Transcript Essay One - Physics & Astronomy

Astronomy 105
Student Information Sheet
 Class Syllabus
 Lab Syllabus
 Course Supplies
 Text
 Lab Manual
 Scantron 882-ES
 Flashlight with red filter

In Search of E.T.'s Breath
This is Astronomy
…not astrology.
A Sense of Scale
The Earth- 13,000km=13x103km (8080 miles)
 Solar System- 6,000,000,000km=6x109km
(4 x 109 miles)
 The Milky Way Galaxy-1018km(6x1018 miles)
 Local Group of Galaxies-1021km(6x1021miles)
 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
How many stars can one see on a clear
night”
 Approximately 3000.
 What is the closest star to Earth?
 The sun
 On what horizon do stars rise? Set?
 Rise from east- Set in the west


The Universe
 the totality of all space, time, matter
and energy

Astronomy
 the study of the universe

Light Year
 the distance traveled by a beam of light
in one year
The Sky Calendar




The sky is a master calendar.
Day
 the time for one Earth rotation.
Year
 the time for one Earth orbit around the Sun
Month
 the approximate time for the Moon to orbit the
Earth
Solar Day and Sidereal Day
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.
The Difference Between a Solar Day
and a Sidereal Day.
Synodic Month and Sidereal Month
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
The time it takes the moon to complete
one revolution around the Earth.
(27.3 solar days)
Sidereal Month and Synodic Month
Tropical Year and Sidereal Year
Tropical Year
The time interval from one vernal equinox to
the next. (365.242 mean solar days)
The tropical year is the year our calendars
measure.
Sidereal Year
The 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.)
Vernal
Equinox
Note:
360o = 24h
Or 15o/h

altitude - the angle of a star above the horizon

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)

The angle of Polaris above your horizon is the
same as your latitude in degrees.
Questions
Where are you if Polaris is directly overhead?
Ans: North Pole
Where
are you if Polaris is on your horizon?
Ans: Equator
What is the altitude of Polaris in Nacogdoches?
Ans:
31o 45’ 35.3’’= 31.7598o
Longitude: -94 39 40.5 = -94.6613
Our Latitude
View from the Equator
View from the North Pole
Circumpolar
Stars
Constellations
Constellations are recognizable patterns of
stars in the sky. (Based on stories and
named in honor of them)
 There are 88 constellations. (e.g. Orion)


The 12 constellations along the ecliptic on
your star chart are called the Zodiac
Constellations.
Asterisms
Asterism is a recognizable pattern of stars
that is not one of the 88 constellations.
 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

The path of our Sun across the celestial sphere
is called the ecliptic. It is inclined 23½° with
respect to the celestial equator.

What causes seasons on Earth?

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
Day and Night are equal
duration.
Shortest day in Northern
Hemisphere
Shortest Day in
Southern Hemisphere.
Hemisphere
Longest Day in
Southern Hemisphere.
Motions of the Sun and Stars
Daily Motion
 The rising and setting of the stars is
caused by the Earth’s rotation about its
axis.
 Annual Motion
 The Earth’s orbit around the Sun causes
different stars to be visible at different
times during the year.

Precession

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

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

A solar eclipse occurs when the Moon
passes between the sun and the earth.

A lunar eclipse occurs when the Moon
passes behind the Earth's shadow.

Note: The shape of the Earth was
determined by observing the shape of this
shadow.
1st Quarter
New Moon
Full Moon
3rd Quarter
Triangulation
Triangulation
A triangle of
fixed baseline is
narrower the
farther away the
object.
BASELINE
Measuring a Star’s Distance
Parallax - the apparent change in the
position of a star due to the motion of the
Earth
 Nearby objects exhibit more parallax than
remote ones.

Stellar Parallax
June
Sun
January
Nearby
Star
Parallax
Parallax
Distance ~ 1/Parallax angle
Angle
End of Section...