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Semester 2 Science > 6.4 > Flashcards

6.4 Flashcards

Learning Intentions Describe stars: formation, brightness and life cycle Use Hertzsprung-Russell diagrams to classify stars in terms of absolute magnitude and temperature

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1
Q

What do all stars begin as?

A

A nebula (collection of dust and gas).

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2
Q

What is the Great Orion Nebula?

A

A nebula visible from Earth with the naked eye.

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3
Q

What forms when a nebula collapses due to gravity?

A

A dense cloud, forming visible globules.

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4
Q

What is a protostar?

A

A dense cloud not yet hot enough for nuclear fusion.

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5
Q

What triggers nuclear fusion in a protostar?

A

High temperatures from increased pressure.

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6
Q

What is nuclear fusion?

A

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

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7
Q

What do larger stars fuse?

A

Larger atomic nuclei to form heavier elements.

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8
Q

Why are larger stars hotter?

A

They fuse heavier elements, increasing gravity and pressure.

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9
Q

What does apparent magnitude measure?

A

The brightness of a star as seen from Earth.

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10
Q

Why might some stars appear brighter than others?

A

They may be closer to Earth, not necessarily brighter.

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11
Q

What is the scale range for apparent magnitude?

A

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

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12
Q

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

A

Full moon: -13; Sun: -27.

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13
Q

What does absolute magnitude measure?

A

The actual brightness of a star.

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14
Q

How is absolute magnitude calculated?

A

By determining the star’s distance from Earth.

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15
Q

What two factors are used to categorize stars?

A

Absolute magnitude and temperature.

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16
Q

What does a red star indicate about temperature?

A

A red star is cooler.

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17
Q

What does a blue or white star indicate about temperature?

A

A blue or white star is hotter.

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18
Q

How do scientists classify stars?

A

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

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19
Q

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

A

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

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20
Q

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

A

Different substances absorb different colors of light.

21
Q

How can astronomers identify elements in a star?

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

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

25
Q

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

A

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

26
Q

What is red shift?

A

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

27
Q

What is blue shift?

A

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

28
Q

What did Edwin Hubble observe in 1929?

A

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

29
Q

What relationship did Hubble discover?

A

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

30
Q

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

A

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

31
Q

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

A

The expansion of space.

32
Q

How does the expansion of space resemble a balloon?

A

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

33
Q

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

A

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

34
Q

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

A

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

35
Q

Who created the HR diagram, and when?

A

Ejnar Hertzsprung and Henry Norris Russell, around 1910.

36
Q

What does the HR diagram help scientists understand?

A

Stellar evolution.

37
Q

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

A

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

38
Q

What is luminosity in astronomy?

A

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

39
Q

How is luminosity often expressed in astronomy?

A

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

40
Q

What is a stellar nebula?

A

A cloud of gas and dust where stars are born.

41
Q

What is a main sequence star?

A

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

42
Q

What is a red giant?

A

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

43
Q

What is a red supergiant?

A

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

44
Q

What is a planetary nebula?

A

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

45
Q

What is a white dwarf?

A

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

46
Q

What is a black dwarf?

A

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

47
Q

What is a supernova?

A

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

48
Q

What is a neutron star?

A

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

49
Q
A

Semester 2 Science (23 decks)

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