CHAPTER 1: Discovering the 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?

Constellations: Finding our place in the sky

Describe the Nature and Use of Constellations Constellations make star locating easy. Constellation : a region and a group of stars Night sky is divided into 88 regions (constellations) Astronomers, requiring more accuracy, now use a coordinate system as well (right ascension and declination: see the celestial sphere)

In order to more easily locate objects in the sky, we divide the sky into regions named after familiar patterns of stars called constellations. 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 Constellations Using the “Big Dipper” as a guide

The “Summer Triangle”

The “Winter Triangle”

Starry Night Exercise Chapter 1 Stars and Constellations

Locating your position on Earth Earth’s coordinate system uses a series of grid lines that circle the globe N-S and E-W and that intersect at right angles…These grid lines are called longitude (north-south) latitude (east-west)

Labeling one hemisphere Latitude Longitude Zenith Horizon Meridians and parallels Prime meridian Equator Label your plastic hemisphere

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

What is the approximate latitude and longitude for Fort Thomas, KY? http://www.nasa.gov/ What is the approximate latitude and longitude for Fort Thomas, KY?

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

Locating your position in the sky Rise and run above the Earth’s surface are called… Altitude (0-90o) starts at the horizon, ends at zenith Azimuth (0-360o) starts at due north

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

Starry Night Exercise Chapter 2 Changing Latitude

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

Celestial Sphere The celestial sphere aids in navigating the sky Earth-based view A coordinate system (it works on the principle of latitude-longitude and altitude-azimuth) Declination Right ascension

Relationships between the three coordinate systems Declination is related to altitude and latitude Right ascension is related to longitude and azimuth

Astronomers describe the universe as an imaginary sphere surrounding the earth on which all objects in the sky can be located, called the CELESTIAL SPHERE. As viewed from Earth, the celestial sphere appears to rotate around two axis points, the north and south celestial poles, which are located directly above the Earth’s poles. Between these is the celestial equator, which divides the celestial sphere into northern and southern hemispheres. We define the position of an object on the celestial sphere using two coordinates, right ascension and declination. See animation 1.1 and interactive exercise 1.1

Starry Night Demo Turn on celestial grid, turn off horizon Note the coordinates listed for each grid line

Angular Diameter and Distance Used to describe the apparent size of or distance between astronomical objects. Uses degrees, arcminutes and arcseconds. Example of a measurement : 60o 30’ 3’’

Usage of Angular Diameter Size of an object (Sun and Moon have very similar angular diameters—0.5o degrees or 30’ arcminutes) Distance between objects Distance object traveles True diameter (calculated)

Ecliptic Plane on the Celestial Sphere The annual path of the Sun as it appears on the celestial sphere. The ecliptic and the celestial equator are tilted at a 23 ½-degree angle Earth orbits the Sun while tilted at a 23 ½- degree angle. Starry Night Demo: the celestial sphere and the ecliptic plane

Starry Night Celestial Sphere Open Starry Night program Go to Options/Guides/celestial grid, pole, meridian, zenith Go to observing/diurnal/diurnal a Go to earth’s orbit/orbit a Go to seasons/view over south pole

What's Your Sign?

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

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

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 facing the Sun is experiencing “day,” while the side of the Earth turned away from the Sun is experiencing “night.” MARCH SEPTEMBER (The Sun is in Virgo) (The Sun is in Pisces)

Zodiac Activity Select one of 13 zodiac constellations. Use the Starry Night Program to find your zodiac constellation Draw your zodiac constellation to scale. Label the stars in your constellation. Classroom demonstration using lamp as the Sun Questions Explain what it means for the Sun to be in your zodiac constellation. When is your zodiac constellation visible?

Stars in 3-D Activity F-8 Three-Dimensional Constellations How far away from the Earth are these stars? Is the brightness of stars an indicator of distance? Explain. How would these constellations appear in different places in space?

Student Activities Chapter 1 Stars and Constellations Chapter 2 Changing Latitude Starry Night Demos Zodiac activity 3-d stars Observing project Questions Research option

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