Info for the Test

Bring a #2 pencil. No electronic devices: No calculators, cell

phones, headphones, etc. No books, notes, etc. No hats. Grades will be posted on the course website.

StudyingStudy questions on website highlight important topicsKnow definitions of BOLD terms in chapter summariesQuestions from lectures will give you some idea of what questions I may ask

- I may reuse or slightly modify some of these!

This review will focus on the more complex topics we have gone over

The "Solar Day" and the "Sidereal Day"

Solar Day

How long it takes for the Sun to return to the same position in the sky (24 hours).

Sidereal Day

How long it takes for the Earth to rotate 360o on its axis.

These are not the same! Which is longer? Why?

One solar day later, the Earth has rotated slightly more than 360o

A solar day is longer than a sidereal day by 3.9 minutes.(24 hours vs. 23 hours 56 minutes 4.091 seconds)

Difference due to rotation and revolution of Earth.

The Earth's Seasons

Why does the Earth have seasons?

How is this related to how high the Sun rises in the sky in Summer? In Winter?

Seasons: Due to tilt of Earth's Axis of Rotation

Summer Winter

In winter, the sun never gets very high in the sky => each bit of ground receives less radiation => cooler

Seasons caused by tilt of Earth’s axis of rotation.

Earth is farthest from sun during summer.

What motion of the Earth acts to slowly change the orientation of the Earth's axis of rotation?

How long does one cycle of this motion take?

Precession

Earth

Moon

Spin axis

**Vega Polaris

Precession Period 26,000 years!

Parallax

How does the parallax angle vary with the distance to the foreground object?

How does the parallax angle vary with the length of the baseline?

Parallax angle:

Decreases with distance to the foreground object.

Increases with the length ofthe baseline.

Eclipses

During which phase(s) can a lunar eclipse occur?

What about a solar eclipse?

How do the angular diameters of the moon and the Sun compare and how do we know?

Geocentric vs. Heliocentric Models

The geocentric model explained the retrograde motion of the planets by introducing _______?

The geocentric model was finally abandoned because it was unable to explain the observed ______ of Venus.

1

2

3

4

56

7

12

3

4

5

67

Earth

Mars

Apparent motion of Mars against "fixed" stars.

*

*

**

*

*

January

July

Heliocentric model easily accounts for phases of Venus

Geocentric model fails to account for phases of Venus

Kepler’s Laws

• What are Kepler's three laws?

Orbits are ellipses with Sun at one focus Planet speeds up as it gets closer to the sun Orbital period increases rapidly with distance

Newton's Laws

Newton's laws categorize objects as _______ and _________.

Newton's Law of Gravity

F =G m

1 m

2

R2

F is the gravitational force.

G is the "gravitational constant".

What factors determine the strength of the gravitational force?

Planetary Orbits

What two competing effects lead to the stability of a planetary orbit?

Gravity and Inertia!

Waves What is a wave?

What are the main properties of waves?

What two things do all waves transport?

What is a photon?

Waves are a type of disturbance that can propagate or travel.Waves carry information and energy.

Properties of a wave

wavelength ()

crest

amplitude (A)

velocity (v)trough

Period (T): time between crest (or trough) passages

Frequency (f): rate of passage of crests (or troughs), f

v = f1

T

(units: Hertz or cycles/sec)

Equilibrium position

What is the radiation spectrum displayed by most astronomical objects called?

What property of the spectrum tells us the temperature of the object?

"cold" dust

"hot" stars

"cool" star

Sun

frequency increases, wavelength decreases

Overall shape of blackbody curve is the SAME for objects at ALL temperatures!

Emission and Absorption Spectra

How are the emission and absorption spectra of a certain element related?

How do the emission (or absorption) spectra of two different elements compare?

For a given element, emission and absorption lines occur at the same wavelengths! Each contains same information and serves as a unique fingerprint for that element.

Sodium emission and absorption spectra

When an atom absorbs a photon, it moves to a higher energy state briefly.

When it jumps back to lower energy state, it emits photon(s) in a random direction, conserving the total energy of the system.

Doppler Shift

How can the doppler shift be used to detect extrasolar planets?

What type of velocity information does this effect give us?

• Star with extrasolar planet wobbles around common center of mass.• Causes small Doppler shift of its absorption lines.• Only gives information about velocity along line of sight!