What causes the dark absorption lines seen in a star's spectrum?

Clouds of dust between us and the star block specific colours of light Atoms in the star's outer atmosphere absorb photons of specific wavelengths, removing those wavelengths from the outgoing light The star's magnetic field bends certain wavelengths away from Earth The spectrum is actually continuous — the dark lines are an artifact of telescopes

What is the correct order of spectral classes from hottest to coolest?

M, K, G, F, A, B, O A, B, C, D, E, F, G O, B, A, F, G, K, M O, A, B, G, F, K, M

What does the numeral in a spectral classification like G2V mean?

The star's age in billions of years The number of planets orbiting the star A subtype from 0 (hottest within the class) to 9 (coolest within the class) — G2 is slightly hotter than G5 The star's distance from Earth in light-years

Which spectral type is the most common type of star in our galaxy?

O-type stars — they are the largest and most noticeable G-type stars — because our Sun is G-type and it is typical A-type stars — they are the brightest visible from Earth M-type stars (red dwarfs) — they make up about 70-75% of all stars in the Milky Way

The star Rigel in the constellation Orion is classified as B8 Ia. What can you conclude from this classification?

Rigel is a cool red star and a dwarf on the Main Sequence Rigel is a hot blue star (B-type), slightly on the cooler end of its class (subtype 8), and a luminous supergiant (Ia) Rigel is a medium-temperature star with a large binary companion Rigel is a young star of class B that has not yet reached the Main Sequence

How can astronomers determine a star's radial velocity (motion toward or away from us) from its spectrum?

By tracking how the star's position in the sky changes from year to year By measuring how much the spectral absorption lines have shifted toward the red or blue end compared to their laboratory wavelengths — the Doppler effect By counting how many spectral lines the star has — more lines means faster motion Radial velocity cannot be measured from spectra — only transverse motion can

What was remarkable about Annie Jump Cannon's contribution to stellar spectral classification?

She invented the telescope that first spread starlight into a spectrum She discovered that all stars have the same chemical composition Working at Harvard Observatory in the early 1900s, she classified over 350,000 stars by eye from photographic plates, creating the standard OBAFGKM system still used today She was the first person to use a spectroscope in space

Which type of star shows the strongest hydrogen absorption lines in its spectrum?

O-type stars — they are the hottest so everything is most active M-type stars — cool temperatures allow the most stable hydrogen configurations A-type stars — at about 10,000 K, hydrogen atoms are in exactly the right state to absorb visible-light photons most efficiently G-type stars like the Sun — because the Sun's spectrum is the reference standard

Cecilia Payne-Gaposchkin made a revolutionary discovery using stellar spectral analysis in 1925. What did she discover?

Stars contain heavy metals like iron and gold, making them valuable resources Stars are made almost entirely of hydrogen and helium — contradicting the prevailing assumption that stars had similar composition to Earth The OBAFGKM sequence was backwards — M-type stars are actually the hottest Spectral lines cannot reveal chemical composition — they only show temperature

What stellar property can astronomers determine from the width (sharpness) of spectral absorption lines?

Only the star's temperature — wider lines mean a hotter star The star's distance — lines broaden over the distance light travels The star's surface gravity and rotation speed — pressure broadening in dense giant atmospheres, and rotational Doppler broadening in fast-spinning stars The star's chemical composition only — each element makes lines of a specific width