6.4

Question 1

What do all stars begin as?

Answer 1

A nebula (collection of dust and gas).

Question 2

What is the Great Orion Nebula?

Answer 2

A nebula visible from Earth with the naked eye.

Question 3

What forms when a nebula collapses due to gravity?

Answer 3

A dense cloud, forming visible globules.

Question 4

What is a protostar?

Answer 4

A dense cloud not yet hot enough for nuclear fusion.

Question 5

What triggers nuclear fusion in a protostar?

Answer 5

High temperatures from increased pressure.

Question 6

What is nuclear fusion?

Answer 6

The fusion of hydrogen isotopes (deuterium and tritium) to form helium, releasing a neutron and energy.

Question 7

What do larger stars fuse?

Answer 7

Larger atomic nuclei to form heavier elements.

Question 8

Why are larger stars hotter?

Answer 8

They fuse heavier elements, increasing gravity and pressure.

Question 9

What does apparent magnitude measure?

Answer 9

The brightness of a star as seen from Earth.

Question 10

Why might some stars appear brighter than others?

Answer 10

They may be closer to Earth, not necessarily brighter.

Question 11

What is the scale range for apparent magnitude?

Answer 11

-30 (brightest) to +30 (dimmest).

Question 12

What is the apparent magnitude of the full moon and the Sun?

Answer 12

Full moon: -13; Sun: -27.

Question 13

What does absolute magnitude measure?

Answer 13

The actual brightness of a star.

Question 14

How is absolute magnitude calculated?

Answer 14

By determining the star’s distance from Earth.

Question 15

What two factors are used to categorize stars?

Answer 15

Absolute magnitude and temperature.

Question 16

What does a red star indicate about temperature?

Answer 16

A red star is cooler.

Question 17

What does a blue or white star indicate about temperature?

Answer 17

A blue or white star is hotter.

Question 18

How do scientists classify stars?

Answer 18

By analyzing the spectrum of light and photographs of the stars.

Question 19

What do dark lines in a star’s light spectrum indicate?

Answer 19

They correspond to colors of light absorbed by substances in the star.

Question 20

Why do different substances show different dark lines in a spectrum?

Answer 20

Different substances absorb different colors of light.

Question 21

How can astronomers identify elements in a star?

Answer 21

By identifying the wavelengths of the colors missing from the spectrum.

Question 22

What is a red shift in a star’s spectrum?

Answer 22

A shift to lower frequencies, indicating the star is moving away from the observer.

Question 23

What is a blue shift in a star’s spectrum?

Answer 23

A shift to higher frequencies, indicating the star is moving toward the observer.

Question 24

What happens to light waves when a star moves toward Earth?

Answer 24

The waves are squeezed together, shortening the wavelength and shifting spectral lines toward blue.

Question 25

What happens to light waves when a star moves away from Earth?

Answer 25

The waves are stretched out, increasing the wavelength and shifting spectral lines toward red.

Question 26

What is red shift?

Answer 26

A shift of spectral lines toward the red end of the spectrum (lower frequencies) when the source moves away from the observer.

Question 27

What is blue shift?

Answer 27

A shift of spectral lines toward the blue end (higher frequencies) when a light source moves rapidly toward the observer.

Question 28

What did Edwin Hubble observe in 1929?

Answer 28

Some galaxies were moving toward Earth, while most were moving away.

Question 29

What relationship did Hubble discover?

Answer 29

A relationship between the size of the red shift and the distance from Earth.

Question 30

What is the relationship between a galaxy's distance and its red shift?

Answer 30

The further a galaxy is from Earth, the greater its red shift and the faster it is moving away.

Question 31

What explains the movement of most objects away from each other in the Universe?

Answer 31

The expansion of space.

Question 32

How does the expansion of space resemble a balloon?

Answer 32

Like a balloon's surface increasing in size as it inflates, increasing distance between objects.

Question 33

What happens to the speed of objects moving apart as distance increases?

Answer 33

The further apart two objects are, the faster they move apart.

Question 34

What is the Hertzsprung–Russell diagram (HR diagram)?

Answer 34

A scatter plot showing the relationship between stars' absolute magnitudes or luminosities and their stellar classifications or effective temperatures.

Question 35

Who created the HR diagram, and when?

Answer 35

Ejnar Hertzsprung and Henry Norris Russell, around 1910.

Question 36

What does the HR diagram help scientists understand?

Answer 36

Stellar evolution.

Question 37

What do some scientists use in the HR diagram aside from luminosity?

Answer 37

Stellar classifications (e.g., white dwarf, supergiant).

Question 38

What is luminosity in astronomy?

Answer 38

An absolute measure of radiated electromagnetic power (light) from an object.

Question 39

How is luminosity often expressed in astronomy?

Answer 39

In terms of the luminosity of the Sun (L⊙).

Question 40

What is a stellar nebula?

Answer 40

A cloud of gas and dust where stars are born.

Question 41

What is a main sequence star?

Answer 41

A stable phase where a star fuses hydrogen into helium in its core.

Question 42

What is a red giant?

Answer 42

A phase where a star expands and cools after exhausting hydrogen in its core.

Question 43

What is a red supergiant?

Answer 43

A massive star that expands further and cools, leading to eventual collapse.

Question 44

What is a planetary nebula?

Answer 44

The outer layers of a star expelled after the red giant phase, surrounding a white dwarf.

Question 45

What is a white dwarf?

Answer 45

The remnant core of a low to medium mass star after it has shed its outer layers.

Question 46

What is a black dwarf?

Answer 46

A theoretical stage where a white dwarf has cooled and no longer emits significant heat or light.

Question 47

What is a supernova?

Answer 47

A powerful explosion marking the death of a massive star, resulting in either a neutron star or black hole.

Question 48

What is a neutron star?

Answer 48

A dense remnant of a supernova, composed mostly of neutrons.