# CELESTIAL COORDINATES

Save this PDF as:

Size: px
Start display at page:

## Transcription

1 ASTR 1030 Astronomy Lab 27 Celestial Coordinates CELESTIAL COORDINATES GEOGRAPHIC COORDINATES The Earth's geographic coordinate system is familiar to everyone - the north and south poles are defined by the Earth's axis of rotation; equidistant between them is the equator. North-south latitude is measured in degrees from the equator, ranging from -90 at the south pole, 0 at the equator, to +90 at the north pole. East-west distances are also measured in degrees, but there is no "naturally-defined" starting point - all longitudes are equivalent to all others. Humanity has arbitrarily defined the prime meridian (0 longitude) to be that of the Royal Observatory at Greenwich, England (alternately called the Greenwich meridian). Each degree ( ) of a 360 circle can be further subdivided into 60 equal minutes of arc ('), and each arc-minute may be divided into 60 seconds of arc ("). The 24-inch telescope at Sommers-Bausch Observatory is located at a latitude 40 0'13" North of the equator and at a longitude '45" West of the Greenwich meridian. Boulder +40 0' 13" Latitude ' 45" Longitude North Pole +90 Latitude Greenwich 0 Longitude Equator 0 Latitude The Earth's Latitude - Longitude Coordinate System Parallels or Small Circles Meridians ALT-AZIMUTH COORDINATES The alt-azimuth (altitude - azimuth) coordinate system, also called the horizon system, is a useful and convenient system for pointing out a celestial object. One first specifies the azimuth angle, which is the compass heading towards the horizon point lying directly below the object. Azimuth angles are measured eastward from North (0 azimuth) to East (90 ), South (180 ), West (270 ), and back to North again (360 = 0 ). The four principle directions are called the cardinal points.

2 ASTR 1030 Astronomy Lab 28 Celestial Coordinates Next, the altitude is measured in degrees upward from the horizon to the object. The point directly overhead at 90 altitude is called the zenith. The nadir is "down", or opposite the zenith. We sometimes use zenith distance instead of altitude, which is 90 - altitude. Every observer on Earth has his own separate alt-azimuth system; thus, the coordinates of the same object will differ for two different observers. Furthermore, because the Earth rotates, the altitude and azimuth of an object are constantly changing with time as seen from a given location. Hence, this system can identify celestial objects at a given time and location, but is not useful for specifying their permanent (more or less) direction in space. In order to specify a direction by angular measure, you need to know just how big angles are. Here s a convenient yardstick to use that you carry with you at all times: the hand, held at arm's length, is a convenient tool for estimating angles subtended at the eye: Index Finger Hand Fist 10 EQUATORIAL COORDINATES Standing outside on a clear night, it appears that the sky is a giant celestial sphere of indefinite radius with us at its center, and upon which stars are affixed to its inner surface. It is extremely useful for us to treat this imaginary sphere as an actual, tangible surface, and to attach a coordinate system to it.

3 ASTR 1030 Astronomy Lab 29 Celestial Coordinates The system used is based on an extension of the Earth's axis of rotation, hence the name equatorial coordinate system. If we extend the Earth's axis outward into space, its intersection with the celestial sphere defines the north and south celestial poles; equidistant between them, and lying directly over the Earth's equator, is the celestial equator. Measurement of "celestial latitude" is given the name declination (DEC), but is otherwise identical to the measurement of latitude on the Earth: the declination at the celestial equator is 0 and extends to ±90 at the celestial poles. The east-west measure is called right ascension (RA) rather than "celestial longitude", and differs from geographic longitude in two respects. First, the longitude lines, or hour circles, remain fixed with respect to the sky and do not rotate with the Earth. Second, the right ascension circle is divided into time units of 24 hours rather than in degrees; each hour of angle is equivalent to 15 of arc. The following conversions are useful: 24 h = m = 15' 1 h = 15 4 s = 1' 4 m = 1 1 s = 15" The Earth orbits the Sun in a plane called the ecliptic. From our vantage point, however, it appears that the Sun circles us once a year in that same plane; hence, the ecliptic may be alternately defined as "the apparent path of the Sun on the celestial sphere". The Earth's equator is tilted 23.5 from the plane of its orbital motion, or in terms of the celestial sphere, the ecliptic is inclined 23.5 from the celestial equator. The ecliptic crosses the equator at two points; the first, called the vernal (spring) equinox, is crossed by the Sun moving from south to north on about March 21st, and sets the moment when spring begins. The second crossing is from north to south, and marks the autumnal equinox six months later. Halfway between these two points, the ecliptic rises to its maximum declination of (summer solstice), or drops to a minimum declination of (winter solstice). As with longitude, there is no obvious starting point for right ascension, so astronomers have assigned one: the point of the vernal equinox. Starting from the vernal equinox, right ascension increases in an eastward direction until it returns to the vernal equinox again at 24 h = 0 h. North Celestial Pole +90 DEC Hour Circles Celestial Equator 0 DEC 16h 18h 20h RA 22h 24h = 0h 2h 4h Earth Ecliptic 23.5 Sun (March 21) Vernal Equinox 0h RA, 0 DEC Winter Solstice 18h RA, DEC

4 ASTR 1030 Astronomy Lab 30 Celestial Coordinates The Earth precesses, or wobbles on its axis, once every 26,000 years. Unfortunately, this means that the Sun crosses the celestial equator at a slightly different point every year, so that our "fixed" starting point changes slowly - about 40 arc-seconds per year. Although small, the shift is cumulative, so that it is important when referring to the right ascension and declination of an object to also specify the epoch, or year in which the coordinates are valid. TIME AND HOUR ANGLE The fundamental purpose of all timekeeping is, very simply, to enable us to keep track of certain objects in the sky. Our foremost interest, of course, is with the location of the Sun, which is the basis for the various types of solar time by which we schedule our lives. Time is determined by the hour angle of the celestial object of interest, which is the angular distance from the observer's meridian (north-south line passing overhead) to the object, measured in time units east or west along the equatorial grid. The hour angle is negative if we measure from the meridian eastward to the object, and positive if the object is west of the meridian. For example, our local apparent solar time is determined by the hour angle of the Sun, which tells us how long it has been since the Sun was last on the meridian (positive hour angle), or how long we must wait until noon occurs again (negative hour angle). If solar time gives us the hour angle of the Sun, then sidereal time (literally, "star time") must be related to the hour angles of the stars: the general expression for sidereal time is Sidereal Time = Right Ascension + Hour Angle which holds true for any object or point on the celestial sphere. It s important to realize that if the hour angle is negative, we add this negative number, which is equivalent to subtracting the positive number. For example, the vernal equinox is defined to have a right ascension of 0 hours; thus the equation becomes Sidereal time = Hour angle of the vernal equinox Another special case is that for an object on the meridian, for which the hour angle is zero by definition. Hence the equation states that Sidereal time = Right ascension crossing the meridian Your current sidereal time, coupled with a knowledge of your latitude, uniquely defines the appearance of the celestial sphere; furthermore, if you know any two of the variables in the expression ST = RA + HA, you can determine the third. The following illustration shows the appearance of the southern sky as seen from Boulder at a particular instant in time. Note how the sky serves as a clock - except that the clock face (celestial sphere) moves while the clock "hand" (meridian) stays fixed. The clock face numbering increases towards the east, while the sky rotates towards the west; hence, sidereal time always increases, just as we would expect. Since the left side of the ST equation increases with time, then so must the right side; thus, if we follow an object at a given right ascension (such Saturn or Uranus), its hour angle must constantly increase (or become less negative).

5 ASTR 1030 Astronomy Lab 31 Celestial Coordinates Sidereal Time = Right Ascension on Meridian = 21 hrs 43 min Vernal Equinox 0 h 0m 23h 20m Ecliptic 22h 40m 22h 0m 21h 20m 20h 40m 20h 0m 19h 20m Sidereal Time = Right Ascension + Hour Angle Saturn RA = 21h 59m Hour Angle of Vernal Equinox = - 2h 17m = 21h 43m = Sidereal Time Hour Angle - 0h 16m Hour Angle + 2h 21m Uranus RA = 19h 22m Saturn: 21h 59m RA + (- 0h 16m) HA = 21h 43m ST Uranus: 19h 22m RA + 2h 21m HA = 21h 43m ST 1:50 am MDT 20 August 1993 SOLAR VERSUS SIDEREAL TIME Every year the Earth actually makes 366 1/4 complete rotations with respect to the stars (sidereal days). Each day the Earth also revolves about 1 about the Sun, so that after one year, it has "unwound" one of those rotations with respect to the Sun; on the average, we observe 365 1/4 solar passages across the meridian (solar days) in a year. Since both sidereal and solar time use 24- hour days, the two clocks must run at different rates. The following compares (approximate) time measures in each system: SOLAR SIDEREAL SOLAR SIDEREAL days days 24 hours 24h 3m 56s 1 day d 23h 56m 4s 24 hours d 1 day 6 minutes 6m 1s The difference between solar and sidereal time is one way of expressing the fact that we observe different stars in the evening sky during the course of a year. The easiest way to predict what the sky will look like (i.e., determine the sidereal time) at a given date and time is to use a planisphere, or star wheel. However, it is possible to estimate the sidereal time to within a half-hour or so with just a little mental arithmetic. At noontime on the date of the vernal equinox, the solar time is 12h (since we begin our solar day at midnight) while the sidereal time is 0h (since the Sun is at 0h RA, and is on our meridian). Hence, the two clocks are exactly 12 hours out of synchronization (for the moment, we will ignore the complication of "daylight savings"). Six months later, on the date of the autumnal equinox (about September 22) the two clocks will agree exactly for a brief instant before beginning to drift apart, with sidereal time gaining about 1 second every six minutes.

6 ASTR 1030 Astronomy Lab 32 Celestial Coordinates For every month since the last fall equinox, sidereal time gains 2 hours over solar time. We simply count the number of elapsed months, multiply by 2, and add the time to our watch (converting to a 24-hour system as needed). If daylight savings time is in effect, we subtract 1 hour from the result to get the sidereal time. For example, suppose we wish to estimate the sidereal time at 10:50 p.m. Mountain Daylight Time on August the 19th. About 11 months have elapsed since fall began, so sidereal time is ahead of standard solar time by 22 hours - or 21 hours ahead of daylight savings time. Equivalently, we can say that sidereal time lags behind daylight time by 3 hours. 10:50 p.m. on our watch is 22h 50 m on a 24-hour clock, so the sidereal time is 3 hours less: ST = 19h 50m (approximately). ENVISIONING THE CELESTIAL SPHERE With time and practice, you will begin to "see" the imaginary grid lines of the alt-azimuth and equatorial coordinate systems in the sky. Such an ability is very useful in planning observing sessions and in understanding the apparent motions of the sky. To help you in this quest, we ve included four scenes of the celestial sphere showing both alt-azimuth and equatorial coordinates. Each view is from the same location (Boulder) and at the same time and date used above (10:50 p.m. MDT on August 19th, 1993). As we comment on each, we'll mention some important relationships between the coordinate systems and the observer's latitude. Looking North From Boulder, the altitude of the north celestial pole directly above the North cardinal point is 40, exactly equal to Boulder's latitude. This is true for all observing locations: Altitude of the pole = Latitude of observer The +50 declination circle just touches our northern horizon. Any star more northerly than this will be circumpolar - that is, it will never set below the horizon. Declination of northern circumpolar stars > 90 - Latitude Most of the Big Dipper is circumpolar. The two pointer stars of the dipper are useful in finding Polaris, which lies only about 1/2 from the north celestial pole. Because these two stars always point towards the pole, they must both lie approximately on the same hour circle, or equivalently, both must have approximately the same right ascension (11 hours RA).

7 ASTR 1030 Astronomy Lab 33 Celestial Coordinates Looking South If you were standing at the north pole, the celestial equator would coincide with your local horizon. As you travel the 50 southward to Boulder, the celestial equator will appear to tilt up by an identical angle; that is, the altitude of the celestial equator above the South cardinal point is 50 from the latitude of Boulder. Your local meridian is the line passing directly overhead from the north to south celestial poles, and hence coincides with 180 azimuth. Generally speaking, then, Altitude of the intersection of the celestial equator with the meridian = 90 - Latitude Since the celestial equator is 50 above our southern horizon, any star with a declination less than - 50 is circumpolar around the south pole, and will never be seen from Boulder. Declination of southern circumpolar stars < Latitude - 90 The sidereal time (right ascension on the meridian) is 19h 43m - only 7 minutes different from our estimate. Looking East The celestial equator meets the observer's local horizon exactly at an azimuth of 90 ; this is always true, regardless of the observer's latitude: The celestial equator always intersects the east and west cardinal points

8 ASTR 1030 Astronomy Lab 34 Celestial Coordinates At the intersection point, the celestial equator makes an angle of 50 with the local horizon; in general, The intersection angle between celestial equator and horizon = 90 - Latitude Our view of the eastern horizon at this particular time includes the Great Square of Pegasus, which is useful for locating the point of the vernal equinox. The two easternmost stars of the Great Square both lie on approximately 0 hours of right ascension. The vernal equinox lies in the constellation of Pisces about 15 south of the Square. Looking Up From a latitude of 40, an object with a declination of +40 will, at some point in time during the day or night, pass directly overhead through the zenith. In general Declination at zenith = Latitude of observer The 24 Ephemeris Stars in the SBO Catalog of Astronomical Objects have Object Numbers ranging from #401 to #424. Each of these moderately-bright stars passes near the zenith (within 10 or so) over the course of 24 hours. At any time, the ephemeris star nearest the zenith will usually be the star whose last two digits equals the sidereal time (rounded to the nearest hour). For example, at the current sidereal time (19h 43m), the zenith ephemeris star is #420 (d Cygni). At the time of the year assumed in this example (late summer), and at this time of night (midevening), the three prominent stars of the Summer Triangle are high in the sky: Vega (in Lyra the lyre), Deneb (at the tail of Cygnus the swan), and Altair (in Aquila the eagle). However, the Summer Triangle is not only high in the sky in summer, but at any period during the year when the sidereal time equals roughly 20 hours: just after sunset in October, just before sunrise in May, and even around noontime in January (though it won't be visible because of the Sun).

### Introduction To Modern Astronomy I: Solar System

ASTR 111 003 Fall 2007 Lecture 02 Sep. 10, 2007 Introduction To Modern Astronomy I: Solar System Introducing Astronomy (chap. 1-6) Planets and Moons (chap. 7-15) Chap. 16: Our Sun Chap. 28: Search for

### Knowing the Heavens. Goals: Constellations in the Sky

Goals: Knowing the Heavens To see how the sky changes during a night and from night to night. To measure the positions of stars in celestial coordinates. To understand the cause of the seasons. Constellations

### The celestial sphere, the coordinates system, seasons, phases of the moon and eclipses. Chapters 2 and S1

The celestial sphere, the coordinates system, seasons, phases of the moon and eclipses Chapters 2 and S1 The celestial sphere and the coordinates system Chapter S1 How to find our way in the sky? Let s

### Celestial Sphere Spectroscopy (Something interesting; e.g., advanced data analyses with IDL)

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

### Chapter S1 Celestial Timekeeping and Navigation. How do we define the day, month, year, and planetary time periods?

Chapter S1 Celestial Timekeeping and Navigation S1.1 Astronomical Time Periods Our goals for learning:! How do we define the day, month, year, and planetary time periods?! How do we tell the time of day?!

### Discovering the Night Sky

Discovering the Night Sky Guiding Questions 1. What role did astronomy play in ancient civilizations? 2. Are the stars that make up a constellation actually close to one another? 3. Are the same stars

### Aileen A. O Donoghue Priest Associate Professor of Physics

SOAR: The Sky in Motion Life on the Tilted Teacup Ride Celestial Coordinates and the Day Aileen A. O Donoghue Priest Associate Professor of Physics Reference Points Poles Equator Prime Meridian Greenwich,

### Meridian Circle through Zenith, North Celestial Pole, Zenith Direction Straight Up from Observer. South Celestial Pole

Chapter 3 How Earth and Sky Work- Effects of Latitude In chapters 3 and 4we will learn why our view of the heavens depends on our position on the Earth, the time of day, and the day of the year. We will

### Astron 104 Laboratory #2 The Celestial Sphere

Name: Date: Section: Astron 104 Laboratory #2 The Celestial Sphere Basic Setup Once the celestial sphere is properly setup, it will serve as an exact model of the heavens relative to your location on Earth.

### 10/17/2012. Observing the Sky. Lecture 8. Chapter 2 Opener

Observing the Sky Lecture 8 Chapter 2 Opener 1 Figure 2.1 Figure 2.2 2 Figure 2.6 Figure 2.4 Annotated 3 The Celestial Sphere The celestial sphere is the vast hollow sphere on which the stars appear fixed.

### Daily Motions. Daily Motions. Solar and Sidereal Days. Annual Motions of the Sun. Coordinate system on Earth. Annual Motion of the Stars.

Sun: rises in the east sets in the west travels on an arc across the sky 24 hours Daily Motions Solar Day = 24 hours Stars: stars travel on arcs in the sky moving from east to west. some stars rise and

### Chapter 2 Discovering the Universe for Yourself. What does the universe look like from Earth? Constellations. 2.1 Patterns in the Night Sky

Chapter 2 Discovering the Universe for Yourself 2.1 Patterns in the Night Sky Our goals for learning: What does the universe look like from Earth? Why do stars rise and set? Why do the constellations we

### Chapter 2 Discovering the Universe for Yourself

Chapter 2 Discovering the Universe for Yourself 2.1 Patterns in the Night Sky Our goals for learning: What does the universe look like from Earth? Why do stars rise and set? Why do the constellations we

### WHAT ARE THE CONSTELLATIONS

CONSTELLATIONS WHAT ARE THE CONSTELLATIONS In popular usage, the term constellation is used to denote a recognizable grouping of stars. Astronomers have redefined the constellations as 88 regions of the

### Chapter 2 Lecture. The Cosmic Perspective Seventh Edition. Discovering the Universe for Yourself

Chapter 2 Lecture The Cosmic Perspective Seventh Edition Discovering the Universe for Yourself Discovering the Universe for Yourself 2.1 Patterns in the Night Sky Our goals for learning: What does the

### Constellations. In ancient times, constellations only referred to the brightest stars that appeared to form groups, representing mythological figures.

Chapter 2 The Sky Constellations In ancient times, constellations only referred to the brightest stars that appeared to form groups, representing mythological figures. Constellations (2) Today, constellations

### Equatorial Telescope Mounting

Equatorial Telescope Mounting Star Catalogs simbad IRSA The Meridian Every line of celestial longitude is a meridian of longitude, but we recognize the line of longitude, or simply the great circle line,

### Local Coordinates. These are centered upon you, the observer.

Astronomy 30, Observing #3 Name: Lab Partners: Date: Materials: This lab, with the star chart completed from the pre-lab. Some sheets of paper for sketches. A pencil with eraser. A small flashlight, ideally

### Before you Sit. Please Pick-up: Blue Information Sheet for Evening Observing. 1 Red and 1 Blue ticket for Observing/ Planetarium

Before you Sit Please Pick-up: Blue Information Sheet for Evening Observing. 1 Red and 1 Blue ticket for Observing/ Planetarium Evening Observing Observing at the Brooks Observatory: Three different weeks

### James T. Shipman Jerry D. Wilson Charles A. Higgins, Jr. Chapter 15 Place and Time

James T. Shipman Jerry D. Wilson Charles A. Higgins, Jr. Chapter 15 Place and Time Place & Time Read sections 15.5 and 15.6, but ignore the math. Concentrate on those sections that help explain the slides.

### The Sky Perceptions of the Sky

The Sky Perceptions of the Sky An Observer-Centered Hemisphere Night & Day - Black & Blue - Stars & Sun Atmospheric & Astronomical Phenomena Weather, Clouds, Rainbows,... versus Sun, Moon, Stars, Planets,...

### Time and Diurnal Motion

Time and Diurnal Motion Time and Diurnal Motion A. Geography: mapping the earth 2 B. Equatorial Coordinates C. Local Horizon System Updated 2014Jan11 A. Geography: mapping the earth Geometry: measure the

### Time and Diurnal Motion. 1a. The Earth Is Flat. 1c. Aristotle ( BC) 1b. The Earth Is Round. Time and Diurnal Motion

Time and Diurnal Motion Time and Diurnal Motion A. Geography: mapping the earth 2 B. Equatorial Coordinates C. Local Horizon System Updated April 12, 2006 A. Geography: mapping the earth Geometry: measure

### ClassAction: Coordinates and Motions Module Instructor s Manual

ClassAction: Coordinates and Motions Module Instructor s Manual Table of Contents Section 1: Warm-up Questions...3 The Sun s Path 1 4 Section 2: General Questions...5 Sledding or Going to the Beach...6

### Exercise 7.0 THE CHANGING DIURNAL CIRCLES OF THE SUN

Exercise 7.0 THE CHANGING DIURNAL CIRCLES OF THE SUN I. The Apparent Annual Motion of the Sun A star always rises and sets at the same place on the horizon and, hence, it is above the horizon for the same

### 2. Descriptive Astronomy ( Astronomy Without a Telescope )

2. Descriptive Astronomy ( Astronomy Without a Telescope ) http://apod.nasa.gov/apod/astropix.html How do we locate stars in the heavens? What stars are visible from a given location? Where is the sun

### Physics Lab #4:! Starry Night Student Exercises I!

Physics 10293 Lab #4: Starry Night Student Exercises I Introduction For today s lab, we are going to let the Starry Night software do much of the work for us. We re going to walk through some of the sample

### Guiding Questions. Discovering the Night Sky. iclicker Qustion

Guiding Questions Discovering the Night Sky 1 1. What methods do scientists use to expand our understanding of the universe? 2. What makes up our solar system? 3. What are the stars? Do they last forever?

### The sky and the celestial sphere

Chapter 1 The sky and the celestial sphere The Sun, and sometimes the Moon are, by and large, the only astronomical objects visible in the day sky. Traditionally, astronomy has been a nocturnal activity.

### Astronomy 291. Professor Bradley M. Peterson

Astronomy 291 Professor Bradley M. Peterson The Sky As a first step, we need to understand the appearance of the sky. Important points (to be explained): The relative positions of stars remain the same

### drinking straw, protractor, string, and rock. observer on Earth. Sun across the sky on March 21 as seen by an

1. The diagram below represents some constellations and one position of Earth in its orbit around the Sun. These constellations are visible to an observer on Earth at different times of the year. When

### 3 - Celestial Sphere

3 - Celestial Sphere Purpose: To construct and use a celestial sphere to show the motion of the Sun and stars in the sky. There are six questions, Q1 Q6, to answer on a separate piece of paper. Due: in

### Lecture #03. January 20, 2010, Wednesday

Lecture #03 January 20, 2010, Wednesday Causes of Earth s Seasons Earth-Sun geometry Day length Solar angle (beam spread) Atmospheric beam depletion Shape and Size of the Earth North Pole E Geoid: not

### 8 - Planetarium. Purpose: To experience the motion of the Sun and the night sky at different times and different locations on Earth.

Name: Date: ASTR 110L 8 - Planetarium Purpose: To experience the motion of the Sun and the night sky at different times and different locations on Earth. During this activity, use only constellations from

### HNRS 227 Fall 2007 Chapter 14. Earth in Space presented by Prof. Geller 25 October 2007

HNRS 227 Fall 2007 Chapter 14 Earth in Space presented by Prof. Geller 25 October 2007 Key Points of Chapter 14 Shape, Size and Motions of the Earth Rotation and Revolution Precession Coordinate Systems

### Astronomy A BEGINNER S GUIDE TO THE UNIVERSE EIGHTH EDITION

Astronomy A BEGINNER S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER 0 Charting the Heavens Lecture Presentation 0.0 Astronmy a why is that subject! Q. What rare astronomical event happened in late summer

### Astronomy 100 Section 2 MWF Greg Hall

Astronomy 100 Section 2 MWF 1200-1300 100 Greg Hall Leslie Looney Phone: 217-244-3615 Email: lwl @ uiuc. edu Office: Astro Building #218 Office Hours: MTF 10:30-11:30 a.m. or by appointment Class Web Page

### Name: Class: Date: ID: A

Name: Class: _ Date: _ Astro Quiz 2 (ch2) Multiple Choice Identify the choice that best completes the statement or answers the question. 1. Star A has an apparent visual magnitude of 13.4 and star B has

### Celestial Sphere & Solar Motion Lab (Norton s Star Atlas pages 1-4)

Name: Date: Celestial Sphere & Solar Motion Lab (Norton s Star Atlas pages 1-4) Italicized topics below will be covered only at the instructor s discretion. 1.0 Purpose: To understand a) the celestial

### 3) During retrograde motion a planet appears to be A) dimmer than usual. B) the same brightness as usual C) brighter than usual.

Descriptive Astronomy (ASTR 108) Exam 1 B February 17, 2010 Name: In each of the following multiple choice questions, select the best possible answer. In the line on the scan sheet corresponding to the

### b. So at 12:00 p.m., are the shadows pointing in the direction you predicted? If they are not, you must explain this observation.

Astronomy 100 Name(s): Exercise 2: Timekeeping and astronomy The following exercise illustrates some basic ideas about time, and how our position in the solar system uniquely configures the measurement

### LEARNING GOALS. Chapter S1: Celestial Timekeeping and Navigation. Supplementary Chapter

9/6/05 10:12 AM Chapter S1: Celestial Timekeeping and Navigation Supplementary Chapter LEARNING GOALS S1.1 Astronomical Time Periods Why isn't the Earth's rotation period exactly equal to the 24 hours

### TIME. Astronomical time Time is defined by astronomical cycles. The day is the average time from noon to noon (the solar day).

ASTRONOMY READER TIME 2.1 TIME Astronomical time Time is defined by astronomical cycles. The day is the average time from noon to noon (the solar day). The month was originally based on the average time

12.215 Modern Navigation Thomas Herring Review of Monday s Class Spherical Trigonometry Review plane trigonometry Concepts in Spherical Trigonometry Distance measures Azimuths and bearings Basic formulas:

### The Measurement of Time

CHAPTER TWO The Measurement of Time Solar Time In antiquity the time of day was measured by the direction of a shadow cast in sunlight. This resulted in the development of a wide variety of sophisticated

### Earth Moon Motions A B1

Earth Moon Motions A B1 1. The Coriolis effect provides evidence that Earth (1) rotates on its axis (2) revolves around the Sun (3) undergoes cyclic tidal changes (4) has a slightly eccentric orbit 9.

### Motion of the Sun. motion relative to the horizon. rises in the east, sets in the west on a daily basis. Basis for the unit of time, the DAY

Motion of the Sun motion relative to the horizon rises in the east, sets in the west on a daily basis Basis for the unit of time, the DAY noon: highest point of Sun in sky relative to the horizon 1 altitude:

### Sky, Celestial Sphere and Constellations

Sky, Celestial Sphere and Constellations Last lecture Galaxies are the main building blocks of the universe. Consists of few billions to hundreds of billions of stars, gas clouds (nebulae), star clusters,

### INDEPENDENT PROJECT: The Autumn Night Sky

INDEPENDENT PROJECT: The Autumn Night Sky Your Name: What is the difference between observing and looking? As John Rummel said to the Madison Astronomical Society, January 11, 2002: Looking implies a passive

### UNIT 3: EARTH S MOTIONS

UNIT 3: EARTH S MOTIONS After Unit 3 you should be able to: o Differentiate between rotation and revolution of the Earth o Apply the rates of rotation and revolution to basic problems o Recall the evidence

### Indoor Lab #2: The Starry Sky

17 Indoor Lab #2: The Starry Sky Objectives: To tour the sky and explore the way in which it moves, using the sky simulation program Starry Night Pro. Check out the information sheet on SN first, and try

### Astronomy 101 Lab: Seasons

Name: Astronomy 101 Lab: Seasons Pre-Lab Assignment: In class, we've talked about the cause of the seasons. In this lab, you will use globes to study the relative positions of Earth and the Sun during

### The Earth is a Rotating Sphere

The Earth is a Rotating Sphere The Shape of the Earth Earth s Rotation ( and relative movement of the Sun and Moon) The Geographic Grid Map Projections Global Time The Earth s Revolution around the Sun

### Earth s Orbit. Sun Earth Relationships Ridha Hamidi, Ph.D. ESCI-61 Introduction to Photovoltaic Technology

1 ESCI-61 Introduction to Photovoltaic Technology Sun Earth Relationships Ridha Hamidi, Ph.D. Spring (sun aims directly at equator) Winter (northern hemisphere 23.5 tilts away from sun) 2 Solar radiation

### Q25: Record the wavelength of each colored line according to the scale given.

C. Measurement Errors and Uncertainties The term "error" signifies a deviation of the result from some "true" value. Often in science, we cannot know what the true value is, and we can only determine estimates

### Coordinate Systems for Astronomy or: How to get your telescope to observe the right object

Coordinate Systems for Astronomy or: How to get your telescope to observe the right object Figure 1: Basic definitions for the Earth Definitions - Poles, Equator, Meridians, Parallels The rotation of the

### 01) The Sun s rays strike the surface of the Earth at 90 degrees at the on December 22.

Package Title: Testbank Course Title: Introducing Physical Geography 6e Chapter Number: 01 Question Type: Multiple Choice 01) The Sun s rays strike the surface of the Earth at 90 degrees at the on December

### The Motion of the Sun in Different Locations

ame: Partner(s): 1101 or 3310: Desk # Date: Purpose The Motion of the Sun in Different Locations Describe the path of the Sun in the sky as seen from the equator of the Earth Describe the path of the Sun

### 6 - Planetarium. Q1) In what cardinal direction did the Sun rise? Be specific. Q2) Record the time of sunrise and sunset: /

Name: Partner(s), if applicable: 6 - Planetarium ASTR110L Purpose: To experience the motion of the Sun and the night sky at different times and different locations on Earth. Answer the questions in the

### Earth rotates on a tilted axis and orbits the Sun.

Page of 7 KY CONCPT arth rotates on a tilted axis and orbits the Sun. BFOR, you learned Stars seem to rise, cross the sky, and set because arth turns The Sun is very large and far from arth arth orbits

### ME 476 Solar Energy UNIT THREE SOLAR RADIATION

ME 476 Solar Energy UNIT THREE SOLAR RADIATION Unit Outline 2 What is the sun? Radiation from the sun Factors affecting solar radiation Atmospheric effects Solar radiation intensity Air mass Seasonal variations

### LONGITUDE AND LATITUDE. Semi great circles joining the true or geographic poles of the earth (true meridians).

MERIDIANS OF LONGITUDE LONGITUDE AND LATITUDE Semi great circles joining the true or geographic poles of the earth (true meridians). They are measured from 0 to 180 degrees East and West of the PRIME MERIDIAN,

### What do you think? 2/3/09. Mastering Astronomy Assignment 2. Constellations the 88 semi-rectangular regions that make up the sky

//09 Mastering Astronomy Assignment Due Feb 0, am Read Chapter Constellations the 88 semi-rectangular regions that make up the sky Northern constellations have Latinized Greek-mythology names: Orion, Cygnus,

### March 21. Observer located at 42 N. Horizon

March 21 Sun Observer located at 42 N Horizon 48 June 21 March 21 A 48 90 S 23.5 S 0 23.5 N 42 N 90 N Equator (June 21) C (March 21) B A 71.5 48 Horizon 24.5 Observer Sun 40 Observer Sun 22 Observer Sun

### 8.9 Observing Celestial Objects from Earth

8.9 Observing Celestial Objects from Earth Celestial objects are visible from Earth both by day and by night. In the daytime you can see the Sun and, sometimes, the Moon. Looking up at the night sky on

### C) the seasonal changes in constellations viewed in the night sky D) The duration of insolation will increase and the temperature will increase.

1. Which event is a direct result of Earth's revolution? A) the apparent deflection of winds B) the changing of the Moon phases C) the seasonal changes in constellations viewed in the night sky D) the

### GLOBE : LATITUDES AND LONGITUDES

2 Figure 2.1 : Globe Let s Do Take a big round potato or a ball. Pierce a knitting needle through it. The needle resembles the axis shown in a globe. You can now move the potato or the ball around this

### Day, Night & the Seasons. Lecture 2 1/21/2014

Day, Night & the Seasons Lecture 2 1/21/2014 Logistics The following students see me after class: A. Gonzalez, Chen Anyone who was not here on first day see me after class Pin Numbers - if you have not

### Astronomy 120 Winter 2005 Highlights of Astronomy. First Midterm Examination

Astronomy 120 Winter 2005 Highlights of Astronomy First Midterm Examination Name: MULTIPLE CHOICE: Choose the one best answer from among the five choices for each of the following 6 questions. Each correct

### Venus Project Book, the Galileo Project, GEAR

1 Venus Project Book, the Galileo Project, GEAR Jeffrey La Favre November, 2013 Updated March 31, 2016 You have already learned about Galileo and his telescope. Recall that he built his first telescopes

### Seasons ASTR 101 2/12/2018

Seasons ASTR 101 2/12/2018 1 What causes the seasons? Perihelion: closest to Sun around January 4 th Northern Summer Southern Winter 147 million km 152 million km Aphelion (farthest to Sun) around July

### A Sense of Scale and The Motions of Earth. The guitar player Pablo Picasso (1910)

A Sense of Scale and The Motions of Earth The guitar player Pablo Picasso (1910) Announcements n Notes from the first lecture are available on the class web site (www.astro.umass.edu/~calzetti/astro100).

### Physics Lab #3:! Starry Night! Observations of the Sun and Moon!

Physics 10293 Lab #3: Starry Night Observations of the Sun and Moon Introduction Today, we are going to use the Starry Night software to learn about motion of the stars, sun and moon on the celestial sphere.

### LEARNING TO USE THE SIMPLIFIED CELESTISTIAL SPHERE

653-8012 LEARNING TO USE THE SIMPLIFIED CELESTISTIAL SPHERE 1.1 INTRODUCTION The instrument that accompanies this guidebook is known as a celestial globe. One major component is an outer globe, which represents

### Sundials and the Celestial Sphere. Katie Hausknecht

Sundials and the Celestial Sphere Katie Hausknecht What is a sundial? A sundial is a device that uses the shadow cast by the sun to indicate what time of day it is, often by hours. The Celestial Sphere

### Student Exploration: Seasons: Earth, Moon, and Sun

Name: Date: Student Exploration: Seasons: Earth, Moon, and Sun Vocabulary: altitude, axis, azimuth, equinox, horizon, latitude, revolution, rotation, solstice Prior Knowledge Questions (Do these BEFORE

### REVIEW CH #0. 1) Right ascension in the sky is very similar to latitude on the Earth. 1)

REVIEW CH #0 TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 1) Right ascension in the sky is very similar to latitude on the Earth. 1) 2) Latitude and right ascension

### Question 1. What motion is responsible for the apparent motion of the constellations (east to west) across the sky?

What motion is responsible for the apparent motion of the constellations (east to west) across the sky? Question 1 1) the motion of Earth around the Sun 2) the motion of the Moon around Earth 3) the motion

### SAMPLE First Midterm Exam

Astronomy 1000 Dr C. Barnbaum SAMPLE First Midterm Exam Note: This is a sample exam. It is NOT the exam you will take. I give out sample exams so that you will have an understanding of the depth of knowledge

### THE SUN. LENGTH: Course of the semester

ASTR 1030 Astronomy Lab 139 The Sun THE SUN SYNOPSIS: This exercise involves making measurements of the Sun every week throughout the semester, and then analyzing your results at semester s end. You ll

### Field Activitie< for Chapter 5 The Cycle of the Sun

for Chapter 5 The Cycle of the Sun N.B.: Many of these activities include making observations and recording data in tables over the same span of months. Therefore, review these activities before starting

### Motions of the Sun Model Exploration

Name Date Bell Motions of the Sun Model Exploration 1. Go to the University of Nebraska-Lincoln Motions of the Sun Simulator: http://astro.unl.edu/naap/motion3/animations/sunmotions.swf 2. This is what

### Guidepost. Chapter 2 A User s Guide to the Sky. Constellations Constellations (2) 8/27/2015. Outline. Outline (continued)

Chapter 2 A User s Guide to the Sky Guidepost Astronomy is about us. As we learn about astronomy, we learn about ourselves. We search for an answer to the question What are we? The quick answer is that

### A Review of Coordinates

A Review of Coordinates Latitude and Longitude On Earth, one way to describe a location is with a coordinate system which is fixed to the Earth's surface. The system is oriented by the spin axis of the

### NAME; LAB # SEASONAL PATH OF THE SUN AND LATITUDE Hemisphere Model #3 at the Arctic Circle

NAME; PERIOD; DATE; LAB # SEASONAL PATH OF THE SUN AND LATITUDE Hemisphere Model #3 at the Arctic Circle 1 OBJECTIVE Explain how latitude affects the seasonal path of the Sun. I) Path of the Sun and Latitude.

### EXPLAINING THE SEASONS AND LOCATING THE NORTH AND SOUTH CELESTIAL POLES

EXPLAINING THE SEASONS AND LOCATING THE NORTH AND SOUTH CELESTIAL POLES Although people are very aware of the seasons, most cannot give a good explanation of why they occur and how they are produced because

### Go to Click on the first animation: The north pole, observed from space

IDS 102 The Seasons on a Planet like Earth As the Earth travels around the Sun, it moves in a giant circle 300 million kilometers across. (Well, it is actually a giant ellipse but the shape is so close

### Unit 2. Cycles of the Sky

Unit 2 Cycles of the Sky The Celestial Sphere Vast distances to stars prevent us from sensing their true 3-D arrangement Naked eye observations treat all stars at the same distance, on a giant celestial

### Tutoring information, as announced in class

Announcements Register for Connect, register your iclickers - Register iclickers at https://www1.iclicker.com/ or REEF account profile - Purchase the REEF polling app, create an account, register and get

### Astronomy AST-1002 Section 0459 Discover the Universe Fall 2017

Astronomy AST-1002 Section 0459 Discover the Universe Fall 2017 Instructor: Dr. Francisco Reyes Web Page: http://www.astro.ufl.edu/~freyes/classes/ast1002/index.htm Textbook: Astronomy: A Beginners Guide

### 2.2 The Reason for Seasons

2.2 The Reason for Seasons Our goals for learning: What causes the seasons? How does the orientation of Earth's axis change with time? Thought Question TRUE OR FALSE? Earth is closer to the Sun in summer

### Practice Exam #3. Part 1: The Circumpolar Constellations

Practice Exam #3 2002 Ann Bykerk-Kauffman, Dept. of Geological and Environmental Sciences, California State University, Chico * Some Comments on the Real Exam This exam covers all material related to astronomy.

### Why does Earth rotate and what s the evidence? (besides watching it from space ships or satellites) Week 18 January 5, 2015

Why does Earth rotate and what s the evidence? (besides watching it from space ships or satellites) Week 18 January 5, 2015 The sun determines our solar time everywhere on earth as Earth rotates. Can you

### Directed Reading. Section: Viewing the Universe THE VALUE OF ASTRONOMY. Skills Worksheet. 1. How did observations of the sky help farmers in the past?

Skills Worksheet Directed Reading Section: Viewing the Universe 1. How did observations of the sky help farmers in the past? 2. How did observations of the sky help sailors in the past? 3. What is the

### Seasonal Path of the Sun and Latitude

Seasonal Path of the Sun and Latitude Overview This lesson is a modification of what Dave Hess and I, Stan Skotnicki, use in our Earth Science classes at Cheektowaga Central High School. It is an extension

### RECOMMENDATION ITU-R S Impact of interference from the Sun into a geostationary-satellite orbit fixed-satellite service link

Rec. ITU-R S.1525-1 1 RECOMMENDATION ITU-R S.1525-1 Impact of interference from the Sun into a geostationary-satellite orbit fixed-satellite service link (Question ITU-R 236/4) (21-22) The ITU Radiocommunication

### PHYSICAL GEOGRAPHY. By Brett Lucas

PHYSICAL GEOGRAPHY By Brett Lucas INTRODUCTION Introduction to Earth Geography as a Field of Learning Geography is from two Greek words, Geo Earth, and Graphien to write. Elements/Branches of Geography