astro 2 Flashcards
describe radiometric dating
Careful measurement of proportions of various radioactive
isotopes = radioactive nuclei that undergo spontaneous
change –i.e. radioactive decay- due to breaking
apart/emission of nuclear particles or conversion of a
proton in a neutron.
describe the rate of radioactive decay
The rate at which this transformation occurs is characterized by
the parent isotope’s half-life = the time necessary to decay for
half of the number of initial parent nuclei.
Formation of terrestrial planets
Solid seeds of metal
& rock in the inner Solar nebula grew through the
accretion process.
Microscopic particles stick together through electrostatic forces
As they
grow larger, their surface area ↑ ↑
easier to make contact with others!
Particles grew in mass until they became planetesimals, where
gravity dominated in the accretion process
For larger planetismals, collisions were increasingly destructive
These planetesimals eventually assembled into terrestrial planets,
which are relatively small in size because rock & metal made up only a
small amount of the materials in the Solar nebula
Formation of Jovian planets
Accretion occurred similarly in the outer solar nebula.
The outer solar system included more abundant ices along with
metal/rock
The Jovian planets began as large icy planetesimals, which
captured H, He & other gases from the Solar nebula.
Their gravity grew stronger as they accumulated matter, allowing
them to capture even more matter (positive feedback)
Each Jovian planet became surrounded by its own
(micro)accretion disk of gas, spinning in the same
direction as the planet’s rotation.
Moons accreted from icy planetesimals within these disk ended up
with nearly circular orbits in the same direction as the planet’s
rotation and lying in (or close to) the planet’s equatorial plane
As the Jovian planets formed, they quickly cleared away their orbital
path inside the Solar nebula
How was the Solar system formed?
Solar nebula probably began as a large & roughly spherical cloud
(a few light-years diameter) of very cold & low-density gas.
Collapse may be triggered by:
Shock wave from the explosion of a nearby star.
Local densification of gas due to solar winds of new stars
Once started, gravity ensures that it would continue
What is the kant laplace theory
Nebular theory = Solar system formed from
the gravitational collapse of an interstellar cloud of gas
where are forming stars always found in the nebular theory
always found within interstellar clouds
where are stars formed
Interstellar clouds (where stars are formed) represent only a stage of a complex galactic recycling process
which planets rotate on their side and “backwards”
f Uranus & Venus
which moon of which planet is unusally large
the moon of earth
what are asteroids and coments
Swarms of smaller bodies populate the solar system:
Asteroids = small rocky bodies orbiting the Sun like planets, but
much smaller.
Comets = small icy bodies (water ice, NH3 ice, CH4 ice, but also N2
ice, CO & CO
2 ices, etc., & rock) orbiting the Sun.
Most asteroids are in the asteroid belt (between the orbits of Mars &
Jupiter).
Comets are found in 2 distinct regions: Kuiper belt & Oort cloud:
The great majority never visit the
inner solar system!
Kuiper belt contains >100,000 icy
objects, of which Pluto & Eris are
the largest known.
The Oort cloud is much more distant
and its comets have orbits randomly
inclined to the ecliptic plane
give
Oort’s cloud a spherical shape
briefly describe asteroids
small rocky bodies orbiting the Sun like planets, but
much smaller.
briefly describe comets
small icy bodies (water ice, NH3 ice, CH4 ice, but also N2
ice, CO & CO2 ices, etc., & rock) orbiting the Sun.
where are comets distinctly found
Kuiper belt & Oort cloud:
The great majority never visit the
inner solar system!
where are most asteroids formed
are in the asteroid belt (between the orbits of Mars &
Jupiter).
what the shape of oort’s cloud
spherical
what is the kuiper’s belt
contains >100,000 icy
objects, of which Pluto & Eris are
the largest known.
is the oort cloud much more distant than kuiper’s belt
yes
describe the oort cloud
The Oort cloud is much more distant
and its comets have orbits randomly
inclined to the ecliptic plane
what are the two major types of planets
terrestrial and jovian
briefly describe terrestrial planets
Earth-like. Smaller size & mass Solid rocky surface Closer to the Sun (and closer together) Made mostly of rock & metal and with abundant metals in their cores Few moons and no rings
briefly describe jovian planets
Jovian = Jupiter-like (gas giants). Large size & mass No solid surface Farther to the Sun (and farther together) Made mostly of H, He & hydrogen compounds (e.g. H2O, CH4, NH3) Numerous moons and have rings
who saw four moons orbiting Jupiter, proving that not all objects orbit the Earth
Galileo
who built the first reflecting telescope
newton
Tides rise & fall _ times a day
2
Orbital energy =
kinetic energy + gravitational potential energy = ct.!
“Kepler’s first two laws
apply to ____________”
“all orbiting objects,
not just planets”
However, because tidal forces stretch Earth itself, the process creates
friction, called tidal friction
describe the strength of earth’s tidal force on moon vs moon’s on earth
Earth’s tidal force
on the Moon has a much greater effect than the Moon’s tidal force on
Earth
What is synchronous rotation between the earth and the moon
The Moon rotates on its axis in exactly the same time period that it takes to orbit Earth
what gives the moon 2 bulges along the earth moon line
Earth’s tidal force
what slows down the moon’s rotation
Earth’s tidal force
on the Moon has a much greater effect than the Moon’s tidal force on
Earth
Earth’s tidal force gives the Moon 2 bulges along the EarthMoon line
The Moon’s gravity tries to keep the tidal bulge on the Earth-Moon line
The Earth’s rotation tries to pull the tidal bulges around with it
The resulting friction slows down Moon’s rotation
Why electrical repulsion doesn’t make the tightly bunched p + in the nucleus to fly apart?
Because an even stronger force, the strong (or nuclear) force, acts at subatomic scales and holds particles together, overcoming electrical repulsion.
Planck’s law
Planck’s law describes the EM radiation emitted by a blackbody in thermal equilibrium at a definite temperature:
Wien’s Displacement Law: λ
The peak wavelength of
a thermal radiation spectrum
changes as a function of temperature
Wien’s Law
explains the shift of the radiation curve’s peak to shorter wavelengths as T Hotter objects emit most of their radiation at shorter wavelengths
