Astronomy Stellar Classification

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Questions and Answers

What do we mean by a star's spectral type, and how is spectral type related to surface temperature and color?

Spectral types are a way of classifying stars according to their color or what spectral lines we see in their light. The spectral types run OBAFGKM, where O stars are the hottest and M are the coolest. Hotter stars look bluer to us, and cooler stars look redder.

Which of these stars has the greatest surface temperature?

a 30MSun main-sequence star

What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?

the time between eclipses and the average distance between the stars

Choose the correct statement explaining what do we mean by a star's luminosity class and how we classify stars by spectral type and luminosity class.

Luminosity classes of stars are designated by Roman numerals and tell us what region of the H-R diagram the star falls in. The spectral type tells us the star's temperature while the luminosity class tells us its radius. Signup and view all the answers

Which of these star clusters is oldest?

a cluster whose brightest main-sequence stars are yellow Signup and view all the answers

If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would?

get smaller Signup and view all the answers

Which of these stars is the most massive?

a main-sequence A star Signup and view all the answers

Which of these stars has the coolest surface temperature?

a K star Signup and view all the answers

What do we need to measure in order to determine a star's luminosity?

apparent brightness and distance Signup and view all the answers

Which of these stars has the largest radius?

a supergiant M star Signup and view all the answers

If a star were moved twice as far away but all else remained unchanged, what would happen to its appearance?

it would get 4 times as faint Signup and view all the answers

How do we determine the distances to nearby stars?

parallax Signup and view all the answers

How does the color correspond to the surface temperature of a star?

the hottest stars are 'bluish white' Signup and view all the answers

Why do the hottest spectral types (types O and B) show few absorption lines?

many atoms in these stars are ionized (have lost electrons) and can't absorb photons Signup and view all the answers

In binary star systems, the orbital period depends on the masses of the stars and the sizes of their orbits. Why is this so valuable to know?

this is the main way we determine the masses of stars Signup and view all the answers

Stars spend about 90% of their lifetime as?

main-sequence stars Signup and view all the answers

A star near the top of the main sequence has a mass about?

60 times the Sun's mass Signup and view all the answers

A star near the top of the main sequence has a luminosity about?

10,000 times the Sun's luminosity Signup and view all the answers

How would you expect the lifetime of a massive star near the top of the main sequence to compare to the Sun's?

it would be much shorter Signup and view all the answers

Clusters in the disk of our galaxy, with no more than a few thousand stars in them are called?

open clusters Signup and view all the answers

Clusters in the halo of our galaxy with hundreds of thousands of stars in them are called?

globular clusters Signup and view all the answers

Why do photographs of a star field show some stars to be larger than others?

photographs make brighter stars appear larger than fainter stars, although they should all be points of light Signup and view all the answers

What do the colors of stars in the Hertzsprung-Russell diagram tell us?

the surface temperature of the star Signup and view all the answers

True or false? Two stars that look very different must be made of different kinds of elements.

False Signup and view all the answers

True or false? Stars that begin their lives with the most mass live longer than less massive stars because it takes them a lot longer to use up their hydrogen fuel.

False Signup and view all the answers

Study Notes

Spectral Classification of Stars

Stars are classified using spectral types which range from O to M, indicating temperature and color.
O stars are the hottest and appear blue, while M stars are the coolest and appear red.

Mass and Surface Temperature Relations

The most massive stars are typically main-sequence A stars.
A 30MSun main-sequence star has the greatest surface temperature.

Eclipsing Binary Systems

To measure the masses of stars in an eclipsing binary, one needs the time between eclipses and the average distance between the stars.

Luminosity Class and H-R Diagram

Luminosity classes are categorized by Roman numerals and indicate a star's location on the H-R diagram.
Spectral type reveals a star’s temperature, while luminosity class indicates its radius.

Star Clusters

The oldest star clusters are characterized by having the brightest main-sequence stars that are yellow.
Open clusters contain a few thousand stars, while globular clusters contain hundreds of thousands and are located in the galaxy's halo.

Parallax and Distance Measurement

Parallax is used to determine the distances to nearby stars.
The parallax angle decreases for a star when it is moved farther away.

Luminosity Determination

A star’s luminosity is determined by its apparent brightness and distance from Earth.

Surface Temperature Indicators

Star color corresponds to surface temperature; hot stars appear bluish-white.
The hottest spectral types (O and B) show few absorption lines due to ionization of atoms.

Stellar Lifetimes and Mass

Stars spend about 90% of their life in the main-sequence phase.
Massive stars, despite their larger hydrogen reserves, have much shorter lifetimes due to rapid fuel consumption.
A massive star near the top of the main sequence can have a mass about 60 times that of the Sun and luminosity around 10,000 times that of the Sun.

Visual Appearance of Stars

Photographs of star fields represent brighter stars as larger than fainter stars, despite them all being points of light.
The Hertzsprung-Russell diagram indicates star surface temperatures through color.

Misconceptions in Stellar Characteristics

Stars may appear different due to age and mass rather than differences in elemental composition.
More massive stars are not longer-lived; they deplete their hydrogen faster due to higher luminosity, contrary to the belief that they take longer to consume hydrogen.

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Description

Explore the fascinating world of star classification with this quiz, which covers spectral types, mass-temperature relations, eclipsing binaries, and the H-R diagram. Challenge your understanding of different star clusters and their characteristics. Perfect for astronomy students or enthusiasts!