What is the Doppler effect?

When a wave source moves relative to an observer, the observed wavelength and frequency change — compressed (shorter wavelength) if approaching, stretched (longer wavelength) if receding Light always bends slightly when passing massive objects, changing its frequency When light passes through a prism it splits into its component wavelengths The delay in receiving signals from distant objects due to the finite speed of light

A distant galaxy has its spectral lines shifted to longer (redder) wavelengths compared to their laboratory values. What does this tell us?

The galaxy is approaching us very rapidly The galaxy has cooler stars than our Sun The galaxy is moving away from us — the expansion of the universe is stretching the light to longer wavelengths The galaxy's elements are heavier than those in the Sun

Why does each element produce a unique pattern of spectral lines?

Each element glows a different color because it has a different temperature Electrons in each element can only occupy specific energy levels; when they jump between levels they emit or absorb photons of very specific wavelengths unique to that element Elements with more protons emit more wavelengths and heavier ones emit fewer Each element absorbs all wavelengths except one, which it reflects

When you look at the Sun's spectrum through a spectroscope, you see a rainbow with hundreds of dark lines. What are these dark lines called and what causes them?

Emission lines — caused by hydrogen atoms in the solar corona emitting light at specific wavelengths Doppler lines — caused by the Sun's rotation shifting wavelengths to darker colors Fraunhofer lines — caused by atoms in the Sun's cooler outer atmosphere absorbing specific wavelengths of light rising from the hotter interior Blackbody lines — caused by the Sun's magnetic field blocking certain wavelengths

How do astronomers use the radial velocity method to detect exoplanets?

Astronomers look for gaps in the star's light caused by a planet passing in front An orbiting planet causes its star to wobble slightly; this wobble produces tiny, regular Doppler shifts in the star's spectral lines that betray the planet's presence The planet's own reflected light shows up as extra spectral lines next to the star's lines The planet's gravity bends the star's light, creating a detectable distortion in the spectrum

The spectral lines of a star are broadened (wider than normal) on one side and narrowed on the other. What is the most likely explanation?

The star is moving directly toward Earth on one side and away on the other The star's atmosphere has two different temperatures on either side The star is rotating — one edge moves toward us (blue-shifted) while the other edge moves away (red-shifted), broadening the overall line Two different elements with nearby spectral lines are both present in the atmosphere

A spectroscope reveals that a star's spectral lines oscillate back and forth in wavelength with a period of 10 days. The star is not pulsating. What is the most likely explanation?

The star is pulsating with a 10-day period like a Cepheid variable The star is rotating very slowly and we see different sides every 10 days The star is part of a binary system — it orbits a companion star every 10 days, and the orbital motion creates periodic Doppler shifts The star is intermittently absorbing light from a nearby nebula every 10 days

Besides identifying composition and measuring motion, spectral line width also reveals stellar temperature. How does this work?

Hotter stars have fewer spectral lines because extreme temperatures strip electrons away entirely In hotter, higher-pressure stellar atmospheres, atoms move faster (thermal broadening) and collide more often (pressure broadening), both of which widen the spectral lines The color of spectral lines shifts from violet to red as temperature increases Hotter stars produce spectral lines at longer wavelengths because their photons carry more energy

Modern telescopes can detect the spectra of exoplanet atmospheres by observing starlight filtered through the planet's atmosphere during a transit. What could this technique reveal about a distant world?

Only the planet's distance from its star, which causes different wavelengths to be absorbed The planet's mass, which can be measured from how much the spectrum brightens during transit The chemical composition of the planet's atmosphere — including whether it contains water vapor, carbon dioxide, methane, or even biosignature gases like oxygen and ozone Only whether the planet has liquid water on its surface, which produces a specific reflection spectrum

A star's spectral lines show that it contains a large proportion of heavy elements like iron and silicon. What can astronomers conclude about this star's history?

It is one of the oldest stars in the universe, formed from the original Big Bang elements It is a younger, Population I star formed from gas already enriched by previous generations of supernovae — it was not among the universe's first stars The star must be a white dwarf because only dead stars contain heavy elements Heavy elements in a star indicate it is near the end of its life and about to become a supernova