AS midterm 2

blinking plates

- look at ecliptic plane - look for slow motion moving objects and take picture with enough time in between each one - how clyde tombaugh founded pluto

future of the sun

- when hydrogen is exhausted, fusion in the suns core will cease - gravity will cause sun to collapse - sun will expand and become giant red star

what determines whether convection or radiation operates?

- when temperature gradient is too steep, radiation is not enough, convection takes over - the convection zone has a steep temperature gradient

Put the layers of the Sun in order, starting with the core. A. Chromosphere B. Convective zone C. Corona D. Photosphere E. Radiative Zone

E,B,D,A,C

asteroids and comets

- "leftovers" from early stages of planet formation - asteroids form inside the front line, comets form outside - scattered by jovian planets into present orbits - comets are icy, astroids are rocky

conduction

- Heat is transferred on microscopic scale, as rapidly moving or vibrating atoms and molecules interact with neighboring particles. Works well with solids. Nothing really moves, just molecules in the solid vibrating around.

convection

- Heat is transported on macroscopic scale, by material circulating through a region that is unevenly heated, e.g., air in a heated room.

brightest stars

- O and B stars - found only in the spiral arms near dark molecular clouds - biggest and hottest, shortest lifetimes - M stars are the dim-est, smallest and coolest, longest lifetimes

refraction telescope

- Refracting telescopes use lenses to bend the light to focus it - The objective lens refracts the light - The objective lens is placed in the end of the telescope facing the sky - The aperture is the diameter of the objective lens - A larger aperture gathers more light disadvantages: - lenses suffer from chromatic aberration - long focal length requires large structures - entire light beam goes through lens, need lens interior to be perfect - lens can only be supported around edges

radiation

- There is no material involved. Heat is transported through space by electromagnetic radiation, i. e., photons.

refraction

- When light enters a different medium, its is slowed down by amount defined by medium's refractive index - Because the speed changes, the light changes direction - This bending of light is called refraction - The amount of refraction depends on the material - glass has refraction index of 1.5

protoplanetary disk

- also called solar nebula - forms the planets - around a protostar

protostar

- as the cloud clump collapses, it will heat itself up (virial theorem), spin faster, and eventually core becomes dense enough to be opaque - heat can no longer escape so temperature and pressure rise and the core becomes a protostar - conservation of angular momentum forms disk around dense core (protoplanetary disk, forms the planets) - magnetic field creates bipolar jets - not a true star until nuclear fusion begins in core (begins when hot enough to fuse hydrogen to helium)

photographic plate

- big glass plate covered by light sensitive film - not very sensitive - capture large part of the sky, not very precise (CCD is better for seeing small things)

radioactive elements

- bigger source of heat in early stage of solar system (less decayed then) - radioactive elements decay into stable ones - rate of decay is fixed by the elements half-life, the time for 50% to decay - parent and daughter elements

solar flare

- burst of light

how can planets orbit expand?

- by scattering planetesimals - bodies can slow down or speed up due to interactions - small body tends to gain angular momentum and get ejected from the solar system - big body then has to lose momentum and its orbit shrinks - giant planets have migrated due to scattering many planetesimals - gravitational slingshot

meteorites

- chondrite meteorites contains the oldest material to form in the solar system - calcium-aluminum-rich inclusions (CAIs) and chondrules - also contain stuff that existed before solar nebula formed - CAIs are white stuff (heated but not melted) - chondrules are grey circles (formed as molten droplets)

molecular clouds

- cold - dense - contains dust - dust and cold gas together = star formation - some regions inside the cloud are denser than others (not uniform) - Mjeans determines if the region will collapse, if the cloud exceeds jeans mass, gravitational collapse can happen

interferometric arrays (VLA)

- combine the signals from many telescopes, increasing effective diameter size which improves resolution of radio telescopes - can more the ends of the telescopes to increase baseline (distance, aka aperture)

neutrinos

- light subatomic particles that are extremely difficult to detect - massless neutral particle produced in nuclear processes

blurring by atmosphere

- contains air cells of slightly different temperatures - cells act like lenses, all tilted in different directions - results in :astronomical seeing" (blurring) - seeing is limited by the size of the air bubble in the atmosphere - air bubble size is equal to 10cm-20cm in most places - telescopes with D>the bubble size range can only approach diffraction limit by using adaptive optics - small aperture is better because you are focused on one air bubble so it is less blurry - short exposure and small aperture is best

sunspot

- cool, dark spot on the sun - appear in pairs - magnetic field lines exit the surface of the sun through one sunspot and enter through the other

magnification power of a telescope equation

- depends on the focal lengths of the objective lens (refraction telescope) or mirror (reflecting telescope) and the eyepiece - M= telescope focal length/ eyepiece focal length

chromatic aberration

- different wavelength is focused at different location

focal length

- distance between lens and the image - longer focal length=more zoomed in image - aperture does not affect the zoom level

planet migration

- due to scattering - Kuiper belt objects, saturn, uranus, and neptune moved outwards while jupiter moved inward

collision growth (binary accretion)

- early solar system contained a lot of dust and gas - dust grains collided and stuck together to grow bigger (accretion) - this process continues until planetesimals form and attract each other gravitationally (the big get richer, a few bodies grow faster than the rest) - planetesimals big enough to have gravity and attract other planetesimals are planetary embryos - planetary embryos collide and merge eventually forming terrestrial planets

charge-coupled device (CCD)

- electronic detectors record number of photons in each pixel - astronomer's detector of choice - worlds largest CCD camera is 1.4 billion pixels

black holes

- emit gravitational waves - when two are orbiting each other they emit gravitational waves, losing energy, so slowly spiral toward each other - eventually collide into each other at half the speed of light and form single more massive black hold - energy is emitted as gravitational waves

convection zone

- energy is transported by convection (rising and falling gas)

radiative zone

- energy is transported by photons (radiation) - largest percentage of the sun - energy is absorbed, emitted and deflected by matter in unpredictable directions

hydrostatic equilibrium

- everywhere in the sun, pressure and gravity are balanced - inward force of gravity is balanced by the outward force of pressure (from energy source in core)

eye as a refracting telescope

- eye has all required features of refracting telescope - the pupil acts as the light gathering aperture - the detector is the retina - the information processor is the brain - the eye suffers from poor angular resolution because the pupil is small - eye needs parallel rays to form image - the faintest we can see is limited by integration time (the time over which the detector (eye) can add up photons, aka exposure) and quantum efficiency (the likelihood that a photon falling on the retina will produce a response)

kuiper belt

- formed due to gravitational influence of neptune, also large distances (long time between collisions)

pluto

- founded because clyde tombaugh was looking when no one else was - object part of kuiper belt - same resonance as neptune - other kuiper objects also have the same resonance as neptune (nothing unique about pluto) - orbit of pluto crosses neptunes orbital path - resonance of 3:2 - mass is too small to perturb any planet

how did the solar system form?

- from a giant molecular cloud that collapsed 1) giant cloud of gas and dust in interstellar space 2) clumps form inside cloud 3) cloud collapses (fragments) into many cores, only collapses if Mjeans is reached 4) cores condense into young stars (protostar) surrounded by disks (protoplanetary disk) 5) after 10^6 years, planets form from the dust within disk - dust particles collide with each other and stick together by electromagnetic forces (accretion) - as these planetesimals grow big enough, they develop gravity and gobble up all the dust and gas - growth process proceeds faster in outer parts of solar nebula, protoplanets can consolidate quicker - giant planets orbits have migrated due to scattering or interation with solar nebula

fusion

- fusing protons - hard because they have positive charge and repel each other - requires slamming protons together at high speed and high temperature

coronal mass ejections (CMEs)

- giant clouds of particles from the corona hurled out into space

core

- high temperature and pressure, where energy is produced by nuclear fusion

interferometer

- improves resolution - several telescopes connected to act as one

frost line

- inside the front line, only rocks and metals can condense - outside the front line, hydrogen compounds can also condense - between present orbits of mars and jupiter (4 AU) - between the astroid belt and jupiter

radio telescopes

- large - radio waves can pass through gas and dust - radio wavelength is long so that is why they are so big (wavelength/ aperture = diffraction limit) - have poor resolution due to long wavelength

diffraction

- light bending around barrier and corners - airy disk is the central spot - diffraction limit is the smallest resolution limited by diffraction - best resolution attainable (diffraction limit) is proportional to wavelength/ telescope aperture - bigger aperture, the better the resolution and longer wavelength the poorer the resolution - diffraction limit is an angle

reflection

- light bouncing off surface back into original medium

proton-proton chain

- main process responsible for energy produced in most main sequence stars - proton + proton forms hydrogen atom and neutrino - then this hydrogen atom + proton atom form helium and gamma ray photon - helium + helium forms helium and two protons - starts out with 4 protons and ends up with one helium nucleus - missing mass in finished helium nucleus got converted into energy during the reaction (E=mc^2) - neutrinos tell us that this is all happening in the sun, the only thing that can pass right through the overlying layers of the sun and can be detected on earth

angular momentum

- momentum of rotating object - = Mvr - M= mass of rotating thing - r= radius - v= rotation speed

mean motion resonance

- objects experience periodic little kicks - add up over time to produce big effects

two comet resevoirs

- oort cloud (long period comets)(circular shape) - kuipaser belt (short period comets)(donut shape)

corona

- outermost layer - high temperature, low density - origin of solar wind

why is it so difficult to take a picture of an extrasolar planet?

- planets are fainter than their stars and cannot be seen in the glare of starlight

solar prominence

- plasma loops that connect two sunspots - suppress convections, less heat reaches surface, sunspots are cooler than photosphere - site of solar flares

occultation

- problem with them is planets can be mixed up with birds - solar system object passes in front of star, temporarily blocks out starlight

pressure

- proportional to temperature (high temp= high pressure) - thermal pressure comes from motion of gas molecules

light gathering power of a telescope equation

- proportional to the square of the aperture size - D squared

random walk

- radiative zone is so dense that photons have many interactions before they can make it out - each time the photons runs into another photon, energy is reduces thus gamma rays become blackbody radiation

different kinds of telescopes

- reflecting - refracting

what ended planet growth?

- running out of material (for the terrestrial planets) - running out of gas (for the jovian planets)(we know the giant planets formed by 10 million years because the gas in the solar nebula dissipated by then) - jupiter and saturn grew fast and had a large amount of nearby gas on which to feed - uranus and neptune took longer to form their cores because fewer types of materials could condense farther outr

virial theorem

- says when a gravitational system collapses, 1/2 of energy goes into heat - other half gets radiated away - potential energy -> kinetic energy when cloud collapses -> thermal energy when heat is created

resolution (resolving power)

- smallest details that can be separated - the smallest angle between close objects that can be seen clearly to be separate - the ultimate resolution of a telescope is the diffraction limit (the smallest resolution limited by diffraction) - smaller number is better - limited by diffraction - resolvable if you can see the stars airy disks clearly - best resolution attainable (diffraction limit) is proportional to wavelength/ telescope aperture - bigger aperture, the better the resolution and longer wavelength the poorer the resolution - limited by 1) atmosphere and 2) telescope size

Mjeans equation

- square root of T^3 (temp) /n (density) times Msun - condition for collapse: dense (big n) and cold (small T)

differential rotation

- sun doesn't rotate like a solid body, equatorial regions rotate faster than the poles

built in thermostat

- sun remains stable - if fusions reactions happen too fast, core heats up, leading to higher pressure, making the core expand and then cools down, slowing the rate of fusion - vice versa process happens if fusion reactions run too slow, core cools leading to lower pressure, making the core contract, and the contraction heats the core fueling the rate of fusion

how did the astroid belt form?

- the gravitational effect of young Jupiter was strong enough to stir rocky planetesimals into more eccentric orbits -collisions between these planetesimals were too violent to allow growth, resulting in fragmentation and forming the astroid belt instead of a planet - short story, because of Jupiter gravitational disturbances

Quantum efficiency

- the likelihood that a photon falling on the retina will produce a response - QE= number of photons counted/ number of photons that hit detectors surface - higher percentage is better

chromosphere

- transition zone between photosphere and corona

magnetic fields

- turbulent motions of gas (in convection zone) generates magnetic fields - also called solar dynamo - located at bottom of convection zone - moving plasma in convection zone creates currents - magnetic field lines get tangles due to turbulent motion - behave like rubber bands

adaptive optics

- use deformable mirrors to correct for distorted wavefront - uses array of tiny mirrors that correct for the turbulent cells - with adaptive optics, ground bases image quality can come close to the Hubble space telescope

reflecting telescopes

- use mirrors - there are primary and secondary mirrors (and sometimes tertiary mirror) - largest telescopes in the world are reflectors (Keck, located on top of Mauna Kea) advantages: - no chromatic aberrations - large mirrors are easier to make than large lenses - telescopes can be more compact - not as heavy as refracting telescopes

photosphere

- visible surface, has sunspots, prominences - where heat and visible light are sent into space - layer where light is emitted

what does a telescope do?

1) collects light 2) magnifies the image

planet formation: explaining the exceptions

1) giant impacts in early solar system - explain roation of venus and uranus - form moon from collision debris 2) satellite capture after near miss - moons of mars captured from the asteroid belt - triton captured from Kuiper belt

Which weighs the most? A. Four hydrogen nuclei B. One 4He nucleus C. One 3He nucleus

A. Four hydrogen nuclei

Where does most of the angular momentum of the original cloud go? A. Into the orbital angular momentum of planets B. Into the star C. Into the spin of the planets D. Lost along the jets from the star

A. Into the orbital angular momentum of planets

Which of the following does not apply to reflecting telescopes? A. they observe light that bends through a medium B. they do not experience chromatic aberration C. they can have long focal lengths in short tubes D. they use multiple mirrors

A. they observe light that bends through a medium

When hydrogen if fueled into helium, energy is released from A. Gravitational collapse. B. Conversion of mass to energy. C. The increase in pressure. D. The decrease in the gravitational field.

B. Conversion of mass to energy.

In our Solar System, the inner planets are rocky because: A. The original cloud had more rocky material near the center. B. Warm temperatures in the inner disk caused the inner planetesimals to be formed only of rocky material. C. The inner disk filled a smaller volume, and so it was denser. D. The hydrogen and helium atoms were too low mass to remain in the inner disk.

B. Warm temperatures in the inner disk caused the inner planetesimals to be formed only of rocky material.

Why does a disk heat up as it collapses? A. conservation of angular Momentum B. conservation of energy C. nebular hypothesis D. the effect is simply a measurement error and it doesn't heat up.

B. conservation of energy

In practice, the smallest angular size that one can resolve with a < 6-cm telescope is governed by the: A. Blurring caused by Earth's atmosphere B. Diffraction limit of the telescope C. Size of the primary mirror D. Magnification of the telescope

B. diffraction limit of the telescope

Suppose you observe a planet with an atmosphere composed mostly of hydrogen and helium. Where in protoplanetary did this planet likely form? A. close to the central star B. far from the central star C. more information is needed

B. far from the central star

The surface of the Sun appears sharp in visible light because: A. the photosphere is cooler than the layers below it. B. the photosphere is thin compared to the other layers in the Sun. C. the photosphere is less dense than the convection zone. D. the Sun has a distinct surface.

B. the photosphere is thin compared to the other layers in the Sun.

Which layer of the Sun is the furthest from the core? A. Chromosphere B. Convective zone C. Corona D. Photosphere E. Radiative Zone

C. Corona

Which of the following pieces of evidence does not support the nebular hypothesis? A. Planets orbit the Sun in the same direction. B. The Solar System is relatively flat. C. Earth has a large Moon. D. We observe disks of gas and dust around other stars.

C. Earth has a large Moon.

How do neutrinos help us understand what is going on the core of the Sun? A. Neutrinos from distant objects pass through the Sun, probing the interior. B. Neutrinos from the Sun pass easily through Earth. C. Neutrinos created in fusion reactions at the core of the Sun easily escape.

C. Neutrinos created in fusion reactions at the core of the Sun easily escape.

Hydrostatic equilibrium in the Sun means that: A. The Sun does not change. B. The Sun absorbs and emits equal amounts of energy. C. The outward force from radiation pressure balances the weight of overlying layers. D. Energy produced in the core per unit time equals energy emitted at the surface per unit time.

C. The outward force from radiation pressure balances the weight of overlying layers.

Spacecraft are the most effective way to study planets in our Solar System because: A. Planets move too fast across the sky for us to image them well from Earth. B. Planets cannot be imaged from Earth. C. They can collect more information than is available just from images from Earth. D. Space missions are easier than long observing campaigns.

C. They can collect more information than is available just from images from Earth.

CCD cameras have much higher quantum efficiency than that of other detectors. Therefore, CCD cameras: A. Can collect photons for longer times B. Can collect photons of different energies C. Can generate a signal from fewer photons D. Can split light into different colors

C. can generate a signal from fewer photons

What type of material is stable near the Sun? A. ice B. organic C. refractory (rocks and metals) D. volatile (ices)

C. refractory (rocks and metals)

Which of the following is not an advantage of CCD cameras over photographic plates? A. their quantum efficiency is higher B. the integration time can be longer C. they turn photons into protons D. they can capture information at wavelengths beyond the visible

C. they turn photons into protons

Which of the following is the biggest disadvantage of putting a telescope in space? A. Astronomers don't have as much control in choosing what to observe. B. Astronomers have to wait until the telescopes come back to Earth to get their images. C. Space telescopes can only observe in certain parts of the electromagnetic spectrum. D. Space telescopes are much more expensive and riskier than similar ground-based telescopes.

D. Space telescopes are much more expensive and riskier than similar ground-based telescopes

Through which material does light travel the fastest? A. glass B. plastic C. a superconductor D. a vacuum

D. a vacuum

where are telescopes currently not located? A. on Earth B. in low Earth orbit C. in solar orbit D. on the Moon

D. on the moon

Sunspots appear dark because: A. they have very low density. B. magnetic fields absorb most of the light that falls on them. C. they are regions of very high pressure. D. they are cooler than their surroundings.

D. they are cooler than their surroundings.

Which layer of the Sun takes up the highest volume on the inside? A. Chromosphere B. Convective zone C. Corona D. Photosphere E. Radiative Zone

E. Radiative Zone

Which of the following is not a tool that astronomers use to study to universe? A. computers B. particle accelerators C. telescopes D. lasers E. all of the above are tools used

E. all of the above are tools used

why are some telescopes at high elevations and in space?

▪ The atmosphere does not transmit all light ▪ Nearly all X-ray, ultraviolet, and infrared wavelengths are blocked ▪ Space-based telescopes are needed for these wavelengths.