Measuring the Sky - Ann Arbor Earth Science

1,000 10,000 kilometers (106 (107 m)m)•© 2004 Pearson Education Inc., publishing as

1,000 10,000 kilometers (106 (107 m)m)•© 2004 Pearson Education Inc., publishing as

10,000 kilometers (104(107m)m)

10,000 100 meters kilometers (102 m) (107m)

How old is **the**Universe?•The CosmicCalendar– if **the** entire ageof **the** Universewere onecalendar year– one monthwould beapproximately1 billion realyears

The Celestial Sphere•The sky above looks like adome…a hemisphere..•If we imagine **the** skyaround **the** entire **Earth**, wehave **the** celestial sphere.•This a 2-dimensionalrepresentation of **the** sky¥Because it represents ourview from **Earth**, we place**the** **Earth** in **the** center ofthis sphere.

The Celestial SphereNorth & South celestial poles**the** points in **the** sky directly above **the** **Earth**’sNorth and South polescelestial equator**the** extension of **the** **Earth**’s equator onto **the**celestial sphereecliptic**the** annual path of **the** Sun through **the** celestial sphere,which is a projection of ecliptic plane

•© 2004 Pearson Education Inc., publishing as

A spinningimaginaryCelestialSpheresurrounding**Earth** aids innavigating**the** sky

**Measuring** **the** **Sky**We measure **the** sky in angles, not distances.•Full circle = 360º•1º = 60 arcmin•1 arcmin = 60 arcsec

Angular Measurements and Notation:•Full circle = 360º•1º = 60 (arcminutes)•1 = 60 (arcseconds)

What is 55.435 degrees in degreesminutes-secondsnotation?55deg0.435(60) 26.1arcmin26 arcmin0.1(60) 6arcsecso,55o26'06"What is73 o 45 33.56in decimal degrees?73deg45/60 .7533.56/360073.7593220.009322

Problem•45.635 degrees is how many degrees, arcminutes, and arcseconds?•How many degrees, arcminutes, and arcseconds does **the** moon moveacross **the** sky in one hour? (**the** lunar day is 24 hours and 48 minuteslong)•The moons diameter is about 30 arcminutes, so find out how long ittakes for **the** moon to travel its diameter.

Answer•45.635 degrees is how many degrees, arcminutes, andarcseconds?45deg0.635(60) 38.1arcmin38 arcmin0.1(60) 6arcsec•How many degrees, arcminutes, and arcseconds does **the** moonmove across 24 hours**the** 48 minutes sky one 24.8hour? hours (**the** lunar day is 24 hours and48 minutes long)The moon moves360 degrees during360deg24.8hours14.516129deg/ hour14that time so :o30 58.06"•The moons diameter is about 30 arcminutes, so find out how long0.5degit takes vfor d/t **the** moon t d/v to travel its diameter. 0.034 hour14.516129deg/ hour(0.034hour)(60minutes/hour) 2.1minutes 2 6

Review: Coordinates on **the** **Earth**•Latitude: position north or south of equator•Longitude: position east or west of primemeridian (runs through Greenwich,England)

Review: Coordinates on **the** **Earth**•Latitude: position north or south of equator•Longitude: position east or west of primemeridian (runs through Greenwich,England)

Review: Coordinates on **the** **Earth**•Latitude: position north or south of equator•Longitude: position east or west of primemeridian (runs through Greenwich,England)

© 2004 Pearson Education Inc., publishing as

A spinningimaginaryCelestialSpheresurrounding**Earth** aids innavigating**the** sky

**Measuring** Angles in **the** **Sky**

The Local **Sky**zenith**the** point directly above youhorizonall points 90° from **the** zenithaltitude**the** angle above **the** horizonmeridiandue north horizon zenith due south horizon

To pinpoint a spot in **the** local sky:Specify altitude anddirection along **the** horizon

Elements of **the** equatorial coordinatesystem on **the** celestial sphere•Vernal Equinox: The position of**the** Sun on **the** first day ofspring (Sets **the** prime meridian)•Right Ascension: How far eastof **the** Vernal Equinox an objectis located (longitude)•Celestial Equator: The lineseparating **the** celestial sphereinto nor**the**rn and sou**the**rnhalves.•Declination: How far above orbelow **the** celestial equator anobject is located.(latitude)

The Daily Motion•As **the** **Earth** rotates, **the** skyappears to us to rotate in **the**opposite direction.•The sky appears to rotate around**the** N (or S) celestial poles.•If you are standing at **the** poles,nothing rises or sets.•If you are standing at **the** equator,everything rises & sets 90 to**the** horizon.

The Daily Motion•As **the** **Earth** rotates, **the** skyappears to us to rotate in **the**opposite direction.•The sky appears to rotate around**the** N (or S) celestial poles.•If you are standing at **the** poles,nothing rises or sets.•If you are standing at **the** equator,everything rises & sets 90 to**the** horizon.

The Daily Motion•As **the** **Earth** rotates, **the** skyappears to us to rotate in **the**opposite direction.•The sky appears to rotate around**the** N (or S) celestial poles.•If you are standing at **the** poles,nothing rises or sets.•If you are standing at **the** equator,everything rises & sets 90 to**the** horizon.

Time Exposure Photograph:• Estimate **the** exposure time• Which direction did stars move?

**Ann**ual Motion•As **the** **Earth** orbits **the** Sun, **the** Sun appears to moveeastward with respect to **the** stars.•The Sun circles **the** celestial sphere once every year.

**Ann**ual Motion•As **the** **Earth** orbits **the** Sun, **the** Sun appears to moveeastward with respect to **the** stars.•The Sun circles **the** celestial sphere once every year.

**Ann**ual Motion•As **the** **Earth** orbits **the** Sun, **the** Sun appears to moveeastward with respect to **the** stars.•The Sun circles **the** celestial sphere once every year.