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The Celestial Sphere and Time: 

The Celestial Sphere and Time 29:50 Dr Bryce

Class notices: 

Class notices Labs begin this week Homework Quiz 1 is available on ICON Deadline is Friday at 5pm Remember drop/add slips are signed in the Physics General Office; Room 203 Van Allen Hall

The paths of stars during the course of a night: 

The paths of stars during the course of a night

Daily Motion: 

Daily Motion The daily (or more easily observed nightly) motion of stars is called the diurnal motion The path stars follow is called a diurnal circle For circumpolar stars we can see the complete diurnal circle, i.e. the star doesn’t set and rise

More Celestial Sphere definitions: 

More Celestial Sphere definitions The Celestial equator is the projection of the Earth’s equator The North Celestial pole is the projection of the Earth’s North Pole Polaris, the pole star lies very close the the North Celestial pole

The Meridian: 

The Meridian The Meridian is a great circle that passes through both poles and your Zenith It divides the sky into East and West

The Equatorial System: 

The Equatorial System Uses the Celestial Poles and the Celestial equator to define postions Declination (equivalent to latitude) gives the position angle north or south of the celestial equator Right ascension (equivalent to longitude) gives the position angle Eastwards around the Celestial equator from the Vernal Equinox These values remain constant as the Earth revolves

Your location: 

Your location Polaris is located in a constellation called the little dipper or Ursa Minor The altitude of Polaris is the same angle as your latitude on Earth Remember that when you are “facing” Polaris you are facing North

Altitude of the celestial pole = your latitude : 

Altitude of the celestial pole = your latitude

Observing at the North Pole: 

Observing at the North Pole

Observing at the Equator: 

Observing at the Equator

Thought Question The North Star (Polaris) is 50° above your horizon, due north. Where are you?: 

Thought Question The North Star (Polaris) is 50° above your horizon, due north. Where are you? You are on the equator. You are at the North Pole. You are at latitude 50°N. You are at longitude 50°E. You are at latitude 50°N and longitude 50°E.

Seasons : 

Seasons One of our most basic observations in Astronomy. In Summer the Sun is above the horizon for more time than it is in Winter. The days are longer and the nights are shorter. In Winter the Sun is above the horizon for less time and so it gets darker earlier.

And the stars we can see change: 

And the stars we can see change

The Motion of the Sun: 

The Motion of the Sun Throughout the year the Sun appears to move relative to the background stars The constellations through which the Sun passes have well know names; the Zodiac The Sun “moves” at a rate of about 1 degree a day

The Sun’s path: 

The Sun’s path The Sun’s path across the Celestial Sphere is called the Ecliptic Tilted in relation to the Celestial Equator This means that the Sun’s declination changes throughout the year NOTE the vernal equinox

Slide18: 

Seasons depend on how Earth’s axis affects the directness of sunlight

The Real Reason for Seasons: 

The Real Reason for Seasons Earth’s axis points in the same direction (to Polaris) all year round, so its orientation relative to the Sun changes as Earth orbits the Sun. Summer occurs in your hemisphere when sunlight hits it more directly; winter occurs when the sunlight is less direct. AXIS TILT is the key to the seasons; without it, we would not have seasons on Earth.

Variation in the Azimuthal angle of Sunrise: 

Variation in the Azimuthal angle of Sunrise

Fig.02.15: 

Fig.02.15

We can recognize solstices and equinoxes by Sun’s path across sky:: 

We can recognize solstices and equinoxes by Sun’s path across sky: Summer solstice: Highest path, rise and set at most extreme north of due east. Winter solstice: Lowest path, rise and set at most extreme south of due east. Equinoxes: Sun rises precisely due east and sets precisely due west.

Dates to remember…: 

Dates to remember… Sept 22, Autumnal Equinox, Sun will rise in the East and set in the West, the day and night will be of equal length. Dec 21, Winter Solstice, Sun rises in SE sets in SW, least amount of day March 21, Vernal Equinox June 21, Summer Solstice, Sun rises in NE, sets in NW, longest day

Extreme “days”: 

Extreme “days”

What do we mean by “day”?: 

What do we mean by “day”? A Solar day is the amount of time between successive Meridian crossings by the Sun A Sidereal day is the amount of time for a star to return Sidereal means relative to the Stars The Sun is moving Eastwards by about a degree a day relative to the stars Solar day is longer!

The Sun passes through the meridian for different observers at different times: 

The Sun passes through the meridian for different observers at different times

The Moon: 

The Moon Earth’s Satellite Takes about 27 days to orbit the Earth On average 380,000,000 m Or 3.8*108 m from the Earth

Phases of the Moon: 

Phases of the Moon

In another example: 

In another example Remember that Moonlight is reflected Sunlight.

Slide31: 

Phases of the Moon: 29.5-day cycle new crescent first quarter gibbous full gibbous last quarter crescent waxing Moon visible in afternoon/evening. Gets “fuller” and rises later each day. waning Moon visible in late night/morning. Gets “less” and sets later each day. } }

There is no dark side!: 

There is no dark side!

Remember the horns point away from the Sun: 

Remember the horns point away from the Sun

Time and the Moon: 

Time and the Moon

Eclipses: 

Eclipses This photo shows an annular Solar Eclipse. The Moon’s angular diameter is too small to cover the Sun Just the Earth the Moon’s orbit is an ellipse so the distance to the Moon varies If the Moon is further away it’s angular diameter is smaller.

Time lapse photography of a Total Solar Eclipse: 

Time lapse photography of a Total Solar Eclipse

Some definitions: 

Some definitions Solar Eclipse: the Moon is between the Earth and the Sun. Lunar Eclipse: the Earth is between the Moon and the Sun As the Earth is much larger it has a bigger shadow so Lunar Eclipses are more common and visible from more of the Earth

More definitions: 

More definitions Totality: The time period in which the Moon completely covers the Sun, normally just a couple of minutes. The sky becomes dark and you can see the stars. Partial: The Moon doesn’t completely cover the Sun and you see a crescent or a bite taken out of the Sun. Health warning: Do not look at the Sun with your naked eye or with binoculars, even during an partial eclipse you can blinded.

The Moon isn’t in the same plane as the Earth/Sun: 

The Moon isn’t in the same plane as the Earth/Sun

So we don’t get eclipses every month…: 

So we don’t get eclipses every month…

Path of Totality: 

Path of Totality

Summary: Two conditions must be met to have an eclipse:: 

Summary: Two conditions must be met to have an eclipse: It must be full moon (for a lunar eclipse) or new moon (for a solar eclipse). AND The Moon must be at or near one of the two points in its orbit where it crosses the ecliptic plane (its nodes).

Planets: 

Planets A view of the Solar System Notice Pluto’s orbit Notice that our part of the Solar System is close to the Sun.

Our view of the planets: 

Our view of the planets Mercury difficult to see; always close to Sun in sky Venus very bright when visible; morning or evening “star” Mars noticeably red Jupiter very bright Saturn moderately bright

The Planets and Our Culture: 

The Planets and Our Culture

Westwards motion?: 

Westwards motion? We see the Sun, Moon and the Superior Planets moving Eastwards relative to the Stars But occassionally we see Westwards motion

The explanation: 

The explanation

Next Stop: 

Next Stop A Historical overview of Astronomy! What did ancient people believe about the Heavens