The Sky:

Naked Eye Stars: "naked eye" = without a telescope.

• ~ 6000 stars
• ~ 88 Constellations  - mesopotamia > ½ - latin & modern < 1/2

 In the past these were taken very seriously! Astrology!! (In fact, an influential astronomer named Kepler made astrological readings for the paying nobility of his research. He also devised astrological musical harmonics for each of the known six wandering stars.)   All around the world cultures (ancient and new) have celebrated heroes, gods, and mythical beasts by naming  groups and patterns of stars, which we call constellations.

Zodiacal Constellations: (Sun's Path across the sky during the year)

Joe Trivia Note!! Your own "sign" is determined by how the sky looked 2000 years ago!! NOT the way it looked when you where actually born!! The astrological sky has been “frozen” since the Babylonian era. Constellations drift with respect to the Sun and time of year, thus it was annoying astrologers that certain zodiacal signs would not always occur during specific times of year. Your actual zodiacal sign, where the Sun was located in the sky on your birth date, is actually about one to one and a half signs backward. For instance, an astrologer would say I’m an Aquarius, while the Sun was actually in Capricorn when I was born. Move one sign backwards.

Figure: The 12 Zodiacal Constellations. Hey? What is your sign, baby?

Asterisms: In addition to the official constellations, the sky also contains a number of less formally defined pop-culture star groupings called asterisms.

• "Ursa Major" = Constellation  "Big Dipper" = Asterism
• Modern View of Constellations: Accidental Alignments:

Caution: When looking at a constellation's star pattern, it is tempting to conclude that you are seeing a group of stars that are all relatively close to each other. In fact, most of these stars are nowhere near each other! Stars are at varying distances and are moving in varied directions!! Constellations are temporary and will distort in about 10⁵ years.)

• Historical & Cultural Value!!
• What's your sign? 
• 1-800-psychic!!

Joe Astronomy: Some night during the semester find a dark patch of night sky. Spend a few hours just looking up at the stars. I am sure you will be amazed at what you see even in as little as two hours. This was the MTV and cable TV of the ancient world. There was always something new to see and some thought new to explore about the night sky.

Brightness of Stars:

Hipparchus of Nicaea (190-120 B.C.) (now Iznik), Bithynia (now Turkey) Died: 125 BC in Rhodes, Greece

"Magnitude Scale"

• The smaller the magnitude the brighter! (Negative too!) The larger the magnitude the dimmer!
• Apparent Visual Magnitudes - "apparent" brightness.
• Absolute Magnitude - intrinsic "real" brightness of the star.
   

1 mag  =  2.512 times in brightness.

2 mag diff. = 2.512´2.512 times in brightness.

3 mag diff. = 2.512´2.512´2.512 times in brightness.

4 mag diff.  = 2.512´2.512´2.512´2.512 times in brightness.

5 mag diff. = (2.512)⁵ = 100 times in brightness.

"There is a time…..TURN,TURN,TURN!!"

Stars: How they move - practical everyday experience. These are observations of the stars that were for centuries made with only the naked eye and great patience. We will start with what may seem the obvious, but often does lead to a few surprises.

Daily (Nightly) - Stars rise in the "East" and set in the "West."

Why??? Earth's rotation is "West" to "East" (Eastward)

Annually (Yearly) - some seasonal, some always, some never (for us)

Figure : The observers latitude on the surface of the Earth will determine the stars that are "always," "seasonal," or "never" visible.

Diurnal Motion –

• Daily progess of the Sun & stars across the sky.
• Why??? Revolution of Earth about the Sun!!

"The Days of Our Lives!" (or) "One Day at a Time!"

• Sidereal Day: Earth makes one complete rotation
• Solar Day: Time between noon one day, and noon he next! (How different?) Apparent Solar Day > Sidereal Day by about 4 minutes
• Variations do occur because
• Earth's orbit is elliptic
• Earth's Axis of Rotation is tilted on its axis!

Celestial "Seasons" Sphere:

Earthly coordinates in Space.

     Reference maps on the sky! - A simple extension of Earth's coordinate structure out into the heavens. To the Ancients: We were inside a hollow sphere centered on us. We know better, but for directions it is very useful.

Ecliptic: Apparent Path of the Sun in the Sky. (Zodiacal Constellations!)

Cycles of the Sky:

Sun moves around the "celestial sphere," through stars along the ecliptic. Why? Because the Earth orbits the Sun!!

Seasons:

Why? Earth's axis is tilted! Without the tilt (23.5o with respect to ecliptic) the "celestial equator equals the ecliptic! Sun would always be over the Earth's equator (no seasons!) With tilt, the sun goes above and below the equator (Tropics of Cancer and Capricorn) Seasons!

Caution: It is a common misconception that the Earth is closer to the Sun in the summer and farther away in the winter. In fact, the Earth is closer to the Sun in January, when it is winter in the northern hemisphere, and farthest away in July!! And this is only true for those of us living on the Earth’s northern hemisphere.

Length of Day & Night

(December in Salisbury)

What is a "day" really?

· Equator: Day = Night (always)

· 32oN (Salisbury) Day< Night (Winter)

· North Pole (above 23.5o from pole) all night!

· 32oS Day>Night (Summer)

· South Pole (all day!)

At an "Equinox"

Sun is directly above equator (ecliptic and CEQ cross) and there is "equal day and night" for everyone!

Long Term Complication: Precession

Earth Wobbles (but it won't fall down) like a spinning top.

· 26,000 year cycle (a complete cycle), Earth's axis remains at 23.5o while precessing. Consequences!

Pole Star is temporary! (Polaris now, Vega in  about 13,000 years.)

Seasons Drift!! What? The seasons shift through calendar over time! (Remember how Astrologers stuck  the sky 2000 years ago?!)

Orbital Sidereal Year - one complete orbit around the Sun  (365d,6h,9m,10s) 

Tropical Year (Year of Seasons) - time between one vernal equinox and the next vernal equinox. (365d,5h,48m,46s)

RESULT:  13,000 orbits = 13000.5 seasonal cycles!

NOTE! Speaking of which! When did the "new" millennium start? 2001? 2000? Or how about around 1995? 1996? Little known trivia! Our Gregorian Calendar is wrong! Gregorian Monks trying to correct for leap years, leap seconds, etc… attempted to "fix" the calendar system a few centuries ago and messed up. They made about a 4 year error. The (Western) "new millennium" has already happened!! Hey! Not to mention, what about other calendars? Hindu, Chinese? Tibetian? All have many different years associated with them.

The Moon's Phases & Tides

Note: The Moon rises in the East about 51 minutes later each day!!

Naming Phases: View From Earth!!

· Crescent when less than 1/2 of face is bright.

· Gibbous  when more than 1/2 of face is bright.

· Waxing when amount bright is growing.

· Waning when amount bright is shrinking.

The Rising and Setting Moon!

(What does "rise" mean? What does "set" mean?)

   Rises Sets Let's Practice a few!!! How about….

· New  Sunrise Sunset

· 1st Qtr. Noon Midnight

· Full Sunset Sunrise

· 3rd Qtr. Midnight Noon

Two Different Lunar Periods:

· Sidereal Lunar Period: One complete orbit around the Earth. Just one complete trip around to the same beginning location. Moon's Sidereal Period is 27.3 days.

· Synodic Lunar Period: Time between one full (new) moon until the next full (new) moon. "Moonth." Why??? Earth is also revolving around the Sun! We need to get the same orientation to get successive like moon phases. Synodic period is 29.5 days. (The month).

 EarthShine

     Leonardo DaVinci ~ 500 years ago. We can actually view a small amount of glow from the shaded portion of the moon. Sunlight manages to reflect off of the Earth and its atmosphere towards the moon. The light then bounces from the moon back to the Earth where we see a dimly lit shadowed portion of the moon not in direct sunlight.

Earthshine is simply the reflection of sunlight off of the Earth’s atmosphere towards the moon that also reflects off the moon back towards the Earth. This gives observers on Earth the ability to slightly see the darkly shaded portion of the moon’s surface.