Astronomy Lesson_Textbook Notes PDF
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This document outlines topics of general astronomy topics, such as different backgrounds in astronomy, the international collaboration, the large hadrons collider, and some of the important discoveries. The document also contains scientific information about space, time, solar system, and galaxies.
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AS-101-OC2 Astronomy I: Our Place Cosmos Chapter 1: The Scale of the Cosmos: Space and Time 1.1 Astronomy: A global human adventure - Different backgrounds - Efforts to make information available to everyone worldwide despite political and geographical boundaries...
AS-101-OC2 Astronomy I: Our Place Cosmos Chapter 1: The Scale of the Cosmos: Space and Time 1.1 Astronomy: A global human adventure - Different backgrounds - Efforts to make information available to everyone worldwide despite political and geographical boundaries - To access results of experiments and observations to compare and contrast and collaborate globally - 10,000 scientists from more than 100 countries (including Canada) - The Large Hadron Collider has been used to discover fundamental particles in nature that make up all matter in the universe - Event Horizon Telescope - Another international collaboration - Produced the first ever photograph of a black hole in a core of a distant galaxy - Consists of telescopes from Europe, Greenland, the United States, Antarctica and Asia, connected into a single instrument the size of the earth - The Atacama Large Millimeter/submillimeter Array - A radio telescope made of 66 individual radio telescopes in the Atacama Desert in northern Chile - A colossal international collaboration involving the United States, the European Union, Canada, South Korea, Japan, and Taiwan - The Japanese spacecraft Hayabusa was designed to travel to a small near-earth asteroid (Itokawa) where it hovered close enough to collect a small sample then returned to Earth - This took 7 years to accomplish - The grains of asteroidal material are now being analyzed for various molecules including water - Being studies in laboratories world wide such as: Arizona State University where Indian and Chinese cosmochemists Maitrayee Bose and Ziliang Jin are analyzing a sample - In 2014 India’s Mars Orbiter Mission (MOM), aka Mangalyaan, arrived at the red planet to study its surface and atmospheric features and the effects of the solar wind on the upper atmosphere - Both NASA (National Aeronautics and Space Administration) and the South African Space Agency provided communications and navigation and tracking support demonstrating global cooperation in space exploration - In January 2019 the Chinese spacecraft Chang’e 4 became the first moon lander to set down on the side of the moon invisible from Earth, near the moon’s south pole - Objective is to learn the age and composition of the unexplored area of the Moon called the Aitken basin where the deep lunar crust may be exposed - 1998 team of astronomers from the Supernova Cosmology project from Berkely, California set their instruments to measure the rate of slowing of the expansion of the universe - Hypothesis: rate of the universe expanding is slowing - Result: it is speeding up - When the study was repeated by an international collaboration of astronomers from the US, Europe, Australia and Chile, they received the same outcome - Astronomers were suddenly faced with the fact our universe contains a component/force driving the expansion of the universe faster and faster - Mysterious components is known as dark energy 1.2 From solar system to galaxy to universe - A museum at the Globe of Science and Innovation at CERN (organisation Européenne pour la Recherche Nucléaire) in Geneva - CERN is the home of the Large Hadron Collider, the largest particle accelerator in operation today, which was designed to simulate the beginning of the universe - 100m underground the globe of science and innovation, massive detectors are looking for the first signs of the big bang, microscopic black holes, and dark matter - Metre becomes too large a unit, instead we use other prefixes (e.g., “mili” which means “one-thousandth”) or using scientific notation - Scientific notation - The system of recording very large or very small numbers by using powers of 10 - Field of view - The area visible in an image, usually given as the diameter of the region - Field of view encompasses an area 10x10 larger than the previous square - Astronomical unit (AU) - Average distance from earth to the sun, 1.5 x 10^8 kilometers - Planets - Small non luminous bodies that shine by reflecting sunlight - Star - A self-luminous ball of hot gas that generates its own energy - A globe of gas held together by its own gravity and supported by the internal pressure of its hot gases, which generate energy by nuclear fusion - Light-year (ly) - Unit of distance equal to the distance light travels in one year - Galaxy - A great cloud of stars, gas, and dust bound together by combined gravity of all the matter - A large system of stars, star clusters, gas, dust, and nebulae orbiting a common centre of mass - Milky way - A hazy band of light that circles our sky, produced by the glow of our galaxy - Milky way galaxy - The spiral galaxy containing our Sun, visible in the night sky as the milky way - Spiral arms - Our galaxy contains over 100 billion stars and like others has graceful spiral arms winding outward through the disk 1.3 The calendar: concepts of time - It has been about 13.8 billion years since the big bang, the instant the universe commenced and perhaps, the beginning of time itself - Cosmic calendar - Imagine a one-year calendar where each month is a little in excess of 1 billion years - Concept devised by Carl Sagan a well-known astronomer in the latter part of the 1900s - Big bang occurred approximately midnight on january 1 - Milkeyway starts to coalesce in late february or march, making it one of the oldest galaxies (although there remains debate about the age of the galaxy, recent estimates place its age possibly 13 billion years) - Our solar system starts being built around mid-august and by the end of september primitive life exists on earth - Not until mid-december on this cosmic calendar the complex living structures such as invertebrate life formed - Not until december 25 when dinosaurs roamed earth - The end of dinosaur era, 65 million years ago occurred december 30 on the cosmic calendar - December 31 is when all recorded history occurred and not until much later in the day (last 30 seconds) - Egyptian pyramids were built 11 seconds ago - Queen Elizabeth the II became queen 0.14 seconds ago - You were born about 0.04 seconds ago (assuming age 18) - Reading this 2 millionths of a second ago Chapter 2: User’s Guide to the Sky: Patterns and Cycles 2.1 the stars - 85% of canadians live in large or medium sized cities - Many of us don’t have an appreciation for the night sky due to light pollution - Constellations - Familiar groupings of the row of three stars in orion’s belt or big dipper - Ancient cultures from all over the world began organizing the stars by naming groups of stars called constellations after mythical creatures and gods - One of the stellar patterns identified by name, usually of mythological gods, people, animals, of objects; also the region of the sky containing that star pattern - Many constellations took rot in the imaginations of civilizations of Mesopotamia, Babylon, Egypt, and Greece as many as 5000 years ago - 48 of the ancient constellations are still in use - In former times a constellation was simply a loose grouping of bright stars, and many of the fainter stars were not included in any constellation - In addition to the 88 official constellations, the sky contains a number of less formally defined groupings called asterisms - Many people thing the Big Dipper as a constellation when it is an asterism within a constellation Ursa Major (the Great Bear) - The constellation Sagittarius (the archer) contains an asterism called the teapot, actually the archers bow - The names of stars - Most individual star names derive from ancient arabic (altered over the centuries) - Betegeuse, the bright red star in Orion, comes from the Arabic phase yad aljawza meaning “armpit of Jawza” (Orion) - Aldebaran the bright red eye of Taurus the bull, comes from the Arabic al-adabar an meaning “the follower” - The brightness of stars - Astronomers measure the apparent brightness of stars using the Magnitude scale - Astronomers divided the stars into 6 brightness groups - Brightest were called first-magnitude stars - Next brightest were second-magnitude and on until sixth-magnitude stars = the faintest visible to the human eye - The larger the magnitude the fainter the star - Stellar brightness expressed in this system is known as apparent visual magnitude (my), describing how the star looks to the human eyes observing from earth - Brightness is subjective depending on both the physiology of eyes and psychology of perception - To be scientifically accurate you should refer to flux – a measure of the light energy from a star that hits one square metre in one second 2.2 The sky and its motions - The celestial sphere - An imaginary sphere of very large radius surrounding Earth to which the planets, stars,m sun and moon seem to be attached - The celestial sphere is an example of a scientific model, a common feature of scientific thought - Notice three points 1. Objects in the sky appear to rotate westward around Earth each day (they rise in the east and set in the west) but that is a consequence of the eastward rotation of earth. This produces day and night 2. What you can see of the sky depends on where you are on earth. For example, Australians see many constellations and asterisms not visible from North America, but they never see the big dipper. Canadians see asterisms and constellations rotate around the North Star in concentric circles 3. Astronomers measure distances across the sky as angles expressed in units of degrees and subdivisions of degrees called arcminutes and arcseconds - Precession - The slow change in orientation of earth’s axis of rotation - One cycle takes nearly 26,000 years 2.3 the cycle of the sun - Rotation - Defined as the turning of a body on its axis - Every object in the universe appears to rotate or spin in space, along with any other motion it may have whether it be Earth, he Sun the planets, the asteroids or even our own Milky Way galaxy - Revolution - The term revolution means the motion of a body around a point outside the body - Earth also revolves around the sun and that produces the yearly cycle - The annual motion of the sun - In the daytime the sky is filled with stars but you can't see because the glare of sunlight fills our atmosphere with scattered light and you can only see blue - If the sun were fainter and you could see the stars, you would notice the sun appears to be moving slowly eastward relative to the background of the distant stars - Through the year the sun moves eastward song the stars following a line called the ecliptic, the apparent path of the sun among the stars - The seasons - Are caused by the revolution of earth around the sun, combined with earth’s rotational axis is tipped 23.4 degrees relative to its orbit - Important to realize earth's equatorial plane is tipped at 23.4 degrees to the ecliptic plane - Two important principles - Seasons are not caused by a variation in the distance between earth and the sun. earth's orbit is almost circular so it is almost about the same distance from the sun - The seasons are caused by changes in the amount of solar energy that earth’s northern and southern hemispheres receive at different times of the year, which results from the tip of earth’s equator and axis relative to its orbit - Zodiac signs are no longer important in astronomy 2.4 The cycles of the moon - Motion of the moon - Watching the moon at night you will notice two things - You will see it moving relative to the background of stars - You will notice the markings on its face don’t change - The moon moves rapidly among constellations, if you watch for an hour you can see it move eastward against the background of stars by slightly more than its own apparent diameter - The cycle of moon phases - Three important points - The moon always keeps the same side facing earth and you never see the far side. This is because the moon is tidally or gravitationally locked to earth resulting in a motion known as synchronous rotation. “The man in the moon” (some cultures see a rabbit) is produced by familiar features on the moon's near side - The changing shape of the moon as it passes through its cycle of phases is produced by sunlight illuminating different parts of the side of the moon you can see. - The orbital period of the moon around earth is not the same as the length of a moon phase cycle. Although the length of the moon’s phase cycle is about 29.5 dyas, the sidereal month–the time needed for the moon to return to the same place in the sky as measured by the stars is 27.3 days. This is because of earth’s continuous motion around the sun 2.5 Eclipses - Occur because of a complicated combination of apparent motions of the sun and moon (easy to predict once understood) - Solar eclipses - The sun is 400 times larger and 390 times further away than the mood - The moon is about the size to cover the sun which causes a solar eclipse - The sun is hidden (eclipsed) because the moon is “in the way” - The moon casts a shadow that reaches all the way to part of earth's surface - The umbra is the region of total shadow - If you are in the shadow you would see no portion of the sun - Usually barely reaches earth’s surface and covers a relatively small zone - In the umbra zone you would be in complete shadow unable to see any of the sons surface - This is a total eclipse - If you moved into the penumbra you would be in partial shadow and see part of the sun peeking around the edge of the moon - Annular eclipse is a solar eclipse in which an annulus (meaning ring) of the sun’s disk is visible around the disk of the moon - The eclipse never becomes total, it never quite gets dark and you can’t see the faint features of the solar atmosphere - Lunar eclipses - The moon darkens and turns copper-red - Occurs only at full moon when the moon moves through the shadow of the earth - Saros cycle - An 18-year, 11 ⅓ day period, after which the pattern of lunar and solar eclipses repeats 2.6 Stellar coordinates - In the sky latitude is called declination and longitude is called right ascension - Declination (dec) is expressed in degrees, rc minutes, and arc seconds, north (+) or south (-) of the celestial equator - Celestial equator is the imaginary line around the sky directly above Earth’s equator - Right ascension (RA) is expressed not in degrees but in hours (h), minutes (m) and seconds (s) of time from 0-24 hours - The angular east-west distance of an object on the celestial sphere measured from the vernal equinox; measured in hours, minutes, and seconds rather than angular disease 2.7 Timekeeping - Timekeeping by day - The average length of time between successive passes of the sun across the local meridian is called a solar day; this time varies slightly throughout the year, which is why we say average - Solar day: the average time between successive crossings of the sun on the local meridian (24 hours) - Another way of determining the length od a day is to measure the time it takes for any star to make successive passes across the local meridian which we call a sidereal day (sy-deer-ial) – this is about 23 hours 56 minutes - Sidereal day: the time between successive crossings of any star on the local meridian (23 hours, 56 minutes, 4.09 seconds) - Timekeeping by month - Lunar phase cycle is about 29.5 solar days corresponding roughly to the average length of a month known as a synodic month - Synodic month: the time for a complete cycle of lunar phases (about 29.5 days) - If we use the stars to measure the length of the lunar cycle, a sidereal month, the time turns out to be 27.3 days which is shorter than a synodic month for the same reason a sidereal day is shorter than a solar day - Sidereal month: the time for the moon to orbit earth once relative to any stay (about 27.3 days) - Timekeeping by year - A sidereal year is the time taken for a complete orbit relative to the start, where as time between successive spring (or autumnal) equinoxes is called a tropical year (solar year) - A sidereal year is longer by about 20 minutes, this is due to precision of the earth’s rotation - The apparent solar time is determined by the Sun’s position in the sky relative to our local meridian - When the sun is on the right meridian it is noon - Before the sun gets to the meridian we say it is ante meridian (ante meaning before) hence a.m - Afternoon when the sun has passed the meridian we say post meridian (post meaning after) hence p.m - Calendars - The tropical year (equinox to equinox) is about 365.25 days - If we chose 365 days for one year (Egyptian concept) the seasons drift through the year by one day in every four years - Julious caesar introduced the idea that every four years an extra day was to be added to account for the discrepancy leap year - The tropical year is not exactly 365.25 days but rather about 11 minutes short resulting in the spring equinox moving backwards through the calendar by 11 minutes each year, or about 14.5 hours per 80 year lifetime or about 12 days every 1600 years - Pope Gregory XIII introduced a slight variation in the calendar which became known as the Gregorian calendar and is what we use today - First set spring equinox to March 21 then adjusted the leap year schedule so each century year would be skipped as a leap year unless it was divisible by 400 - This adjustment made the calendar good for thousands of years into the future and is now globally used 2.8 Night sky tours -