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In Search of E.T.'s Breath

This is AstronomyThis is Astronomy

……not astrologynot astrology..

A Sense of ScaleA Sense of Scale

The Earth- 13,000km=13x10The Earth- 13,000km=13x1033km (8080 miles) Solar System- 6,000,000,000km=6x10Solar System- 6,000,000,000km=6x1099km km

(4 x 10(4 x 1099 miles) miles) The Milky Way Galaxy-10The Milky Way Galaxy-101818km(6x10km(6x101818 miles) miles) Local Group of Galaxies-10Local Group of Galaxies-102121km(6x10km(6x102121miles)miles) Universe-bigger than we can imagine.Universe-bigger than we can imagine.

The Earth

The Sun

A Typical Galaxy

1 light year = 10,000,000,000,000 km 6,000,000,000,000 miles (10 trillion km) (6 trillion miles)

QuestionsQuestions

How many stars can one see on a clear How many stars can one see on a clear night”night”

Approximately 3000.Approximately 3000. What is the closest star to Earth?What is the closest star to Earth? The sunThe sun On what horizon do stars rise? Set?On what horizon do stars rise? Set? Rise from eastRise from east - Set in the west- Set in the west

The UniverseThe Universe the totality of all space, time, matter and energythe totality of all space, time, matter and energy

AstronomyAstronomy the study of the universethe study of the universe

Light YearLight Year the distance traveled by a beam of light in one the distance traveled by a beam of light in one

yearyear

The Sky CalendarThe Sky Calendar

The sky is a master calendar.The sky is a master calendar. DayDay

the time for one Earth rotation.the time for one Earth rotation. YearYear

the time for one Earth orbit around the Sunthe time for one Earth orbit around the Sun MonthMonth

the approximate time for the Moon to orbit the the approximate time for the Moon to orbit the EarthEarth

Solar DayThe time from one noon to the next. This is our 24 hr day.

Sidereal DayA day measured by the slight shift of the stars positions from one evening to the next. This is roughly 23h, 56min. the Solar Day is approximately 4min. longer than the sidereal day.

Solar Day and Sidereal Day

The Difference Between a Solar Day and a Sidereal Day.

Synodic Month and Sidereal Month

The time it takes the moon to complete one revolution around the Earth. (27.3 solar days)

Synodic (Lunar) MonthThe time it takes the moon to complete one full cycle of phases, from one new moon to the next new moon) (29.5 solar days)

Sidereal Month

Sidereal Month and Synodic Month

Tropical Year and Sidereal Year

Tropical YearThe time interval from one vernal equinox to the next. (365.242 mean solar days)

Sidereal YearThe time required for the Earth to complete one orbit around the Sun, relative to the stars.

(365.256 mean solar days – about 20 minutes longer than a tropical year.)

The tropical year is the year our calendars measure.

Vernal Equinox

360o = 24h

Or 15o/h

Note:

altitudealtitude - the angle of a star above the horizon - the angle of a star above the horizon

The The North StarNorth Star, Polaris, is not the brightest star , Polaris, is not the brightest star in the sky but remains in a fixed position in the in the sky but remains in a fixed position in the sky. (near the North Celestial Pole)sky. (near the North Celestial Pole)

The angle of Polaris above your horizon is the The angle of Polaris above your horizon is the same as your same as your latitudelatitude in degrees. in degrees.

QuestionsQuestions

Ans: 31Ans: 31oo 45 45’’ 35.3 35.3’’’’= 31.7598= 31.7598oo

Where are you if Polaris is directly overhead?Where are you if Polaris is directly overhead?

Where are you if Polaris is on your horizon?Where are you if Polaris is on your horizon?

What is the altitude of Polaris in Nacogdoches?What is the altitude of Polaris in Nacogdoches?

Ans: North PoleAns: North Pole

Ans: EquatorAns: Equator

Longitude: -94 39 40.5 = -94.6613

Our Latitude

View from the EquatorView from the Equator

View from the North PoleView from the North Pole

Circumpolar StarsCircumpolar Stars

ConstellationsConstellations

ConstellationsConstellations are recognizable patterns of are recognizable patterns of stars in the sky. (Based on stories and stars in the sky. (Based on stories and named in honor of them)named in honor of them)

There are 88 constellations. (e.g. Orion) There are 88 constellations. (e.g. Orion)

The 12 constellations along the ecliptic on The 12 constellations along the ecliptic on your star chart are called the your star chart are called the Zodiac Zodiac ConstellationsConstellations..

AsterismsAsterisms

AsterismAsterism is a recognizable pattern of stars is a recognizable pattern of stars that is not one of the 88 constellations.that is not one of the 88 constellations.

For Example: The Big DipperFor Example: The Big Dipper

Asterisms developed as navigational tools for early seafarers.

Asterisms can include parts of constellations (subsets), or can include two or more constellations (supersets).

SeasonsSeasons

The path of our Sun across the celestial sphere The path of our Sun across the celestial sphere is called the is called the eclipticecliptic. It is inclined 23½° with . It is inclined 23½° with respect to the respect to the celestial equatorcelestial equator..

What causes seasons on Earth?What causes seasons on Earth?

Answer: The tilt of the Earth's rotational axis.Answer: The tilt of the Earth's rotational axis.

Inclined Pole causes SeasonsInclined Pole causes Seasons

Ecliptic

Horizon CalendarHorizon Calendar

June(Summer Solstice)

March & September(Equinoxes)

December(Winter Solstice)

Longest day in Northern

Hemisphere

Shortest Day in Southern Hemisphere.

Shortest day in

Northern Hemisphere

Longest Day in Southern Hemisphere.

Day and Night are equal duration.

Motions of the Sun and StarsMotions of the Sun and StarsMotions of the Sun and StarsMotions of the Sun and Stars

Daily MotionDaily MotionThe rising and setting of the stars is The rising and setting of the stars is

caused by the caused by the Earth’s rotationEarth’s rotation about its about its axis.axis.

Annual MotionAnnual MotionThe The Earth’s orbitEarth’s orbit around the Sun causes around the Sun causes

different stars to be visible at different different stars to be visible at different times during the year.times during the year.

PrecessionPrecession

PrecessionPrecession is the slow wobble of the is the slow wobble of the Earth’s axis due to the influence of the Earth’s axis due to the influence of the Moon.Moon.

Precession – The Earth wobbles like a spinning top!Precession – The Earth wobbles like a spinning top!

The Lunar PhasesThe Lunar PhasesThe Lunar PhasesThe Lunar Phases

As the moon orbits the Earth, the moon goes As the moon orbits the Earth, the moon goes through through phases phases. Since the name of our moon is . Since the name of our moon is Luna, these are called Luna, these are called Lunar PhasesLunar Phases..

Eclipses

Why Don’t We Have a Lunar Eclipse Every Month?

Ans: The orbit of the moon is also tilted!!

Eclipses

A A solar eclipsesolar eclipse occurs when the Moon occurs when the Moon passes between the sun and the earth.passes between the sun and the earth.

A A lunar eclipselunar eclipse occurs when the Moon occurs when the Moon passes behind the Earth's shadow.passes behind the Earth's shadow.

Note: The shape of the Earth was Note: The shape of the Earth was determined by observing the shape of this determined by observing the shape of this shadow.shadow.

New MoonFull Moon

1st Quarter

3rd Quarter

Triangulation

Triangulation

A triangle of fixed baseline is narrower the farther away the object.

BASELINE

Measuring a Star’s DistanceMeasuring a Star’s DistanceMeasuring a Star’s DistanceMeasuring a Star’s Distance

ParallaxParallax - the apparent change in the - the apparent change in the position of a star due to the motion of the position of a star due to the motion of the EarthEarth

Nearby objects exhibit more parallax than Nearby objects exhibit more parallax than remote ones.remote ones.

Stellar ParallaxStellar Parallax

Sun

January

June

Nearby Star

Parallax

Distance ~ 1/Parallax angle

Parallax

Angle

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