Astronomy 105 ä Student Information Sheet ä Class Syllabus ä Lab Syllabus ä Course Supplies ä Text ä Lab Manual ä Scantron 882-ES ä Flashlight with red filter

In Search of E.T.'s Breath

This is Astronomy …not astrology.

A Sense of Scale ä The Earth- 13,000km=13x10 3 ä The Earth- 13,000km=13x10 3 km (8080 miles) ä Solar System- 6,000,000,000km=6x10 9 km (4 x 10 9 miles) ä The Milky Way Galaxy km(6x10 18 miles) ä Local Group of Galaxies km(6x10 21 miles) ä 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)

Questions ä How many stars can one see on a clear night” ä Approximately ä What is the closest star to Earth? ä The sun ä On what horizon do stars rise? Set? ä Rise from east- Set in the west

ä The Universe ä the totality of all space, time, matter and energy ä Astronomy ä the study of the universe ä Light Year ä the distance traveled by a beam of light in one year

The Sky Calendar ä The sky is a master calendar. ä Day ä the time for one Earth rotation. ä Year ä the time for one Earth orbit around the Sun ä Month ä the approximate time for the Moon to orbit the Earth

Solar Day The time from one noon to the next. This is our 24 hr day. Sidereal Day A 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) Month The 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 Year The time interval from one vernal equinox to the next. ( mean solar days) Sidereal Year The time required for the Earth to complete one orbit around the Sun, relative to the stars. ( mean solar days – about 20 minutes longer than a tropical year.) The tropical year is the year our calendars measure.

Vernal Equinox

360 o = 24 h Or 15 o /h Note:

ä altitude - the angle of a star above the horizon ä The North Star, Polaris, is not the brightest star in the sky but remains in a fixed position in the sky. (near the North Celestial Pole) ä The angle of Polaris above your horizon is the same as your latitude in degrees.

Questions ä Ans: 31 o 45 ’ 35.3 ’’ = o Where are you if Polaris is directly overhead? ä Where are you if Polaris is on your horizon? What is the altitude of Polaris in Nacogdoches? ä Ans: North Pole ä Ans: Equator Longitude: -94   =  Our Latitude

View from the Equator

View from the North Pole

Circumpolar Stars

Constellations ä Constellations are recognizable patterns of stars in the sky. (Based on stories and named in honor of them) ä There are 88 constellations. (e.g. Orion) ä The 12 constellations along the ecliptic on your star chart are called the Zodiac Constellations.

Asterisms ä Asterism is a recognizable pattern of stars that is not one of the 88 constellations. ä For 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).

Seasons ä The path of our Sun across the celestial sphere is called the ecliptic. It is inclined 23½° with respect to the celestial equator. ä What causes seasons on Earth? ä Answer: The tilt of the Earth's rotational axis.

Inclined Pole causes Seasons

Ecliptic

Horizon 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 Stars ä Daily Motion ä The rising and setting of the stars is caused by the Earth’s rotation about its axis. ä Annual Motion ä The Earth’s orbit around the Sun causes different stars to be visible at different times during the year.

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

Precession – The Earth wobbles like a spinning top!

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

Eclipses Why Don’t We Have a Lunar Eclipse Every Month? Ans: The orbit of the moon is also tilted!!

Eclipses

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

ä A lunar eclipse occurs when the Moon passes behind the Earth's shadow. ä Note: The shape of the Earth was determined by observing the shape of this shadow.

New MoonFull Moon 1 st Quarter 3 rd Quarter

Triangulation

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

Measuring a Star’s Distance ä Parallax - the apparent change in the position of a star due to the motion of the Earth ä Nearby objects exhibit more parallax than remote ones.

Stellar Parallax Sun January June Nearby Star

Parallax Distance ~ 1/Parallax angle Parallax Angle

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