Electromagnetic Radiation + Astronomy

Waves

A periodic disturbance created from a source that travels through a medium

• Can travel two ways:

  • Longitudinal (ex. slinky)

  • Transverse (ex. rope) -vibrations are at right angles to their direction of travel

Frequency and Wavelength

Frequency + Wavelength are inversely proportional

• As frequency increases, wavelength decreases

• Opposite for energy, as energy increases, frequency also increases

Mechanical vs Electromagnetic Waves

• Mechanical - require a material (matter) and cannot travel through a vacuum

• Electromagnetic - radiation and therefore able to travel through a vacuum

EMR - Electromagnetic Radiation

EMRS are transverse waves consisting of changing electric and magnetic fields that are at 90 degree angles to one anotherand propagate through space without the need for a medium.

EMR Waves

• The looser the waves are, the lower and longer it is

• The tighter the waves are , the higher and shorter it isThis describes how the amplitude and frequency of electromagnetic waves relate to their energy and wavelength. Looser waves signify lower frequency and energy, while tighter waves indicate higher frequency and energy.

Signals + Frequencies

• signals - steady, big waves

• AM - erratic, height are often changing

• PM - height does not change, only distance between wavesSignals are patterns of varying frequencies that transmit information over a medium. AM (Amplitude Modulation) varies the amplitude of the signal, while PM (Phase Modulation) alters the phase without changing the amplitude.

Reflection vs Refraction

• Reflection - return of a wave from a boundary

• Refraction - the bending of a wave as it changes speed as it passes through a medium (snell’s law)

Polarization

Occurs when a wave’s oscillations are confined to a single plane or direction. The waves therefore singles out and becomes less focused, causing a dimmer image for the observer.

Diffraction

Bending of wave as it passes by obstacles or the edges of an opening.

• when light passes through a large opening, diffraction patterns are minimal

  • when light passes through a small opening, diffraction patterns are overlapping, and have fuzzy edges

Refracting Telescope

Galileo's Telescope

• Concave

  • small openings lead to dim images and diffraction limiting resolution

Reflecting Telescope

Newton’s Telescope

• Convex lens

  • Larger openings for brighter images while eliminating chromatic aberration

Doppler Effect

An object’s frequency shifts relative to an observer due to motion, revelaed our universe is expanding

Blue Shift

An increase in frequency of a wave as the source moves closer to the observer, compressing the wavelength

Red Shift

A decrease in the frequency of a wave as the source moves further to the observer, stretching the wavelength

Evolution of Small Stars

Small Star → Red Giant → Planetary Nebula → White Dwarf

Evolution of Medium + Large Stars

Medium/ Large Stars → Red Supergiant → Supernova → Neutron Star (M) / Black Hole (L)

Spectrums

• Continuous: no gasses, no lines

• Emission: hot gasses emit light directly - dark + bright lines

• Absorption: continuum, light passes cooler gas - bright + dark lines