Astronomy 1020Spring_2015

Day-15Stellar Astronomy

Course Announcements• 1st Quarter observing night:

• Wed. Feb. 25

• Lab this week – Spectrometer

• Smartworks Chapters 5: Due Mon. 3/2• Smartworks Chapters 6: Due Mon. 16

(??)• APSU Research and Creativity Forum April 11-1

2, 2014• Abstracts are due: 4:30pm Fri., March 21

• Feb. 26 – Last day to drop with an automatic “W”

Exam SadisticsMetric Ex-1Number 28/32Mean 70.7StdDev 15.3Median 73.2Mode ---High 95.2Low 40

Like the flavors of Ice cream – they each provide us with different information.

EM Spectrum

But what do you get when you put all the flavors (light) together?

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

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

What Light Can Tell Us.Photometry – Study of Brightness:

Luminosity, Est. of Distance, Rough Temp. of StarSpectroscopy – Study of the EM Spectrum:

Composition, Radial Velocity, Temp., Surface-gravity

Mass for compact objectsAstrometry – Study of Positions:

Tangential Motion, DistancePolarimetry – Study of Polarization of Light:

Magnetic Field

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

Knowing the speed of light and one other variable, either the wavelength or frequency of the light in question, you can find the remaining quantity.

Example: Find the wavelength of the light wave coming from a radio station broadcasting on 770 AM:

MATH TOOLS 5.1

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

Photons Light also behaves as a particle. Photon: particle of light. Photons carry energy and can have

different amounts of energy. Photons with high energy = light with high

frequency. Photons with low energy = light with low

frequency. Atoms can absorb or emit photons.

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.

Atoms have a dense nucleus of protons and neutrons.

Electrons surround the nucleus in a “cloud.”

Electrons can have certain energies; other energies are not allowed.

Each type of atom has a unique set of energies.

Energy level diagram represents this.

Lowest energy is the ground state.