8 March subst for Roberta Stars

8 March subst for Roberta

( PARENTHETICAL ) STAR NAMES SIRIUS  CMa ( Alpha Canis Majoris ) HR 2491 HD SAO and other STAR CATALOGS

8 March subst for Roberta DISTANCES OF STARS

8 March subst for Roberta DISTANCES OF STARS EARLIEST IDEA: PARALLAX

8 March subst for Roberta TRIGONOMETRIC PARALLAX

8 March subst for Roberta STELLAR PARALLAX

8 March subst for Roberta ( SOMETIMES IT’S CALLED ANNUAL PARALLAX )

8 March subst for Roberta PARALLAX GETS SMALLER AS DISTANCE GROWS LARGER ( and vice-versa )

8 March subst for Roberta

LET’S CHOOSE GOOD MEASUREMENT UNITS …

8 March subst for Roberta ANGLES 360 degrees ( 360 ° ) in a circle 60 arc-minutes ( 60 ) in 1 ° 60 arc-seconds ( 60  ) in 1 

8 March subst for Roberta ANGLES 360 degrees ( 360 ° ) in a circle 60 arc-minutes ( 60 ) in 1 ° 60 arc-seconds ( 60  ) in 1  so … 1,296,000 arc-seconds in a circle! An arc-second ( arcsec ) is small;

8 March subst for Roberta ANGLES 360 degrees ( 360 ° ) in a circle 60 arc-minutes ( 60 ) in 1 ° 60 arc-seconds ( 60  ) in 1  1 inch subtends 1 arcsec at a distance of 3.3 miles.

8 March subst for Roberta ANGLES 360 degrees ( 360 ° ) in a circle 60 arc-minutes ( 60 ) in 1 ° 60 arc-seconds ( 60  ) in 1  we measure parallaxes in arcsec.

8 March subst for Roberta UNITS FOR DISTANCES ASTRONOMICAL UNIT ( AU ) = AVERAGE DISTANCE OF SUN = RADIUS OF EARTH’S ORBIT

8 March subst for Roberta UNITS FOR DISTANCES ASTRONOMICAL UNIT ( AU ) = AVERAGE DISTANCE OF SUN = RADIUS OF EARTH’S ORBIT = about 150 million kilometers = about 93 million miles

8 March subst for Roberta

STAR’S DISTANCE = _____________________ 206,265 AU PARALLAX IN ARCSEC

8 March subst for Roberta UNITS FOR DISTANCES ASTRONOMICAL UNIT ( AU ) = AVERAGE DISTANCE OF SUN = RADIUS OF EARTH’S ORBIT

8 March subst for Roberta UNITS FOR DISTANCES 1 PARSEC = 206,265 AU (explain) usually abbrev. “PC”

8 March subst for Roberta STAR’S DISTANCE = _____________________ 1 PARSEC PARALLAX IN ARCSEC

8 March subst for Roberta UNITS FOR DISTANCES 1 PARSEC = 206,265 AU = almost 31 trillion kilometers, urggh.

8 March subst for Roberta By the way … 1 parsec = 3.26 LIGHTYEARS. Nearest star is 1.3 pc or 4.3 ly.

8 March subst for Roberta c. 1590: TYCHO BRAHE TRIED TO DETECT PARALLAX AND FAILED. (explain)

8 March subst for Roberta c. 1680: NEWTON PREDICTED PARALLAX WOULD BE VERY SMALL, D ( nearest star ) = maybe 300,000 AU (explain how he guessed)

8 March subst for Roberta

SUCCESSFUL PARALLAXES, AROUND 1839: 61 CYGNI (BESSEL, GERMANY) VEGA (STRUVE, RUSSIA) ALPHA CENTAURI (HENDERSON, S.AFRICA)

8 March subst for Roberta ALPHA CENTAURI A, B, C DISTANCE = 270,000 AU 1.3 PC ( parsec ) 4.3 LY ( lightyear )

8 March subst for Roberta ALPHA CENTAURI 9 MILES

8 March subst for Roberta THE THREE STARS OF ALPHA CENTAURI A : YELLOW, SOMEWHAT BRIGHTER THAN THE SUN; B : ORANGE, 40% AS BRIGHT AS THE SUN; C : RED, 1 / AS BRIGHT AS THE SUN. “PROXIMA CENTAURI”

8 March subst for Roberta PARALLAX DISTANCES SHOWED THAT STARS ARE NOT ALIKE

8 March subst for RobertaAst 1001, 29 March KD HIPPARCOS SATELLITE MEASURED ULTRA - PRECISE PARALLAXES

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NEXT: MOTIONS OF THE STARS IN SPACE

8 March subst for Roberta PROPER MOTION OF BARNARD’S STAR ( 6 L.Y. AWAY )

8 March subst for Roberta THE SUN, FOR EXAMPLE, MOVES ABOUT 15 KILOMETERS PER SECOND = 33,000 M.P.H. = 3 A.U. PER YEAR.

8 March subst for Roberta

“STATISTICAL PARALLAX” BASED ON PROPER MOTIONS ( explain ) -- GOOD ONLY ON AVERAGE, BUT OK OUT TO ABOUT 5000 L.Y. --

8 March subst for Roberta REMEMBER THE DOPPLER EFFECT?

8 March subst for Roberta RADIAL VELOCITY measured with the Doppler effect … Examples …  20 km / s means the star is moving toward us ( “blueshift” ) + 15 km / s means it’s moving away ( “redshift” )

8 March subst for Roberta

WE QUOTE THE BRIGHTNESS OF EACH STAR AS A “MAGNITUDE”.

8 March subst for Roberta ABOUT 2100 YEARS AGO, HIPPARCHUS (= HIPPARCOS) MADE A LIST OF 1000 STARS...

8 March subst for Roberta ABOUT 2100 YEARS AGO, HIPPARCHUS (= HIPPARCOS) MADE A LIST OF 1000 STARS... BRIGHTEST: “STARS OF THE FIRST MAGNITUDE”. THEN “SECOND MAGNITUDE”, THIRD, ETC. FAINTEST WE CAN SEE: “SIXTH MAGNITUDE”.... simple “eye estimates”.

8 March subst for Roberta MANY CENTURIES LATER, ASTRONOMERS LEARNED HOW TO MEASURE THE STARS’ MAGNITUDES... for example -- Aldebaran... m = 0.85 (fairly bright) Tau Ceti HD (faint)

8 March subst for Roberta

THE MAGNITUDE SCALE TURNED OUT TO BE LOGARITHMIC -- LIKE DECIBELS USED TO MEASURE SOUND. 80 DECIBELS = 1 90 DB = DB = and so on.

8 March subst for Roberta THE MAGNITUDE SCALE IS LOGARITHMIC magnitude = = 39.8 (2.512 x fainter)

8 March subst for Roberta THE MAGNITUDE SCALE IS LOGARITHMIC magnitude = = 39.8 (2.512 x fainter) 3.0 = 15.8

8 March subst for Roberta THE MAGNITUDE SCALE IS LOGARITHMIC magnitude = = 39.8 (2.512 x fainter) 3.0 = = = = 1.0

8 March subst for Roberta THE MAGNITUDE SCALE IS LOGARITHMIC magnitude = = 39.8 (2.512 x fainter) 3.0 = = = = = etc.

8 March subst for Roberta THE MAGNITUDE SCALE IS LOGARITHMIC -- THE DIFFERENCE BETWEEN TWO STARS’ MAGNITUDES CORRESPONDS TO THE RATIO OF THEIR BRIGHTNESS. Example: star A has m = 2.3, star B has m = 7.3; Difference magnitudes. So star A is 100 x as bright as star B.

8 March subst for Roberta “APPARENT VISUAL MAGNITUDES” Sun: m = -27 Moon: -10 Venus: -4 Mars: -2.5 Sirius: -1.4 Vega: 0.0 Antares: 1.0 Polaris: 2.3

8 March subst for Roberta “APPARENT VISUAL MAGNITUDES” BRIGHTEST STAR (SIRIUS): m = th –BRIGHTEST STAR: +1.5 FAINTEST VISIBLE:... about 6.5 WITH BINOCULARS: about 8 6-INCH TELESCOPE: about 12 PLUTO: 14 LIMIT WITH MODERN DETECTORS ON BIG TELESCOPES:

8 March subst for Roberta MAGNITUDES ALSO GIVE COLORS. WE USE FILTERS, FOR INSTANCE ‘V’ = “visual”, yellow-green, ‘B’ = “blue” U B V R I J K L... filters

8 March subst for Roberta MAGNITUDES ALSO GIVE COLORS. WE USE FILTERS, FOR INSTANCE ‘V’ = “visual”, yellow-green, ‘B’ = “blue” ( B magnitude ) - ( V magnitude ) is a measure of the star’s color. B – V = blue, very hot = like the Sun = red, cool star

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF A STAR

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF A STAR upper-case M ( m is apparent magnitude.)

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF A STAR M = THE APPARENT MAGNITUDE m THAT THE STAR WOULD HAVE AT A STANDARD DISTANCE OF 10 PARSECS = 33 LIGHTYEARS

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF A STAR TO CALCULATE M, WE NEED TO KNOW BOTH m AND D.

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF STARS M FOR THE SUN = + 4.8

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF STARS M FOR THE SUN = FAINTEST RED DWARF STARS: M = + 18

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF STARS M FOR THE SUN = FAINTEST RED DWARF STARS: M = + 18 MOST LUMINOUS STARS: M = - 12

8 March subst for Roberta LUMINOSITY OR ABSOLUTE MAGNITUDE OF STARS M FOR THE SUN = FAINTEST RED DWARF STARS: M = + 18 MOST LUMINOUS STARS: M = - 12 OVERALL RANGE: 30 MAGNITUDES, = A LUMINOSITY FACTOR OF 1,000,000,000,000 ( A TRILLION )

8 March subst for Roberta