Light Telescopes and the Sun PSCI 131 Light

Light, Telescopes, and the Sun

PSCI 131: Light, Telescopes, & The Sun Light, Telescopes, & the Sun • Light: Messenger From Space • Spectroscopy • The Doppler Effect

PSCI 131: Light, Telescopes, & The Sun Electromagnetic (EM) Spectrum • Energy waves (radiation) emitted by matter

PSCI 131: Light, Telescopes, & The Sun Nature of Light • Wave properties – Wavelength: Distance from one wave crest to the next – Frequency: The number of waves that pass a point during 1 second – Can’t see most light because it occurs at wavelengths that are too long or too short for our eyes • Visible light or white light is the light that humans can see

PSCI 131: Light, Telescopes, & The Sun Nature of Light • Particle properties – Light particles (photons) can exert pressure on matter (radiation pressure) – Photons have specific amount of energy, related to wavelength • Short wavelengths – more energetic photons – Gamma rays are the most energetic, while radio waves are least – X-rays – plow through matter before they are absorbed » Readily pass through soft tissue but are absorbed by bones which are denser.

PSCI 131: Light, Telescopes, & The Sun EM Radiation from Celestial Objects • Emitted radiation can be collected and used to study the object – Telescopes: optical, radio, space-based – Spectroscopy

PSCI 131: Light, Telescopes, & The Sun What Can We Learn from Light?

PSCI 131: Light, Telescopes, & The Sun What can we learn from light? • Most astronomical observations can only use light radiation – Most objects too far away to visit • Spectroscopy: study of light and the way it interacts with matter – Spectra can give key information about the object the light came from • Spectroscope: an instrument that contains a prism that spreads out the wavelengths of light so that they can be accurately measured.

PSCI 131: Light, Telescopes, & The Sun Continuous Spectrum • Uninterrupted band of light emitted by an incandescent solid, liquid, or gas under pressure – Continuous band of wavelengths that looks like the rainbow • Shows surface temperature of object • Shows total energy emitted by object

PSCI 131: Light, Telescopes, & The Sun Continuous Spectrum Shows Surface Temp exaggerated COOLER HOTTER

PSCI 131: Light, Telescopes, & The Sun Continuous Spectrum Shows Total Energy • Proportional to fourth power of object’s surface temperature (Stefan-Boltzman law) – Example: if Star B is five times as hot as Star A… – …Star B emits 54, or 5 x 5 x 5 = 625 times more energy that Star A

PSCI 131: Light, Telescopes, & The Sun Emission Line Spectrum • Bright lines produced by an incandescent gas under low pressure • Shows what elements are present in object – Each element emits a unique wavelength pattern when heated

Absorption Line Spectrum

PSCI 131: Light, Telescopes, & The Sun Absorption Line Spectrum • Dark lines produced when white light is passed through a comparatively cool, low-pressure gas • Shows what elements are present in object – Each element absorbs a unique pattern of visible light wavelengths

Which elements are in this mystery star?

PSCI 131: Light, Telescopes, & The Sun Light tells us about • Composition – Elements emit and absorb a unique set of wavelengths • Temperature – All objects radiate a continuous thermal spectrum – Hotter objects emit more light per unit area and emit more of their light at shorter wavelengths (higher energy) • Motion of distant objects (Doppler effect)

PSCI 131: Light, Telescopes, & The Sun The Doppler Effect • Apparent shift in wavelength relative to a stationary observer

PSCI 131: Light, Telescopes, & The Sun Red and Blue Shift • Light waves undergo Doppler Effect

PSCI 131: Light, Telescopes, & The Sun Red/Blue Shifts Change Absorption Spectra • Star moving away from Earth = RED shift • Star approaching Earth = BLUE shift • Large shifts either way indicate high velocities

Types of Doppler shifts • Caused by local motions – How fast one star orbits another (2 -star system) – How fast a pulsating star expands or contracts • Caused by expansion of universe – How far away distant objects are

Our Farthest Travels In Space • Voyager 1 and 2