DOCSLIB.ORG

The Globe and Coordinate Systems the Earth Really Is Flat!

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Globe and Coordinate Systems the Earth Really Is Flat! The Earth Really is Flat! The Globe and Coordinate Systems Intro to Mapping & GIS The Earth is Flat Long History of Mapping • Day to day, we live life in a flat world • Prehistoric Renderings, Rock – sun rises in east, sets in west Paintings from the KhoiSan – sky is above, ground is below People in South Africa – we orient travel by north-south, east-west thinking • Ex. Philly is “north west” of Glassboro • Map = Representation or Model of landscape • Traditional Australian Aboriginal Art Symbols • A Flat map (ie model of space) is a perfectly Communicated Place rational model for a local or regional scale Long History of Mapping Mapping on a flat surface is • Ancient tablet from the 7th Century BC relatively easy depicting the world at the time of Sargon (2300 BC) as a circle surrounded by water, with Babylon at its center. (British Museum) graphic symbols • Map of known world by Hecataeus store – about 500 BC – Greeks believed world a sphere abstraction house reality map 1 Map Making • Cartographic Symbology – Abstracting spatial reality with graphic representation • Extent – The area being mapped • Scale – relationship of size of realworld to map – Fraction 1/24,000 – Ratio 1:24,000 – Written statement “1 inch equals 1 mile” – Bar style 0 1 2 3 4 • Generalization – The amount of detail included in the map – Depends on the scale Coordinate Systems Cartesian Coordinates (knowing where it’s at) II Y I • Origin P 1 • Numerical systems that y1 specify location in space. • Abscissa or X Axis P 2 y • Ordinate or Y Axis 2 • Types of coordinate • Position X,Y systems: • Quadrants I through IV – Plane coordinates x x (i.e. FLAT Surface) • Point Locations: 2 1 X • Cartesian Point X Y 1 x y • Angular / polar 1 1 – Global or spherical 2 x2 y2 coordinates • Used for most projections. III IV Distance Calculation for Points Most Flat Maps Utilize a Measured in Cartesian Coordinates Cartesian Coordinate System Y • Point Locations: I P 1 Point X Y y1 1 x1 y1 2 x2 y2 y - y • Distance Formula: 1 2 – Distance from Point 1 to Point P 2: 2 SOUTH AXIS y2 – x1 - x2 2 2 (X1 – X2) + (Y1 – Y2) NORTH EAST – WEST AXIS x x 2 1 X Ancient Plan of Jerusalem 2 The Flat Earth Model Doesn’t Work at a Large Scale. Defining Location on a Spear, the Global Coordinate System Long distance travel required a better model. Basis of Global Coordinate System Terms to Specify Position on Globe • Earth’s rotation gives poles and axis as two • Latitude:degrees north and south of equator. natural points of reference on the sphere. • Longitude:degrees east and west of Greenwich, – Equator: locus of points on sphere’s surface that England. are equidistant from the poles. • Meridian = line of constant longitude. – Great Circle: • Pass a plane through a sphere’s center. • Parallel = line of constant latitude • Connect the points along which plane intersects sphere’s • Great circle = circle inscribed on surface by a surface. plane passing through earth’s center. • Line defined by the points is a great circle. • Small circle = circle inscribed on surface by a – Equator is only great circle perpendicular to axis plane that passes through earth, but misses the of rotation. center. Global Coordinate System Units of Measure All meridians are • Angular Measure: • Great Circle Degree great circle arcs. Distances: – Degrees: 360 per – Degree = 69 miles. circle. – Minute = 1.15 miles. – Minutes: 60 per degree. – Second= .02 miles – Seconds: 60 per – One tenth second = minute. 10.12 feet – One hundredth second All parallels, except = 1.012 feet. for the equator, are small circles. 3 Units of Measure Decimal Degrees • Traditional Angular • Based on decimal fraction • Decimal Degree Measure: of a degree Conversion: – Degrees: 360 per • Easier to work with – Multiply minutes by 60 circle. • can express angles to – Add seconds to results – Minutes: 60 per any precision - to of minutes multiplied degree. hundredths of a degree, by 60. to thousandths of a – Seconds: 60 per – Divide total by 3,600 degree, and so on minute. – Add result to degrees • Better for digital mapping Example of Decimal Conversion Global Grid Properties Traditional Measure: 45°20’30” 1. All meridians equal length Convert minutes to seconds: * 60 = 1200” 2. All meridians converge at poles (true north orientation) Add seconds to + = 1230” 3. All lines of latitude are parallel to the equator converted minutes: 4. All parallels maintain the same spacing Convert seconds / 3600 = .3416667 5. Meridians and parallels intersect at right to degree fraction: angles 6. The scale on a globe is the same everywhere Add whole degree 45.3416667 ° (unlike a map) to fraction: Arc and Great Circle Distance Great Circle Arc Distance • Proper measure for long distances Given the latitude and the longitude of two locations on the globe. How do you • Data required: measure the distance in degrees – Latitude in decimal degrees of each place. of great circle arc? – Longitude in decimal degrees of each place. • Procedure: – Calculate angular distance over the great circle route. q° = Arccos (Sine(Lat )*Sine(Lat )) + – Convert angular distance into miles or 1 2 kilometers. (Cosine(Lat1)*Cosine(Lat2)* Cosine(|Long1 - Long2|)) 4 Great Circle Arc Distance Given the great circle arc distance between two locations on the on the globe. How do you measure the distance in miles? Distance in miles = 69*q° Windows Calculator Seasonal Variation of Solar Angle Tropics and Polar Circles Earth-Sun Relations 5 Arctic Circle Polar Axis Northern Limit Tropic of Cancer Prime Meridian Southern Limit Tropic of Capricorn Equator Earth’s Shape What Shape is the Earth? Question: What kind of argument is this? • Earth’s shape in history: Inductive – Aristotle: Deductive • Humans are nearly perfect animals. Empirical • Home of humans should be as perfect as they are. • Most perfect shape is the sphere • Therefore the Earth must be a sphere. – He was almost perfectly correct!!! Earth’s Shape Question: What kind of argument is this? Shape of the Earth • Earth’s shape in history: Inductive – Isaac Newton: Deductive • Earth rotates about axis. Empirical • This implies greater centrifugal force is exerted on material near equator where movement is faster than near poles. • This force pulls on the Earth and causes it to deviate from a perfect sphere. • Therefore the Earth must be an oblate spheroid. – He also was almost perfectly correct!!! 6 Shape of the Earth Earth Ellipsoid • Ellipsoid: Earth as slightly flattened ball b • Ellipse of Earth's shape: – Semi-major axis = 6,378,137 meters a – Semi-minor axis = 6,356,733 meters – 1/298th difference pole to pole versus equatorial – Resulting ellipsoid provides mathematical model of planet’s shape. – Used for creating accurate large scale maps Does It Matter? Which Ellipsoids Are Used? • Small scale maps. No, go ahead and use • NAD 1927: Based on calculations by the sphere as model. British geodesist Alexander Clark. • Large scale maps. Yes, use ellipsoid as • NAD 1983: Based on Geodetic model. Referencing System of 1980. • Difference in length of a degree of latitude due to flattening: • Conversion from NAD27 to NAD83 can be troublesome – 0° = 68.708 miles – 45° = 69.054 miles – 90° = 69.403 miles The Geoid Represents mean sea level The Geoid Diverges from the Ellipsoid which varies due to gravity anomalies by as much as 100 meters Geoid highs - max. +73 m Geoid lows - min. -105 m Earth is actually lumpy – proper term Oblate Geoid 7 Who cares about the Geoid? Earth’s Surface varies from the Geoid Size of the Earth: • We all do • Maximum Vertical Surface – It is the reference level against which elevations are Difference: measured – Greatest ocean depth = 36, 161 feet [Mariana – It skews the orbit of satellites Trench]. – Greatest mountain height = • Earth scientists do 29, 028 feet [Mount Everest]. – It tells us about the deep interior of Earth – Difference = 65, 189 feet. • Maximum Elevation • Surveyors do Difference as Proportion of – It purturbs leveling measurements Diameter – .001558 which on a 12” – That is, it changes the direction of "straight down" globe is equal to .0186 inches. Who First Measured Earth? Size of the Earth Alexandria • Eratosthenes in 250 B.C. NP Class survey • q = q’= 7.2° • 7.2 = 1/50 0f 360° Which of the following closest to • Arc length = 5,000 q’ the circumference of the earth? stadia. • 5,000 x 50 = q 250,000 stadia – He was very close!! Well at A)9,000 miles Syene B)12,500 miles C) 25,000 miles D) 50,000 miles E) 120,000 miles SP Earth’s Size Earth’s Rotational Speed Size of the Earth: Rotation Earth: • Diameter: • Circumference: – 12, 756,370 meters. – 24, 901 miles. – 41, 851, 607 feet. Divide by 24 hours – 7, 926 miles. = 1,038 mph • Circumference: Faster than – 40, 075, 318 meters. commercial jet – 131,480, 703 feet. (580 mph) – 24, 901 miles. Faster than sound (769 mph) 8 Time and Time Zones Mean Solar Time • A sundial keeps apparent solar time and it will differ from the time on your watch during the course of a year. • This means that the true Sun is not always on the meridian at exactly noon. – Sometimes the Sun is on the meridian before noon and sometimes after noon. – The difference, called the equation of time, can be as much as 17 minutes. Sundial Apparent Solar Time – The path of the Sun at noon during the year makes a figure 8 shape called the analemma. • The north-south motion is due to the 23.5 degree tilt of the celestial sphere with respect to the ecliptic. • The east-west motion is primarily caused by the varying speed of Earth in its orbit around the Sun.
Load more

Recommended publications
  • AS/NZS ISO 6709:2011 ISO 6709:2008 ISO 6709:2008 Cor.1 (2009) AS/NZS ISO 6709:2011 AS/NZS ISO 6709:2011
    AS/NZS ISO 6709:2011 ISO 6709:2008 ISO 6709:2008 Cor.1 (2009) AS/NZS ISO 6709:2011AS/NZS ISO Australian/New Zealand Standard™ Standard representation of geographic point location by coordinates AS/NZS ISO 6709:2011 This Joint Australian/New Zealand Standard was prepared by Joint Technical Committee IT-004, Geographical Information/Geomatics. It was approved on behalf of the Council of Standards Australia on 15 November 2011 and on behalf of the Council of Standards New Zealand on 14 November 2011. This Standard was published on 23 December 2011. The following are represented on Committee IT-004: ANZLIC—The Spatial Information Council Australasian Fire and Emergency Service Authorities Council Australian Antarctic Division Australian Hydrographic Office Australian Map Circle CSIRO Exploration and Mining Department of Lands, NSW Department of Primary Industries and Water, Tas. Geoscience Australia Land Information New Zealand Mercury Project Solutions Office of Spatial Data Management The University of Melbourne Keeping Standards up-to-date Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased. Detailed information about joint Australian/New Zealand Standards can be found by visiting the Standards Web Shop at www.saiglobal.com.au or Standards New Zealand web site at www.standards.co.nz and looking up the relevant Standard in the on-line catalogue.
    [Show full text]
  • International Standard
    International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATlON.ME~YHAPO~HAR OPI-AHH3AWlR fl0 CTAH~APTM3Al&lM.ORGANISATION INTERNATIONALE DE NORMALISATION Standard representation of latitude, longitude and altitude for geographic Point locations Reprksen ta tion normalis6e des latitude, longitude et altitude pbur Ia localisa tion des poin ts gkographiques First edition - 1983-05-15i Teh STANDARD PREVIEW (standards.iteh.ai) ISO 6709:1983 https://standards.iteh.ai/catalog/standards/sist/40603644-5feb-4b20-87de- d0a2bddb21d5/iso-6709-1983 UDC 681.3.04 : 528.28 Ref. No. ISO 67094983 (E) Descriptors : data processing, information interchange, geographic coordinates, representation of data. Price based on 3 pages Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodies (ISO member bedies). The work of developing International Standards is carried out through ISO technical committees. Every member body interested in a subject for which a technical committee has been authorized has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. International Standard ISO 6709 was developediTeh Sby TTechnicalAN DCommitteeAR DISO/TC PR 97,E VIEW Information processing s ystems, and was circulated to the member bodies in November 1981. (standards.iteh.ai) lt has been approved by the member bodies of the following IcountriesSO 6709 :1: 983 https://standards.iteh.ai/catalog/standards/sist/40603644-5feb-4b20-87de- Belgium France d0a2bddRomaniab21d5/is o-6709-1983 Canada Germany, F.
    [Show full text]
  • QUICK REFERENCE GUIDE Latitude, Longitude and Associated Metadata
    QUICK REFERENCE GUIDE Latitude, Longitude and Associated Metadata The Property Profile Form (PPF) requests the property name, address, city, state and zip. From these address fields, ACRES interfaces with Google Maps and extracts the latitude and longitude (lat/long) for the property location. ACRES sets the remaining property geographic information to default values. The data (known collectively as “metadata”) are required by EPA Data Standards. Should an ACRES user need to be update the metadata, the Edit Fields link on the PPF provides the ability to change the information. Before the metadata were populated by ACRES, the data were entered manually. There may still be the need to do so, for example some properties do not have a specific street address (e.g. a rural property located on a state highway) or an ACRES user may have an exact lat/long that is to be used. This Quick Reference Guide covers how to find latitude and longitude, define the metadata, fill out the associated fields in a Property Work Package, and convert latitude and longitude to decimal degree format. This explains how the metadata were determined prior to September 2011 (when the Google Maps interface was added to ACRES). Definitions Below are definitions of the six data elements for latitude and longitude data that are collected in a Property Work Package. The definitions below are based on text from the EPA Data Standard. Latitude: Is the measure of the angular distance on a meridian north or south of the equator. Latitudinal lines run horizontal around the earth in parallel concentric lines from the equator to each of the poles.
    [Show full text]
  • Geodesy Methods Over Time
    Geodesy methods over time GISC3325 - Lecture 4 Astronomic Latitude/Longitude • Given knowledge of the positions of an astronomic body e.g. Sun or Polaris and our time we can determine our location in terms of astronomic latitude and longitude. US Meridian Triangulation This map shows the first project undertaken by the founding Superintendent of the Survey of the Coast Ferdinand Hassler. Triangulation • Method of indirect measurement. • Angles measured at all nodes. • Scaled provided by one or more precisely measured base lines. • First attributed to Gemma Frisius in the 16th century in the Netherlands. Early surveying instruments Left is a Quadrant for angle measurements, below is how baseline lengths were measured. A non-spherical Earth • Willebrod Snell van Royen (Snellius) did the first triangulation project for the purpose of determining the radius of the earth from measurement of a meridian arc. • Snellius was also credited with the law of refraction and incidence in optics. • He also devised the solution of the resection problem. At point P observations are made to known points A, B and C. We solve for P. Jean Picard’s Meridian Arc • Measured meridian arc through Paris between Malvoisine and Amiens using triangulation network. • First to use a telescope with cross hairs as part of the quadrant. • Value obtained used by Newton to verify his law of gravitation. Ellipsoid Earth Model • On an expedition J.D. Cassini discovered that a one-second pendulum regulated at Paris needed to be shortened to regain a one-second oscillation. • Pendulum measurements are effected by gravity! Newton • Newton used measurements of Picard and Halley and the laws of gravitation to postulate a rotational ellipsoid as the equilibrium figure for a homogeneous, fluid, rotating Earth.
    [Show full text]
  • AS/NZS ISO 6709:2008 Standard Representation of Latitude, Longitude
    AS/NZS ISO 6709:2008 ISO 6709:1983 AS/NZS ISO 6709:2008 Australian/New Zealand Standard™ Standard representation of latitude, longitude and altitude for geographic point locations AS/NZS ISO 6709:2008 This Joint Australian/New Zealand Standard was prepared by Joint Technical Committee IT-004, Geographical Information/Geomatics. It was approved on behalf of the Council of Standards Australia on 25 July 2008 and on behalf of the Council of Standards New Zealand on 21 July 2008. This Standard was published on 16 September 2008. The following are represented on Committee IT-004: ACT Planning and Land Authority ANZLIC - the Spatial Information Council Australian Antarctic Division Australian Bureau of Statistics Australian Hydrographic Office Australian Key Centre In Land Information Studies Australian Map Circle Australian Spatial Information Business Association CSIRO Exploration & Mining Department for Administrative and Information Services (SA) Department of Defence (Australia) Department of Lands NSW Department of Natural Resources and Water (Qld) Department of Planning and Infrastructure (NT) Department of Primary Industries and Water Tasmania Department of Sustainability and Environment (Victoria) Geoscience Australia InterGovernmental Committee on Surveying and Mapping Land Information New Zealand Office of Spatial Data Management Western Australian Land Information System Keeping Standards up-to-date Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased.
    [Show full text]
  • Geodetic Position Computations
    GEODETIC POSITION COMPUTATIONS E. J. KRAKIWSKY D. B. THOMSON February 1974 TECHNICALLECTURE NOTES REPORT NO.NO. 21739 PREFACE In order to make our extensive series of lecture notes more readily available, we have scanned the old master copies and produced electronic versions in Portable Document Format. The quality of the images varies depending on the quality of the originals. The images have not been converted to searchable text. GEODETIC POSITION COMPUTATIONS E.J. Krakiwsky D.B. Thomson Department of Geodesy and Geomatics Engineering University of New Brunswick P.O. Box 4400 Fredericton. N .B. Canada E3B5A3 February 197 4 Latest Reprinting December 1995 PREFACE The purpose of these notes is to give the theory and use of some methods of computing the geodetic positions of points on a reference ellipsoid and on the terrain. Justification for the first three sections o{ these lecture notes, which are concerned with the classical problem of "cCDputation of geodetic positions on the surface of an ellipsoid" is not easy to come by. It can onl.y be stated that the attempt has been to produce a self contained package , cont8.i.ning the complete development of same representative methods that exist in the literature. The last section is an introduction to three dimensional computation methods , and is offered as an alternative to the classical approach. Several problems, and their respective solutions, are presented. The approach t~en herein is to perform complete derivations, thus stqing awrq f'rcm the practice of giving a list of for11111lae to use in the solution of' a problem.
    [Show full text]
  • Models for Earth and Maps
    Earth Models and Maps James R. Clynch, Naval Postgraduate School, 2002 I. Earth Models Maps are just a model of the world, or a small part of it. This is true if the model is a globe of the entire world, a paper chart of a harbor or a digital database of streets in San Francisco. A model of the earth is needed to convert measurements made on the curved earth to maps or databases. Each model has advantages and disadvantages. Each is usually in error at some level of accuracy. Some of these error are due to the nature of the model, not the measurements used to make the model. Three are three common models of the earth, the spherical (or globe) model, the ellipsoidal model, and the real earth model. The spherical model is the form encountered in elementary discussions. It is quite good for some approximations. The world is approximately a sphere. The sphere is the shape that minimizes the potential energy of the gravitational attraction of all the little mass elements for each other. The direction of gravity is toward the center of the earth. This is how we define down. It is the direction that a string takes when a weight is at one end - that is a plumb bob. A spirit level will define the horizontal which is perpendicular to up-down. The ellipsoidal model is a better representation of the earth because the earth rotates. This generates other forces on the mass elements and distorts the shape. The minimum energy form is now an ellipse rotated about the polar axis.
    [Show full text]
  • World Geodetic System 1984
    World Geodetic System 1984 Responsible Organization: National Geospatial-Intelligence Agency Abbreviated Frame Name: WGS 84 Associated TRS: WGS 84 Coverage of Frame: Global Type of Frame: 3-Dimensional Last Version: WGS 84 (G1674) Reference Epoch: 2005.0 Brief Description: WGS 84 is an Earth-centered, Earth-fixed terrestrial reference system and geodetic datum. WGS 84 is based on a consistent set of constants and model parameters that describe the Earth's size, shape, and gravity and geomagnetic fields. WGS 84 is the standard U.S. Department of Defense definition of a global reference system for geospatial information and is the reference system for the Global Positioning System (GPS). It is compatible with the International Terrestrial Reference System (ITRS). Definition of Frame • Origin: Earth’s center of mass being defined for the whole Earth including oceans and atmosphere • Axes: o Z-Axis = The direction of the IERS Reference Pole (IRP). This direction corresponds to the direction of the BIH Conventional Terrestrial Pole (CTP) (epoch 1984.0) with an uncertainty of 0.005″ o X-Axis = Intersection of the IERS Reference Meridian (IRM) and the plane passing through the origin and normal to the Z-axis. The IRM is coincident with the BIH Zero Meridian (epoch 1984.0) with an uncertainty of 0.005″ o Y-Axis = Completes a right-handed, Earth-Centered Earth-Fixed (ECEF) orthogonal coordinate system • Scale: Its scale is that of the local Earth frame, in the meaning of a relativistic theory of gravitation. Aligns with ITRS • Orientation: Given by the Bureau International de l’Heure (BIH) orientation of 1984.0 • Time Evolution: Its time evolution in orientation will create no residual global rotation with regards to the crust Coordinate System: Cartesian Coordinates (X, Y, Z).
    [Show full text]
  • Equation of Time — Problem in Astronomy M
    This paper was awarded in the II International Competition (1993/94) "First Step to Nobel Prize in Physics" and published in the competition proceedings (Acta Phys. Pol. A 88 Supplement, S-49 (1995)). The paper is reproduced here due to kind agreement of the Editorial Board of "Acta Physica Polonica A". EQUATION OF TIME | PROBLEM IN ASTRONOMY M. Muller¨ Gymnasium M¨unchenstein, Grellingerstrasse 5, 4142 M¨unchenstein, Switzerland Abstract The apparent solar motion is not uniform and the length of a solar day is not constant throughout a year. The difference between apparent solar time and mean (regular) solar time is called the equation of time. Two well-known features of our solar system lie at the basis of the periodic irregularities in the solar motion. The angular velocity of the earth relative to the sun varies periodically in the course of a year. The plane of the orbit of the earth is inclined with respect to the equatorial plane. Therefore, the angular velocity of the relative motion has to be projected from the ecliptic onto the equatorial plane before incorporating it into the measurement of time. The math- ematical expression of the projection factor for ecliptic angular velocities yields an oscillating function with two periods per year. The difference between the extreme values of the equation of time is about half an hour. The response of the equation of time to a variation of its key parameters is analyzed. In order to visualize factors contributing to the equation of time a model has been constructed which accounts for the elliptical orbit of the earth, the periodically changing angular velocity, and the inclined axis of the earth.
    [Show full text]
  • Moon-Earth-Sun: the Oldest Three-Body Problem
    Moon-Earth-Sun: The oldest three-body problem Martin C. Gutzwiller IBM Research Center, Yorktown Heights, New York 10598 The daily motion of the Moon through the sky has many unusual features that a careful observer can discover without the help of instruments. The three different frequencies for the three degrees of freedom have been known very accurately for 3000 years, and the geometric explanation of the Greek astronomers was basically correct. Whereas Kepler’s laws are sufficient for describing the motion of the planets around the Sun, even the most obvious facts about the lunar motion cannot be understood without the gravitational attraction of both the Earth and the Sun. Newton discussed this problem at great length, and with mixed success; it was the only testing ground for his Universal Gravitation. This background for today’s many-body theory is discussed in some detail because all the guiding principles for our understanding can be traced to the earliest developments of astronomy. They are the oldest results of scientific inquiry, and they were the first ones to be confirmed by the great physicist-mathematicians of the 18th century. By a variety of methods, Laplace was able to claim complete agreement of celestial mechanics with the astronomical observations. Lagrange initiated a new trend wherein the mathematical problems of mechanics could all be solved by the same uniform process; canonical transformations eventually won the field. They were used for the first time on a large scale by Delaunay to find the ultimate solution of the lunar problem by perturbing the solution of the two-body Earth-Moon problem.
    [Show full text]
  • 1 the Equatorial Coordinate System
    General Astronomy (29:61) Fall 2013 Lecture 3 Notes , August 30, 2013 1 The Equatorial Coordinate System We can define a coordinate system fixed with respect to the stars. Just like we can specify the latitude and longitude of a place on Earth, we can specify the coordinates of a star relative to a coordinate system fixed with respect to the stars. Look at Figure 1.5 of the textbook for a definition of this coordinate system. The Equatorial Coordinate System is similar in concept to longitude and latitude. • Right Ascension ! longitude. The symbol for Right Ascension is α. The units of Right Ascension are hours, minutes, and seconds, just like time • Declination ! latitude. The symbol for Declination is δ. Declination = 0◦ cor- responds to the Celestial Equator, δ = 90◦ corresponds to the North Celestial Pole. Let's look at the Equatorial Coordinates of some objects you should have seen last night. • Arcturus: RA= 14h16m, Dec= +19◦110 (see Appendix A) • Vega: RA= 18h37m, Dec= +38◦470 (see Appendix A) • Venus: RA= 13h02m, Dec= −6◦370 • Saturn: RA= 14h21m, Dec= −11◦410 −! Hand out SC1 charts. Find these objects on them. Now find the constellation of Orion, and read off the Right Ascension and Decli- nation of the middle star in the belt. Next week in lab, you will have the chance to use the computer program Stellar- ium to display the sky and find coordinates of objects (stars, planets). 1.1 Further Remarks on the Equatorial Coordinate System The Equatorial Coordinate System is fundamentally established by the rotation axis of the Earth.
    [Show full text]
  • Sun-Synchronous Satellites
    Topic: Sun-synchronous Satellites Course: Remote Sensing and GIS (CC-11) M.A. Geography (Sem.-3) By Dr. Md. Nazim Professor, Department of Geography Patna College, Patna University Lecture-3 Concept: Orbits and their Types: Any object that moves around the Earth has an orbit. An orbit is the path that a satellite follows as it revolves round the Earth. The plane in which a satellite always moves is called the orbital plane and the time taken for completing one orbit is called orbital period. Orbit is defined by the following three factors: 1. Shape of the orbit, which can be either circular or elliptical depending upon the eccentricity that gives the shape of the orbit, 2. Altitude of the orbit which remains constant for a circular orbit but changes continuously for an elliptical orbit, and 3. Angle that an orbital plane makes with the equator. Depending upon the angle between the orbital plane and equator, orbits can be categorised into three types - equatorial, inclined and polar orbits. Different orbits serve different purposes. Each has its own advantages and disadvantages. There are several types of orbits: 1. Polar 2. Sunsynchronous and 3. Geosynchronous Field of View (FOV) is the total view angle of the camera, which defines the swath. When a satellite revolves around the Earth, the sensor observes a certain portion of the Earth’s surface. Swath or swath width is the area (strip of land of Earth surface) which a sensor observes during its orbital motion. Swaths vary from one sensor to another but are generally higher for space borne sensors (ranging between tens and hundreds of kilometers wide) in comparison to airborne sensors.
    [Show full text]