Spectroscopy, Telescopes, and Stellar Properties: Key Concepts for Astronomy

Order of electromagnetic radiation from longest to shortest wavelength

Radio → Microwave → Infrared → Visible → UV → X-ray → Gamma Ray.

Indication of low energy

A long wavelength.

Indication of high energy

A short wavelength.

Composition of a hydrogen atom

1 proton + 1 electron.

Ionization energy of hydrogen

13.6 eV.

Ionization wavelength of hydrogen

91.2 nm (UV).

Spectrum produced by a hot solid, liquid, or dense gas

Continuous spectrum.

Spectrum produced by a hot, low-density gas

Emission spectrum.

Spectrum produced by a cool gas in front of a continuous source

Absorption spectrum.

Type of spectra most stars produce

Absorption spectra.

Kirchhoff's Law 1

A dense object produces a continuous spectrum.

Kirchhoff's Law 2

A hot thin gas produces an emission spectrum.

Kirchhoff's Law 3

A cool thin gas produces an absorption spectrum.

Position of absorption lines in relation to emission lines for the same element

At the same wavelengths.

Information that spectra reveal about celestial objects

Composition, temperature, motion, density, rotation, and magnetic fields.

Measurement provided by the Doppler shift

Radial velocity.

Indication of an object moving away

Redshift.

Indication of an object moving toward

Blueshift.

Zeeman Effect

A magnetic field splits spectral lines.

Type of transitions associated with electronic molecular transitions

Visible/UV.

Type of transitions for vibrational molecular transitions

Infrared.

Type of transitions associated with rotational molecular transitions

Radio.

Photoelectric effect relationship between frequency and electron energy

Higher frequency results in more energetic electrons.

Formula for photon energy

E = hf.

Behavior of light

As both a wave and a particle.

Purpose of a telescope

To collect and focus light.

Advantage of larger telescopes

They collect more light and detect fainter objects.

Refractor telescope characteristics

A telescope that uses a lens.

Reflector telescope characteristics

A telescope that uses a mirror.

Definition of refraction

The bending of light through material.

Definition of reflection

The bouncing of light from a surface.

Dominating type of telescope in modern astronomy

Reflectors.

Definition of chromatic aberration

Different colors focus at different points.

Mirrors and chromatic aberration

No, mirrors do not suffer from chromatic aberration.

Cause of imperfect focus in telescopes

Diffraction.

Improvement of diffraction limit

With larger diameter and shorter wavelength.

Relationship between resolution, wavelength, and diameter

Resolution ∝ wavelength/diameter.

Conditions that lead to better observing

High altitude and dry climates.

Atmospheric turbulence effect

Creates a seeing disk.

Function of active optics

Correct mirror shape slowly.

Function of adaptive optics

Correct atmospheric blurring rapidly.

Type of telescopes with better natural resolution

Optical telescopes.

Operational capability of radio telescopes

Day or night.

Ability of radio telescopes to work through

Clouds.

Resolution characteristic of radio wavelengths

Poor diffraction-limited resolution.

Interferometry definition

Combines multiple telescopes to improve resolution.

Effective diameter in interferometry

Baseline distance between telescopes.

Avoidance by space telescopes

Atmospheric blurring.

Requirement of UV astronomy

Must be done in space due to ozone blocking UV radiation.

Radiation types blocked by Earth's atmosphere

X-rays and gamma rays.

Primary observation focus of JWST

Infrared light.

Type of mirror used by JWST

Segmented mirror.

Comparison of infrared light to visible light regarding dust penetration

Infrared penetrates dust better than visible light.

Main sequence stars and fusion process

Hydrogen into helium.

Percentage of stars on the main sequence

About 90%.

Closest star system

Alpha Centauri.

Distance to Alpha Centauri

1.3 parsecs (~4 light-years).

Measurement method used by parallax

Observations six months apart.

Light-years in one parsec

3.26 light-years.

Proper motion definition

Motion across the sky.

Radial velocity definition

Motion toward or away from Earth.

True space motion

Radial + transverse motion.

Luminosity representation

True energy output.

Influence of apparent brightness

Distance.

Brightness relationship

Follows inverse square law.

Hotter stars identification

Blue stars.

Comparison of temperatures between blue and red stars

Red stars are cooler.

Order of star types from hottest to coolest

OBAFGKM.

Hottest type of star

O stars.

Coolest type of star

M stars.

Stars with the strongest hydrogen lines

A stars.

Sun classification

G2V.

Approximate temperature of the Sun

5800 K.

Vertical axis representation of the H-R Diagram

Luminosity.

Horizontal axis representation of the H-R Diagram

Temperature.

Temperature change on the H-R Diagram

Increases to the left.

Main sequence representation on the H-R Diagram

A diagonal band.

Location of red giants on the H-R Diagram

Upper right.

Location of white dwarfs on the H-R Diagram

Lower left.

Characteristics of red giants in terms of temperature and luminosity

Cool but very luminous.

Characteristics of white dwarfs in terms of temperature and brightness

Hot but faint.

Spectroscopic parallax purpose

Find distances to faraway stars.

Luminosity Class I representation

Supergiant.

Luminosity Class III representation

Giant.

Luminosity Class V representation

Main sequence.

Eclipsing Binary

a binary star system whose stars pass in front of one another as seen from Earth, producing periodic decreases in brightness.

Determination achieved by eclipsing binaries

Stellar masses and radii.

Most important stellar property

Mass.

Mass determination in stars

Luminosity, temperature, lifetime, and evolution.

Luminosity and mass relation

Luminosity ∝ Mass⁴.

Lifetime and mass relation

Lifetime ∝ 1/Mass³.

Characteristics of massive stars

Hotter, brighter, and shorter-lived.

Characteristics of low-mass stars

Cooler, dimmer, and longer-lived.

Location of fusion in the Sun

In the core.

Definition of the radiative zone

Where energy is moved by radiation.

convection zone

the layer of the Sun where energy is transported outward by convection—hot plasma rises toward the surface, cools, and then sinks back down.

Visible surface of the Sun

Photosphere.

Temperature of the photosphere

5800 K.

Layer located above the photosphere

Chromosphere.

Transition zone definition

Where there is a rapid temperature increase.