Lecture 3 – The Sky Constellations, Star Names, and Magnitudes.

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Lecture 3 – The Lecture 3 – The Sky Sky Constellations, Star Names, and Constellations, Star Names, and Magnitudes Magnitudes

Transcript of Lecture 3 – The Sky Constellations, Star Names, and Magnitudes.

Page 1: Lecture 3 – The Sky Constellations, Star Names, and Magnitudes.

Lecture 3 – The Lecture 3 – The SkySky

Constellations, Star Names, and Constellations, Star Names, and MagnitudesMagnitudes

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Homework 2 – Due Monday, February Homework 2 – Due Monday, February 55 Unit 5: Problem 2, Test Yourself 3Unit 5: Problem 2, Test Yourself 3 Unit 6: Review Questions 1, 3Unit 6: Review Questions 1, 3 Unit 9: Review Question 2, Test Yourself 1Unit 9: Review Question 2, Test Yourself 1 Unit 11: Review Question 2, Test Yourself Unit 11: Review Question 2, Test Yourself

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The ConstellationsThe Constellations

OriginsOrigins Star patterns named Star patterns named

by ancient peoples by ancient peoples after gods, after gods, goddesses, animals, goddesses, animals, monsters, and mythic monsters, and mythic heroes.heroes.

The constellations The constellations used by Western used by Western Culture today Culture today originated in originated in Mesopotamia around Mesopotamia around 3,000 B.C.3,000 B.C.

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The ConstellationsThe Constellations Only certain stars were Only certain stars were

part of the pattern and part of the pattern and belonged to the belonged to the constellation. Faint constellation. Faint stars were not part of stars were not part of any constellations.any constellations.

Frequently Frequently constellations were constellations were named for their named for their brightest star.brightest star.

Of the constellations Of the constellations defined by the defined by the Babylonians, Egyptians, Babylonians, Egyptians, and Greeks, 48 are still and Greeks, 48 are still used today.used today.

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The ConstellationsThe Constellations The ancient The ancient

civilizations we got civilizations we got the 48 classical the 48 classical constellations from constellations from couldn’t see the couldn’t see the entire southern sky.entire southern sky.

During the Age of During the Age of Sail, European Sail, European explorers added 40 explorers added 40 modern modern constellations in the constellations in the “uncharted” areas of “uncharted” areas of the sky.the sky.

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The ConstellationsThe Constellations

The 48 classical and the 40 modern The 48 classical and the 40 modern constellations make up the 88 official constellations make up the 88 official constellations used by astronomers today.constellations used by astronomers today.

The term The term constellationconstellation also now has a also now has a new meaning:new meaning: No longer refers to the pattern of stars itself.No longer refers to the pattern of stars itself. Now refers to a well defined region of the sky Now refers to a well defined region of the sky

that contains the traditional star pattern.that contains the traditional star pattern. EverythingEverything inside that region of the sky is now inside that region of the sky is now

part of the constellation, like a “celestial state”.part of the constellation, like a “celestial state”.

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The ConstellationsThe Constellations

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What Is An Asterism?What Is An Asterism?

In addition to the 88 In addition to the 88 official constellations official constellations there are several there are several unofficial but unofficial but popular star popular star patterns.patterns.

Called Called asterismsasterisms.. Examples:Examples:

The Big DipperThe Big Dipper The Little DipperThe Little Dipper The Northern CrossThe Northern Cross The Great SquareThe Great Square

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Daily Grade 3 – Question Daily Grade 3 – Question 11

1.1. Which statement below most Which statement below most accurately describes accurately describes modernmodern constellations?constellations?

A.A. They are 88 well defined regions in the They are 88 well defined regions in the sky.sky.

B.B. They are 88 connect-the-dot mythological They are 88 connect-the-dot mythological sky figures.sky figures.

C.C. They are 13 connect-the-dot mythological They are 13 connect-the-dot mythological sky figures along the ecliptic.sky figures along the ecliptic.

D.D. They are 13 well defined sky regions They are 13 well defined sky regions along the ecliptic.along the ecliptic.

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3D Constellations3D Constellations The stars of a The stars of a

constellation only constellation only appearappear to be close to be close to one anotherto one another

Usually, this is only Usually, this is only a projection effect.a projection effect.

The stars of a The stars of a constellation may constellation may be located at very be located at very different distances different distances from us.from us.

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The Celestial SphereThe Celestial Sphere Many ancient cultures, Many ancient cultures,

including the Greeks and including the Greeks and Romans, assumed that the Romans, assumed that the Earth was stationary in Earth was stationary in the center of the Universe.the center of the Universe.

Given this assumption, Given this assumption, they concluded that the they concluded that the Sun, Moon, planets, and Sun, Moon, planets, and stars were attached to stars were attached to gigantic crystalline gigantic crystalline spheres that surrounded spheres that surrounded the Earth.the Earth.

Today we call this Today we call this imaginary globe the imaginary globe the Celestial SphereCelestial Sphere. .

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Celestial Sphere Celestial Sphere ConceptsConcepts

THE CELESTIAL SPHERE REPRESENTS THE THE CELESTIAL SPHERE REPRESENTS THE APPARENT VIEW OF THE UNIVERSE AS SEEN APPARENT VIEW OF THE UNIVERSE AS SEEN FROM THE EARTH.FROM THE EARTH.

A huge globe of stars surrounding the Earth. A huge globe of stars surrounding the Earth. An ancient concept of the Cosmos. An ancient concept of the Cosmos. IT IS A USEFUL CONCEPT TODAY BECAUSE: IT IS A USEFUL CONCEPT TODAY BECAUSE: it is understandable in terms of spherical geometry. it is understandable in terms of spherical geometry. it can be used to extend map concepts for the Earth it can be used to extend map concepts for the Earth

to the sky. to the sky. it is useful in navigation. it is useful in navigation. RELATIONSHIP TO THE VISIBLE SKY RELATIONSHIP TO THE VISIBLE SKY The visible sky is 1/2 the celestial sphere. The visible sky is 1/2 the celestial sphere. Half of the celestial sphere is above the horizon, Half of the celestial sphere is above the horizon,

while the other half is below the horizon.while the other half is below the horizon.

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Zenith = Point on the celestial sphere directly overhead

Nadir = Point on the c.s. directly underneath (not visible!)

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 Celestial SphereThe Celestial Sphere

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Angular Measure In The Angular Measure In The SkySky

360360oo = A = A COMPLETE COMPLETE CIRCLECIRCLE

11oo = 60’ = 60’ (minutes)(minutes)

1’ = 60” 1’ = 60” (seconds)(seconds)

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Latitude Affects Visible Latitude Affects Visible SkySky

What we see in the sky depends What we see in the sky depends on our latitude.on our latitude.

At the north pole, the At the north pole, the north north celestial polecelestial pole is at the zenith. is at the zenith.

At the equator, the north celestial At the equator, the north celestial pole is at the horizon.pole is at the horizon.

The altitude of the north celestial The altitude of the north celestial pole = latitude.pole = latitude.

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The Sky From Abilene – The Sky From Abilene – 32.432.4oo N N

North Celestial PoleNorth Celestial Pole is 32.4 is 32.4oo above the above the northern horizon.northern horizon.

Celestial EquatorCelestial Equator is 57.6 is 57.6oo above the above the southern horizon.southern horizon.

Circumpolar stars lie within 32.4Circumpolar stars lie within 32.4oo of of the North Celestial Pole.the North Celestial Pole.

Rising & Setting stars are visible from Rising & Setting stars are visible from 32.432.4oo away from the South Celestial away from the South Celestial Pole.Pole.

Stars within 32.4Stars within 32.4oo of the South Celestial of the South Celestial Pole are never visible from Abilene.Pole are never visible from Abilene.

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Looking NorthLooking North The stars appear to circle around the North The stars appear to circle around the North

Celestial Pole (near Polaris) once in 24 hours.Celestial Pole (near Polaris) once in 24 hours. Stars within the angle of the observer's latitude Stars within the angle of the observer's latitude

away from the North Celestial Pole never rise or set.away from the North Celestial Pole never rise or set. They are always above the horizon (They are always above the horizon (circumpolar circumpolar

starsstars).).

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Circumpolar Circumpolar ConstellationsConstellations

Never Rise Or SetNever Rise Or Set Are Always Above The HorizonAre Always Above The Horizon Circumpolar Region Depends On LatitudeCircumpolar Region Depends On Latitude

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Daily Grade 3 – Question Daily Grade 3 – Question 22

2.2. At what location on Earth is an At what location on Earth is an observer that has the South Celestial observer that has the South Celestial Pole directly overhead?Pole directly overhead?

A.A. At Earth's equator (0 degrees latitude).At Earth's equator (0 degrees latitude).

B.B. At Earth's North Pole (90 degrees North At Earth's North Pole (90 degrees North latitude).latitude).

C.C. At Earth's South Pole (90 degrees South At Earth's South Pole (90 degrees South latitude).latitude).

D.D. At 45 degrees North latitude.At 45 degrees North latitude.

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Naming The StarsNaming The Stars

The brightest stars have had proper The brightest stars have had proper names for thousands of years.names for thousands of years. Typically from ArabicTypically from Arabic

Islamic astronomers produced many Islamic astronomers produced many detailed star charts during the middle ages.detailed star charts during the middle ages.

Also many stars have names that are Also many stars have names that are from the Greekfrom the Greek Greek astronomers also produced many star Greek astronomers also produced many star

charts.charts.

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Naming the StarsNaming the Stars Proper names are often a literal description Proper names are often a literal description

of the star’s location in the constellation:of the star’s location in the constellation: Betelgeuse – “Shoulder of the giant”Betelgeuse – “Shoulder of the giant” Rigel – “Foot”Rigel – “Foot” Deneb – “Tail”Deneb – “Tail” Procyon – “Before the dog”Procyon – “Before the dog” Algol – “Eye of the ghoul”Algol – “Eye of the ghoul”

Star proper names also sometimes describe Star proper names also sometimes describe the star.the star. Sirius – “Scorching”Sirius – “Scorching” Antares – “Rival of Mars”Antares – “Rival of Mars” Kochab – “Star”Kochab – “Star”

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Scam Alert!Scam Alert! NO organization has NO organization has

been given official legal been given official legal power to name the stars.power to name the stars.

Astronomers consider Astronomers consider the names designated by the names designated by the International the International Astronomical Union Astronomical Union official, but the IAU has official, but the IAU has no true legal authority to no true legal authority to name stars (or demote name stars (or demote planets, for that matter).planets, for that matter).

Companies that sell star Companies that sell star names as gifts are a names as gifts are a SCAM!SCAM!

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Bayer Letter NamesBayer Letter Names Johann BayerJohann Bayer

Bavararian lawyerBavararian lawyer Published a sky atlas: Published a sky atlas:

UranometriaUranometria.. Assigned lower case greek Assigned lower case greek

letters to brighter stars in letters to brighter stars in each constellation.each constellation.

Usually assigned in rough Usually assigned in rough order of brightness.order of brightness.

Alpha = brightest star.Alpha = brightest star. Beta = second brightestBeta = second brightest Gamma = third brightestGamma = third brightest And so on…And so on…

Astronomers continue to Astronomers continue to use these “Bayer letters”use these “Bayer letters”

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Bayer Letter NamesBayer Letter Names A star’s Bayer Letter Name is:A star’s Bayer Letter Name is:

It’s greek letter first…It’s greek letter first… ……followed by the possessive form of the constellation name.followed by the possessive form of the constellation name.

Example: Example: The star Rigel Kentarus is the brightest The star Rigel Kentarus is the brightest star in the constellation Centarus:star in the constellation Centarus: Alpha CentauriAlpha Centauri

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Daily Grade 3 – Question Daily Grade 3 – Question 33

3.3. What is the most likely Greek What is the most likely Greek letter name of the letter name of the secondsecond brightest star in the brightest star in the constellation Lyra?constellation Lyra?

A.A. Alpha Lyrae.Alpha Lyrae.B.B. Beta Lyrae.Beta Lyrae.C.C. Gamma Lyrae.Gamma Lyrae.D.D. Delta Lyrae.Delta Lyrae.

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The Magnitude ScaleThe Magnitude Scale Invented by the Greek Invented by the Greek

Astronomer Hipparchus Astronomer Hipparchus in the 2in the 2ndnd century B.C. century B.C.

Called the brightest Called the brightest stars in the night sky stars in the night sky “stars of the first “stars of the first magnitude.”magnitude.”

Second brightest were Second brightest were “stars of the second “stars of the second magnitude.”magnitude.”

All the way down to All the way down to “stars of the sixth “stars of the sixth magnitude.”magnitude.”

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The Magnitude ScaleThe Magnitude Scale

Very useful system, but not perfectVery useful system, but not perfect Technically, it refers to Apparent Visual Technically, it refers to Apparent Visual

MagnitudeMagnitude Brightness in visible wavelengths as seen from Brightness in visible wavelengths as seen from

EarthEarth Does NOT tell how bright the star actually is Does NOT tell how bright the star actually is

(absolute magnitude) because it does not take (absolute magnitude) because it does not take into account how far away the star is from us.into account how far away the star is from us.

Still useful because it is related to the Still useful because it is related to the brightness that you “see” (even through a brightness that you “see” (even through a telescope).telescope).

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The Magnitude ScaleThe Magnitude Scale Used for centuries, and then refined by Used for centuries, and then refined by

modern astronomers.modern astronomers. 11stst magnitude stars are 100 times brighter than magnitude stars are 100 times brighter than

66thth magnitude stars. magnitude stars. So 5 “steps” in the magnitude scale corresponds So 5 “steps” in the magnitude scale corresponds

to a 100× difference in brightness.to a 100× difference in brightness. What brightness difference corresponds to 1 step in What brightness difference corresponds to 1 step in

magnitude?magnitude? Need to know what number you have to multiply by Need to know what number you have to multiply by

itself five times to get 100.itself five times to get 100. That number is 2.5118864315095…. (usually rounded to That number is 2.5118864315095…. (usually rounded to

2.512 when used in calculations).2.512 when used in calculations). So 1 step in magnitude corresponds to a 2.512× So 1 step in magnitude corresponds to a 2.512×

difference in brightness.difference in brightness.

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The Magnitude ScaleThe Magnitude Scale

If If Star AStar A is has a is has a magnitude this much magnitude this much lessless than than Star BStar B……

……then then Star AStar A is this is this many times brighter many times brighter than than Star BStar B..

11 2.512×2.512×

22 6.310×6.310×

33 15.85×15.85×

44 39.82×39.82×

55 100×100×

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Sirius (brightest star in the sky): mv = -1.42Full moon: mv = -12.5

Sun: mv = -26.5

The magnitude scale system can be extended towards negative numbers (very bright) and numbers > 6 (faint objects):

The Magnitude ScaleThe Magnitude Scale

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The Magnitude ScaleThe Magnitude Scale

Here’s the actual equation:Here’s the actual equation:

IIAA/I/IBB = (2.512) = (2.512)(m(mBB-m-mAA))

This number right here is “how bright star A is compared to star B”

If it is >1, then star A is brighter than star B.

If it is <1, then star A is fainter than star B.

This thing in parentheses here is an exponent. So say mB – mA is a number we’ll call X. You would read this equation as “2.512 raised to the X power.”

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Daily Grade 3 – Question Daily Grade 3 – Question 44

4.4. The apparent visual magnitude of star A The apparent visual magnitude of star A is 2 and the apparent visual magnitude is 2 and the apparent visual magnitude of star B is 1. Based on this information of star B is 1. Based on this information which statement below must be true?which statement below must be true?

A.A. Star A emits more light than star B.Star A emits more light than star B.

B.B. Star B emits more light than star A.Star B emits more light than star A.

C.C. Star A is closer than star B.Star A is closer than star B.

D.D. Light output and distance cannot be Light output and distance cannot be determined from a star's apparent visual determined from a star's apparent visual magnitude alone.magnitude alone.

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