Astronomy Unit 4
Rare earth hypothesis
The specific circumstances that have made it possible for evolution to progress beyond microbes to complex creatures might be so rare that ours might be the only inhabited planet in the galaxy that harbors anything beyond simplest life
How was the spectral sequence OBAFGKM discovered?
The spectral sequence was discovered by examining patterns of absorption lines in spectra of thousands of stars. The original sequence was based on the strength of the hydrogen lines. Annie Jump Cannon reorganized the sequence to be the familiar OBAFGKM that is still used today.
How did SETI begin?
Although there were some attempts at radio contact w/ aliens in the early twentieth century, in retrospect we know that these efforts were doomed because they used frequencies that are blocked by Earth's ionosphere and because they focused on nearby worlds like Mars, where complex life is unlikely to exist. The origin of modern SETI is generally credited to ideas proposed by physicists Giuseppe Cocconi and Philip Morrison. Frank Drake's Project Ozma was the first organized search.
What is Saturn V
a chemical rocket that had 3 stages: burned liquid oxygen and kerosene
Sentinel hypothesis
a sophisticated galactic civilization might reveal itself to new societies only after they reach a certain level of technology
What is indirect evidence of for extrasolar planets?
precise measurements of a star's properties may indirectly reveal the effects of orbiting planets
What does it mean if the doppler shift is a blueshift
Because shorter wavelengths of visible light are bluer, the Doppler shift of a star coming toward us is called a blueshift
Matter-antimatter annihilation
an event that occurs when a particle of matter and a particle of antimatter meet and convert all of their mass-energy to photons
zoo hypothesis
civilizations are aware of our presence but have deliberately chosen to keep us in the dark
How are hot Jupiters found
doppler technique
significance of 1420 MHz
frequency at which neutral H gas produces a natural radio static
Einstein's special theory of relativity
it's impossible to travel through space faster than the speed of light
What determines the properties of a star?
it's mass
Where is everybody?
leads to the Fermi paradox
What does luminosity of a star mean?
luminosity tells us how brightly the star shines and how rapidly it is fusing its hydrogen
What are the implications of the Fermi paradox for human civilization
- 1st solution: implies we're the only piece of the universe that has ever attained self-awareness - 2nd: civilizations either change or destroy themselves before attaining the ability to travel to the stars - 3rd: we might someday meet up with a galactic civilization that predates us by millions or billions of years.
Briefly summarize the life cycles of stars from birth to death
- A star forms from a large, cold interstellar molecular cloud. - As the cloud collapses, the interior gets denser and hotter. Eventually, if the protostar is massive enough, the temperatures are sufficiently hot for fusion reactions to initiate. This marks the birth of the star. - The star spends majority of lifetime in stable hydrogen fusion (the Main Sequence). At some point, the hydrogen in the core is exhausted and the fusion reaction will cease. - At that point, the weight of the star's outer layers is able compress the star's core. The core's temperature goes up and hydrogen begins to fuse in a shell around the core. That combination produces enough energy to cause the star to expand and become more luminous. At that point the star becomes a red giant. - When the core temperature increases enough, the helium by-product of hydrogen fusion begins to fuse in the core. That stops the core collapse and pushes the hydrogen fusion shell outwards in the star - The combined effect causes the luminosity of the star to decrease bit, the star's size decreases and temperature increases. At some later time, the helium is exhausted in the core and the process repeats. However, whether the core will ever get hot enough for new fusion reactions depends on the mass of the star. - For stars less massive than about 8M the shell burning becomes unstable and the atmosphere of the star is ejected forming a planetary nebula. The remnant core becomes a white dwarf. Stars more massive than about 8M explode as supernovae.
Why do SETI researchers assume that beacon signals would be designed for easy decoding and how might we recognize them?
- An assumption underlying SETI is that an alien civilization would send a signal designed to be detected and understood. - Whether we would be clever enough to understand a message from a more advanced civilization, or even know if we had received one, is debatable. - An alien signal would have characteristics that demonstrate that it clearly originates in outer space. For example, the source would have a sidereal rather than a synodic period and we would expect to see a Doppler effect in the signal's frequency. -Beyond that, we make some assumptions about an intentional signal's characteristics. We assume that it would be a narrow band signal which would be easier to detect and cheaper to send, it might have a pattern of some kind to it, and it might be repetitious. - All of these characteristics would suggest that the signal is not from a natural source in space. We also assume that the message content would be based on understanding mathematics and physics.
Why are the hot Jupiters surprising?
- Based on our model of solar system formation, massive planets would form beyond the "frost line" where there would be substantial amounts of ice as well as rock to accrete. - more massive protoplanets would be better able to hold on to gas as well, resulting in the gas giants in our solar system. - Terrestrial planets form closer to the Sun where the ices sublimate so only the rocks accrete.
Would other civilizations really colonize the galaxy?
- Based on the idea that other beings would have evolved in response to evolutionary pressures similar to those that led to human evolution on Earth, would expect other civilizations have the same inherent drive to colonize that we seem to possess. - If so, a civilization should be able to colonize the galaxy in a time that is short compared to the age of the universe, even with technology not much beyond our own.
Is there a case for alien visits?
- Based on the tenets of science, there is no current case for alien visits to Earth, either past or present. - Keep in mind, however, that absence of evidence is not evidence of absence. If civilizations really are common, then it is conceivable that some aliens have come our way.
how and why did the Hertzsprung-Russel diagram develop?
- By the beginning of the twentieth century, astronomers had methods for measuring both the intrinsic luminosities and the colors (which are related to surface temperatures) of stars. Ejnar Hertzsprung in Denmark and Henry Norris Russel in the United States independently realized that classifying stars by plotting these two easily observed quantities clustered the stars into groupings. The graph based on these quantities is now called the Hertzsprung-Russel Diagram
Will intelligence inevitable spawn technology?
- Certainly, there are some species with physical limitations, such as a lack of hands, that would seem to prevent the development of technology. But our own case is ambiguous: it took us a long time to develop technology, but we - don't know if this means the development was a fortunate accident or something destined to have eventually happened.
Why is interstellar travel so difficult?
- Convenient interstellar travel is beyond our technological capabilities - Current spacecraft would take more than 100,000 years just to traverse the distance to the nearest stars. - The energy requirements for sending people on interstellar trips are enormous, so far greater than all current world energy usage.
How might we build interstellar spacecraft with "conventional" technology?
- nuclear rocket engines, solar sails, and ion engines - in principle could build starships that travel at speeds up to about 10% of the speed of light—fast enough to reach nearby stars in less than a century.
Super-Earth
- Designated based on mass originally - Kepler added radius as a property
Stars brightness depends on
- Distance, intrinsic luminosity, dimming effects of any interstellar dust that might lie between us and the star
What does the rare earth hypothesis suggest?
- Earth-like planets can form only in relatively small regions of the Milky Way galaxy - Argue there is a small narrow ring at about our solar system's distance in the MW that makes up a galactic habitable zone - according to the arguments for a galactic habitable zone, outer regions of our galaxy are unlikely to have terrestrial planets b/c of low abundance of elements beside H and He - impact rates and Jupiter are another issue
What evidence supports Einstein's theory?
- Experiments with light confirm that its speed is always the same. - Experiments with subatomic particles in particle accelerators confirm the predication of time dilation and mass increase at speeds close to the speed of light - time dilation has been verified at relatively low speeds in aircraft and spacecraft - Nuclear power plants and bombs release energy in accordance with the formula E=mc2, which is also a prediction of special relativity.
How would we detect life on extrasolar planets?
- Future telescopes would allow us to obtain crude images or spectra of planets within stellar habitable zones. - An image of an extrasolar planet—even if only a few pixels in size—might indicate the presence of snow or clouds, and would tell us the planet's rotation period. - Spectroscopic analysis: might reveal combinations of atmospheric gases, such as oxygen and methane, that would be evidence for life.
For the 3 general categories of broadcast signal, what are the current prospects for detecting each type of signal through SETI efforts?
- Given our technology, first two would most likely not be detectable because the signals would be too weak unless the alien civilization happened to be quite nearby. - If an alien civilization intentionally broadcast a signal with the intent that it be detected, we would presumably have a better chance. That's the premise behind SETI.
How might future images and spectroscopy allow us to determine whether distant planets are habitable or have life?
- If we can measure the spectrum of the atmosphere of an exoplanet, we could determine what gases are present. - We could also be able to make an estimate of the temperature. - Gases like methane and especially oxygen in sufficient quantity would suggest that life is present. - Our current technology allows us to detect organics and evidence of water vapor in the atmospheres of some exoplanets. - Eventually, we might have imaging capability that would allow us to look for evidence of land masses or oceans. We might be able to distinguish seasons due to changes in cloud or ice cover.
Why do infrared observations help?
- In the visible part of the spectrum, the contrast can be as much as 10 orders of magnitude. - In the infrared, the brightness difference is still large, but not as large as in the visible (maybe 5 orders of magnitude). - Also, the distance between a planet and its star is an extremely small angular size as seen from the Earth.
contrast the doppler technique's advantages and limitations.
- It requires precise measurements of the positions of lines in the star's spectrum since the effects are generally small. - Since it can only measures the velocity in the line of sight, the geometry has to be right in order for the technique to work. - it's more likely to detect planets with shorter periods.
What role does Jupiter play with impact rates
- Jupiter's large size causes comets to go into different directions - If Jupiter did not exist, comets might have remained in the part of the solar system that could put Earth in danger
What are some features that make earth seem "lucky"
- Jupiter--impact rates - climate stability: plate tectonics, large moon
Are there ways around the speed of light limitation?
- No known physical laws prevent hyperspace, wormholes, or warp drive from offering "loopholes" from one place to another - don't know if these are possible
Could we travel to the stars with existing rockets?
- No. almost all rockets are chemical rocket engines - these types of engines can't to speeds of even 1% of the speed of light - impractical for interstellar travel
Which stars would make good suns?
- O/B lifetimes are too short to permit life to arise on surrounding planets - A/F stars may live long enough for life to evolve, probably not long enough for intelligent life. - G stars like the Sun clearly can have habitable planets. - K/M stars have small habitable zones, but makes up for that in their sheer numbers, since they are the most common types of stars. Many stars are members of multiple stars systems, but they may still have habitable planets in stable orbits
3 distinct categories of civilizations
- Planetary (or Type I): use the resources of their home planet - Stellar (type II): corral the resources of their home star - Galactic (type III): employ the resources of their entire galaxy
galactic contraints
- Rare earth hypothesis suggest Earth-like planets can form only in relatively small regions of the Milky Way Galaxy - Argue there is a small narrow ring at about our solar system's distance in the Milky way that makes up a galactic habitable zone - According to the arguments for a galactic habitable zone, outer regions of our galaxy are unlikely to have terrestrial planets b/c of low abundance of elements besides H and He - Impact rates and Jupiter are another issue
Plausble/not: A brilliant teenager working in her garage discovers a way to build a rocket that burns coal as its fuel and can travel half the speed of light.
- not plausible. - energy released from coal burning would not be enough to power a rocket, let alone achieve travel at half the speed of light.
How do we search for intelligence today?
- SETI searches for either radio or optical signals transmitted by distant civilizations. - There may be other means of interstellar communication, but it seems reasonable to suppose that radio or optical signals will be used by at least some, if not all, other technological societies. - Current signal detection efforts are probably sensitive enough to find only deliberately broadcast beacon signals.
What have they taught us about the formation of planetary systems?
- Since we find massive planets close to some stars, either this model is wrong or there must be a way for massive planets to form farther from the star but migrate inwards. - migration may be common b/c interactions between disk material and young planets which would change the planets' orbits - Close encounters b/w planets could also cause orbits to change. Simulations indicate that planetary migration probably happened in our young solar system. Simulations also suggest that migration of massive planets would have a disruptive effect on smaller planets' orbits, either inhibiting their formation or ejecting the smaller planets completely from the system or causing them to orbit into the star.
Why, so far at least, do claims about alien visitation on Earth seem not to reach the level of scientific evidence?
- So far, we have no unequivocal evidence that aliens have visited the Earth. - Without physical evidence, the claims cannot be evaluated scientifically.
What is "relative" about relativity?
- Special relativity: tells us motion is relative, but everyone always agrees on the speed of light. - From this it follows that different observers can measure time, distance, and mass differently, and that no material object can reach or exceed the speed of light.
What future technologies or missions should improve our ability to detect planets directly?
- Telescopes in orbit have the potential to achieve better resolution and infrared sensitivity than current technology which would improve the likelihood of direct imaging of extrasolar planets. - Advancements in ground-based telescopes, such as segmented mirrors and adaptive optics along with advanced data processing techniques, have also enabled the direct detection of exoplanets.
What is the value of the Drake equation?
- The Drake equation helps us to think about the factors that would be important in estimating the likelihood of there being other intelligent civilizations.
How can we use transits to find extrasolar planets?
- The Kepler spacecraft monitored 100,000s of stars to look for variations in brightness that could be the result of a planet in transit. - brightness changes are very small when transits happen, the geometry has to be correct for a transit to be detected. - There are some characteristics intrinsic to stars that cause their brightness to change a small amount and - so generally Doppler effect measurements are used to confirm whether the change in brightness is really due to a transiting planet.
What happens if SETI succeeds?
- The scientific and technological issues of SETI are important but may well pale in comparison to the societal issues if a signal is found. - an important part of SETI work involves thinking about what will happen if the search ultimately proves successful.
What is convergent evolution
- The tendency of organisms of different evolutionary backgrounds that occupy similar ecological niches to resemble one another - ex. vision, shape of large marine predators
What are possible solutions to the Fermi paradox?
- There are three general categories of solution to the fermi paradox: 1. We are alone 2. Civilizations are common, but no one has colonized the galaxy 3. There is a galactic civilization, but it has deliberately avoided revealing its existence to us.
For the Drake equation, describe the current state of understanding regarding the possible values of each term
- We can estimate the star formation rate in the Milky Way - we are now able to get a decent estimate of the number of stars that have planets, as well as some idea of the number of planets per star. - The number that could support life is more uncertain and we have no real idea what fraction actually have life or whether there are any advanced life forms. - L is also highly uncertain because we only have been an advanced civilization for a short time and we have no basis for being able to reliably estimate for how long an advanced civilization might exist.
Are Earth-like planets rare or common?
- We don't know. - Some of the key questions are whether our galaxy, like a star, has a relatively narrow habitable zone, whether the role Jupiter has played in lowering our solar system's impact rate is rare or critical to life and whether Earth's relatively stable climate, due largely to plate tectonics and our large moon, is rarely found on otherwise similar worlds. Arguments can be made on both sides of each question, and at present we lack the data to determine which side is correct.
Discuss the prospects of finding habitable worlds in systems with hot Jupiters.
- We don't yet have sufficient observations to know whether terrestrial type planets are found in systems with "hot Jupiters"
What do we mean by "hot Jupiters."
- also find a large number of massive planets in orbits close to their stars. - called "hot Jupiters". Based on how we think solar systems form, we wouldn't expect massive stars to form near stars. - Therefore, we consider models where the planets form farther out and migrate in towards the star.
Even if life is widespread is intelligence common? 1st view:
- biology might be widespread but the evolution of technological intelligence extremely rare - Our existence seems to have resulted from a number of chance events (Cambrian explosion, snowball earth episodes, massive asteroid strikes, K-T impact--mammals)
Properties of Hot jupiters
- close in orbits - highly elliptical - very hot - unlikely to be habitable
Kepler discover mission
- designed to survey one region of the MW to detect and characterize hundreds of Earth-size and smaller planets in or near the habitable zone - uses transit method to detect exoplanets
Why is the direct detection of extrasolar planets so difficult?
- difficult because the difference in brightness between a planet and its star is so great.
How well do we know the terms of the Drake equation?
- don't know the values of any of the terms well - have some data from extrasolar planets that can allow us to make at least an educated guess about the first term, NHP; it seems likely to be quite large, perhaps 100 billion or more habitable planets in our galaxy. - For the rest of the terms, we have only the example of Earth to look to, making any guesses far more uncertain
Even if life is widespread, is intelligence common?
- don't know, b/c only have the example of Earth - Nevertheless, evolutionary studies indicate at least some drive toward intelligence, so it is at least plausible to imagine intelligence appearing on any planet with life, at least if given enough time.
Briefly discuss some of the issues that would surround an actual SETI detection.
- first issues = confirm the signal is real, originates in outer space, and is artificial - current plan: make the knowledge of the detection public, and to seek independent verification. - There is an agreement among the participants in the International Academy of Astronautics regarding how to proceed: protect the frequency, archive the data, and agreeing that no response would be sent prior to some sort of international consultation. - One other issue would be whether we would ever be able to decode an intelligible message in an alien signal.
What is the Drake equation?
- gives us a way to organize our thinking about the question of the number of civilizations in the Milky Way Galaxy - In its modified form, says that the number of civilizations with which we could potentially communicate is N = NHP x flife x fciv x fnow - Where NH is the number of habitable planets in the galaxy - flife = fraction of habitable planets that actually have life on them - fciv = fraction of lifebearing planets on which a civilization capable of interstellar communication has at some time arisen - fnow = fraction of all these civilizations that exist now.
Plausble/not: Aliens from a distant star system invade Earth with the intent to destroy us and occupy our planet, but we successfully fight them off when their technology proves no match for ours.
- implausible - Any advanced civilization that could travel to Earth would necessarily have technology far beyond what we have and we would stand no chance if they chose to invade. - Perhaps our best defense would be like in "War of the Worlds" where they would be susceptible to our Earth diseases, although a truly advanced civilization would probably have thought about and planned for that problem.
Plausble/not: In the year 2011, we finally uncover definitive evidence of alien visits to Earth when a flying saucer crashes in the Rocky Mountains and its oxygen-kerosene fuel ignites a forest fire.
- implausible. - An advanced technology would not use oxygen-kerosene rockets. - Interstellar travel with that technology would be highly improbable - An advanced civilization would have found a way to travel that was much more efficient.
Plausble/not: In the year 2750, we receive a signal from a civilization around a nearby star telling us that the Voyager 2 spacecraft recently crash landed on its planet.
- implausible. - likelihood of Voyager ever encountering any star system in the Milky Way is very low. - at the speed Voyager travels it would take much longer than 700 years to get to the nearest star, even if it were headed in the direction of the Alpha Centauri system (which it isn't).
Dyson spheres
- in principle, a technologically adept civilization could capture all of its star's energy by fashioning a large, thin-walled sphere around its solar system and covering the inner surface with solar cells or their equivalent
What have we learned from UFO sightings?
- learned people see things in the sky that they cannot identify or explain, but we have not found any convincing evidence pointing toward an alien origin for such sightings
Briefly discuss what we have learned about extrasolar planets.
- learned that planetary systems are relatively common. - The textbook says that at least 10% and maybe as many as 50% of stars probably have planets. - Based on what we're learning from Kepler, there's a recent study that concludes that there are at least as many planets in the Milky Way as there are stars (100 billion or more). - beginning to discover planets that are roughly Earth-sized, and some appear to be in the habitable zones around their stars.
Describe the Doppler technique by which we can measure gravitational effects of planets on stars, and contrast their advantages and limitations
- measures the changes in a star's radial velocity due to its motion about the CM due to a planet. - preferentially detects massive planets close to their stars.
Describe the astrometric technique by which we can measure gravitational effects of planets on stars
- measures the positions of stars in the sky to look for "wobbles". - Since (by Kepler's First Law) the star and the planet orbit about their common center of mass, precision observations could show the motion of the star due to its small orbit around the CM.
How do stellar life cycles affect the possibility of habitable planets?
- most basic requirement for a star to be able to support life on orbiting planets = stable long enough to allow that life to originate - limits us to stars that are in the long-lived, hydrogen-burning phases of their lives. - Giants and supergiants are stars that have used up the bulk of their core hydrogen fuel, and undergo substantial change on time scales of millions of years. not thought to be suitable for hosting planets with life.
What can we learn from the Hertzsprung-Russel diagram?
- most stars fall along a continuous swath, called the main sequence, that runs from hot, luminous stars at the upper left to cool, dim stars at the lower right. - Other stars—giants and supergiants—clump in the part of the diagram where stars are luminous but have cool surface temperatures. - The stellar corpses--white dwarfs are dim but hot, so they are found in the lower left of the diagram. - realize that mass is a star's most fundamental property, and the organizational power of the diagram makes it one of astronomy's most useful tools.
What does credible evidence look like?
- narrow bandwidth signal - repeatability - detectable over several days; independent observer confirmation -signal originates from space
Have aliens left any compelling evidence of visitation?
- none of these claims has ever withstood scientific scrutiny.
Discuss several types of claims about alien visitation on Earth.
- numerous reports of UFO sightings. - Although some people assume that UFOs are alien spacecraft, UFO means Unidentified Flying Objects. They are unidentified. - Some individuals have claimed abduction by alien visitors. People such as Erich von Daniken have claimed to have found evidence in artifacts or artwork that alien visitations took place and provided assistance to past civilizations.
gravitational lensing
- one object's gravity bends or brightens the light of a more distant object - allows us to detect planets far away, but the special alignment of stars required for its application never repeats, so generally no opportunity for follow-up observation
Define each of its terms
- original Drake equation, N= R* x Fp x Ne x Fl x Fi x Fe x L - N = # of intelligent civilizations - R* = average star formation rate in the Milky Way - Fp = fraction of stars that have planets - Ne = # of planets that could support life per star that has planets - Fl = fraction of those planets that have life - Fi = fraction of the planets with life that have intelligent life - Fc = fraction of intelligent civilizations that actually communicate - L = lifetime of a communicating civilization.
What is the fermi paradox
- our general assumption that Earth is not unique leads us to expect that many other civilizations should by now have arisen and had the opportunity to colonize the Milky Way Galaxy. Yet we see no evidence of a galactic civilization.
What have learned about extrasolar planets?
- planets are common. - other surprises, such as hot Jupiters—jovian planets that orbit close to their stars.
Plausble/not: Human colonization of the moons of Saturn occurs using spaceships powered by dropping nuclear bombs out of the backs of the ships.
- plausible. - Designs for spacecraft using nuclear bombs as a source of propulsion have been around for at least 50 years. - It would have both high thrust and high efficiency allowing for the transport of significant mass. - However, such a spacecraft would be prohibited at the present time by nuclear test ban treaties. If it could be done, it might be the most productive way to use existing stockpiles of nuclear weapons. - Colonization of the moons of Saturn might seem implausible, but in class I showed you some concepts that NASA has thought about for setting up a colony on Calisto that would be a base for exploration of the outer solar system.
Pulsar Timing method
- pulsars emit radio waves as they rotate - method was not designed for the detection of planets. It is so sensitive tho, that is capable of detecting planets far smaller than any other method can, down to less than a tenth the mass of Earth
targeted search
- radio telescope that is pointed in selected directions such as toward individual stars - assumes that not all locations in space are equally probable sites for Intel. life
contrast astrometric technique's advantages and limitations.
- requires very accurate measurements, which are hard to do - more effective looking for planets around nearby stars. - Due to the high precision required for this method to be successful, no planet has been conclusively discovered by the astrometric method (from the ground) - It's more likely to detect a massive planet far from its star where the effect would be more evident.
Based on Table 11.1, briefly summarize how the properties of hydrogen-fusing stars change as you look down the sequence from O to M.
- spectral sequence is a temperature sequence. - For stars on the main sequence (hydrogen- fusing) as you go from O to M, the star masses decrease, the star radii decrease, temperatures decrease and the lifetimes get longer. The number of stars in each spectral class increases from O to M; viz., cool, small stars are the most abundant.
How do we categorize stars?
- spectral sequence: OBAFGKM runs from hot to cool in terms of the surface temperatures of stars - For stars in their hydrogen-fusing phases, this sequence also runs in mass order. - O stars are the hottest, most massive, most luminous, and shortest lived. - The Sun is a G star, and the far end of the scale has the cool, dim, low-mas, and long-lived M stars.
How might we build spacecraft that could approach the speed of light?
- tech is beyond us - matter-antimatter engines and interstellar ramjets that scoop up fuel as they go
Direct imaging
- tend to find planets that are bright in the IR and farther from their star - very high resolution is required to separate the planet from its nearby host
At which stage of stellar life does it seem possible that life-bearing planets would exist?
- the main sequence. During that time, the star is stable and the main sequence stage lasts long enough for life to get started and to evolve on a planet with the right conditions
Even if life is widespread is intelligence common? 2nd view:
- there is evolutionary pressure for intelligence - various evolutionary mechanisms consistently encourage an increase in intelligence for a wide range of species
How do we detect planets around other stars?
- two fundamental methods for detecting extrasolar planets = direct observation and measuring their indirect effects.
What is a transit?
- when a planet passes in front of its star which causes some of the starlight to be blocked so we would observe a decrease in the brightness of the star that was periodic.
Brown dwarfs
-Substellar objects, very dim and difficult to detect (like a failed star) -no habitable zones - some have planets
"evidence" found of aliens
-phoenix 2008: 4 lights seen over phoenix - the mantle incident: a pilot lost his life chasing a UFO in 1948. people believe he was killed by a blue beam from a UFO - project blue book - Roswell incident
Sky survey
-radio telescope that is swept across the heavens to study a larger section of the sky - makes no assumption where aliens might be
3 categories of signals
1. Signals used for local communication on the world where intelligent beings live. (radio, tv signals, radar) 2. Signals used for communication b/w a civilization's home world and some other site, like a colony or spacecraft on another world 3. intentional signal beacons, like ones searched by project Ozma
What are the absolutes of the theory of relativity
1. the laws of nature are the same for everyone 2. the speed of light is the same for everyone
Binary star systems
2 stars
Downside of doppler shift?
Can't detect a planet whose orbit is face-on, only if it is orbiting at an angle
Microlensing
Derived from one of the insights of Einstein's theory of general relativity. Light rays are bent when passing through space that is warped by the presence of a massive object such as a star. This effect has been proven by observations of the Sun's gravitational effect on starlight
Project ozma
Drake's project searched for a deliberately broadcast signal at a specific frequency that would be known to astronomers anywhere - searched for interstellar hailing signal, or beacon
What doe sit mean if the doppler shift is a red shift
If an object is moving away from us, its light is shifted to longer wavelengths, called red shift
Planet trying to orbit between the two stars. If the distance b/w the planet and at least one of the stars is not sufficiently different form the distance b/w the two stars, its orbit will not be stable
Not stable
Project Orion
One way to get a rocket to much higher speed would be to toss small nuclear (fusion) bombs out the rear and let the resulting explosion push the craft forward
A planet could orbit one star or the other. If the two stars are themselves widely separated, then a planet near either one can orbit steadily because it will feel little disturbing effect from the second star.
Potentially stable
Planet could orbit around both stars. IF the planets orbits the stellar pair at a distance greater than the separation between the two stars, then gravitationally the two stars act much as one and the planet can orbit w/o disruption around its distant twin hosts
Potentially stable
What makes interstellar travel so hard?
Vast distance
What two techniques are used to look for a planet's gravitational effect?
We can look for a planet's gravitational effect on its star through the - astrometric technique: looks for small shifts in stellar positions - Doppler technique: looks for the back-and-forth motion of stars revealed by Doppler shifts. - We can also search for transits in which a system becomes slightly dimmer as a planet passes in front of its star.
Project Rover
aimed to develop nuclear fission reactors that could be flown in a rocket
What does the energy required to put an object in motion depend on?
an Object's mass and the speed with which you want it to move
Why can't you exceed the speed of light
as the mass approaches infinite as the ship's speed nears the speed of light--no force in the universe can give a push to an infinite mass
What does mass of a star mean?
how much H fuel it has available for fusion
Are most extrasolar planet detection indirect or direct
indirect
interstellar ramjets
o Collect fuel as it goes, using a giant scoop to sweep up interstellar gas b/c it would be mostly H funneled into a nuclear reactor, fused into helium, and the expelled ut the back to propel the ship
Coral model
overall result is a gradually expanding region in which all habitable planets are colonized
What is direct evidence of for extrasolar planets?
pictures or spectra of the planets themselves consititue direct evidence of their existence
the more massive the star.....
shorter the lifetime
What is the purpose of the Hertzsprung-Russel diagram?
show the relationship b/w luminosity and surface temperature
Doppler and transit technique require planets...
to be close to a parent star
multiple star systems
two or more stars orbit each other closely
time dilation
when a spaceship travels at close to the speed of light, its length becomes noticeable greater, and time measure aboard proceeds slower than time measured by clocks at rest
