PG. 127 Measuring the Stars. Groups of stars Long ago, people grouped bright stars and named them...
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Transcript of PG. 127 Measuring the Stars. Groups of stars Long ago, people grouped bright stars and named them...
PG. 127
Measuring the Stars
Groups of stars
Long ago, people grouped bright stars and named them after animals, mythological characters or every day objects.
Called constellationsThere are 88 constellationsConstellations that appear to move around the north pole
are called circumpolar (Big Dipper)Classified as summer, fall, winter, and spring constellations
Star clusters
Groups of stars that are gravitationally bound to one another are called clusters
Open cluster- stars that are not densely packed
Globular cluster-stars that are densely packed into a spherical shape
Binaries
Binaries
Two stars that are gravitationally bound that orbit a common center of mass are binaries
More than half the stars are binaryAppear to be single stars
Stellar positions and distances
Two units to measure long distances Light Year (ly) =9.461 x 1012 km) Parsec (pc)= 3.26 ly
Scientists use parallax to calculate the distance to a star
The closer the star, the larger the shift
Properties of Stars
Diameter, mass, brightness, energy output, surface temperature, and composition.
Can be smaller than the Sun or bigger (our Sun is average)
Brightness is measured using magnitudeApparent magnitude relies on what we seeAbsolute magnitude takes into account how far a
star is from Earth (can only be calculated if you know the distance of the star)
Luminosity measures the energy output and you must know the apparent magnitude
Spectra of stars
The rainbow you see when you shine white light through a prism is called a spectrum.
3 types: continuous, emission, and absorptionStars have an absorption spectrum
Classification of stars
Stars are assigned spectral types (O, B, A, F, G, K, and M)
Each spectral type is then subdivided into more specific divisions using numbers 1-9
O stars are the hottest and M the coolestHotter stars have simple spectra while cooler
stars have more lines in their spectraOur Sun- G273% Hydrogen and 25% helium and 2% other
elements
Wavelength shifts
Shifts in spectral lines happen when there is motion between the source of light and the observer
If the star is moving toward the observer, the spectral lines are shifted toward shorter wavelengths (called blueshifted)
Star is moving away, wavelengths become longer (redshifted)
H-R Diagrams
Properties of mass, luminosity, temperature, and diameter can be related and shown on a graph called the Hertzsprung-Russell diagram (H-R diagram)
Absolute magnitude is plotted on the vertical axis and temperature or spectral type is plotted on the horizontal axis
90 % of stars fall on a strip of the H-R diagram called the main sequence (runs from upper left corner to lower right)
Upper left = hot, luminous starsLower right= cool, dim stars
Classification on the H-R
Upper-right= cool but luminous; very large; red giants (100x larger than the Sun)
Lower-left= hot but dim; very small; white dwarfs
Use the spectra to answer the question.
Each element absorbs light at a particular wavelength. This absorption of light produces dark lines in spectra. Scientists analyze spectra to identify the composition of a star. According to the spectra shown, which elements does the unknown star contain?
1.A. calcium and sodium2.B. calcium and iron3.C. iron and magnesium4.D. sodium, iron, and magnesium