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Stars a Long Preamble...How Do We Name the Stars?

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Stars a Long Preamble...How Do We Name the Stars? We have always divided the sky up into “patterns” or constellations Stars • But remember: The stars that make up Orion are random lights in the sky • They do not represent a mythical figure! They do not represent a mythic figure! Peter Watson Credit & Copyright: Matthew Spinelli A long preamble...how do we name the stars? • Subsequently stars named with Greek letters, in order of brightness • The brightest stars have names that derive from (usually) Arabic: e.g. Ursa Major • α-Orionis = Betelgeuse • β-Orionis = Rigel • (Unfortunately, Rigel is brighter than Betelgeuse, since it is much hotter & radiates mainly in UV! • so system refers to visual • Now we mostly use catalogs: the best known is Messier (pr Messié) Now most objects are referred to by catalogue numbers: • A catalog of objects that e.g. BD + 59° 1915 is 1915th star classified in Bonner aren’t comets Durchmesterung • M1 = Crab nebula New General Catalog has ∼ 10000 galaxies • M3 = Globular cluster so NGC 224 = M31 So what’s the system? • M31 = Andromeda galaxy • M45 = Pleiades cluster • M51 = Spiral galaxy Credit© P. Gitto • M57 = Ring nebula Brightness/Magnitude α Canis Majoris There is NO system α CMa 9 Canis Majoris for naming objects in 9 CMa • Easiest observation about stars is that some HD 48915, are brighter than others. HR 2491 the heavens BD -16°1591 GCTP 1577.00 A/B, • Hipparchus defined brightest to be of first the same object can GJ 244 A/B magnitude, down to the dimmest of sixth LHS 219 magnitude. have several names! ADS 5423 e.g Sirius (Dog Star) is also LTT 2638 • A first mag. star turns out to be 100 x HIP 32349 brighter than a 5th mag. PW Binaries This seems backwards (it is!) • many stars are in multiple star systems: • a twentieth magnitude star is .00000000001 about 40% in pairs times as bright as a first magnitude star (sigh!). Credit & Copyright: Richard Yandrick (Cosmicimage.com) • Need to have negative magnitude stars which are brighter than positive magnitude stars (double sigh!) • Finally we have close dim stars (like Sirius) which are much brighter than distant bright stars (like Rigel) (triple sigh!) • Albireo: orbital period of 75000 years PW PW Stars: some numbers Mass governs how a star works •Mass: will refer to mass of sun as Mo •If M ~ Mo , ⇒ star like the sun •Jupiter ~ Mo /1000 •If M ~ Mo /10 ⇒ red dwarf •Smallest stars (brown dwarfs) ~ Mo /100 •If M ~ Mo /100 ⇒ Smallest stars (brown dwarfs) •Largest “normal” stars ~ 20 Mo •If M ~ 20 Mo ⇒ Supergiant (like Rigel or •Maybe R136a1 ~ 300Mo, but any star this Betelgeuse) size loses material very fast Stars: some numbers • To find distance, can use “parallax” • Position of star will vary over year •Radius: sun is ~ 1000000 km •Time: One million years (1 Myr) is fairly short one second of arc (dime at 10 km)=> distance of one parsec Takes us out to 100 parsecs (400 light years) Stars: some numbers • Note that if we see a 3-D view of Orion, the picture changes totally! •Distance: light year is distance traveled by light in 1 yr •Astronomers usually use the "parsec": 1 pc ~ 4 ly (thirty trillion km). •Closest star (α Centauri) is at a distance of ~1.3 pc. Sirius is at about 5 pc. Pearson publishing And the most important thing we learn is from barbecues • What’s hot and what’s not: roughly • red is 800°C • orange is 1500°C • yellow is 2000°C • blue is 15000°C • X-rays are 1 million °C Doppler shift • Light is part of the whole electromagnetic spectrum • Roughly: shorter wavelength • Can measure how fast something is moving requires higher temps by looking at the light • 1000 ° for red light • 1000000° for X-rays • 1000,000,000° for gamma rays PW • We can see all this around Orion • Blue shift: something moving towards us (and appears hotter) • Sirius; fairly dim star that is very close • Red shift: something moving away from us • Rigel: blue supergiant: would be 1000 times (and appears cooler) brighter than Sirius if it were at the same distance Aldebara Betelgeus Milky M42 Rigel Sirius Betelgeuse: red supergiant: How do stars “work”? • This is the stellar structure 10000 times larger than the sun problem Orbits of Mercury, Venus, Earth and Mars would be • Hadyja HBV (BR) (Don El Chall inside it! Harley FHP) 16 March 2002 In foal to *Magic Dream CAHR - foal date In fact it may be 3 stars! 3/2/2011 • Hadyja embodies the definitive C traits of a Brazil mare - big, bold, grey mare and still enchantingly feminine with a proportional harmonious design and enrapturing charisma. and stellar structure. PW PW But seriously A rather small set of equations governs a star • Note that stars are much simpler than (e.g..) human beings: on PW the other hand we still need a computer to solve for one!PW Stellar evolution once over lightly: Stellar evolution once over lightly: • Stars are born, mature and grow old. • We call this stellar evolution, which is stupid, since we don't talk about the evolution of a 10,000,000,000 baby into an adult. 100,000 1,000,000 10,000,000 • Also note: ALL stars go through ALL the stages. • We don't (usually) see them change because 1,000,000,000 ……… Forever! a human lifetime is so short compared to stellar 100,000 Small stars (like the sun) PW Times are approximate in years. Big stars work much faster: • M42 (Orion's sword) is a vast cloud of gas turning into stars as we watch 1,000,000 100,000 100,000 100,000 Forever 3 hours! Live fast, Die Young! Star Nurseries Star Birth: Stars are born from • Eagle Nebula (M16) vast clouds of gas and dust • Cluster of stars just formed in centre of dark shell of dust and gas dark lanes where stars are about to form group of young stars glowing "lanes" of gas heated star still blowing by large stars away cocoon of gas The Eagle's EGGs: Adulthood Temperature is dull x Rigel Evaporating Gaseous Globules • Don’t we know it! x Betelgeuse (EGGs). • 99.9 % of stars are Very dense parts of the Eagle • • “main-sequence” nebula form new stars which x Sirius blow away the dust and x Sun i.e. stable, hydrogen illuminate the columns • “burning”, very slowly changing. • H-R diagram is temp- brightness plot • only real variable is mass Brightness Richard Powell Mostly cannot see inside stars • Finally star will run low on fuel and expand • Becomes red giant • Sun is only one close enough to see neutrinos • However helio-seismology lets you see inside (like seismology on earth) • Stars vibrate like a (3-D) drumhead Peter Watson Then • Planetary nebula • Central star is a white dwarf (50000°C) • Hot blue gas at centre If stars are • Coolest red gas along the outer boundary. small, (like the sun) they puff away their outer layers This is M57 (Ring Nebula) Peter Watson Peter Watson • This will happen to the sun, in 5.5 billion years. • But we find all sorts of weird shapes. • The star blows away its outer layers, so almost • This is the Cats-eye nebula: looks like successive all the older ones we knew look like this. explosions Peter Watson Peter Watson • Mz3: The Ant Nebula. White dwarfs • After the outer shell has disappeared, we are left with a • Probably magnetic field is creating a star about the same mass as sun but size of earth "focussed" planetary nebula (~10000 km ) • Density: ~1 million: ~ 100,000 times as dense as lead. This shows some in M4 (a dense cluster of stars). Since they are small, they cool very slowly. Peter Watson Peter Watson • The Eight Burst Sirius Nebula Brightest • White dwarf star in the and companion, sky will probably look like Sirius Has an in 100000 years almost invisible companion white dwarf Peter Watson Peter Watson •IC 4406: •a really weird planetary nebula •probably a cylinder that we see side on. Credit: H. Bond (STScI), R. Ciardullo (PSU), WFPC2, HST, NASA Peter Watson.
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