PROPERTIES OF LIGHT, TELESCOPES AND OBSERVING TECHNIQUES

Pre-lab Review  Wave Properties  Frequency: the number of complete waves that pass a point in one second  Wavelength: the length of one complete wave cycle  Amplitude: maximum amount of displacement of a particle from its rest position  Period: the time it takes for one complete wave to pass a given point

What can we observe?  Light (of course!) But what else and how?  Any ideas??  Cosmic rays and other charged particles  Meteorites  Gravitational waves  These are all often difficult to observe, infrequently observed or not especially helpful  Since light is the most common and useful observable, we will focus on light and its various properties

Wave-Particle Duality  Light can be interpreted as both a wave and a particle Waves Light has a “color” or place on the EM spectrum (wavelength, frequency) Particles Light consists of particles called photons, as discussed by Einstein Light has “quantized” energy levels, meaning it can only be at one particular energy level at a time Wave-Particle Duality Pt. 1 Wave-Particle Duality Pt. 2

Electromagnetic Spectrum

Constellation Map

Observing Techniques: EM Spectrum  There are many different techniques for observing depending on what type (wavelength) of light you want to observe  Long wavelength astronomy: use an array of radio dishes (interferometry) to collect light  Visible astronomy: Use telescopes to take images, use spectrometers that disperse (separate) light to obtain spectrum and composition  Short wavelength astronomy: Difficult to observe from the ground due to the atmosphere, so need to go to space to observe at these wavelengths

Telescopes: Some Definitions  Telescopes are made to collect and concentrate light  Come in two types: refractors and reflectors  Focal Length: distance needed to focus light to a point  Resolution: how close two objects can be before they can’t be differentiated  Magnification: ratio of the focal lengths of the telescope and the eyepiece  More zoomed in ≠ better!  Aperture: diameter of primary lens or mirror

Telescopes  Mounts  Equatorial (use RA and Dec as coordinates)  Dobsonian (use altitude and azimuth as coordinates)  CCDs  Like little photon buckets that convert photons to electrons  Basic cameras and cellphones use CCDs!  Astronomers used to have to draw their observations; using CCDs is much easier and generally more accurate!

Telescopes: Refractors

Telescopes: Newtonian Reflectors

Telescopes: Cassegrain Reflectors

Observing Techniques  Since we will observe in the visible part of the EM spectrum, from the ground and with small telescopes, we’ll focus on techniques for observing under these conditions.  Star hopping – “hop” between bright, easily found objects in the sky to lead to a fainter object that is difficult to spot  Using constellations – similar to star hopping  Using coordinates – useful when doing astrophotography and using an equatorial mount  The only way to improve is with practice!

Observing Difficulties  There are many things we need to consider when observing  Earth’s daily motion  Earth’s yearly motion  Location  Earth’s atmosphere (H 2 0, O 2 ) absorbs incoming light at certain wavelengths  Put telescopes at high altitudes or in deserts to minimize atmospheric absorption  To avoid atmosphere and light pollution completely, move to space  Putting telescopes in space is VERY expensive!

This lab…  Some useful quantities…  Refractor: 15 foot focal length, 12’’ aperture  Dobsonian: 1200mm focal length, 8’’ aperture  Galileoscope focal length: 50 cm, 51 mm aperture  Magnification = focal length of telescope focal length of eye piece