EARTHEARTH

IN SPACEIN SPACE

A reminder about earthA reminder about earth The earth is almost a sphereThe earth is almost a sphere We locate points on the sphere We locate points on the sphere

with 3 coordinateswith 3 coordinates– Longitude (180º W -- 180º Longitude (180º W -- 180º

E)E)– Latitude (90º S -- 90º N)Latitude (90º S -- 90º N)– Altitude (m above/below sea Altitude (m above/below sea

level)level) These are referred to as These are referred to as

Terrestrial CoordinatesTerrestrial Coordinates

Finding Polaris: The North StarFinding Polaris: The North Star

Polaris is naturePolaris is nature’’s s compasscompass

Draw a line straight Draw a line straight from Polaris to the from Polaris to the horizon with your horizon with your finger and you will finger and you will be pointing toward be pointing toward geographic northgeographic north

Position of Polaris Position of Polaris Polaris stays in the Polaris stays in the

same spot same spot throughout the night. throughout the night.

We say it has the We say it has the same altitude and same altitude and azimuth throughout azimuth throughout the night.the night.

Altitude and azimuth Altitude and azimuth are the local are the local coordinatescoordinates

Celestial CoordinatesCelestial Coordinates

Declination and Declination and right ascension:.right ascension:.

Declination is the Declination is the same as latitudesame as latitude

Right ascension Right ascension is the same as is the same as longitude.longitude.

CELESTIAL MOTION CELESTIAL MOTION

Every celestial object changes position over time Every celestial object changes position over time (it is in motion).(it is in motion).

This motion This motion is not random.is not random. The movement is from The movement is from East to WestEast to West.. All move All move at the same rate.at the same rate. Celestial objects appear to follow a circular path Celestial objects appear to follow a circular path at at

a constant rate of 15 degrees per hour (or one a constant rate of 15 degrees per hour (or one complete circle every day).complete circle every day).

This motion is called the This motion is called the apparent daily motionapparent daily motion

Celestial SphereCelestial Sphere

CELESTIAL SPHERECELESTIAL SPHERE An imaginary sphere surrounding the EarthAn imaginary sphere surrounding the Earth.. on which all celestial objects would appear. Celestial object = any object in the sky that

appears to rise in the east and set in the west. Examples: moon, sun, stars, planets.

Celestial poles are Celestial poles are directly over Earthdirectly over Earth’’s poless poles Celestial equator lies Celestial equator lies over Earthover Earth’’s equators equator Zenith is a point Zenith is a point directly above the observerdirectly above the observer Celestial meridian is the Celestial meridian is the circle that runs through circle that runs through

the celestial poles and the zeniththe celestial poles and the zenith.. As Earth rotates from As Earth rotates from west to eastwest to east, all objects in , all objects in

the sky appear to move the sky appear to move from east to westfrom east to west, , revolving around the north celestial pole revolving around the north celestial pole

What About EarthWhat About Earth’’s Motions?s Motions?

Two Motions:Two Motions:Rotation: Spinning of Earth on itRotation: Spinning of Earth on it’’s axiss axisRevolution: Motion (orbit) or Earth around the Revolution: Motion (orbit) or Earth around the

Sun.Sun.How do we know Earth rotates?How do we know Earth rotates? Day/NightDay/Night Coriolis EffectCoriolis Effect Foucault PendulumFoucault Pendulum

Rate of RotationRate of Rotation

How many degrees are in a circle? How many degrees are in a circle? 360360

How many hours are in a day? 24How many hours are in a day? 24 If you divide the number of degrees If you divide the number of degrees

by the number of hours, you get by the number of hours, you get the degrees the Earth rotates per the degrees the Earth rotates per hour!hour!

The Earth rotates 15The Earth rotates 15°/hour°/hour

Path of a Star

Stars that are overhead: follow the same path as the sun (rise in the east and set in the west).

Stars that are close to Polaris: (Celestial North Pole) – appear to move in circles around Polaris (circumpolar stars) – They are in the Northern sky.

Stars that are in the Southern Sky: Rise and set near the horizon because they are mainly visible in the Southern hemisphere.

Earth Rotation = Sky RotationEarth Rotation = Sky RotationEarth Rotation = Sky RotationEarth Rotation = Sky RotationPolaris - The North Star

Circumpolar Star

*image taken from http://apod.nasa.gov/apod/ap051220.html

Noncircumpolar Star

Horizon - where the sky meets the earth

ConstellationsConstellations

Apparent pattern that people use to Apparent pattern that people use to mark the position of the starsmark the position of the stars

88 Constellations88 Constellations The sky is divided into these 88 The sky is divided into these 88

regions, each associated with a regions, each associated with a constellationconstellation

Constellations change with the seasonConstellations change with the season