Locating Objects Locating Objects in Space in Space

ConstellationsConstellations

88 constellations in the night sky88 constellations in the night sky 28 northern hemisphere, 12 zodiac, 48 28 northern hemisphere, 12 zodiac, 48

southern hemispheresouthern hemisphere Used as navigational guideUsed as navigational guide Each culture has different names, all Each culture has different names, all

recognize the same star groupingsrecognize the same star groupings Greek letters are used for identifying the Greek letters are used for identifying the

brightest stars in constellationsbrightest stars in constellations Alpha Alpha Beta Beta γγ Gamma Gamma

Bright Bright Dim Dim

Reference PointsReference Points ZenithZenith – point directly above you in the sky – point directly above you in the sky

Celestial SphereCelestial Sphere – imaginary sphere surrounding – imaginary sphere surrounding the earth on which the stars are located (Stars the earth on which the stars are located (Stars only appear to be on celestial sphere)only appear to be on celestial sphere)

Celestial PolesCelestial Poles – extensions of earth’s – extensions of earth’s geographic poles (North Pole – Polaris…the pole geographic poles (North Pole – Polaris…the pole star) star)

Celestial EquatorCelestial Equator – extension of Earth’s equator – extension of Earth’s equator

EclipticEcliptic – apparent path of the sun on the – apparent path of the sun on the celestial spherecelestial sphere

Celestial Coordinates: “directions” to help you find objects in the night sky

•Declination: degrees North & South of the celestial equator

*like latitude on Earth or altitude above the horizon

•Right Ascension: hours, minutes, & seconds east of the vernal equinox (where the celestial equator and ecliptic cross one another)

*like longitude on Earth

Zodiac Zodiac ConstellationsConstellations: 12 : 12 constellations constellations through which the through which the sun passes in a sun passes in a years time (found years time (found along ecliptic) along ecliptic)

Circumpolar Circumpolar ConstellationsConstellations: : constellations that constellations that can be seen can be seen throughout the throughout the year at your year at your latitude (“circle latitude (“circle the pole”) the pole”)

How do we locate the How do we locate the planets? planets?

All planets orbit within a few degrees of All planets orbit within a few degrees of the eclipticthe ecliptic

Superior Planets (Jupiter – Neptune) can Superior Planets (Jupiter – Neptune) can generally be seen any night, except when generally be seen any night, except when on the opposite side of the sun on the opposite side of the sun

Generally move eastward in celestial Generally move eastward in celestial sphere from night to nightsphere from night to night

Retrograde Motion – occasional westward Retrograde Motion – occasional westward motion due to Earth “overtaking” the motion due to Earth “overtaking” the planet in its orbit planet in its orbit

Planets – December 2008

Planets – April 2009

Visible in the morning sky

Properties of StarsProperties of Stars Can be measured in terms of diameter, Can be measured in terms of diameter,

mass, brightness, energy output (power), mass, brightness, energy output (power), surface temperature, & composition surface temperature, & composition

DiametersDiameters: range from 0.1 times the : range from 0.1 times the Sun’s diameter to 100 times largerSun’s diameter to 100 times larger

MassMass: ranges from 0.01 to 20 or more : ranges from 0.01 to 20 or more times the Sun’s mass…some are 50 – 100 times the Sun’s mass…some are 50 – 100 times the Sun’s mass but are extremely times the Sun’s mass but are extremely rare rare

Apparent MagnitudeApparent Magnitude: how bright a : how bright a star appears to be.star appears to be. Ranges from 1Ranges from 1stst – 6 – 6thth magnitude, 1 magnitude, 1stst is is

100 times brighter than 6100 times brighter than 6thth Difference of 1 magnitude corresponds Difference of 1 magnitude corresponds

to a factor of 2.512 in brightness to a factor of 2.512 in brightness Does not take into account the distance Does not take into account the distance

of the starof the star

Absolute MagnitudeAbsolute Magnitude: : the brightness of an the brightness of an object if they were all object if they were all lined up at the same lined up at the same distance away distance away Changes the scale a Changes the scale a

bit since distance is bit since distance is taken into account taken into account

Sun is brighter than Sun is brighter than Sirius on apparent Sirius on apparent magnitude scale, but magnitude scale, but less bright on absolute less bright on absolute magnitude scale magnitude scale

Determine distance Determine distance using using parallaxparallax – – apparent shift in apparent shift in position of star caused position of star caused by motion of observer by motion of observer

Luminosity: total amount of energy Luminosity: total amount of energy given off by a stargiven off by a star Depends on distance and magnitude Depends on distance and magnitude

Extremely wide range (millions of times Extremely wide range (millions of times greater than the sun to thousands of times less greater than the sun to thousands of times less than the sun)than the sun)

Composition: Composition: Hydrogen and Helium make up 98% of all Hydrogen and Helium make up 98% of all

starsstars 1 – 2 % Oxygen, Carbon, Nitrogen, 1 – 2 % Oxygen, Carbon, Nitrogen,

Calcium Calcium

Temperature: determined by star’s Temperature: determined by star’s spectrum (hotter the star, greater the spectrum (hotter the star, greater the ultraviolet and less the infrared rays) ultraviolet and less the infrared rays)

Spectral classes: O, B, A, F, G, K, M Spectral classes: O, B, A, F, G, K, M

((OOh h BBoy oy AAn n FF GGrade rade KKills ills MMe!)e!) O is the hottest and M is the coolestO is the hottest and M is the coolest Each class is divided into 10 subdivisions Each class is divided into 10 subdivisions

labeled labeled

0 to 9 (a B1 star is hotter than a B8 star) 0 to 9 (a B1 star is hotter than a B8 star)

H-R Diagrams H-R Diagrams Hertzsprung – Russell Diagrams compare Hertzsprung – Russell Diagrams compare

luminosity and temperatureluminosity and temperature Main sequence stars (80-90%) trend from faint, cool Main sequence stars (80-90%) trend from faint, cool

stars in lower right to hot, bright stars in upper leftstars in lower right to hot, bright stars in upper left Giants and Supergiants - located above main Giants and Supergiants - located above main

sequencesequence White dwarfs – stars located below the main White dwarfs – stars located below the main

sequence sequence Largest stars in the upper right and smallest Largest stars in the upper right and smallest

stars in the lower leftstars in the lower left Five Luminosity Categories: I. supergiants, II. Five Luminosity Categories: I. supergiants, II.

bright giants, III. giants, IV. subgiants, V. main bright giants, III. giants, IV. subgiants, V. main sequence sequence

Our Sun is a G2V starOur Sun is a G2V star

Mass: determines type of length of the life of a star Mass: determines type of length of the life of a star The more massive a star, the shorter its life will The more massive a star, the shorter its life will

bebe

Stages of Life: Stages of Life: 1.1. NebulasNebulas: begin as huge clouds of gas and dust: begin as huge clouds of gas and dust2.2. ProtostarProtostar: gravity causes nebula to contract or : gravity causes nebula to contract or

collapse on itself forming a disk shape collapse on itself forming a disk shape i.i. During early stages, not yet hot enough for nuclear During early stages, not yet hot enough for nuclear

fusion & emits no visible light fusion & emits no visible light ii.ii. Core temperatures finally reach 8-10 million Kelvins, Core temperatures finally reach 8-10 million Kelvins,

high enough for nuclear fusion & star is “born” high enough for nuclear fusion & star is “born” iii.iii. Hydrogen is converting to Helium Hydrogen is converting to Helium

Stellar Evolution Stellar Evolution

A - North American Nebula - emission nebula B - Jewel Box open cluster

C - Globular Cluster 47 Tucanae D - Cygnus Loop - supernova remnant

Three main evolutionary Three main evolutionary paths based on initial mass paths based on initial mass

of star of star 11stst Path: (0.1 to 8 solar masses) Path: (0.1 to 8 solar masses)

Main SequenceMain Sequence – lifetime determined by – lifetime determined by amt of fuel available & rate of amt of fuel available & rate of consumption consumption Greater the star’s mass the faster it burns Greater the star’s mass the faster it burns

up its fuel & the shorter the time it will be a up its fuel & the shorter the time it will be a main sequence starmain sequence star

Some stars spend 90% of life as main Some stars spend 90% of life as main sequence starsequence star

Red GiantRed Giant: star is running out of hydrogen fuel, : star is running out of hydrogen fuel, cools, gets bigger and becomes more luminouscools, gets bigger and becomes more luminous Helium flash occurs at red giant stage that many Helium flash occurs at red giant stage that many

only last a few minutes/seconds, star shrinks briefly only last a few minutes/seconds, star shrinks briefly than resumes red giant statusthan resumes red giant status

Planetary nebulaPlanetary nebula: expanding shell of gases : expanding shell of gases expelled into space expelled into space Gases keep expanding until they dissipate in Gases keep expanding until they dissipate in

interstellar spaceinterstellar space Core star left, but center becomes white dwarf. Core star left, but center becomes white dwarf.

White dwarfWhite dwarf: small star (about size of Earth), : small star (about size of Earth), super dense, very high temperatures. super dense, very high temperatures. Cools over billions of years to become black dwarf Cools over billions of years to become black dwarf Some can become supernovaSome can become supernova

22ndnd Path: stars 8 – 25 solar masses Path: stars 8 – 25 solar masses

Main sequenceMain sequence: much shorter than for : much shorter than for smaller stars, more fuel but consumed at a smaller stars, more fuel but consumed at a faster ratefaster rate

Red SupergiantRed Supergiant: larger and more luminous : larger and more luminous

SupernovaSupernova: star that blows off its outer shell : star that blows off its outer shell into interstellar space, luminosity soars & into interstellar space, luminosity soars & may outshine entire galaxy may outshine entire galaxy Estimates show 1 supernova per galaxy every 25-Estimates show 1 supernova per galaxy every 25-

100 years…we have never observed a supernova 100 years…we have never observed a supernova in our galaxy with a telescopein our galaxy with a telescope

Neutron StarNeutron Star: small (about size of large city), : small (about size of large city), compact starscompact stars Can give rise to Can give rise to pulsarspulsars – rapidly rotating stars – rapidly rotating stars

that give off pulses of energy that give off pulses of energy

33rdrd Path: stars 25 – 130 solar masses Path: stars 25 – 130 solar masses Main Sequence: Main Sequence: consume fuel at a consume fuel at a

much faster rate than any of the much faster rate than any of the previous stars previous stars

Red SupergiantRed Supergiant: similar to red : similar to red supergiants for path 2supergiants for path 2

SupernovaSupernova: referred to as Type II : referred to as Type II supernova for paths 2 and 3supernova for paths 2 and 3

Black HoleBlack Hole: density so high that escape : density so high that escape velocity of star becomes equal to the velocity of star becomes equal to the speed of light, so even light cannot speed of light, so even light cannot escapeescape