Astronomy: Understanding Luminosity, Brightness, Stars, and Constellations - Prof. Thomas , Study notes of Astronomy

Download Astronomy: Understanding Luminosity, Brightness, Stars, and Constellations - Prof. Thomas and more Study notes Astronomy in PDF only on Docsity! 1. Luminosity, brightness, and distance: the inverse square law Luminosity: the amount of energy that a body radiates each second, does not depend on distance Brightness: amount of energy the observer receives Difference between the two: Luminosity of a fixed source is constant, but the brightness changes depending on the distance between the source and point of observance What’s the relationship between brightness, luminosity, and distance? Brightness depends on both luminosity and distance More luminous = more bright Parallax used to find brightness. Brightness is the amount of light that I would see. The luminosity is the brightness that doesn’t change with distance. They are directly proportional. Brightness and distance squared are inversely proportional. If I change one of the quantities how will the others be affected? Need to know… B= 1 L 4Π d2 How can you calculate the difference between two unknown bulbs? If you have a 200W bulb and a 100W bulb, the photometer would need to be closer to the 100W bulb to make the sides have equal brightness. The 200W is brighter by a factor of 2, so… B100w∝ L100w d100w.2 B200w∝ L200w d200w .2 Know how to solve for diff. terms in the brightness equation and how to use the equation when you are comparing two different light sources 2. Stars, Light and Spectra Example of important information or properties, which can be found using a spectrum: In order of decreasing wavelength: radio waves, microwaves, infrared light, visible light, ultraviolent light, X-rays, gamma rays What are the three basic types of spectra? Describe each type and provide an example Continuous spectra- the intensity changes smoothly with wavelength and all colors are present…very hot solids, liquids, and some dense opaque gases emit continuous spectra Example: Halogen lamp aka incandescent- rainbow of all colors Emission- the light is emitted at only a few particular wavelengths producing bright lines; while most of the other wavelengths remain dark… hot gases, aurora, and interstellar gas clouds are examples of objects that emit emission spectra Example: Florescent lighting aka overhead lighting- green and red Absorption- nearly all colors ae present but light is either absent or considerably dimmer at some wavelengths producing dark lines. This is produced when light from a hot dense body, a continuous spectrum, passes through cooler gas. Absorption spectra are therefore a special case of continuous spectra with some light missing How do filters work? What do the filters used in the lab represent in astronomy? Filters are used to allow specific light through and blocks others. Four filters: red, green, blue, and an enhancing filer (made from neodymium glass— it enhances reds and oranges in color photography…these will have a faint bluish color) You estimate the brightness by looking through a spectrometer… the color is NOT estimated by the width of the color band, that is NOT the brightness. Red: allows lots of orange, yellow! Red is bright…little green, blue, violet Green: allows lots of green! Yellow and blue are bright…little blue, barely any red, orange, or violet Blue: allows lots of green and blue! Violet is bright…little red, orange, yellow The enhancing filter is VERY bright in all colors except yellow. These filters represent the Earth’s atmosphere, and how it blocks high frequency light. The upper atmosphere blocks almost all light with a WV shorter than Ultra- Violet (300nm). The atmosphere is almost totally transparent to visible light. What will you see if you combine filters together? Each filter absorbs a certain portion, What is the range of electromagnetic radiation that the human eye can detect? 400nm to 700nm- referred to as the visible spectrum What is the rel. bt wavelength and frequency? How does the energy of a photon relate to the wavelength and frequency? Be able to describe what is happening at the atomic level to create an emission spectrum or an absorption spectrum The absorption process is exactly the opposite of the emission process. i.e. the bright lines in an emission spectra are the dark lines in an absorption spectra Know what type of spectrum comes from an object made up of many elements Be familiar with a solar spectrum **Know how to solve for different terms in the brightness equation and how to use the equation when you are comparing two different light sources. **Also know how to compare brightness of the same source when you are at different distances from the source [Do the math by yourself to be confident with solving this equation and using the calculator properly] 3. Starry Night Introduction Define circumpolar: the constellations that never set at your location, they are visible every night of the year How does your location on earth effect circumpolar constellations? ~~ ~ Aquila s i... \ fai ty t \ i \ * / \ Summer triangle: page 260... ~~ « Aquila \Y Altair Equ hs Delphinus i \ “a \ sy Pa 4 if SI V) Lira <, Cygnus ere a hn \ . Vega ~ ~~ ~®Deneb Composed of: Cepheus: What is the definition of a sidereal day? Why is it different than a solar day? Why did we need to go to the ‘dark site’ to observe the night sky?