ASTRO 101 Final Exam Review
Extraterrestrial Life
life on earth centers itself around carbon
o Crucial:
held together by strong nuclear force
most common form is a chain
it can form chains with other elements
carbon-carbon chain has a strong backbone
very large and stable
DNA contains billion of atoms, yet the arrangement holds 4
o Silicon is a dead end bc it is too simple
Meteorites contain amino acids strings of carbon atoms with nitrogen, oxygen,
hydrogen
Terrestrial Life:
o We define terrestrial life as series of processes by which material are
taken in and used for metabolism, respiration, and reproduction with the
possibility of change - the potential for mutations to occur.
o large molecules and complex chemistry
o life on earth originated in water
water provides protection from UV light
oldest fossils were aquatic life forms (3.5 billion years)
Requirements for Habitability:
o A source of nutrients from which to build cells0
o Energy to fuel activities: sunlight, chem reactions, heat from Earth
o Liquid Water: transports nutrients into cells, waste out
Habitable zone - the orbital region around a star in which an Earth-like planet can
possess liquid water on its surface and possibly support life. Liquid water is essential to
all life on Earth
Miller-Urey Experiment: found that Earth’s “primitive” atmosphere did NOT
contain O2
Black Smoker: geothermal vent seen on ocean floor
o microbes that are found in these mineral enriched environments are
ancient on the evolutionary scale
o **Could be similar on Europa**
Early Models for the Arrangement of Stars
Herschel’s Model:
o Milky Way galaxy is disk shaped (CORRECT)
o Our Sun is at the center of the galaxy (INCORRECT)
Shapley’s Model: observed globular star clusters
o we are not at the center of the galaxy bc he viewed globular clusters!!
if we were at the center of the galaxy, we would see the same
number of stars in all directions
o came after stellar parallax
,Milky Way Galaxy
Structure: Spiral galaxy
o spiral arms blend into a thin disk that contains more than 100 billion stars
o center of the disk; find a bright central bulge, supermassive black hole
o surrounding the disk is a vast, spherical halo, which contains globular star
clusters
o disk=100,000 LY in diameter
o sun=28,000 LY from center
Galactic disk is filled with interstellar gas and dust→ known as the interstellar
medium
o obscures our view when we try to peer directly in it
21 CM RADIATION: when the hydrogen atoms in hydrogen gas have a slight
change in energy, they emit a wavelength of radio energy. The wavelength they
emit is 21.1 cm. The slight change in the energy in a hydrogen atom occurs
when the electron moving around the proton flips from a parallel spin to an anti-
parallel spin in order to be in a lower energy state. Remember that all atoms
prefer to be in the lowest energy state as possible. hyperfine transition**
o If proton and electron are spinning the same direction, they’re in a spins
aligned state
slightly greater energy
o If protons and electrons are spinning in opposite directions, they’re in a
spins opposite state
slightly less energy
o When it changes from spins aligned to spins opposite, it is called a
hyperfine transition
hyperfine transitions release low energy, long wavelength photon!
21cm = radio photon
o 21cm radiation is used by astronomers to see further into the Universe
The interstellar medium (gas and dust) does not block 21cm
radiation (RADIO WAVES!!!)
Center of our galaxy:
o infrared image of galactic center: we find a lot of red giants
o The galactic center is a turbulent place
gas flung outward from the galaxy’s center about 10 million years
ago (from doppler shift)
Synchrotron emission (electrons and strong mag field)
There are 4 million solar masses within 10AU from each other…
***Supermassive black hole***
Mysterious Spiral Nebulae
Messier catalogued nebulae so that he wouldn’t confuse them with comets
o star forming regions
o planetary nebulae = dying stars
o star clusters
, o spirals
Herschel and Lord Rosse made detailed sketches of spirals
Cepheid Variable Stars change in Brightness Regularly
not eclipses - variable stage of stars’ evolution
Henrietta Leavitt identified cepheid variables in the Magellanic Clouds
brightest ones had the longest periods of variation
if all are at the same approx distance, the brightest ones must be more luminous
Edwin Hubble used Mt. Wilson 100’’ Telescope
Hubble saw Cepheid variables in the Andromeda spiral nebula
Plotted light curves - found periods
Used the P/L relation to estimate distance
2.5 million LY away, so this is distance to Andromeda spiral
Hubble’s contributions:
Discovered that Andromeda spiral nebula is a galaxy
o used cepheid variables to determine distance
o 2 million LY beyond Milky Way’s boundaries
Developed the classification system for galaxies
o based on visual appearance
o spirals, ellipticals, irregulars
o observed spectra of galaxies
Redshift/Distance Correlation:
o angular size of a galaxy decreases with increasing red-shift
Hubble’s Law: V = H x d
o V = velocity of recession measured from redshift, spectrum
o H = Hubble’s constant, 20-40 km/sec/MLY
o d = distance in MLY (10^6 LY)
o Law explained:
most distant galaxies have greatest redshifts
these galaxies are moving away at huge velocities
explained as the “expansion of space”
galaxies at greater distance have more of this expanding space
between us and them
produces greater redshift
***Observational basis for space expansion model***
Types of Galaxies
Elliptical: round to oval subclasses
Spiral: bright centers w/ thin disk made by visible spiral arms or dust
o Barred Spirals: visible extension across center
Irregular: some appear distributed
Orbits of Disk Stars
o stars in the disk orbit in a circular path
o arises from its gravitational attraction toward the galactic center; bobbing
arises from localized pull of gravity within the disk
Extraterrestrial Life
life on earth centers itself around carbon
o Crucial:
held together by strong nuclear force
most common form is a chain
it can form chains with other elements
carbon-carbon chain has a strong backbone
very large and stable
DNA contains billion of atoms, yet the arrangement holds 4
o Silicon is a dead end bc it is too simple
Meteorites contain amino acids strings of carbon atoms with nitrogen, oxygen,
hydrogen
Terrestrial Life:
o We define terrestrial life as series of processes by which material are
taken in and used for metabolism, respiration, and reproduction with the
possibility of change - the potential for mutations to occur.
o large molecules and complex chemistry
o life on earth originated in water
water provides protection from UV light
oldest fossils were aquatic life forms (3.5 billion years)
Requirements for Habitability:
o A source of nutrients from which to build cells0
o Energy to fuel activities: sunlight, chem reactions, heat from Earth
o Liquid Water: transports nutrients into cells, waste out
Habitable zone - the orbital region around a star in which an Earth-like planet can
possess liquid water on its surface and possibly support life. Liquid water is essential to
all life on Earth
Miller-Urey Experiment: found that Earth’s “primitive” atmosphere did NOT
contain O2
Black Smoker: geothermal vent seen on ocean floor
o microbes that are found in these mineral enriched environments are
ancient on the evolutionary scale
o **Could be similar on Europa**
Early Models for the Arrangement of Stars
Herschel’s Model:
o Milky Way galaxy is disk shaped (CORRECT)
o Our Sun is at the center of the galaxy (INCORRECT)
Shapley’s Model: observed globular star clusters
o we are not at the center of the galaxy bc he viewed globular clusters!!
if we were at the center of the galaxy, we would see the same
number of stars in all directions
o came after stellar parallax
,Milky Way Galaxy
Structure: Spiral galaxy
o spiral arms blend into a thin disk that contains more than 100 billion stars
o center of the disk; find a bright central bulge, supermassive black hole
o surrounding the disk is a vast, spherical halo, which contains globular star
clusters
o disk=100,000 LY in diameter
o sun=28,000 LY from center
Galactic disk is filled with interstellar gas and dust→ known as the interstellar
medium
o obscures our view when we try to peer directly in it
21 CM RADIATION: when the hydrogen atoms in hydrogen gas have a slight
change in energy, they emit a wavelength of radio energy. The wavelength they
emit is 21.1 cm. The slight change in the energy in a hydrogen atom occurs
when the electron moving around the proton flips from a parallel spin to an anti-
parallel spin in order to be in a lower energy state. Remember that all atoms
prefer to be in the lowest energy state as possible. hyperfine transition**
o If proton and electron are spinning the same direction, they’re in a spins
aligned state
slightly greater energy
o If protons and electrons are spinning in opposite directions, they’re in a
spins opposite state
slightly less energy
o When it changes from spins aligned to spins opposite, it is called a
hyperfine transition
hyperfine transitions release low energy, long wavelength photon!
21cm = radio photon
o 21cm radiation is used by astronomers to see further into the Universe
The interstellar medium (gas and dust) does not block 21cm
radiation (RADIO WAVES!!!)
Center of our galaxy:
o infrared image of galactic center: we find a lot of red giants
o The galactic center is a turbulent place
gas flung outward from the galaxy’s center about 10 million years
ago (from doppler shift)
Synchrotron emission (electrons and strong mag field)
There are 4 million solar masses within 10AU from each other…
***Supermassive black hole***
Mysterious Spiral Nebulae
Messier catalogued nebulae so that he wouldn’t confuse them with comets
o star forming regions
o planetary nebulae = dying stars
o star clusters
, o spirals
Herschel and Lord Rosse made detailed sketches of spirals
Cepheid Variable Stars change in Brightness Regularly
not eclipses - variable stage of stars’ evolution
Henrietta Leavitt identified cepheid variables in the Magellanic Clouds
brightest ones had the longest periods of variation
if all are at the same approx distance, the brightest ones must be more luminous
Edwin Hubble used Mt. Wilson 100’’ Telescope
Hubble saw Cepheid variables in the Andromeda spiral nebula
Plotted light curves - found periods
Used the P/L relation to estimate distance
2.5 million LY away, so this is distance to Andromeda spiral
Hubble’s contributions:
Discovered that Andromeda spiral nebula is a galaxy
o used cepheid variables to determine distance
o 2 million LY beyond Milky Way’s boundaries
Developed the classification system for galaxies
o based on visual appearance
o spirals, ellipticals, irregulars
o observed spectra of galaxies
Redshift/Distance Correlation:
o angular size of a galaxy decreases with increasing red-shift
Hubble’s Law: V = H x d
o V = velocity of recession measured from redshift, spectrum
o H = Hubble’s constant, 20-40 km/sec/MLY
o d = distance in MLY (10^6 LY)
o Law explained:
most distant galaxies have greatest redshifts
these galaxies are moving away at huge velocities
explained as the “expansion of space”
galaxies at greater distance have more of this expanding space
between us and them
produces greater redshift
***Observational basis for space expansion model***
Types of Galaxies
Elliptical: round to oval subclasses
Spiral: bright centers w/ thin disk made by visible spiral arms or dust
o Barred Spirals: visible extension across center
Irregular: some appear distributed
Orbits of Disk Stars
o stars in the disk orbit in a circular path
o arises from its gravitational attraction toward the galactic center; bobbing
arises from localized pull of gravity within the disk
