Introduction to Stars Electromagnetic Radiation Stellar Parallax Given
- Slides: 27
Introduction to Stars & Electromagnetic Radiation
Stellar Parallax • Given p in arcseconds (”), use d=1/p to calculate the distance which will be in units “parsecs” • By definition, d=1 pc if p=1”, so convert d to A. U. by using trigonometry • To calculate p for star with d given in lightyears, use d=1/p but convert ly to pc. • Remember: 1 degree = 3600” • Note: p is half the angle the star moves in half a year
Our Stellar Neighborhood
Scale Model • If the Sun = a golf ball, then – – – Earth = a grain of sand The Earth orbits the Sun at a distance of one meter Proxima Centauri lies 270 kilometers (170 miles) away Barnard’s Star lies 370 kilometers (230 miles) away Less than 100 stars lie within 1000 kilometers (600 miles) • The Universe is almost empty! • Hipparcos satellite measured distances to nearly 1 million stars in the range of 330 ly • almost all of the stars in our Galaxy are more distant
Luminosity and Brightness • Luminosity L is the total power (energy per unit time) radiated by the star, actual brightness of star, cf. 100 W lightbulb • Apparent brightness B is how bright it appears from Earth – Determined by the amount of light per unit area reaching Earth – B L / d 2 • Just by looking, we cannot tell if a star is close and dim or far away and bright
Brightness: simplified • 100 W light bulb will look 9 times dimmer from 3 m away than from 1 m away. • A 25 W light bulb will look four times dimmer than a 100 W light bulb if at the same distance! • If they appear equally bright, we can conclude that the 100 W lightbulb is twice as far away!
Same with stars… • Sirius (white) will look 9 times dimmer from 3 lightyears away than from 1 lightyear away. • Vega (also white) is as bright as Sirius, but appears to be 9 times dimmer. • Vega must be three times farther away • (Sirius 9 ly, Vega 27 ly)
Distance Determination Method • Understand how bright an object is (L) • Observe how bright an object appears (B) • Calculate how far the object is away: B L / d 2 So L/B d 2 or d √L/B
Homework: Luminosity and Distance • Distance and brightness can be used to find the luminosity: L d 2 B • So luminosity and brightness can be used to find Distance of two stars 1 and 2: d 21 / d 22 = L 1 / L 2 (since B 1 = B 2 ) i. e. d 1 = (L 1 / L 2)1/2 d 2
Homework: Example Question • Two stars -- A and B, of luminosities 0. 5 and 2. 5 times the luminosity of the Sun, respectively -- are observed to have the same apparent brightness. Which one is more distant? • Star A • Star B • Same distance
Homework: Example Question • Two stars -- A and B, of luminosities 0. 5 and 2. 5 times the luminosity of the Sun, respectively -- are observed to have the same apparent brightness. How much farther away is it than the other? • LA/d 2 A = BA =BB = LB/d 2 B d. B = √LB/LA d. A • Star B is √ 5=2. 24 times as far as star A
The Magnitude Scale • A measure of the apparent brightness • Logarithmic scale • Notation: 1 m. 4 (smaller brighter) • Originally six groupings – 1 st magnitude the brightest – 6 th magnitude is 100 x dimmer • So a difference of 5 mag is a difference of brightness of 100 • Factor 2. 512=1001/5 for each mag.
Absolute Magnitude • The absolute magnitude is the apparent magnitude a star would have at a distance of 10 pc. • Notation example: 2 M. 8 • It is a measure of a star’s actual or intrinsic brightness called luminosity • Example: Sirius: 1 M. 4, Sun 4 M. 8 – Sirius is intrinsically brighter than the Sun
Finding the absolute Magnitude • To figure out absolute magnitude, we need to know the distance to the star • Then do the following Gedankenexperiment: – In your mind, put the star from its actual position to a position 10 pc away – If a star is actually closer than 10 pc, its absolute magnitude will be a bigger number, i. e. it is intrinsically dimmer than it appears – If a star is farther than 10 pc, its absolute magnitude will be a smaller number, i. e. it is intrinsically brighter than it appears
“Light” – From gamma-rays to radio waves • The vast majority of information we have about astronomical objects comes from light they either emit or reflect • Here, “light” stands for all sorts of electromagnetic radiation • A type of wave, electromagnetic in origin • Understanding the properties of light allows us to use it to determine the – temperature – chemical composition – (radial) velocity of distant objects
Waves • Light is a type of wave • Other common examples: ocean waves, sound • A disturbance in a medium (water, air, etc. ) that propagates • Typically the medium itself does not move much
Wave Characteristics • Wave frequency: how often a crest washes over you • Wave speed = wavelength ( ) frequency (f)
Electromagnetic Waves • Medium = electric and magnetic field • Speed = 3 105 km/sec
Electromagnetic Spectrum Energy: low medium high
Electromagnetic Radiation: Quick Facts • There are different types of EM radiation, visible light is just one of them • EM waves can travel in vacuum, no medium needed • The speed of EM radiation “c” is the same for all types and very high ( light travels to the moon in 1 sec. ) • The higher the frequency, the smaller the wavelength ( f = c) • The higher the frequency, the higher the energy of EM radiation (E= h f, where h is a constant)
Visible Light • Color of light determined by its wavelength • White light is a mixture of all colors • Can separate individual colors with a prism
Three Things Light Tells Us • Temperature – from black body spectrum • Chemical composition – from spectral lines • Radial velocity – from Doppler shift
Temperature Scales Fahrenheit Centigrade Kelvin 459 ºF 273 ºC 0 K 32 ºF 0 ºC 273 K Human body temperature 98. 6 ºF 37 ºC 310 K Water boils 212 ºF 100 ºC 373 K Absolute zero Ice melts
Black Body Spectrum • Objects emit radiation of all frequencies, but with different intensities Ipeak Higher Temp. Ipeak Lower Temp. fpeak<fpeak
Cool, invisible galactic gas (60 K, fpeak in low radio frequencies) Dim, young star (600 K, fpeak in infrared) The Sun’s surface (6000 K, fpeak in visible) Hot stars in Omega Centauri (60, 000 K, fpeak in ultraviolet) The higher the temperature of an object, the higher its Ipeak and fpeak 14
Wien’s Law • The peak of the intensity curve will move with temperature, this is Wien’s law: Temperature * wavelength = constant = 0. 0029 K*m So: the higher the temperature T, the smaller the wavelength, i. e. the higher the energy of the electromagnetic wave
Example • Peak wavelength of the Sun is 500 nm, so T = (0. 0029 K*m)/(5 x 10 -7 m) = 5800 K • Instructor temperature: roughly 100 F = 37 C = 310 K, so wavelength = (0. 0029 K*m)/310 K = 9. 35 * 10 -6 m = 9350 nm infrared radiation
- What is stellar parallax?
- There are millions of stars in the sky
- Intensity of em wave is
- Facts about electromagnetic radiation
- Electromagnetic wavelength formula
- Types of radiation in the electromagnetic spectrum
- Intensity of electromagnetic radiation
- Which telescope detects invisible electromagnetic radiation
- Light waves are electromagnetic waves true or false
- Electromagnetci spectrum
- When electromagnetic radiation of wavelength 300
- Electromagnetic radiation
- Stellar heaven
- Stellar flux
- Stages of stellar evolution of a low-mass star
- Stellar evolution diagram
- Stellar motion matlab
- Virgo stellar
- Masses in the stellar graveyard
- Stellar evolution flowchart
- Stellar hosting iptv
- Stellar assessment
- Stellar saga
- Stellar evolution
- Stellar
- Stellar formation
- Stellar asset management
- Stellar evolution