Intro to Night Sky Diurnal Motion - Los Angeles Mission ... F2015... · Intro to Night Sky Diurnal Motion. ... • 1st magnitude = the brightest stars ... given as the angular difference

Astronomy 1 — Elementary Astronomy LA Mission College

Spring F2015

Intro to Night Sky Diurnal Motion

Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015

Quotes & Cartoon of the Day

“Mortal as I am, I know that I am born for a day. But when I follow at my pleasure the serried multitude of the stars in their circular course, my feet no longer touch the earth.”

― Ptolemy

“Excuse me while I kiss the sky.”

― Jimi Hendrix


Last Class

• Welcome


Last Class

• The paperwork that got missed last time

• What is Science?

• Definition

• The Scientific Method

• Recognizing Science

• What is Astronomy?

• Astronomy and Astrology

• In-class exercise: Numbers, Correlation and Causality aka “Allstate ICE”


This Class

• In-class exercise: Numbers, Correlation and Causality aka “Allstate ICE”

• Intro to the Night Sky

• Apparent Magnitude

• Diurnal Motion

• LT “Position” time permitting


Spring F2015

In-Class Exercise

Allstate & Astrology

ALLSTATE DEBRIEF





Side by Side


Lies, damned lies & statistics

• “Figures often beguile me, particularly when I have the arranging of them myself; in which case the remark attributed to Disraeli would often apply with justice and force: "There are three kinds of lies: lies, damned lies and statistics."”

• - Mark Twain's Own Autobiography: The Chapters from the North American Review

http://www.twainquotes.com/Statistics.html#


Spring F2015

Intro to Night Sky

CONSTELLATIONS AND ASTERISMS


Video — Constellations

• http://www.amazon.com/gp/product/B0054ELDYO/ref=dv_dp_ep10

• 1:00 to 3:50

• 11:25 to 19:00

http://www.amazon.com/gp/product/B0054ELDYO/ref=dv_dp_ep10


Constellations

• IAU recognizes 88 covering the sky

• Other “star pictures” like Big Dipper are “asterisms”

THE MAGNITUDE SCALE


Apparent Magnitude

• Magnitude scale was first empirical, later became precise

• The Greeks divided the stars into 6 magnitude categories

• 1st magnitude = the brightest stars

• 2nd = bright

• 3rd = less bright

• 4th = getting faint

• 5th = definitely faint

• 6th = faintest human eyes can detect


Apparent Magnitude

• Scale has been extended to account for objects brighter than stars seen from Earth and for the use of binoculars & telescopes

• Has also been made numerically precise

http://www.ucolick.org/~bolte/AY4_00/week4/star_propertiesC.html

Let’s Practice


If star Primrose has an apparent magnitude of 2 and star Katniss has an apparent magnitude of 4, which appears brighter?

A. Katniss

B. Primrose

C. Both appear the same brightness


If star Obiwan has an apparent magnitude of -3 and star Anniken has an apparent magnitude of 1, which appears brighter?

A. Anniken

B. Obiwan

C. Both appear the same brightness

MAPPING THE SKY


The Celestial Sphere

• Essentially a convenient fiction

• 2 ways to describe where something is:

• relative to you

• Zenith — point overhead

• Horizon

• Fixed relative to the stars


Coordinates

Celestial equator = projection of

Earth’s equator onto the c.s.

North celestial pole = projection of

Earth’s north pole onto the c.s.

The North and South Celestial Poles and the Celestial Equator are fixed with respect to the background stars


Relationship between Celestial Poles and Zenith/Nadir

• The relationship between Celestial Poles and Zenith/Nadir depends on the location in latitude of the observer

• At the North Pole (lat=90°) the zenith and NCP are the same

• At the South Pole (lat=-90°) the zenith and the SCP are the same

• In So Cal (lat = ~34° N) the NCP is ~34° above the horizon to the North

• At the equator, the NCP is on the horizon (lat = 0°)

• In Sydney, Australia (lat = ~34° S or ~-34°) the SCP is about 34° above the horizon to the South


Navigation

• Recognize constellations, general orientation

• Establish N,S,E & W

• Distance of Polaris above horizon (N hemisphere) gives latitude

• Need to track time for longitude

• Sun, Moon provide additional info


Angular Distance

• The distance between two stars on the celestial sphere can only be given as the angular difference between the lines of sight to the stars.

• These are measured as angles in degrees, arc minutes and arc seconds • 360° in a circle • 60 arc-minutes in a degree (60’) • 60 arc-seconds in a minute (60”)


Angular Distance vs. True Distance

• The stars that appear to make a picture often only seem to be close to one another

• They are a small angular distance from each other

• They may be located at very different distances from us along the line of sight

• Many light-years different


Equatorial Coordinates

• Right Ascension: RA

• angle west along the celestial equator

• measured in hours (h), minutes (m) & seconds (s), where 24h = 360°.

• Declination: Dec

• Angle N (+°) or S (-°) from the celestial equator.

• Measured in degrees, arcmin, arcsec

• Similar to latitude and longitude.

http://astronomy.swin.edu.au

http://astronomy.swin.edu.au

DIURNAL MOTION


Diurnal Motion

• “Diurnal” means “daily”

• From Earth, the sky as a whole appears to move from east to west continuously, including the sun, moon, planets and stars

• More accurately, it moves in circles around the North Celestial Pole

• The Ancients assumed the sky was moving

• We now know the earth is rotating


Diurnal Motion Demonstration


Circumpolar Stars

• Stars very near the N and S Celestial Poles are called “circumpolar” and never set, they just circle the pole

• You could see them all night and all day if the scattering of sunlight in the atmosphere were much less

WARM UP QUESTION FOR LT POSITION


You observe a star rising directly in the East. When it reaches its highest position above the horizon, where will it be?

A. high in the northern sky

B. high in the eastern sky

C. high in the southern sky

D. high in the western sky

LECTURE-TUTORIAL “POSITION” PP 1-2


You observe a star rising directly in the East. When it reaches its highest position above the horizon, where will it be?

A. high in the northern sky

B. high in the eastern sky

C. high in the southern sky

D. high in the western sky

Let’s Practice


If you observe the constellation Orion just above the horizon to the east, where will it appear to be an hour later?

A. Closer to the horizon, to the East.

B. Further above the horizon, to the East.

C. In the same location.

D. It will not be visible.


Stars that rise due East are above the horizon 12 hours. Circumpolar stars are always above the horizon. About how long do you think a star that rises nearer the NE compass point could be above the horizon?

A. 6 hours

B. 12 hours

C. 18 hours

D. 24 hours

W

E

N S


In the northern hemisphere, stars rise in the East, set in the West and travel counter-clockwise in circles around the North celestial pole.

In the southern hemisphere, the stars

A. rise in the West, set in the East and travel clockwise around the South celestial pole.

B. rise in the East, set in the West and travel counter-clockwise around the South celestial pole.

C. rise in the East, set in the West and travel clockwise around the South celestial pole.

D. rise in the West, set in the East and travel counter-clockwise around the South celestial pole

WRAP-UP


Topic for Next Class

• Night Sky II

• Annual Patterns

• Seasons


Reading Assignment

• Ch 2 in either text


Homework

• None Assigned yet

Documents

Intro to Night Sky Diurnal Motion - Los Angeles Mission ... F2015... · Intro to Night Sky Diurnal Motion. ... • 1st magnitude = the brightest stars ... given as the angular difference