Astronomical Instruments and : Everyday Light Sensors How does your eye form an image? How do we record images? How does your eye form an image? Refraction Refraction is the of light Eye uses refraction to light Focusing Light Image Formation Refraction can cause parallel light rays to to a The is where light from different directions comes into focus The image behind a single (convex) lens is actually upside-down! 1
Focusing Light Telescopes: Giant Eyes A camera focuses light like an eye and captures the image with a detector Detectors in digital cameras are similar to those used in modern telescopes What are the most important properties of a telescope? What are the two basic designs of telescopes? What do astronomers do with telescopes? Three main functions of a telescope Most important followed by (called resolution or angular resolution) and least important, magnification = (objective lens focal length / eyepiece lens focal length) Light Collecting Area A telescope s tells us its lightcollecting area: Area = π(diameter/2) 2 The largest telescopes currently in use have a diameter of about How does the collecting area of a 10- meter telescope compare with that of a 2- meter telescope? Area goes like (diameter) 2 or Power What is the smallest separation a telescope can detect? 2
Interference Angular Resolution or Resolving Power α = 11.6 / D D is diameter of main lens or mirror (in cm) α is resolving power (in arc-seconds) lens = angular resolution Recall: 1 degree = 60 arcmin 1 arcmin = 60 arcsec One light source Two close light sources Magnification Depends on both the and the. M = focal length obj / focal length eye A bigger objective lens has a larger area, but not necessarily a larger Focal length depends on of the lens A larger objective lens provides a brighter image There are two different types of optical telescopes 3 inch, 100x 5 inch, 200x 11 inch, 400x A telescope uses a glass lens to concentrate incoming light A telescope uses mirrors to concentrate incoming light 5 inch, 400x 3 inch, 400x 3
A telescope uses a to concentrate incoming light telescopes use to concentrate incoming starlight If you pass white light through a prism, it separates into its component. long wavelengths short wavelengths R O Y G B I V But visible light is only one type of (light) emitted by stars Astronomers are truly interested in the entire spectrum of Light! Observations at other reveal previously invisible sights The Sun as seen in visible light from Earth and from space in X-rays by satellites UV infrared Ordinary visible Map of Orion region 4
Why do we put telescopes into space? Earth s gets in the way! Image of stars taken with a telescope on the Earth s surface Same picture taken with Hubble Space Telescope high above Earth s blurring atmosphere Calm, High, Dark, Dry The best observing sites are atop remote mountains Summit of Mauna Kea, Hawaii Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth s atmosphere. Not all EM radiation can penetrate Earth s atmosphere. Hubble Space Telescope Main Mirror: 5
Telescopes and Earth s Atmosphere Lecture Tutorial: Page 49-51 Work with a partner or two Read directions and answer all questions carefully. Take time to understand it now! Come to a consensus answer you all agree on before moving on to the next question. If you get stuck, ask another group for help. If you get really stuck, raise your hand and I will come around. Telescopes & Light Telescopes gather information from the entire Why do some objects glow in IR light? Why do some give off x-rays? Interactions between light & Chapter 6: Starlight and Atoms Properties of Matter of matter of matter How is stored in atoms How do light and matter interact? To study the largest objects in the universe, we must first understand the smallest objects in the universe! What is the structure of matter? Electron Cloud Atomic Terminology Atomic Number = # of in nucleus Atomic Mass Number = # of + Atom Nucleus Molecules: consist of two or more (H 2 O, CO 2 ) 6
Atomic Terminology Isotope: same # of protons but different # of. ( 4 He, 3 He) What are the phases of matter? Familiar phases: Solid (ice) Liquid (water) Gas (water vapor) Phases of same material behave differently because of differences in Phase Changes How is energy stored in atoms? : Breaking of rigid chemical bonds, changing solid into liquid : Breaking of flexible chemical bonds, changing liquid into gas : Breaking of molecules into atoms : Stripping of electrons, changing atoms into plasma Electrons in atoms are restricted to particular (electron shells) Energy Level Transitions An electron can only go from one level to another, not in between A Simple Atom Only 2 energy levels Ground (E1) Excited (E2) Right now electron is at E1 7
Excitation A Simple Atom Electron a photon and jumps from E1 to E2 Photon only absorbed if it has energy = (E2-E1) Ionization A Simple Atom Electron a photon and leaves! Only works if electron is in higher energy levels De-excitation A Simple Atom Electron a photon of energy (E2-E1) Electrons like to be in the ground state What are the three basic types of spectra? Spectrum Spectrum Spectrum Spectra of astrophysical objects are usually combinations of these three basic types Spectrum Spectrum All wavelengths, no breaks Rainbows! Bright, individual lines Also called - spectrum Electrons are moving to lower energy levels, emitting photons of light 8
Spectrum Kirchhoff s Laws Rainbow with dark lines on top Also called - spectrum Atoms in the cloud are absorbing photons, moving to higher energy levels I. A hot, dense substance will give off spectrum II. A hot, low-density gas will give off an spectrum III. A cool, low-density gas in front of a continuous-spectrum source will give off an spectrum Chemical Fingerprints Chemical Fingerprints Energy levels of Hydrogen Each type of atom has a unique set of energy levels Each transition corresponds to a unique photon energy, frequency, and wavelength Downward transitions produce lines Upward transitions produce lines Chemical Fingerprints Energy Levels of Molecules Each type of atom has a unique spectral fingerprint, due to of Molecules have additional energy levels because they can vibrate and rotate 9
Energy Levels of Molecules Light and Atoms Lecture Tutorial: page 63 Spectrum of Molecular Hydrogen (H 2 ) Spectra of molecules can be very complicated Lots of energy modes Molecular transitions are typically in the IR Work with a partner or two Read directions and answer all questions carefully. Take time to understand it now! Come to a consensus answer you all agree on before moving on to the next question. If you get stuck, ask another group for help. If you get really stuck, raise your hand and I will come around. 10