Unit 8: Discoveries About Stars

What is Earth’s orbit diameter?

2 astronomical units

What explains why stellar parallax can only be measured for nearby stars?

• higher distance = lower stellar parallax

• limited baseline

What is the largest stellar parallax?

1 arcsecond

• 1/3600 of a degree

What was incorrectly assumed about stars in the 17th & 18th centuries?

brighter star = nearer

What did Edmund Halley compare in 1718?

Almagest & current star catalog

What did Edmund Halley discover in 1718?

3 moving stars

What was the method of revealing moving stars in the early 1800s?

repeated star catalog

What did Edmund Halley discover about stellar motion?

stars have motion

What is the fastest star?

Barnard’s Star

What is a “pc?”

• parsec

  • hypothetical star distance that has 1 arcsecond p shift

• 1 parsec = 206 235 astronomical units = 31 000 000 000 kilometres

What is a “ly?”

• lightyear

  • light travel distance in 1 year

• 1 lightyear = 63 239 astronomical units = 9 500 000 000 kilometres ~ 1/3 parsecs

What did Von Struve find in 1837?

Vega parallax

• 1/8 arcseconds

• 8 parsecs

What explains why Von Struve measured Vega?

• 5th brightest star

• moved 30 arcseconds in 100 years

What was assumed about the nearest stars in the 1830s?

• brighter

• larger motion

• wider space binary

What did Bessel find in 1838?

61 Cygni parallax

• 1/3 arcsecond

• 3 parsecs

What explains why Bessel measured 61 Cygni?

• moved 4 arcseconds in 1 year

• widely spaced binary

What did Thomas Henderson find in 1838?

Alpha Centauri parallax

• 3/4 arcseconds

• 4/3 parsecs

What explains why Thomas Henderson measured Alpha Centauri?

• 1 of brightest southern stars

• quickly moved across sky

• widely spaced binary

  • triple star

What is the nearest star?

Alpha Centauri

What did the Hipparcos Space Telescope measure starting in 1989?

measure 100 000 star distances

What method did the Hipparcos Space Telescope use?

parallax method every 6 months above atmosphere

What is the number of Milky Way stars?

400 000 000 000

What did Gaia study starting in 2013?

400 000 000 (1%) Milky Way stars

What did Robert Hooke publish in 1665?

light textbook

• light travels as wave

What did Christiaan Huygens publish a decade after Robert Hooke?

light textbook

• light travels as electromagnetic radiation

What is “electromagnetic radiation?”

• oscillating blue electric energy field & red magnetic energy field wave

What characteristics differentiate light sources?

• amplitude

• wavelength & frequency

What does amplitude determine?

light intensity

What is “amplitude?”

• peak height

What does wavelength determine?

light colour

What is “wavelength?”

• peak distance

What is “frequency?”

• wavelength number leaving light source per second

What is the wavelength & frequency relation?

higher frequency = shorter wavelength

What differentiates red & blue light wavelengths?

red > blue

What are the wavelength units?

• µm

• nm

• Å

What is a “µm?”

• micron

  • 1 000 000th of metre

What is a “nm?”

• nanometre

  • 1 000 000 000th of metre

What is an “Å?”

• Angstrom

  • 10 000 000 00th of metre

What is the electromagnetic spectrum appearance?

What are the electromagnetic spectrum left side’s properties?

• short wavelength

• high frequency

• high energy

What are the electromagnetic spectrum right side’s properties?

• long wavelength

• low frequency

• low energy

What is the longest & lowest-energy wave?

radio

What is the shortest & highest-energy wave?

gamma

What explains why Sun UV waves damage humans?

• high amplitude

What are radio wave uses?

• radio

• TV

What are microwave wave uses?

• cooking

• communications

What are infrared wave uses?

• heat

  • Sun

  • fire

  • radiator

What are visible light uses?

• makes things able to be seen

What are UV wave uses?

• fluorescent tubes

• skin absorbs

• purifies water

What are x-ray wave uses?

• view inside of body & object

What are gamma wave uses?

• kill cancer cell

What method produces gamma waves?

nuclear reaction

What was 1 method Joseph Fraunhofer used to test glass?

pass sunlight through lenses & ensure no colour separation

What process did Joseph Fraunhofer use to discover Fraunhofer’s spectrum in 1814?

1. passed sunlight through prism

2. placed spectrum on white screen

3. looked at spectrum through telescope

4. saw 600 thin dark lines

5. labeled with letters → designated wavelength

What was “Fraunhofer’s spectrum?”

1st dark Sun line visible light map

What did German chemist Robert Bunsen & physicist Gustav Kirchhoff produce in 1859?

heated gas spectra

What did Robert Bunsen & physicist Gustav Kirchhoff conclude in 1859?

gas spectra contains unique bright coloured line sequence

What explains why Robert Bunsen & physicist Gustav Kirchhoff were interested in Fraunhofer’s spectrum?

Fraunhofer passed flame light through prism

What did Joseph Fraunhofer see in his other expriment?

mostly dark area with few bright coloured lines

What was Robert Bunsen & Gustav Kirchhoff’s response to Joseph Fraunhofer’s other experiment?

built apparatus (spectroscope) & placed chemical metals

What is “spectroscopy?”

• light source spectrum analysis to determine chemical composition

What did Robert Bunsen and Gustav Kirchhoff realize about the Sun spectrum & gas spectra?

Sun dark lines = gas bright lines

What was Robert Bunsen & Gustav Kirchhoff’s response to Sun’s dark lines matching the gases’ bright lines?

produced sunlight spectrum passing through gas flame

What did Robert Bunsen & Gustav Kirchhoff initially believe by producing a sunlight spectrum passing through a gas flame?

no more dark line

What did Robert Bunsen & Gustav Kirchhoff finally believe by producing a sunlight spectrum passing through a gas flame?

thicker dark line

What did Robert Bunsen & Gustav Kirchhoff correctly conclude about the Sun core?

produces full light spectrum

What did Robert Bunsen & Gustav Kirchhoff correctly conclude about the Sun core’s surroundings?

atmosphere

What did Robert Bunsen & Gustav Kirchhoff correctly conclude about the dark line?

Sun atmosphere’s molecules absorb light at signature wavelengths equal to ones the gas emits on its own

What did Robert Bunsen & Gustav Kirchhoff correctly conclude about the thicker dark line?

also passes sodium flame that absorbs more light

What was Robert Bunsen & Gustav Kirchhoff’s process of correctly concluding the thicker dark line?

1. looked at atmosphere alone

• heated it up

  → glowed

2. got emission line on spectrum

What’s an “absorption line?”

light absorbed on its way to Earth

What’s an “emission line?”

light emitted by atoms

What reveals Robert Bunsen & Gustav Kirchhoff’s emission lines in the 1860s & 1870s?

Sun atmosphere spectra was collected during solar eclipses

What do Robert Bunsen & Gustav Kirchhoff conclude about the Sun atmosphere chemical composition?

match spectra to known substances

What is the Sun’s “lower atmosphere?”

layer containing elements for most absorption lines

What is the Sun’s hottest layer?

lower atmosphere

What is the Sun’s “upper atmosphere?”

hydrogen & helium layer

What is the Sun’s coolest layer?

upper atmosphere

What explains why people were able to measure the Sun layers at the same time?

• as telescope moved across atmosphere, emission lines changed

What gas spectrum was produced in the 1860s?

hydrogen

• matched with dark lines

What was concluded by producing hydrogen spectra?

in Sun atmosphere

What was the identity of the person that produced the 1st hydrogen spectra in the 1860s?

Julis Plücker

What was Julius Plücker’s method of producing gas spectra in the 1860s?

• constructed vacuum tube

• heated up

What did Norman Lockyer & Pierre Janssen discover in 1868?

yellow emission line in Sun upper atmosphere spectra during solar eclipse

What was concluded about the yellow emission line in the Sun upper atmosphere spectra?

helium

What are the word origins of “helium?”

Helios

• Greek sun god

What explains why the yellow emission line hadn’t been seen by others?

close in wavelength to thick sodium line

What are the 2 spectra types?

• visual

• graphical

What is a “visual spectrum?”

• continuum light

• emission line

• absorption line

What is a “graphical spectrum?”

• intensity at each wavelength

  • continuum emission

• dip = absorption line

• peak = emission line

What spectrum did English astronomers William Huggins & Margaret Lindsay Huggins produce in 1864?

planetary nebula

What are “Nebulium?”

unidentified emission lines on planetary nebula spectrum

What was discovered to be Nebulium?

oxygen

What was the Huggins’ 1st reported nebula?

Cat’s Eye Nebula

What was the Huggins’ Cat’s Eye Nebula spectrum appearance?

1 strong green line

What explains the Cat’s Eye Nebula strong bright line?

highly excited oxygen

What did the complete Cat’s Eye Nebula spectrum reveal?

emission-line nebula

• hot gas cloud

What nebula types did Huggins find?

• emission-line

• continuum

• absorption-line

What nebula types are actually star clusters?

• continuum

• absorption-line

What are a continuum nebula’s properties?

• continuous emission

• absorption line

• no emission line