Astronomy 1010-H Planetary Astronomy Fall_2015 Day-17.

Astronomy 1010-HFall_2015Day-17

Planetary Astronomy

Course Announcements• How is the sunset/sunrise observing going?

• Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at 7:30pm – at the Observatory.

• Exam-2 will be Friday, Oct. 9

• SW-chapter 4 posted: due Mon. Oct. 5• SW-chapter 5 posted: due Fri. Oct. 9

Definitions & Terms -1• Light: The primary source of information in

astronomy for all objects. When we say “light” we are talking about everything from gamma-rays to radio-waves. This does NOT include gravity waves.

Gravitational objects create Roche limits within which the effects from their tidal forces can destabilize other objects.

Planets, stars, and galaxies can be affected.

Galaxies can be distorted with tidal tails. Moons of planets can have great internal

activity because of tides, perhaps allowing for conditions for life.

In order to leave a planet’s surface, an object must achieve a velocity greater than the planet’s escape velocity.

Therefore, Earth’s escape velocity is

MATH TOOLS 4.3

The net tidal force is the difference in force on the two sides of the planet.

The Moon’s tidal forces on Earth are 2.2 times as strong as the Sun’s tidal forces on Earth, resulting in greater lunar tides than solar tides.

MATH TOOLS 4.4

Almost all knowledge of the universe beyond Earth comes from light.

Light can tell us about objects in space: temperature, composition, speeds, and more.

Light moves at 300,000 km/s in a vacuum. First measured by Rømer when observing

Jupiter’s moons. Speed is slower in other materials, e.g.,

glass.

Light is a wave of combined electricity and magnetism, called an electromagnetic wave.

Changing electric and magnetic fields create a self-sustaining electromagnetic wave.

Wavelength (): length between crests.

Amplitude: height. Frequency (f):

number of waves that pass by each second.

Period (P): time to complete one cycle.

A long wavelength means low frequency.

A short wavelength means high frequency.

The speed of light, c,is constant.

SpeedWavelength

Frequency

cor

f

Visible spectrum: small range of wavelengths that humans can see.

Red light = longest wavelength ( ~ 750 nm).

Violet light = shortest wavelength ( ~ 380 nm).

“Roy G. Biv.”

Visible light is just one small part of the electromagnetic spectrum:

Gamma rays X-rays UV Visible IR Microwave RadioGamma rays X-rays UV Visible IR Microwave Radio

increasingincreasing

ff decreasingdecreasing

Lecture Tutorial EM Spectrum: (pg. 47)

• Work with a partner!

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one another. Take time to understand it now!!!!

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask another group.

Concept Quiz—AM and FM

On the FM dial, the frequencies run from 88 to 107 MHz (million cycles per second). On the AM dial, the range is 570 to 1600 kHz (thousand cycles per second). Which statements are true?

A. FM photons have shorter wavelengths than AM.

B. FM photons have higher energies than AM.

C. FM photons travel at the same speed as AM.

D. All the above statements are true.