Review Questions How do you write Scientific Notation? How do you write Scientific Notation? What is the difference between Angular Measurements and Linear Measurement? What is the difference between Angular Measurements and Linear Measurement? What are the names of the scientists mentioned in class? What are the names of the scientists mentioned in class?

How do you write Scientific Notation? Move the decimal until it is after the first non-zero digit. Every space it is moved to the left is a positive power of ,395,  x ,000  1.25x10 5 Every space it is moved to the right is a negative power of  x  1.654x10 -1

What is the difference between Angular Measurements and Linear Measurement? Is the man standing on the bottle of coke? Which is larger the bottle of Coke or the man? The bottle covers a larger percent of the picture – so it has a larger angular size. The man covers a smaller percent of the picture – because he is farther away.

What are the names of the scientists mentioned in class? Tycho Brahe ( ): Danish Astronomer – made careful measurements of planetary motion. Died of burst bladder. Tycho Brahe ( ): Danish Astronomer – made careful measurements of planetary motion. Died of burst bladder. Johannes Kepler ( ) French Mathematician and Astronomer. Used Brahe’s measurements to study planetary motion. Johannes Kepler ( ) French Mathematician and Astronomer. Used Brahe’s measurements to study planetary motion. Nicolaus Copernicus ( ) Italian Monk. Proposed Sun-centered universe. Nicolaus Copernicus ( ) Italian Monk. Proposed Sun-centered universe.

January Night Sky

JanuaryNightSkyStarGroupings

JanuaryNightSkyStarGroupingsConstellations

JanuaryNightSkyStarGroupingsConstellations Sky Boundaries

Big Dipper – Ursa Major

Leo – The Lion

Orion – The Hunter

Constellations 88 groups of stars (as seen from Earth) cover the entire sky 88 groups of stars (as seen from Earth) cover the entire sky Named by Ancient Greek stargazers – and associated with Greek mythology Named by Ancient Greek stargazers – and associated with Greek mythology Used by Astronomers to name and locate stars. Used by Astronomers to name and locate stars. 12 Constellations that lie along the celestial equator are called the Signs of the Zodiac and are associated with the months of the year. 12 Constellations that lie along the celestial equator are called the Signs of the Zodiac and are associated with the months of the year.

Motion of Stars - Daily Daytime: Dispersed light from sun makes the sky blue – hides stars Nighttime: Earth blocks sunlight. Stars are visible

Show Animation Apparent Motion of Stars around Earth

Daily Motion of Stars  Earth Rotates on its Axis  At North (or South Pole)  Star at Zenith does not moves  All other stars move in a circle around the Zenith  Stars to not rise nor set  At Equator  Stars travel from eastern horizon to western horizon.  If you look north, stars rise vertically to the east of north, arc above due north, and set vertically to the west of north.  At Middle Latitudes  At a point due north, above the horizon at an angle equal to your latitude is the celestial pole. All stars appear to orbit this point.  Stars rise and set at an angle.

Show Animation Diurnal Motion

Diurnal Motion Due to Intensity of sunlight and dispersed sunlight (blue sky) – Stars are not visible during the day (when we face the sun) Due to Intensity of sunlight and dispersed sunlight (blue sky) – Stars are not visible during the day (when we face the sun) Astronauts above the Earth’s atmosphere see the stars 24 hours a day. Astronauts above the Earth’s atmosphere see the stars 24 hours a day. As with the sun, the stars generally travel across the sky from the East to West due to the rotation of the Earth. As with the sun, the stars generally travel across the sky from the East to West due to the rotation of the Earth.

Annual Motion of the Stars Earth orbits Sun once per year Stars visible at night change as the earth moves around the sun.

Celestial Sphere Celestial Sphere: Location of Stars around the Earth Celestial Sphere: Location of Stars around the Earth Celestial Poles: Points on Celestial Sphere directly above Earth’s Axis of Rotation – These stars do not appear to move Celestial Poles: Points on Celestial Sphere directly above Earth’s Axis of Rotation – These stars do not appear to move Celestial Equator: Stars directly above earths Equator. Celestial Equator: Stars directly above earths Equator.

Tilt of Earth’s Axis Orbit of Earth around Sun is tilted relative to Earth’s rotation axis. Orbit of Earth around Sun is tilted relative to Earth’s rotation axis. Ecliptic: Apparent path of sun around the celestial sphere. Ecliptic: Apparent path of sun around the celestial sphere.

Earth’s Orbit as viewed from Sun

Tilt points in same direction all year Cause of Seasons

Arctic Circle, Tropics, and Equator

Sun above the Arctic Circle in Summer

Seasons Celestial Sphere determined by Earth’s Axis of Rotation Celestial Sphere determined by Earth’s Axis of Rotation Axis of Rotation is tilted relative to the Earth’s Orbit around the Sun Axis of Rotation is tilted relative to the Earth’s Orbit around the Sun Summer Solstice: North Pole points toward sun (northern hemisphere) Summer Solstice: North Pole points toward sun (northern hemisphere) Winter Solstice: North Pole points away from sun Winter Solstice: North Pole points away from sun Equinox: North Pole is perpendicular to the sun. Vernal (spring) Autumnal (fall) Equinox: North Pole is perpendicular to the sun. Vernal (spring) Autumnal (fall)

Celestial Sphere Measurements Zenith: Point directly above the observer. Zenith: Point directly above the observer. Meridian: Line from North Pole to South Pole that passes through the Zenith Meridian: Line from North Pole to South Pole that passes through the Zenith Horizon: Circle around observer where sky and ground appear to meet. Horizon: Circle around observer where sky and ground appear to meet.

Vernal Equinox Point on the Celestial Sphere directly behind the sun during the First day of Spring (March 21). Point on the Celestial Sphere directly behind the sun during the First day of Spring (March 21).

Celestial Coordinates Angle of Right Ascension: Measured in Hours, Min, Sec. Angle of Right Ascension: Measured in Hours, Min, Sec. If Vernal Equinox at midnight is at Zenith, then the Angle of Right ascension is the time at which the star of interest is at Zenith. If Vernal Equinox at midnight is at Zenith, then the Angle of Right ascension is the time at which the star of interest is at Zenith. Angle of declination is the angle toward the north pole the object is from Zenith. Angle of declination is the angle toward the north pole the object is from Zenith.

Example: We want to locate the star Vega. It’s coordinates are We want to locate the star Vega. It’s coordinates are RA: 18h 36m 56.3s Dec: +38° 47' 01“ Locate Vernal Equinox: Move 18 h 36 m 56.3s east. Move 38° 47' 01“ toward the north. Locate Vernal Equinox: Move 18 h 36 m 56.3s east. Move 38° 47' 01“ toward the north.

Sidereal vs Solar Time Solar Time: Solar Time: Day: Time for sun to move from Meridian back to Meridian = 24 hours.

Sidereal time Sidereal Day: Time for Earth to rotate once on its axis, relative to the celestial sphere Sidereal Day: Time for Earth to rotate once on its axis, relative to the celestial sphere 23 hours 56 min.

Summary