Astronomy Picture of the Day

Orbit of Earth around Sun(Demo - Ball on String)

Gravity and Orbits

• Throwing an object fast enough will put the object into orbit! (Neglecting air resistance)

• Moon is continually “falling” towards the Earth in its orbit (Gravity vs. inertia)

Correction to Kepler’s Third Law

• Earth and sun actually rotate about their common center of mass

• Corresponds to a point inside sun

• Used to detect extrasolar planets

Review Question

● The force of gravity between two objects decreases rapidly with the:

● A)product of the two masses.● B)ellipticity of the orbit.● C) separation distance.● D)orbital velocity.

Review Question

● The acceleration experienced by a falling object due to Earth's gravity _____ the mass of the object.

● A)increases with● B) decreases with● C) is independent of

Review Question

● A Mars-sized and a Jupiter-sized planet both orbit a star at the same distance. The Mars-sized planet has ______ orbital period when compared to that of the Jupiter-sized planet.

● A)a shorter● B)a longer● C) the same

Chapter 2: EM Waves

● What is a wave?

● What are the main properties of waves?

● What two things do all waves transport?

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

is a distance, so its units are m, cm, or mm, etc.

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)

Waves bend when they pass through material of different densities.

swimming pool

air

water

prism

airairglass

Refraction

All radiation (including visible light) travels as Electromagnetic waves.

That is, waves of electric and magnetic fields travelling together.

What are some examples of objects with magnetic fields:

What are some examples of objects with electric fields:

All radiation (including visible light) travels as Electromagnetic waves.

That is, waves of electric and magnetic fields travelling together.

What are some examples of objects with magnetic fields:

a bar magnetthe Earththe Sun

What are some examples of objects with electric fields:

protonselectrons } "charged" particles that

make up atoms.

Anything with too many or to few electrons!

Electrical appliancesLightning

• Electric Force - opposites attract, likes repel

• Oscillating charges radiate

• All objects have temperatures greater than absolute zero - random thermal motion

• All objects radiate!• Why don’t we see the

radiation coming from many ordinary objects?– Dog whistle analogy

Electromagnetic Radiation

(How we get information about the cosmos)

What are some examples of electromagnetic radiation and what are the different ways in which we might experience them or make use of them?

Electromagnetic Radiation

(How we get information about the cosmos)

What are some examples of electromagnetic radiation and what are the different ways in which we might experience them or make use of them?

Light (see)Infrared (heat)Ultraviolet (sunburn)Microwaves (cooking, communication)AM radio (communication)FM radio (communication)TV signals (communication)Cell phone signals(communication)X-rays (medical applications)

How might you go about attempting to contact (or detect the presence of)

an alien race?