CHAPTER 1:CHAPTER 1:Discoveringthe Night Sky—

Constellations,Asterisms and the Celestial Sphere

WHAT DO YOU THINK?

Is the North Star—Polaris—the brightest star in the night sky?

Do astronomers regard constellations as the familiar patterns of stars in the sky?

Describe the Nature and Describe the Nature and Use of Use of

ConstellationsConstellations Constellations make star locating Constellations make star locating easy.easy.

Constellation : a region and a group of Constellation : a region and a group of starsstars

Night sky is divided into 88 regions Night sky is divided into 88 regions (constellations)(constellations)

Astronomers, requiring more Astronomers, requiring more accuracy, now use a coordinate accuracy, now use a coordinate system as well (right ascension and system as well (right ascension and declination: see the celestial sphere)declination: see the celestial sphere)

In order to more easily locate objects in the sky, we In order to more easily locate objects in the sky, we divide the sky into regions named after familiar divide the sky into regions named after familiar patterns of stars called patterns of stars called constellationsconstellations..

Ancient constellations were imaginary pictures outlined by familiar patterns of stars.

Modern astronomers divide the sky into 88 official constellations or regions of space, many of which contain the ancient star patterns.

Some Common Guides to Finding ConstellationsSome Common Guides to Finding Constellations

Using the Using the ““Big DipperBig Dipper”” as a guide as a guide

The The ““Summer TriangleSummer Triangle””

The The ““Winter TriangleWinter Triangle””

Starry Night ExerciseStarry Night Exercise

Chapter 1Chapter 1 Stars and ConstellationsStars and Constellations

Locating your position on Locating your position on EarthEarth

EarthEarth’’s coordinate system uses a s coordinate system uses a series of grid lines that circle the series of grid lines that circle the globe N-S and E-W and that globe N-S and E-W and that intersect at right angles…These grid intersect at right angles…These grid lines are calledlines are called

longitude (north-south)longitude (north-south) latitude (east-west)latitude (east-west)

Labeling one hemisphereLabeling one hemisphere

LatitudeLatitude LongitudeLongitude ZenithZenith HorizonHorizon Meridians and parallelsMeridians and parallels Prime meridianPrime meridian EquatorEquator

Label your plastic hemisphereLabel your plastic hemisphere

Latitude vs. LongitudeLatitude vs. Longitude

http://www.hammondmap.com/sites/hammond/geography/latlong1.html

What is the approximate What is the approximate latitude and longitude for Fort latitude and longitude for Fort

Thomas, KY?Thomas, KY?

http://www.nasa.gov/

The latitude of Fort Thomas is 39.075N. The longitude is 84.447W.

Locating your position in the Locating your position in the skysky

Rise and run above the EarthRise and run above the Earth’’s s surface are called…surface are called…– Altitude Altitude (0-90(0-90oo) starts at the horizon, ) starts at the horizon,

ends at zenithends at zenith– AzimuthAzimuth (0-360 (0-360oo) starts at due north) starts at due north

http://geology.isu.edu/geostac/Field_Exercise/topomaps/bearing.htm

http://meteorites.pdx.edu/measurements.htm

Starry Night ExerciseStarry Night Exercise

Chapter 2Chapter 2 Changing LatitudeChanging Latitude

……to envision the to envision the night sky rotating night sky rotating eastward like the eastward like the outer shell of a outer shell of a hollow sphere...hollow sphere...

Celestial SphereCelestial Sphere

The celestial sphere aids in The celestial sphere aids in navigating the skynavigating the sky

Earth-based viewEarth-based view A coordinate system (it works on the A coordinate system (it works on the

principle of latitude-longitude and principle of latitude-longitude and altitude-azimuth)altitude-azimuth)– DeclinationDeclination– Right ascensionRight ascension

Relationships between the Relationships between the three coordinate systemsthree coordinate systems

Declination is related to altitude and Declination is related to altitude and latitudelatitude

Right ascension is related to Right ascension is related to longitude and azimuthlongitude and azimuth

Astronomers describe the universe as an imaginary Astronomers describe the universe as an imaginary sphere surrounding the earth on which all objects in sphere surrounding the earth on which all objects in the sky can be located, called the the sky can be located, called the CELESTIAL SPHERECELESTIAL SPHERE..

As viewed from Earth, the As viewed from Earth, the celestial sphere appears to rotate celestial sphere appears to rotate around two axis points, the around two axis points, the north north and south celestial polesand south celestial poles, which , which are located directly above the are located directly above the EarthEarth’’s poles.s poles.

Between these is the Between these is the celestial celestial equator,equator, which divides the which divides the celestial sphere into northern and celestial sphere into northern and southern hemispheres.southern hemispheres.

We define the position of an We define the position of an object on the celestial sphere object on the celestial sphere using two coordinates, using two coordinates, right right ascensionascension and and declinationdeclination. .

See animation 1.1 and interactive exercise 1.1

Starry Night DemoStarry Night Demo

Turn on celestial grid, turn off horizonTurn on celestial grid, turn off horizon Note the coordinates listed for each Note the coordinates listed for each

grid linegrid line

Angular Diameter and Angular Diameter and DistanceDistance

Used to describe the apparent size of Used to describe the apparent size of or distance between astronomical or distance between astronomical objects.objects.

Uses degrees, arcminutes and Uses degrees, arcminutes and arcseconds.arcseconds.

Example of a measurement : 60Example of a measurement : 60oo 30 30’’ 33 ’’’’

Usage of Angular DiameterUsage of Angular Diameter

Size of an object (Sun and Moon have Size of an object (Sun and Moon have very similar angular diameters—0.5very similar angular diameters—0.5oo degrees or 30degrees or 30’’ arcminutes) arcminutes)

Distance between objectsDistance between objects Distance object travelesDistance object traveles True diameter (calculated)True diameter (calculated)

Ecliptic Plane on the Celestial Ecliptic Plane on the Celestial SphereSphere

The annual path of the Sun as it The annual path of the Sun as it appears on the celestial sphere.appears on the celestial sphere.

The ecliptic and the celestial equator The ecliptic and the celestial equator are tilted at a 23 ½-degree angleare tilted at a 23 ½-degree angle

Earth orbits the Sun while tilted at a Earth orbits the Sun while tilted at a 23 ½- degree angle.23 ½- degree angle.

Starry Night Demo: the celestial Starry Night Demo: the celestial sphere and the ecliptic planesphere and the ecliptic plane

Starry Night Celestial Starry Night Celestial SphereSphere

Open Starry Night programOpen Starry Night program Go to Options/Guides/celestial grid, Go to Options/Guides/celestial grid,

pole, meridian, zenithpole, meridian, zenith Go to observing/diurnal/diurnal aGo to observing/diurnal/diurnal a Go to earthGo to earth’’s orbit/orbit as orbit/orbit a Go to seasons/view over south poleGo to seasons/view over south pole

One effect of this motion is to change the location in the EarthOne effect of this motion is to change the location in the Earth’’s orbit at s orbit at which summer and winter occur, and thus change the time of year which summer and winter occur, and thus change the time of year when the Sun appears in certain constellations. when the Sun appears in certain constellations.

Astrology TableAstrology Table Pisces - February 20- March 20 - February 20- March 20 Aries - March 21 - April 20 Aries - March 21 - April 20 Taurus - April 21 - May 21 Taurus - April 21 - May 21 Gemini - May 22 - June 21 Gemini - May 22 - June 21 Cancer - June 22 - July 22 Cancer - June 22 - July 22 Leo - July 23 -August 21 Leo - July 23 -August 21 Virgo - August 22 - September 23 Virgo - August 22 - September 23 Libra - September 24 - October 23 Libra - September 24 - October 23 Scorpio - October 24 - November 22 Scorpio - October 24 - November 22 Sagittarius - November 23 - December 22 Sagittarius - November 23 - December 22 Capricorn - December 23 - January 20 Capricorn - December 23 - January 20 Aquarius - January 21 - February 19 Aquarius - January 21 - February 19

We can see how different stars appear at different times of day by looking at We can see how different stars appear at different times of day by looking at the position of the Sun against the backdrop of stars. The side of the Earth the position of the Sun against the backdrop of stars. The side of the Earth facing the Sun is experiencing facing the Sun is experiencing ““day,day,”” while the side of the Earth turned away while the side of the Earth turned away from the Sun is experiencing from the Sun is experiencing ““night.night.””

SEPTEMBER MARCH

(The Sun is in Virgo) (The Sun is in Pisces)

Zodiac ActivityZodiac Activity Select one of 13 zodiac constellations.Select one of 13 zodiac constellations. Use the Starry Night Program to find your Use the Starry Night Program to find your

zodiac constellationzodiac constellation Draw your zodiac constellation to scale.Draw your zodiac constellation to scale. Label the stars in your constellation.Label the stars in your constellation. Classroom demonstration using lamp as the Classroom demonstration using lamp as the

SunSun QuestionsQuestions

– Explain what it means for the Sun to be in your Explain what it means for the Sun to be in your zodiac constellation.zodiac constellation.

– When is your zodiac constellation visible?When is your zodiac constellation visible?

Stars in 3-DStars in 3-D

Activity F-8Activity F-8 Three-Dimensional Three-Dimensional ConstellationsConstellations

How far away from the Earth are How far away from the Earth are these stars?these stars?

Is the brightness of stars an indicator Is the brightness of stars an indicator of distance? Explain.of distance? Explain.

How would these constellations How would these constellations appear in different places in space?appear in different places in space?

Student ActivitiesStudent Activities

Chapter 1Chapter 1 Stars and ConstellationsStars and Constellations Chapter 2Chapter 2 Changing LatitudeChanging Latitude Starry Night DemosStarry Night Demos Zodiac activityZodiac activity 3-d stars3-d stars Observing projectObserving project QuestionsQuestions Research optionResearch option

http://www.whfreeman.com/dtu7ehttp://www.whfreeman.com/dtu7e