Unit 8: Characterizing Stars Flashcards
Why do stars appear in different colors?
because of their temperature
What is an Astronomical Unit
The average distance between the earth and sun
What is a Light Year
The distance that light travels in a vacuum in one year
What is a Parsec
1 pc= 3.26
What is the most convenient measurement for measuring interstellar and inter galaxies distance
- Light year and Parsec
What are the properties of interest of Stars
Distance Visible brightness luminosity surface temperature size age mass
What is the Parallax Method used for?
This is a measurement of the distances to nearby stars
- This method only works for closer and nearby stars
- not more than 1000 pc away from the earth
The Parallax Method is the only method allowing what?
Only method allowing to express distances to stars in terms of diameter of Earth’s orbit.
When was the first parallax measurement made? By who?
1838 by Friderich Wilhem Bessel
What is Apparent Magnitude?
The brightness of stars without regard to their distances
(m)
the brightness of stars as seen from Earth
Objects which are brighter than first-magnitude stars have apparent magnitudes ______ than 1, even _______ ones.
- Less
2. Negative
What is the apparent magnitude of Sirius
This is the brightest star in the night sky, has a negative apparent magnitude: m= -1.44
What is the apparent magnitude of Venus
m= -4.4
What are the Moon and Sun’s apparent magnitudes
Moon (-12.6)
Sun (-26.7)
What is the contemporary measurement of an apparent magnitude based on?
Electronic devices directly measuring an intensity of light
What us the naked eye limit of apparent magnitude
+6.0
What is a star’s absolute magnitude
M
The stars apparent magnitude the star would have if it were 10 pc from the Earth
What is the range of absolute magnitude
Absolute magnitude range from roughly M= -10 for the brightest stars to M= +17 for the dimmest
What is Luminosity
the total amount of energy radiating from the star’s surface each second
The absolute magnitude of a star and its luminosity are _____ _________.
directly proportional
What is the Harvard Classification Scheme and who created it?
The first serious attempt to organize and classify stars based on their temperatures
- Edward Charles Pickering and Annie Jump Cannon
What are the Stellar Classes
O, B, A, F, G, K, M,
0= coldest (blue violet)
M= hottest (red-orange)
What does the Hertzsprung-Russell Diagram show
that stars luminosity and surface temperature are correlated
What percent of stars belong to the main sequence band
over 90%
What does the lower right side of the Hertzsprung-Russell Diagram show
- dim and red
What does the top left side of the Hertzsprung-Russell Diagram show
- cold and bright
Where are White Dwarfs on the Hertzsprung-Russell Diagram
bottom left
High mass and low luminosity
Where is the sun on the Hertzsprung-Russell Diagram
in the main sequence band
Where are the super giants on the Hertzsprung-Russell Diagram
top right
low temperature, high luminosity
What is the Spectroscopic Parallax
the indirect method for the measurement of distances to stars.
What kind of stars can the Spectroscopic parallax be applied to
any main sequence star
~10,000parsec
What are Cepheid Variables and what can it be used for
Stars which brighten and dim periodically.
- allows them to be used as cosmic yardsticks out to distances of a few thens of millions of LY
What are the steps to determine main sequence stars distance
- Determine the spectro class (line up from the bottom of the chart in line with the start to the main sequence line)
- Absolute Magnitude M
- Apparent Magnitude m
How/when were Cepheid Stars discovered
absolute magnitude combined with apparent magnitude = distance
What are Optical Doubles/Apparent Binaries
Physically far from each other. They are unrelated stars that appear close together thought chance alignment with Earth
What are Binary Stars?
Stars that are physically close and form the system
- two stars that orbit each other
How many stars in the sky are Binary stars
1/3 to half of the stars in the sky
What are visual binary stars vs Spectroscopic Binary
Visual are seen separately by telescopes and spectroscopic are hard to see separately even with telescope
What is the Big Dipper Constellation called
Ursa Major
- is a binary star
What does Keplers Law tell us
the combined mass of binary stars
More luminous stars are _____?
Bigger
