Equatorial Coordinates Review

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Equatorial Coordinates Review Ast 401/Phy 580 Fall 2015 Equatorial Coordinates Review Hour Angle Numerically it’s the LST - RA. Conceptually, it’s the amount of time after a star has reached the meridian. If negative, it hasn’t happened yet. All stars at a given RA have the same hour angle at a given instant of time. Hour Angle What is the hour angle of a star due east on the horizon? A. -12 hr B. -6 hr C. -3 hr D. It depends upon your latitude. Hour Angle What is the hour angle of a star due east on the horizon? A. -12 hr B. -6 hr C. -3 hr D. It depends upon your latitude. Hour Angle What is the hour angle of a star that is due north on the horizon? A. +/- 12 hr B. 0 hr C. +6 hr D. It depends upon your latitude. Hour Angle What is the hour angle of a star that is due north on the horizon? A. +/- 12 hr B. 0 hr C. +6 hr D. It depends upon your latitude. Where Are You? If the celestial equator is on the horizon in all directions, you are likely at: A. The north pole B. The south pole C. The equator D. The Bronx Where Are You? If the celestial equator is on the horizon in all directions, you are likely at: A. The north pole B. The south pole C. The equator D. The Bronx Where Are You? If a star on the celestial equator passes north of the zenith, you must be: A. At the north pole B. In the northern hemisphere C. In the southern hemisphere D. On the moon. Where Are You? If a star on the celestial equator passes north of the zenith, you must be: A. At the north pole B. In the northern hemisphere C. In the southern hemisphere D. On the moon. Ecliptic If you are in Flagstaff, a planet on the meridian will always be: A. South of the zenith B. North of the zenith. Ecliptic If you are in Flagstaff, a planet on the meridian will always be: A. South of the zenith B. North of the zenith. Ecliptic If you’re on the equator, a planet on the meridian will always pass: A. North of the zenith B. South of the zenith C. Depends upon the date Ecliptic If you’re on the equator, a planet on the meridian will always pass: A. North of the zenith B. South of the zenith C. Depends upon the date Having probelems with RA, DEC, ETC?.

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Basic Principles of Celestial Navigation James A
Basic principles of celestial navigation James A. Van Allena) Department of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242 ͑Received 16 January 2004; accepted 10 June 2004͒ Celestial navigation is a technique for determining one’s geographic position by the observation of identified stars, identified planets, the Sun, and the Moon. This subject has a multitude of refinements which, although valuable to a professional navigator, tend to obscure the basic principles. I describe these principles, give an analytical solution of the classical two-star-sight problem without any dependence on prior knowledge of position, and include several examples. Some approximations and simplifications are made in the interest of clarity. © 2004 American Association of Physics Teachers. ͓DOI: 10.1119/1.1778391͔ I. INTRODUCTION longitude ⌳ is between 0° and 360°, although often it is convenient to take the longitude westward of the prime me- Celestial navigation is a technique for determining one’s ridian to be between 0° and Ϫ180°. The longitude of P also geographic position by the observation of identified stars, can be specified by the plane angle in the equatorial plane identified planets, the Sun, and the Moon. Its basic principles whose vertex is at O with one radial line through the point at are a combination of rudimentary astronomical knowledge 1–3 which the meridian through P intersects the equatorial plane and spherical trigonometry. and the other radial line through the point G at which the Anyone who has been on a ship that is remote from any prime meridian intersects the equatorial plane ͑see Fig.
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3.- the Geographic Position of a Celestial Body
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2 Coordinate Systems
2 Coordinate systems In order to find something one needs a system of coordinates. For determining the positions of the stars and planets where the distance to the object often is unknown it usually suffices to use two coordinates. On the other hand, since the Earth rotates around it’s own axis as well as around the Sun the positions of stars and planets is continually changing, and the measurment of when an object is in a certain place is as important as deciding where it is. Our first task is to decide on a coordinate system and the position of 1. The origin. E.g. one’s own location, the center of the Earth, the, the center of the Solar System, the Galaxy, etc. 2. The fundamental plan (x−y plane). This is often a plane of some physical significance such as the horizon, the equator, or the ecliptic. 3. Decide on the direction of the positive x-axis, also known as the “reference direction”. 4. And, finally, on a convention of signs of the y− and z− axes, i.e whether to use a left-handed or right-handed coordinate system. For example Eratosthenes of Cyrene (c. 276 BC c. 195 BC) was a Greek mathematician, elegiac poet, athlete, geographer, astronomer, and music theo- rist who invented a system of latitude and longitude. (According to Wikipedia he was also the first person to use the word geography and invented the disci- pline of geography as we understand it.). The origin of this coordinate system was the center of the Earth and the fundamental plane was the equator, which location Eratosthenes calculated relative to the parts of the Earth known to him.
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The Celestial Sphere
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AST326, 2010 Winter Semester • Celestial Sphere • Spectroscopy • (Something interesting; e.g ., advanced data analyses with IDL) • Practical Assignment: analyses of Keck spectroscopic data from the instructor (can potentially be a research paper) − “there will be multiple presentations by students” • Telescope sessions for spectroscopy in late Feb &March • Bonus projects (e.g., spectroscopic observations using the campus telescope) will be given. Grading: Four Problem Sets (16%), Four Lab Assignments (16%), Telescope Operation – Spectrograph (pass or fail; 5%), One Exam(25%), Practical Assignment (28%), Class Participation & Activities (10%) The Celestial Sphere Reference Reading: Observational Astronomy Chapter 4 The Celestial Sphere We will learn ● Great Circles; ● Coordinate Systems; ● Hour Angle and Sidereal Time, etc; ● Seasons and Sun Motions; ● The Celestial Sphere “We will be able to calculate when a given star will appear in my sky.” The Celestial Sphere Woodcut image displayed in Flammarion's `L'Atmosphere: Meteorologie Populaire (Paris, 1888)' Courtesy University of Oklahoma History of Science Collections The celestial sphere: great circle The Celestial Sphere: Great Circle A great circle on a sphere is any circle that shares the same center point as the sphere itself. Any two points on the surface of a sphere, if not exactly opposite one another, define a unique great circle going through them. A line drawn along a great circle is actually the shortest distance between the two points (see next slides). A small circle is any circle drawn on the sphere that does not share the same center as the sphere. The celestial sphere: great circle The Celestial Sphere: Great Circle •A great circle divides the surface of a sphere in two equal parts.
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SUNDIALS \0> E O> Contents Page
REG: HER DEPARTMENT OF COMMERCE Letter 1 1-3 BUREAU OF STANDARDS Circular WASHINGTON LC 3^7 (October Jl., 1932) Prepared by R. E. Gould, Chief, Time Section ^ . fA SUNDIALS \0> e o> Contents Page I. Introduction „ 2 II. Corrections to be applied 2 1. Equation of time 3 III. Construction 4 1. Materials and foundation 4 2. Graphical construction for a horizontal sundial 4 3. Gnomon . 5 4. Mathematical construction ........ 6 5,. Illustrations Fig. 1. Layout of a dial 7 Fig. 2. Suggested forms g IV. Setting up the dial 9 V. Mottoes q VI. Bibliography -10 . , 2 I. Introduction One of the earliest methods of determining time was by observing the position of the shadow cast by an object placed in the sunshine. As the day advances the shadow changes and its position at any instant gives an indication of the time. The relative length of the shadow at midday can also be used to indicate the season of the year. It is thought that one of the purposes of the great pyramids of Egypt was to indicate the time of day and the progress of the seasons. Although the origin of the sundial is very obscure, it is known to have been used in very early times in ancient Babylonia. One of the earliest recorded is the Dial of Ahaz 0th Century, B. C. mentioned in the Bible, II Kings XX: 0-11. , The Greeks used sundials in the 4th Century B. C. and one was set up in Rome in 233 B. C. Today sundials are used largely for decorative purposes in gardens or on lawns, and many inquiries have reached the Bureau of Standards regarding the construction and erection of such dials.
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