Astronomy 1020-H Stellar Astronomy Spring_2016 Day-15

Course Announcements 1 st “Hot Topics in Science”: Coming soon … Topics this semester are: Human Cloning, Environmental Toxicology, & Fracking … includes pizza. Dark Night Observing: Mon. 2/29 & Wed. 3/2 – 7:30pm at the APSU Observatory Exam-2 – Fri. 3/4 Chapters 5 & 6 Smartworks Chapters 5 & 6: Due Fri. 3/4 Spring Break Mar (Sat.-Sun.) APSU Research and Creativity Forum April 15, 2016 Abstracts are due: 4:00pm Fri., March 18 Feb. 29 – Last day to drop with an automatic “W” Apr. 1 – Last day to drop a class with W, F, FA

 The motion of a light source toward or away from us changes our perception of the wavelength of the waves reaching us.  Doppler effect.

Concept Quiz—Doppler Shift Hydrogen emits light at = 656 nm. You see a distant galaxy in which the light from hydrogen has = 696 nm. This galaxy is A. moving toward us. B. moving away from us.

 Temperature is a measure of the average speed of the motions of atoms.  Kelvin scale: Water freezes/boils at 273 K / 373 K.  Absolute zero is when thermal motion stops.

Emitted Light  Luminosity: amount of light leaving a source.  The amount and type of light leaving a source changes as an object heats up or cools down.  The hotter an object is, the more luminous it is.  The hotter an object is, the bluer it is.

 Dense objects emit a blackbody (or Planck) spectrum.  Continuous.  Gives light at all wavelengths.  Example: incandescent light bulb.

 For two objects of the same size, the hotter one will: Emit more total light at all wavelengths. Emit more total energy every second. Emit light at shorter wavelengths, on average.

Stefan’s Law  Flux is the total amount of energy emitted per square meter every second (the luminosity per area).  Then: where T is the temperature, F is the flux, and  (sigma) is called the Stefan- Boltzmann constant.  Hotter objects emit much more energy (per square meter per second) than cool objects.

Wien’s Law  The peak wavelength of a blackbody is inversely proportional to its temperature.  Peak wavelength peak : the wavelength of light of a blackbody that is emitted the most.  Here the wavelength is in nanometers and the temperature is in kelvin.  “Hotter means bluer.”

 With the Stefan-Boltzmann law, you can find Earth’s flux using its average temperature of 288 K.  Using Wien’s law, you can find the Sun’s surface temperature using the fact that its peak wavelength is around 500 nm. MATH TOOLS 5.3

Luminosity is the total energy (light) emitted by an object in each second. Stefan-Boltzmann law Luminosity depends on an surface area (A), and its temperature (T 4 ); Surface Area ∝ R 2 Luminosity = 4π R 2  T 4 Big and Hot objects have greater luminosity than small cool objects

Great Blizzard of 2015 – Part 3

Exam Sadistics MetricEx-1 Number28/32 Mean70.7 StdDev15.3 Median73.2 Mode--- High95.2 Low40

How BIG Are the Stars? While We Wait for Everyone

Luminosity is the total energy (light) emitted by an object in each second. Stefan-Boltzmann law Luminosity depends on an surface area (A), and its temperature (T 4 ); Surface Area ∝ R 2 Luminosity = 4π R 2  T 4 Big and Hot objects have greater luminosity than small cool objects

Lecture Tutorial Luminosity: (pg 55) 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.

20,000 10,000 5,000 Luminosity (solar units) Temperature (K) , ,000 Hertzsprung-Russell Diagram

Which star is Hot and Dim? Temperature (K) 20,000 10,000 5,000 Luminosity (solar units) Temperature (K) , ,000

Which star is Cool and Dim? Temperature (K) 20,000 10,000 5,000 Luminosity (solar units) Temperature (K) , ,000

Which star is Largest? 20,000 10,000 5,000 Luminosity (solar units) Temperature (K) , ,000

Which star is smallest? Temperature (K) 20,000 10,000 5,000 Luminosity (solar units) Temperature (K) , ,000

 Brightness is the amount of light arriving at a particular place.  Decreases as the distance from a light source increases, obeying an inverse square law.  The light spreads out over a greater area.

Lecture - Tutorial: Blackbody Radiation (pg. 59) 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.

Energy Output per second V I B G Y O R Star A Star B Wavelength Star C V I B G Y O R Star D V I B G Y O R Star A

Which has the longer peak wavelength? 1. Star A 2. Star C 3. Same Star C Wavelength V I B G Y O R Energy Output per second Star A

Which has the lower surface temperature? 1. Star A 2. Star C 3. Same Star C Wavelength V I B G Y O R Energy Output per second Star A

Which star looks red? 1. Star A 2. Star C 3. Both 4. Neither Star C Wavelength V I B G Y O R Energy Output per second Star A

Which has the greater energy output? 1. Star A 2. Star C 3. Same Star C Wavelength V I B G Y O R Energy Output per second Star A

Which star is larger? 1. Star A 2. Star C 3. Same Star C Wavelength V I B G Y O R Energy Output per second Star A

Which star is larger? 1. Star A 2. Star D 3. Same Star D Wavelength V I B G Y O R Star A Energy Output per second

Try to determine EVERYTHING about how these four stars compare!! Temp, Energy output, color, size (area)….. Object A Wavelength V I B G Y O R visible range Energy Output per second Object C Wavelength V I B G Y O R visible range Energy Output per second Object B Wavelength V I B G Y O R visible range Energy Output per second Object D Wavelength V I B G Y O R visible range Energy Output per second

 The telescope is the astronomer’s most important tool.  Purpose: to gather light of all kinds.  Two kinds of optical telescopes: reflecting and refracting.  Invented in 1608 by Hans Lippershey.

Telescopes Telescopes have three functions: 1. Gather light LGP ∝ Area = πR 2 2. Resolve objects Θ = 2.06 X 10 5 ( λ/D) 3. Magnify EXTENDED objects

 When light encounters a new material, it can either experience reflection or refraction.  In refraction, the light will be bent depending on the value of the index of refraction relative to the first material. CONNECTIONS 6.1

 Refraction depends on the wavelength— violet light is bent more than red.  Dispersion: the resulting spreading out of the wavelengths of light.  Causes chromatic aberration in lenses, which can be fixed by a compound lens. CONNECTIONS 6.1

 Refracting telescopes use lenses.  Objective lens: refracts the light.  Aperture: size of the objective lens (larger aperture gathers more light).  The objective lens is placed in the aperture.

 Focal length: distance between lens and the image (longer = larger image).  Aperture sets the light-collecting power.  Focal length determines the image size.

 The largest refracting telescope has a 1-meter aperture.  Problems with refractors: Need to be large to have a long focal length. Lenses suffer from chromatic aberration.

 Reflecting telescopes use mirrors.  There are primary and secondary mirrors.  Focal length is determined by the path the light takes reflecting off the mirrors.

 Reflectors have advantages over refractors.  No chromatic aberration.  Bigger telescopes due to increased focal length in the same amount of physical space and no need for massive lenses.  The largest telescopes in the world are reflectors.

A concave mirror focuses light

Spherical Aberration

Spherical aberration can be eliminated by a parabolic shape or a corrector plate Correcting S.A.

There are several types of reflecting telescopes Focal Arrangements

Schmidt-Cassegrain

 The light-gathering power of a telescope is proportional to the square of the aperture size.  A telescope’s magnification depends on the focal lengths of the objective lens or mirror and the eyepiece. MATH TOOLS 6.1