Astronomical Observations: Distance & Light 7/2/09 Astronomy 101
Astronomy Picture of the Day Astronomy 101
Something Cool: Lasers on the Moon Astronomy 101
Outline for Today Astronomy Picture of the Day Something Cool Business Return Lab 2 Q&A session Distance Lecture Light Lecture Minute Writing Break Lab 4 Astronomy 101
Questions for Today How big is the Solar System, Galaxy, Universe? How can we use parallax to find distance? What is light? What is the electromagnetic spectrum and how does wavelength relate to energy? What are brightness and luminosity and how do they change with distance? How can we use standard rods and candles to find distance? Astronomy 101
Solar System Astronomy 101
Solar System Astronomy 101
The Sun is One of Many Stars Solar System Milky Way The Local Group of Galaxies
htt://xkcd.com/482 Astronomy 101 htt://xkcd.com/482
Place in Order from Smallest to Largest: Galaxy, Solar System, Universe, Local Galaxy Cluster A) Solar System, Galaxy, Local Cluster, Universe B) Local Cluster, Galaxy, Solar System, Universe C) Galaxy, Solar System, Universe, Local Cluster D) Solar System, Universe, Galaxy, Local Cluster Astronomy 101
Place in Order from Smallest to Largest: Galaxy, Solar System, Universe, Local Galaxy Cluster A) Solar System, Galaxy, Local Cluster, Universe B) Local Cluster, Galaxy, Solar System, Universe C) Galaxy, Solar System, Universe, Local Cluster D) Solar System, Universe, Galaxy, Local Cluster Astronomy 101
Parallax
Angular Sizes We measure how big objects appear to be in degrees, arcminutes, & arcseconds. 1 degree = 60 arcminutes = 3600 arcseconds
Angular Sizes 1 degree = 60 arcminutes = 3600 arcseconds
Parallax -> Distance Parallax Angle, Distance distance 1/(parallax angle)
The Facts of Light Emission of Light = Radiation Light sometimes acts like a massless particle Light also acts like a wave.
Light as Wave & Particle We ll talk about emission and absorption of individual photons. We ll also often assign wave-like qualities to it 1.Wavelengt h 2.Frequency 3.Velocity 4.Energy
Wavelength The distance over which the wave pattern repeats is the wavelength.
Wavelength The color of light depends upon its wavelength. Short wavelengths are Blue Long wavelengths are
Wavelength We see with our eyes only a tiny fraction of the range of possible wavelengths (radio) Size of atomic nucleus! Size of Mt. Everest! Logarithmic scale : each tic mark represents a factor of ten increase.
1. Wavelength (radio )
If you were to design a pair of glasses for seeing animals at night, you would want them to convert A) Infrared photons to X-ray photons B) X-ray photons to optical photons C) Infrared photons to optical photons D) Optical photons to UV photons
If you were to design a pair of glasses for seeing animals at night, you would want them to convert A) Infrared photons to X-ray photons B) X-ray photons to optical photons C) Infrared photons to optical photons D) Optical photons to UV photons
Frequency The rate at which peaks pass a given location is the frequency.
Velocity The speed of light is constant. The speed of light is closely related to its wavelength and its frequency. If you know one, you can calculate the other! Speed of light (c) = distance between peaks = wavelength X frequency time between peaks
Light Years How far light travels in a year About 1016 meters About 5.8 1012 miles The Sun is eight light minutes away
Why use light years? Nearest Star: 40,000,000,000,0 00 kilometers (4 X 1013 km) = 4 light years 206,000 times further than the Earth is from the Sun)
It takes a green laser 2.5 seconds to reach the surface of the Moon, off and return. Howbounce long does it take a radio wave to complete the same journey? A) Less time because radio waves have smaller frequency B) More time because radio waves have longer wavelengths C) More time because radio waves are less powerful D) The same time
It takes a green laser 2.5 seconds to reach the surface of the Moon, off and return. Howbounce long does it take a radio wave to complete the same journey? A) Less time because radio waves have smaller frequency B) More time because radio waves have longer wavelengths C) More time because radio waves are less powerful D) The same time
Energy The energy of a photon depends entirely on its frequency (or wavelength) Energy is greater when.. FREQUENCY WAVELENGTH
Energy Dangerous!!! Burns you! Goes through you! Mostly Harmless. (Microwaves only hurt because they have a peculiar interaction with water)
Energy Watch your intuition here! BLUE Short wavelength High frequency HIGH ENERGY RED Long wavelength Low frequency LOW ENERGY
Which has a longer wavelength? A) Ultraviolet light (UV) B) Visible light C) Infrared Light (IR)
Which has a longer wavelength? A) Ultraviolet light (UV) B) Visible light C) Infrared Light (IR)
How does light interact with matter? Emit Reflect Absorb Transmit
Which is an example of reflected light? A) UV Light from the Sun B) The green color of grass C) Heat from a stove D) Gamma ray radiation from Uranium
Which is an example of reflected light? A) UV Light from the Sun B) The green color of grass C) Heat from a stove D) Gamma ray radiation from Uranium
Brightness he brightness of a star depends on both distance and luminosity
Luminosity And Apparent Brightness Luminosity: Amount of power a star radiates (energy per second = Watts) Apparent Brightness or Flux: Amount of starlight that reaches Earth (energy per second per square meter)
These two stars have about the same luminosity -which one appears brighter? A. Alpha Centauri B. The Sun
These two stars have about the same luminosity -which one appears brighter? A. Alpha Centauri B. The Sun
Another Inverse Distance Squared Law Flux = Luminosity 2 Distance
How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright B. It would be only 1/6 as bright C. It would be only 1/9 as bright D. It would be three times brighter
How would the apparent brightness of Alpha Centauri change if it were three times farther away? A. It would be only 1/3 as bright B. It would be only 1/6 as bright C. It would be only 1/9 as bright D. It would be three times brighter
Standard Candles If we know how much light something is emitting (its luminosity) and how much of its light we are receiving (flux) we can tell how far it is
The Magnitude Scale Don't Memorize m = apparent magnitude, M = absolute magnitude apparent brightness of Star 1 1/ 5 m1 - m 2 = (100 ) apparent brightness of Star 2 luminosity of Star 1 = (1001/ 5 ) M 1 - M 2 luminosity of Star 2
Minute Writing What concept came most easily to you and what concept was the most difficult? Astronomy 101
Assignments Read Chapters 5.3, 5.4, 5.5; Send Jeff and me two questions by Tuesday Read Lab 5; Send Jeff and me one question by Tuesday Lab 4 dues Tuesday News article due Tuesday Astronomy 101