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. 1Wave-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 (H20, O2) 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