declination over the course of one year?

The RA of the sun would increase ~2 hours per month (12 months to go 24h). The declination of the sun would be constant at 0o.

Why can't an observer in Ames see the Southern Cross constellation (located very close to the south celestial pole?

The constellation is at too low a declination and never rises above the observer's horizon - or more simply the Earth is always in the way!

What is the name given to the line that passes through the due north point on the horizon, the observer's zenith point and continues on to the due south point?

The meridian.

Why don't we see eclipses at every full and new moon?

The moon's orbit is tilted by about 5 degrees to the ecliptic. At full and new moon the moon is typically above or below the ecliptic so its shadow misses the Earth (no solar eclipse) and the Earth's shadow misses the moon (no lunar eclipse).

How did Galileo's observations of the phases of Venus support the Copernican model of the solar system?

They naturally occur if Venus is orbiting the Sun

What are the approximate RA and DEC of a first quarter moon occurring near the summer solstice?

This puts the moon at RA~12h. At this RA the ecliptic has a DEC~0o

Tidal forces

are caused by the difference in the force of gravity experience by different parts of an extended object

Total solar eclipses allow us to see

chromosphere, prominences, and corona

Orbit shape

depends on velocity at closest distance.

Eccentricity

describes how much an ellipse deviates from a perfect circle.

Newton

developed a comprehensive theory of motion based upon the idea of a gravitational force that was not only responsible for the motion of objects on the Earth but also for the motion of planets

what is the moons apparent path on the sky

eastward motion relative to stars

What is the shape of the Earth's orbit around the Sun?

ellipse

Galileo is best known

for making the first astronomical observations with a telescope but he also developed a new description of how objects moved.

Johannes Kepler

inherited the observations of Tycho and set about using them to develop a better description of how planets moved.

Astronomy is a

science

As the Earth orbits the Sun

the Sun appears to move eastward with respect to the stars.

Spring Tides

tidal force of Sun & Moon aligned

Neap Tides

tidal force of Sun & Moon perpendicular

What causes seasons

tilt