Chapter 1 INTRODUCTION ∙ Definition of astronomy: science studying celestial bodies. Studies everything beyond earths atmosphere. Everything inside the atmosphere does not concern astronomy ∙ Object of astronomy: universe as whole. Nearest astronomy object is the moon Astronomy/astrophysics: understanding universe from phDon't forget about the age old question of What do you mean by improper integrals?
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ysics. physical processes in detail of the astronomy, the astronomy in somewhere in between experimental and theory. They are equivalent but astronomers are more traditional, not in full detail of some kind ∙ It's not the same as astrology Astronomy is an observational science. They still rely on observation, on what the telescope tells the,. They use the eyes to explore the universe (only tool before technology came in). Today, astronomy counts with technology to see deeper into space, father away in space. Pluto was considered until 2006, the night planet. Scientists considered it after 2006 a dwarf planet. All they knew of Pluto was from photos (it was this tiny mass compared to the other planets). In the actuality there's a research investigation for Jupiter to find out about the magnetosphere and chemical elements of this planet. MILKY WAY ∙ Iis made of stars but Greeks thought there was actually a band of milk in the universe so the name was kept. ∙ Universe is expanding. Galaxies are the main consistencies of groups in the universe. ∙ Filamentary structure- complicated network of filaments, this is the structure of the universe. Filaments represent the places in the universe where the density is higher and the ones that are "empty" spaces. Cosmology- astronomy in a larger scale. Cosmologers are studying a much deep focus of the universe. They study these complicated networks. ∙ The universe had a beginning. This expansion leads to the idea that everything originated from one central point. One origin. According to our observations, all coincides. It is still expanding DETECTING GALAXIES FROM HUMAN EYE ∙ It is possible to detect galaxies from eye. Even from EP. We don't need a telescope to spot different sources.∙ Stars are the most abundant element from our sky. ∙ The greatest is the sun, but it is only one among billions at the Milky Way. ∙ If we would be at the center of the Galaxy, there would be no concept of night, all stars would be shining and there would not be a night period because of the concentration of the stars. ∙ We're not at the center of the Milky Way. ∙ Only the brightest objects can be identified by the human eye. It is close to us, it is big. ∙ We are all astronomical bodies. All objects from space rise from East to West. All stars, galaxies, planets, etc. it is called the daily motion. This is the sense of motion. NORTH CELESTIAL POLE ∙ Many methods for astronomy come from Greeks. We imagine all objects in a spherical model. The movement is slowly, takes 24 hrs to complete motion. Stars are supposed to be attached to this sphere. ∙ Celestial sphere was introduced by Greeks in order to explain the motion of the elements of the sky (North Pole Sphere). Movement is from East to West. We place ourselves at the center of the universe in order to make this calculations. ∙ Greeks also introduced the idea of axis of rotation, imaginary line that passes through the center of the earth. Imagine the axis is infinite and cuts the sphere of the earth and touched the points of north and south. This is an imaginary device (all of this is imaginary). Chapter 2 DIFFERENT OBJECTS IN THE UNIVERSE ∙ Constellations are patterns of bright stars that are defined with the human eye that are associated with objects here in earth ∙ North Star is real. It happens to be located almost at the same location of the north celestial pole. Poles are the only points that show no motion (from the sphere), they remain static. 33 degrees high in the sky (we begin at the horizon, ground. This term is used to see what we can see from this ground line, we can only see half of the universe then). According to the hemispheres, there's an angle of 32 degrees up and then you'll see the North Star. ∙ If you're at south, you'll never see the North Star. It's impossible. ∙ If you're at Ecuador, you're 0 degree angle. The North Star will be 0 degree high. But in practical terms, it's impossible to see it because of buildings and other "distractions." ∙ If you want to verify the true shape of an object you can identify the connection of the North Star and the earth, a spherical planet∙ Earth’s shape justifies because of this connection (North Star and an object throughout the different angles of the earth) ∙ Constellations: we don't need telescopes to identify them because they are simply groups of stars (patterns of stars identified by human eye). Different civilizations names these constellations according to their heroes and we have kept their names. ∙ Around noon, the objects are at their highest point in the sky ∙ Sun, moon, Venus, are the brightest objects respectively. ∙ Venus is the closest planet to us. It's surrounded by CO2 gas all the time. His clouds reflect the sun light very well. You'll be able to see it from night sky ∙ 88 constellations in total ∙ North Star name is Aplha Ursae Minoris (Polaris) ∙ We name stars alphabetically using Greek alphabet (alpha. Beta... ∙ Jupiter can be seen from the South Pole ∙ There are only south points from the North Pole ∙ Cassiopeia and The Big Dipper, closest constellations to North Star. These constellations are detectable because of their bright and size. ∙ We don't have the equivalent of the southern hemisphere of the North Star ∙ We can see planets from earth, planets move differently than stars. Both of them rise in east, but if you track the motion of a planet against the star background, planets contrast the movement of the stars, we can see 5 planets because they are bright, Mercury Venus Mars Jupiter and Saturn can be seen from earth. They appear bright enough to be detected. The other planets are further and too thin to be detected by eye, but with telescope they're detectable ∙ We can also see comets by human eye. Comets consist of head and tale. DETECTING WITH THE EYE ∙ It's possible to detect few galaxies from human eye. Andromeda is the nearest galaxy to us, about 2 million ____, from Southern Hemisphere we can see the two Magellanic Clouds (satellites). ∙ Milky Way is in the shape of a disk, a flat disk ∙ The objects that have just emerged, are the closest. The objects that rose before are far away. ∙ Objects passing through zenith means they are at their highest point. ∙ The all reach their highest points when they pass to the meridian line NORTH STAR OBSERVATIONS ∙ From North Pole, objects are rounding ∙ From equator, objects straight up and straight down ∙ From horizon, they rise and set at a certain inclinationCIRCUMPOLAR STARS ∙ Most of the stats rise and set, they remain visible for several hours and invisible the rest of the day. But there are other stars that are always at the horizon that don't rise nor set. Circumpolar stars are an example of this. Stars that rise remain visible and they set and remain invisible. Stars that remain at the horizon are circumpolar ∙ This doesn't imply that we can always see them. ∙ Sun and moon are only visible objects in the day. Other stars are undetectable during the day. Farther away from the North Star, the bigger the circle of these stars make. ∙ If the circle is bigger, one section of the trajectory may touch the horizon. ∙ We see approx. 3000 stars with our eyes at night from any location on earth LOCATION OF OBJECTS ∙ A problem in astronomy was always to position objects in the sky, in order to locate them. ∙ One way to position them is to name the constellation in which they are. ∙ Local celestial coordinates: another way of locating objects in the sky. We measure from the horizon ∙ Altitude: the height technical term in astronomy. Vertical angle measured vertically. Measured in degrees. From 0-90 degrees ∙ We locate objects in earth according to the altitude (vertical angles), or meridians (vertical line). Because of this, we have western latitudes and eastern latitudes. ∙ Azimuth: horizontal angle measured from the north. Geographers use this with south as the main reference for calculations, instead of north in astronomy. From 0-260 ∙ If you want to locate a star from your location, you have to know the altitude and the azimuth of the star. DIFFERENT LUMINOSITY ∙ Other problem is how to characterize the different luminosity of the stars. Not all stars appear equally bright. ∙ There's a scale introduced by the Greeks. The magnitude system, introduced by Hipparchus. It is a system when you assign a number to an object depending on its luminosity. Not an intuitive approach. In the actuality, we measure it in watts (bigger number, bigger luminosity), but in astronomy it's opposite (the bigger, the less luminosity). H was just estimating with eye observation, and named it. ∙ The human eye can only see objects brighter than Magnitude 6 objects. They define the limiting optical in the sky, they're bright enough to be detected. EXAMPLES Sun is the brightest in our sky so he has the least number -26 Moon -12.5 Venus -4.4 Sirius is the brightest star at night -1.46 Jupiter -2.5 Polaris 2.2 ∙ Planets are brighter than most stars, except Sirius ∙ Beyond Uranus, our eyes cannot detect anything. Planets are so thin that we cannot detect them ∙ Practically speaking Uranus is not visible to the naked eye because of pollution on earth. All these particles and light prevent us from detecting planets. COMPARING MAGNITUDES ∙ We use the number line to compare magnitudes. ∙ Absolute magnitude: in addition to the apparent magnitude, it measure how bright something really is. A parent is just a number that tells us how something appears too bright, but he absolute. Sometimes these two differ. It depends on the question. ∙ If you're asked on how bright something LOOKS (appears), you are asked about the apparent magnitude. If you're asked about how bright something IS, you're asked the absolute magnitude. ∙ By comparing these two magnitudes, we can determine the star's distance from earth. ∙ Light year is the distance covered by light in one year. Apparent is represented as m, absolute is represented as M ∙ If two magnitudes are the same, that object is exactly 10 pc away (PC is unit in astronomy close to 3 light years). ∙ When apparent is less than absolute, the star is closer to 10 pc. The object is less than 10 pc. ∙ When apparent is greater than absolute, the distance is farther than 10 pc. All of these are approximations.∙ Smaller number is the brighter star. JUSTIFICATION OF THE EARTH’S SHAPE ∙ Pythagoras thought that since the moon and sun appear to us as flat, but are really round, the same conclusion could be driven to the earth’s shape ∙ If you would see a curved shadow to the moon, it is the earth’s shadow ∙ During an eclipse, we can confirm the earth shape because the shadow of the earth is round. MEASURING THE SIZE OF A PLANET ∙ Eratosthenes logically came to the conclusion the earths shape was a circumference. ∙ He worked at the library all day and he was accustomed to the different papers of scholars back then. From everything. He was in charge of the library. So he found people leaving outside from Alexandria, they reported having seen the sun during the longest day of the year (summer solstice), sun was at zenith. His comments cousin was that the earth was round due to the relationship of those two comparisons of cities and observers of sun. ∙ He got as an answer 40,000 km as the circumference of the earth planet, which is pretty good estimate. ∙ Antipode is the exact same location but in the opposite hemisphere ∙ We can drag the conclusion that people are sometimes upside down, but we don't feel that, we just the sky above us. But this is because we tend to think there is a universe with an up and down direction, there's no way to measure up and down directions in universe. These make sense only when we're standing on an astronomical object, like the horizon, or Jupiter's surface. Up and down parameters change depending on our locations. ∙ Down-direction to the center of the object you're standing. Only correct definition in astronomy. ∙ Stars don't fall on us because we're too far away, ∙ Scholars agreed the circle is perfect, this is the shape of the universe, circular shapes are objects of the universe ∙ Movement of the earth is translation and rotation ∙ Perihelion- defines the point in which our planet is closest to the sun ∙ Aphelion- point where earth is furthest from the sun ASTRONOMICAL UNITS This is the astronomical unit- average distance from our plants to the sun 1 au - 149.6 million km average distance from our planet to sun DIFFERENCE BETWEEN STARS AND PLANETS, ∙ Planets are brighter than stars because they are closer to us (distance)∙ Another difference is their motion. Although everything is from east to west, there is a subtle difference between planets and stars. Planets move against the motion of stars. They move up when stars move down. ∙ Constellations remain the same after thousands of years. ∙ Stars appear fixed, just as constellations. But planets do move. All three move but different. These are observations from one planet to the sky. MODELS OF THE UNIVERSE ∙ Some scientists believe there should be a coherent model for what we see in the universe. Others think elements in the universe are different. ∙ Based on this observations, the first model of the visible universe was introduced by Ptolemy in the 2nd century AD. ∙ Earth-centered: the model was inspired by Aristotle’s ideas, which Aristotle believed we were the center of the universe. The model puts the earth as the center and everything moving around the earth. It's geocentric model. By the time, only 6 planets were known (Hasta Saturn). They didn't have telescopes so they didn't have access to more elements in universe. ∙ Saturn is the further planet detectable with the eye. The closest was moon and after Saturn ∙ The new model was by Nicolas Copernicus in the 16th century. It is called Sun-centered model. It came in form of a book. The earth is not the center anymore, the sun is. It is heliocentric model. With this explanation, it was easier to explain the motion of the planets. Mercury was the closest and then Venus, to the sun. You can never see Venus in the night sky, it is only visible at 6 am or 6 pm, because it follows the sun. This model simplifies planet's motion. Mercury is the fastest in moving around the sun because it is the closest planet to it. Now planets move at different speeds around the sun. The circle motion was still a thing in his model. ∙ This last model had tremendous interest from Galileo Galilei, he was the first one in using the telescope as an astronomical tool. This was in Italy 17th century, he invented it. ∙ With this, there are two discoveries that supported the second model. The first one is the discovery of the four satellites surrounding Jupiter. PHILOSOPHICAL IDEAS: ∙ Heavens represent perfection ∙ Heavens are immutable ∙ Circle is perfect shape ∙ All heaven motions must be circular then... ∙ But, at those times, the idea was that all motion was circular. But when observations demonstrated planets move differently than stars, motions are peculiar then. Greeks found observations seemed to fail if we compare the trajectory of planets circular, they weren't circular, not perfect. It was a loop, planets trace a series of loops in their trajectory. Planets move in a circular way and they have the same speed. ∙ But some Greeks didn't give up the idea of the circle ruling the trajectory, so they interpreted the loops can still be a circle. The problem was some planets had a complex trajectory that they didn't seem to fit into the theory, so it was complicated. Some thoughts raised the idea of it not being so complex, that the universe should be explained in a simpler way. ∙ Planets seem to move with the loops inside their trajectory. FACT MODELS AND CONFRONTATION The second observation became the final prove. According to Ptolemy, we shouldn't see a whole Venus from the earth, it wasn't possible. But with Copernicus, we should be able to see all possible faces of Venus, because the model allows it. Galileo just appointed his telescope to Venus and his observations showed all faces of Venus at a certain period of time. This was the ultimate proof. ∙ Aristarchus was the first scientist to propose the idea of the sun in the center and the planets surrounding it. If we stick to the first model, we explain reality using two circles, or the combination of these two. The orbits are in form of ellipses. Chapter 3 TELESCOPES Telescope was the key to demonstrate the heliocentric model of the universe. According to Ptolemy, we couldn't see all the faces of Venus, but according to Copernicus, we could see them all. So when Galileo invented his telescope and got to see all the faces, then it was confirmed. We are another planet in the solar system. But people didn't believe this. Investigations began again. Kepler comes in here. He didn't understand the idea of circular orbits around the sun, contrary to the public belief (this was a solid tradition). He noticed some observations were not consistent with this idea so he reviewed again. ∙ According to Greek geometry, there are only 5 tridimensional shapes. Kepler believed the reason why there are only 6 planets known at the time is because these 6 are nested within invisible perfect solids. This was wrong, this didn't exist in nature. TELESCOPE BIOGRAPHY ∙ 1609 by Galileo, he used it first as a tool that could open horizons for discovering the universe through observation.∙ Purpose of a telescope: to be able to collect as much light as possible so that we can create a very sharp light image to be able to collect scientific information from it. ∙ Goal is to collect light. The size of the telescope is obviously bigger than eye so it gives the viewer more proportion to collect light than the eye itself. This is the advantage. Telescope amplifies the power of human eye to observe. ∙ It was invented by Holland. But the first person to use it for astronomical purposes was Galileo. He built his own telescope and started observing the sky. It was first used by the military to see the enemy from distant areas. ∙ At the edges, we place two lenses. They are connected by a tube. It uses a convex shape to focus light. This lens collects the light and focuses it to the focus of the telescope. ∙ Galileo discovered the moons of Jupiter, the moon became a solid world with craters with Galileo opposed to the idea of a simple object in sky, he discovered sun spots (people couldn't believe the sun was not a pure object. It showed dark spots, indication of the magnetic fields), ∙ People believed celestial bodies were perfect, and Galileo took that away. He resolved the universe in different approaches (he showed the details). ∙ Resolve-ability to see details. ELLIPSES But this research let him review all of the model of the solar system to conclude that Copernicus was not entirely right about the circular orbits. He came up with ellipses instead of circles. ∙ An ellipse is an oval. It has a fixed length. Kepler has one first law: this is a universal law, refers to the ellipses trajectories do the planets. ∙ Eccentricity: ellipses have different shapes. It changes and we characterize it by introducing the concept of eccentricity. It is a measure of how much the snaps of an orbit departs from the true shape of a circle.It has large eccentricity if it is too squashing. ∙ If it is closed to a circle. It's 0. Every circle is 0 and every eccentricity is up to 1. The levels are from 0 to .999999, never exactly 1 SECOND LAW OF KEPLER When we spend attention to the speed of the planets around the sun, we noticed that the planets get closer to the sun and sometimes further away from the sun. Not at the same distance (not a circle). THIRD LAW OF KEPLER It established that the smaller the orbit, the shorts it will take the planet to complete an orbit around the sun FOUR CONIC SECTIONS Conic sections are resulting shapes after cutting a cone. They are relevant because they represent the shapes in the universe depending on the speed and energy given to an object. ∙ The first cut would be horizontal and it results in a circle ∙ The second in a little in climates and results in an ellipse ∙ The third cut is parallel to the extreme side of the cone and it results in a parabola. Parabola is unbound trajectory. It is never bound, it never closes, it is not a part of an ellipse. They are unbound and open trajectory. They come and go back to infinity. ∙ The fourth cut is done parallel to the axis of the cone and it results in an hyperbola Chapter 4 LIGHT • It has a limit in speed. • It is responsible for the creation of views of images. Light is electromagnetic phenomenon • It is a wave that propagates light from one place to another. • Modern physics tells us this is a phenomenon that is closely related to an electromagnetic wave. • Thoughts were that light was traveling to the infinity If the speed is not zero. It is finite. Physicians were able to measure long distances but not the short intervals. Galileo failed in his experiment from releasing light from one village to another. So we had to wait until this proposal: If we have to deal with long distances and short times, let's consider observation. EXPERIMENTS ∙ Let's measure distance between planets and observe. Measure the time and so astronomers turned to astronomy and measure the time of travel for light between planets. ∙ If you have a lover distance to cover, you'll have a slower movement from light to travel to that distance. ∙ Light does not travel infinitely, it is a finite speed. This was the first conclusion from this experiment. ∙ Speed of light now we know is 1.32 AU. Light can go 7.5 times per second around the earth. Speed of light is the same for all kinds of objects, including galaxies. SPEED OF LIGHT ∙ It is constant so this leads to the idea that it is used as a reference. It defines an upper limit to how fast we can travel in the universe. Light is the only phenomenon that can travel this fast, as we know so far. ∙ Light marks this speed barrier because if we say something else can travel faster than light, then we contradict. In order for the laws of nature to make sense, there must be a speed limit. This limit is the speed of light. This came from Einstein. ∙ Light behaves as a wave. It rounds objects. ∙ Sometimes it behaves as a particle, but sometimes it behaves as a wave. PROPERTIES OF LIGHT ∙ How in nature we find that light adopts different forms. They all have the same speed. The speed of light is 2hundred thousand. It takes 8 minutes. ∙ 1AU is the average distance between the earth and the sun. 8 minutes. 150 million km ∙ 186 thousand miles per second is the speed of light ∙ They all travel at the same speed but have different waves. It justifies the speed of light because we can get different combinations. You have to decrease a number as the other increases for the result to be constant. As you increase frequency, you must decrease wavelength. This gives the speed of light as a result. It represents an inverse relationship. ∙ Gama Rays represent the biggest energy given in the universe. ∙ The higher the frequency the more energy it has. Rays can carry energy as well. HUMAN EYE'S SECOND LIMITATION Human eye is sensitive enough to detect objects that are no more than 6 magnitude scale. We cannot see anything beyond magnitude 6. This is the first limitation. Second limitation has to do with light detectable directly. Optical window: ranges from 4000 to 7000 A wavelengths. It is the colors that the human eye can detect. • If our eyes see an object that has greater measures than this, we cannot see it. • Blue and red, respectively, represent the extreme colors that we can see. EXPERIMENT ∙ You start measuring the amount of energy coming from each color. Photometer a are the detectors. You measure it coming from the sun. ∙ Not all the colors of the rainbow contribute the same amount of energy, certain contribute more or less energy. ∙ Energy increases with yellow and orange colors and it goes down when red and blue show. ∙ The curves that gets because of this difference of energy contributed is attributed to the black bodies. ∙ Different stars have different temperatures, these are superficial temperatures, not the center of the object. The outer mode of the temperature of the star is the only thing that determines the color so a star ∙ If I change the temperature, we change or display the position of e curve for the red that's lower temperatures or blue the highest temperatures. CONCLUSIONS • Light from any object consists of a combination of colors. There's always a contribution from objects in colors. They're always present. • All forms of light are emerged by a black body (they admit all forms of objects) You get the same combination of colors from any object. But in different amounts. • From the graph, we can determine the pick wavelength and it will tell us about the dominant form of life because it gives us the temperature of the surface. • The dominant form of life of the sun comes in yellow and orange colors that is why the sun is yellow and orange. CONNECTION BETWEEN TEMPERATURE AND COLOR As we increase Temperatures are associated to blue colors. Cool objects emit long wavelengths (red color association). Three real stars Proxima Centauri, sun, Vega. Three stars in different temperatures and thus, different colors. Objects with lower temperature, it has lower wavelengths, red colors. If the star has a higher pick, it is brighter the star and the bluer it appears. BLACK BODIES ∙ Black body: These are perfect absorbers of light. After years, this concept change to understand it from the viewpoint of a perfect emitter of light. An object that emits all lights from the object. ∙ Black body will emit light perfectly if the temperature of the object is constant, only then, an object can become a black body.∙ Black bodies are defined by a curve that shows a behavior and a peak, the maximum height. The horizontal line of a graphic is wavelength (also understood as temperature). IN BRIEF Objects appearing in blue, have temperatures very hot Objects appearing in red have temperatures that are very cold. Temperature = surface temperature. The temperature is higher, the object is blue. Lambda max is the peak. That's how it is represented in astronomy. It is the highest point in the curve. It tells us about the temperature of the black body. WIEN'S LAW ∙ Temperature has to always be in kelvin degrees. ∙ Peak = lambda max = 3x10/ T ∙ Lambda max= wavelength in which there the peak is (meaning the highest point in the curve) ∙ 3x10 to 7 exponential is a constant. It is thirty million. ∙ Humans have to use infrared detectors which detect the heat in a human body. If both curves have the same wavelength, that means they have the same temperature, if this happens, they should have the same peak wavelength, same brightness, and same color. If the stars shown different heights only, the luminosity is what changes only due to the sizes of the stars. The vertical axis measures the luminosity, the horizontal axis measures wavelengths (temperature). ∙ Stars are much larger than planets. Fact. If the two have different wavelength, they have different temperatures, and different luminosity. ∙ Size plays a role in the different wavelengths. Size creates all these possibilities of observable black bodies in space. Luminosity= 5.67x10 to -3 exponential Chapter 5THE SOLAR SYSTEM ∙ It has a flat structure: all orbits are constrained in the same “plane.” This is a a general feature to all solar systems, this feature seems to appear when planets are orbiting around a star (solar system) ∙ The spacing between the planets is unique to just our solar system. It is geometric since its sequence is the distance of a planet will be the doubled to the next one. PLANETS ∙ They are divided in Terrestrial (Mercury, Venus, Earth, Mars) and Giants (Jupiter, Saturn, Neptune). ∙ Terrestrial planets: they have satellites, they are close to the sun, and have small masses ∙ Giant planets: they have many satellites, they are far from the sun, have bigger masses, and they have rings. ∙ Hot Jupiters: planets that have both characteristics THE SUN ∙ It is made of plasma (like every other star) ∙ Largest object in the solar system ∙ It has more mass than planets PLANETS ∙ There were just 5 planets known by ancient civilizations ∙ We can only see these same 5 planets by the naked eye ∙ Harschel reported a comet in 1700’s, but it was actually the planet Uranus. ∙ Neptuno: it was discovered using a mathematical theory. The conclusion of it was that it should be a massive object farther away from Earth. The theory was based in the law of gravitation of Newton and performed by astronomers Adams and Leverrier (they worked separately and got the same results) ∙ Pluto: is not considered a planet since 2006 because it does not have the sufficient mass to attract the ice that surrounds it. We only know about this planet because of telescopes because it is small, away from us, and not as bright. There are records of geologic activity. It is still active. SATELLITES ∙ It is the same as moons ∙ These are objects orbiting around the planets ∙ The first known satellite was our moon. The first group of satellites reported were the moons of Jupiter (Galileo).∙ Titan is the largest moon of Saturn. It is in the middle, empty space between the rings of this planet. DISCOVERING ∙ Uranus was the first planet discovered win a telescope ∙ Now, discovering new members of the solar system are discovered using the telescope and Newton’s mechanics theory ∙ There's a formula, a recipe to estimate the distance between the planets ASTEROIDS ∙ The largest asteroid discovered was Ceres. It was discovered by piazzi on Jan 1 1801 ∙ It ai a big chunk of metals that happen to be located between Mars and Jupiter. Ceres is located here. We find thousands of asteroids, a lot of them are irregular,they go around the sun, trading ellipses. ∙ Beyond Saturn, the predictions begin to fail and to not be accurate. COMETS ∙ Smaller than planets smaller than moons. Sometimes the size of a nucleus of a planet ∙ Made of ice or dirty snowballs. It is a big sphere of ice with dust ∙ They are not close to sunlight ∙ They occupy two regions in the solar system, they behave differently. ∙ 2 families: those that take less than 200 years, and those who take longer than that ∙ First region is of a disk shape, it is of ice. Dwarf planets are located inside this region. This region is abundant in ice. A tail can be as long as 1 au long, or even longer. ∙ Comets approach the sun and start evaporating, this is when they develop a tail. They trace very elongated trajectories. Comets spin as they approach to an object Chapter 6 This chapter is pretty much a review of the Earth's moon system The first section deals with the concept of stars wobbling around planets CENTER OF MASS This is the case for two gravitational objects in space. Whatever the comparison. ∙ It is also called center of gravity. ∙ It is the point of symmetry or balance for a system of gravitationally bound objects. ∙ Center of mass justifies the earth moon system Moon and earth are both orbiting one another. GRAVITY Gravity was the first force understood in science. It explains the physical reality at all scales. ∙ It depends on the interaction between mass and distance. To maximize the force of gravity, we increase the mass of the objects and decrease the distance between them. MASSES AND LOCATION Possible cases of the masses of the objects 1. Simplest most symmetric possibility happens when two objects have same mass. Here, the CM is at the mid-point (origin) between the two objects. The speed, trajectories, eccentricity are the same as well. Everything is symmetric. In numbers, this first case appears when the CM is 0. When this happens, the CM is located at the origin (mid-point between the two objects) which means the two objects have same masses. 2. When one of the masses is bigger than the other, the CM will be closer to the object with the bigger mass. There is asymmetry in their orbits. This justifies the wobble of stars around planets. In numbers, when one mass is twice the size as the other, the CM is +1/3 the distance from the origin to the heavier object. 3. When one of the masses is much greater than the other. This is the case of the solar system. The rest of the planets are in case 2, but since the Sun is heavier than all planets together (it is much greater than planets), then the sun won't move as the other planets move around it. The CM shifts to the center of the Sun. Mass ratio: the number of times an object is bigger (or more massive) than the other. EXAMPLES IN CALCULATING THE CM When calculating the CM, you will be given the mass radio. From this number, the only thing you have to do is to subtract 1 number to the mass radio, add 1 number to the mass ratio and then place your results like a fraction. For example, if you are given a mass radio of 4 (this means the heavier object is 4 times more massive than the other object)1. The CM would be calculated by, first, subtracting 1 number to the mass radio (4-1). This gives us 3. 2. Then, you have to add 1 number to the mass ratio (4+1). This gives us 5. 3. Lastly, you place your results as a fraction putting the subtraction at the top. So in fraction it is 3/5. 4. CM=3/5 THAT’S IT. Now that we got the CM, we now have to locate it in the illustration. This works almost the same as the numerical line. You have two stars at a given distance. (Let’s imagine it is symmetrical). In order to place the CM, you walk from the center of the heavier object 5 times. Once you are at that point, you then reduce from the origin 3 times. That's the CM. MOON SYSTEM ∙ The moon is outshined by the sun ∙ We see a contrast between light and shadows of the moon by the naked eye. ∙ We see also the phases by the naked eye From other civilizations, we thought of the moon as a goddess, as a strange form of god that was far from this world. But with Galileo’s observations, we discovered craters in the moon so it became something real, something that man could discover Barycenter: refers to the center of mass, or center of gravity (just another name). CENTER OF MASS After finding the CM, from the location we can say ∙ Whether the objects are at the same distance or not ∙ We also know about their speeds, ∙ The orbits are also knowledgeable because of the two ellipses, ∙ We also know that when an object is heavier than the other, the CM gets closer to the heavier object ∙ The heavier object moves slower. The orbit of the heavier object is physically closer to the CM than the orbit traced by the other object, so the heavier star must move slower as the other one will move faster to catch up, for them to complete an orbit at the same time. CM is the point in which everything moves in the system. All systems follow this model. All members from that system, every member will move around the CM In the solar system, the CM lies inside the sun, almost at the center of it. UNSTABLE AND STABLE SYSTEMS ∙ Unstable system happens when two bodies are at rest and gravity acts between them and makes them collide. ∙ But in a stable system, one of the objects has an initial velocity such that when gravity acts, the object does not collide with the other, but it allows both objects to have orbits. MOON ∙ 1 month is the time it takes the moon to go around the earth ∙ We always see the same side of the moon as seen from earth. The first explanation of this was that the moon is not spinning in itself, but a static moon is not possible, so the moon must be rotating. ∙ The real explanation of this is that the moon has movements of translation and rotation, both at the same time. A month for translation and rotation movements (synchronous rotation). ∙ The yellowish and huge appearance of the moon at 6 pm and 6 am is because when light has to pass to any planet, light has to bend into the atmosphere, so the light that the moon is reflecting becomes yellowish when it interacts with the atmosphere of the earth (it has an atmospheric effect). ∙ The moon appears huge when it is rising because of the optical effect, when the moon is rising or setting in the horizon, there's a way for us to compare it to other objects in the horizon (buildings) so this comparison creates the illusion that the moon appears bigger. But in reality it's not bigger. CONCLUSION WITH SOME FACTS ∙ Seen from earth, moon has the same angular size as the sun, half of degree each. This feature makes solar eclipses totally possible. ∙ Seen from the moon, planet earth shows phases. ∙ Earth is 81 times heavier than moon (81 is its mass ratio) ∙ Moon does not have an atmosphere, so the craters are explained. There's nothing there to erode them. There's no air, water or any wind that would wipe out surface features. Chapter 7 and 8 LIFE CYCLE OF STARS Stars have a life cycle, they eventually die. The reason of this is because stars require hydrogen to remain stable, and they create energy (their fuel). So they consume all of this energy created, so stars start expanding first (they become red Giants) and they become redder and they finally die. ∙ Our sun will die someday. According to theories, sun will not dramatically die. Like some stars explode when they die, the sun will not have that dramatic end. ∙ The age of the sun is 5 billion years, approx ∙ So if the Sun is that age, the solar system is that age too. ∙ We're still expecting the sun to evolve until it finally dies in 5 billion years more. Our sun is an intermediate star (in the middle of its age) KEPLER LAWSIn an ellipse, there are two points called focal. We move in these two points ∙ The sun is located at one of the two focal Third law: relates distance of planet from sun to its orbital period. ∙ Period in years ∙ Average distance of that planet from the sun, in AUs). ∙ Semi major axis is a half of an ellipse ∙ Focal distance is the distance from the center of the ellipse to one of the focal points inside an ellipse ∙ If the period is one year, then the planet is 1 au distant from the sun (earth) ∙ The law is not exclusive to planets. It can be applied to dwarfs or comets, or asteroids, to any bound member in the solar system CLASSIFICATION OF PLANETS ∙ Inferior planets: the ones that are inside earth orbit. Mercury and Venus ∙ Exterior planets: the ones that are outside earth orbit. Mars jupiter, Saturn Uranus Neptune We use that classification to classify planets in different alignments ∙ Conjunction: alignment, it occurs when an object happens to be in the same place of the sun in the sky. If Mercury or Venus is located in the same region in the sky as the sun, then we say they are in conjunction. ∙ The moon is in conjunction when it is new moon (invisible to us) ∙ Every planet has two possibilities of conjunction ∙ Opposition: when a planet is in the opposite direction in accordance to the sun and our view in earth The myth of Mars was born in 1877, a year in which Mars was in opposition. The planet was close to earth so we could observe better and astronomers found these channels (structures built by some civilization). QUESTIONS 1) What determines the death of a star in the SS? The lack of hydrogen that starts its inestability 2) What will the Sun become 5 billion years in the future? White dwarf planet 3) Estimate the distance of a terrestrial planets from the Sun in AU and km Distances in AU is given by Titius-Bode law starting with number 0 and 3. For km, multiply the number in AU times 150 million4) Aldebaran is red giant visible from EP in constellation Taurus. It has a radius of 30 million km. If placed at the Sun's location, would it engulf Mercury? This star is big and bright. This is one of the cases of a red giant which is big and bright. To answer this, we have to know the distance of Mercury from the Sun (AUs, which is already given by TBLaw). If a star is red giant, let's remember it is because of the lack of hydrogen, this creates deformations of stars until they die because they no longer have energy. The first process of this transformation is the expansion of the star. So, examining the size of our planet, earth is 12 thousand km as diameter. The star is about a million km across. 5) In the far future, the Sun will grow in size and ungulf the first 3 terrestrial planets. What would its size be in km? You would have to calculate this the same way as the previous questions 6) Sketch one of the possible conjunctions of Venus Conjunctions and oppositions are nothing else but alignments of planets. It happens when we see two objects in the same region of the sky. Sun earth Venus (their order) Venus sun earth (the other possible order) 7) Sketch Jupiter at opposition Only possible for remote planets (superior planets, the ones located beyond earths orbit). So it's possible to have all of those planets at opposition 8) Name two advantages of observing a planet in opposition We see in greater detail. Opposition allows us to get more information from the planet. Given the geometry, opposition means the planet is in one direction opposite to the sun, one is rising and the other is setting, so this creates greater detail 9) A planet at opposition is visible, in principle, from sunset to sunrise. For how many hours is it visible during the day? 10) How does the opposition of Mars in 1877 relates to the myth of Martians? In that year, we had good telescopes around the world. In Italy, an astronomer observed Mars during his opposition and he got to see more details since the planet got closer to the earth. He reported having seen straight lines in the surface of Mars, crisscross lines. He named it canali (channels in English), but the word was misinterpreted as canals (a structure built by a civilization like human beings). There was other Arizonan astronomer who built an observatory mainly to explore Mars, he confirmed the channels, he drew maps, he named the regions; years after this, we confirmed this was an optical effect. The brain has a tendency of creating forms by looking at dark and light areas. They did an experiment of asking to children what they saw and they noticed this tendency. KEPLER’S THIRD LAW ∙ Says the farther away you are, the slower the motion and the longer the period. We can confirm this by using the formula ∙ The average distance from the planet is equal to its semi major axis of an ellipse ∙ Just by looking at a graph, we can identify the average distance of a planet from the sun MERCURY ∙ Mercury resembles many features from the sun: it has presence of many craters, the planet lacks an atmosphere, it's perpendicular to the planets orbital plane, period of orbit is 58 days. ∙ Mercury is the only planet that happens to be perfectly vertical in relation to its orbit. ∙ For many years, we thought Mercury had a normal elliptical orbit. But we noticed differences but there was no explanation to why the theory of Newton did not match our observations ∙ So this was explained by Einstein’s theory of relativity. The long term trajectory of a planet is created by a rosette trajectory (when an orbit orbits) VENUS ∙ Is the third brightest object in the SS. The first one is sun, then full moon is the second. ∙ Its atmosphere plays an important role because it reflects light into the space and because is the closest planet to us. ∙ There is an effect that Venus has related to the global warning in earth. There is a dramatic green house effect in Venus. Because of this, Venus is the hottest planet in the SS. QUESTIONS 1. Mercury resembles the surface of what other object? Moon2. Why does Mercury lacks seasonal? Because it doesn't have a tilt 3. How do we explain mercury a long term orbit? 4. Name 2 consequences of the absence of an atmosphere on Mercury? 5. Why is Venus so bright? Because it is the closest planet to the earth and 6. Why is it called Earth's twin planet? Because it has almost the same mass, same size, and they share the greenhouse effect consequences. 7. Why is Venus the hottest planet in the SS? Because it has a thick atmosphere that creates a greenhouse effect on the planet. 8. Describe the greenhouse effect. It happens when the radiation that comes from space gets trapped between the horizon and the atmosehere becase the thick atmosphere does not let the rays get out into space again. 9. Venus rotates clockwise, meaning the sun rises in the --- and sets in the ----, as seen from the planet's surface 10. Why does Venus lack small impact craters on its surface? 11. Why is it so difficult to see planet Mercury from earth? VENUS ∙ It's the closest planet to earth ∙ Belief was that it was impossible to see detail of Venus because of its clouds. But this was because we wanted to see its surface. We have to use other methods to be able to see its surface ∙ The third brightest object ∙ After WW2, there were radar techniques. Astronomers used radio waves to penetrate the clouds. A map was drawn by this. ∙ Venus has lowlands and highlands. In the North Pole of the planet there are mountains higher than the Everest (Ishtar Terra is an example) ∙ We discovered the presence of volcanos too, there's also a moon surrounding Venus that also has volcanos (Moon is called Io) ∙ Venus' temperatures are hotter than Mercury’s (the closest planet to the Sun). ∙ The phenomenon of global warming was first discovered on Venus. The accumulation of energy (heat) resulting from the presence of CO2. ∙ Greenhouse effect: at the atmosphere level of Venus, there is certain energy restored in the planet during the day, and during night, it releases light (energy). Heated surface emits infrared radiation and then this is released to space. But in Venus, because of the thick atmosphere, the infrared radiation gets trapped by the atmosphere, so it heats both the surface and the atmosphereOTHER QUESTIONS 1. What explains the color of a star? It’s temperature 2. What explains the color of a planet? It’s chemical composition or the atmosphere’s chemical composition 3. Mars is red because its soil... it’s cold 4. Why is Mars the best candidate planet to be terra formed by humans? It has almost the same orbital period than the Earth's. It undergoes seasonal changes each season lasting 6 months. 5. What is terraformation? Transformation into Earth-like conditions in order for humans to assimilate conditions lived on Earth to other planets. 6. What were the canali reported on the red planet by the Italian astronomer Schiaparelli and Lowell (U.S.)? Stripped structures on the planet’s surface 7. What's the short explanation (two words) for such "canals"? Optical illusion. This happened because our eyes tend to see figures in line forms that do not exist, but we create them because of the light and dark contrasts. 8. How is Mars' atmosphere compared to Earth's? Mars was warmer than it is today. It has to do with the absence of magnetic field, this is why it got colder. The magnetic field prevents a planet to lose its atmosphere. So Mars has a thin atmosphere now, not breathable (but there's still some air surrounding the planet, but not abundant enough to create a greenhouse effect). 9. Compare planets Mars and earth using these adjectives: wet, dry, cold, warm, oxygen-rich, and oxygen-depleted. Earth is wetter, has more oxygen than Mars. Mars is colder, drier, and has more oxygen-depleted than Earth. 10.What's the evidence today that liquid water flowed on the red planet long ago? The surface’s features and the fact that there is ice because there used to be liquid water but it froze because the planet got colder. 11.How many satellites does Mars have? Name them. Phobos and Deimos 12.Name two surface features on Mars (see light regions and mountains). Volcanos and desert-like mountains 13.Explain two roles played by a planetary atmosphere. The atmosphere regulates the temperature on the surface of a planet. Moon and Mercury do not have an atmosphere so temperatures change drastically. Another role is that an atmosphere has an ozone layer, it prevents rays to reach the surface. It acts like a filter to different forms of radiation from outer space. Another role will be the existence of water in the surface of a planet. That planet has to have an atmosphere to have water because the atmosphere creates pressure and it regulates the temperature. 14.Why can't Jupiter become a star? Despite being so massive, is not massive enough. If you want to create a planet, the least mass is the one of Mercury. If your object is not as massive as Mercury, then you don't have a planet. The minimum mass of a star should be heavier. You need the mass of 80 Jupiters for a star. 15.An object has a mass of 25 Jupiter masses. What is it? A planet 16.What's Jupiter's most dominant atmosphere feature? A storm, it's been there at least four hundred years. 17.Name Jupiter's largest satellites? Ganimedes, io, Europa, and Callisto 18.What if a newly formed object has a mass that's less than Mercury? It is a dwarf planet GENERAL REMARKS ∙ Venus and Mercury do not have moons. Earth just one and Mars has two. ∙ Earth and Venus have active volcanos , as well as Io, one of the Jupiter's moons ∙ Europa is the icy one ∙ Ganymede is the largest moon of the entire SS ∙ All Jovian planets have rings ∙ We use Jupiter mass as a reference for extra solar planets ∙ Solar eclipse