2 Characteristics of Stars Groups of stars that form patterns in the sky are called constellationsExample: Ursa Major (Big Bear), Ursa Minor (Little Bear), and OrionThe last two stars in Ursa Major’s “dipper” are called the “Pointer Stars” and are be used to find Polaris (North Star)Polaris is located directly above the North Pole (90º N), and is only visible in the northern hemisphere (above the Equator)
4 Circumpolar Constellations Because of the Earth’s rotation, the constellations appear to moveIf the constellations 1) appear to move around Polaris and 2) can be seen at all times of year and 3) can be seen at all times of night, they are called circumpolar constellationsThe constellations Ursa Major and Ursa Minor are both circumpolar constellationsUsing time exposure photography, the apparent motion of the stars around Polaris can be recorded as circular trails
5 The stars don’t move – WE DO!!!! VIFThe apparent motion of stars is due to the Earth’s daily rotation on its axis.The stars don’t move – WE DO!!!!
6 Here is a time-lapse photo of circumpolar star movement… Here is a time-lapse photo of circumpolar star movement…
8 The positions of the constellations as viewed from Earth changes from season to season This is caused by the revolution of the Earth and the change in Earth’s position in its orbit around the sunExample: Orion the Hunter is a winter constellation
9 Ex – when the Earth is in this position (Nov 21), the bright sun during the day blocks our view of all of the constellations toward the lower right side of the diagram
11 Physical Properties of Stars Stars differ in size, density, mass, composition, and colorThe color of a star is determined by it surface temperature (ESRT’s P. 15 top)The hotter the star, the bluer the color. The cooler the star, the redder the color. (yeah, yeah, I know, it’s backwards….)The sun is an AVERAGE SIZE, medium, yellow star
15 Physical Properties of Stars Most stars are made up of mostly hydrogen and helium (approx. 98%)The remaining 2% may be other elementsA spectral analysis (remember Ch. 20) of the star can tell us what elements a star is made of, since the radiated spectrum depends on a star’s composition and temperature
16 (See the H-R Diagram in the ESRT’s P.15) Some stars may appear to be brighter than othersThe star’s brightness may be described in three ways 1. APPARENT MAGNITUDE 2. LUMINOSITY 3. ABSOLUTE MAGNITUDE(See the H-R Diagram in the ESRT’s P.15)
17 Apparent Magnitude How bright a star appears (apparent) to us on Earth The farther a star is from Earth (increasing distance), the dimmer it will look even though it may actually be a very bright starBecause of this, apparent magnitude does not tell the true brightness of a star
18 Luminosity The actual (true) brightness of the star Depends on the size and temperature of the starHotter stars are more luminous (brighter) than cooler starsIf the temperatures are the same, a larger star will be more luminous
19 Absolute MagnitudeThe luminosity of the stars if they all brought to the same distance from Earthaka – picture all the stars lined up the same distance from Earth, then compare their brightnessThis is the most useful when comparing the brightness of the stars
23 The sun is the closest star to Earth It is approx. 150,000,000 km (93,000,000 miles) from the EarthThis distance is called an astronomical unit (AU)The next closest star to Earth, after the sun, is Proxima CentauriIt is 300,000 times farther away from Earth than the sun. Because of the great distances in space, larger units of measure must be usedThe light-year is the distance that light travels in one yearSince light can travel 300,000 km/sec (186,000 miles/sec), light travels 9.5 trillion km/year!!!Proxima Centuri is 4.3 light-years from Earth!
24 One Astronomical Unit (AU) = 150,000,000 km So…One Astronomical Unit (AU) = 150,000,000 kmAnd, one light year (LY)= trillion km (9,500,000,000,000 km)
25 Okay… let’s calculate the distances from Earth to each planet in Astronomical Units (AU)
26 Just divide the distance from the Sun in km by 150,000,000 km. Remember – 1 AU = 150,000,000 kmJust divide the distance from the Sun in km by 150,000,000 km.Example: Jupiter = 778,300,000 km ,000,000 kmJupiter is 5.19 AU from the Sun
28 large clouds of dust and gas in space are the basic materials needed for star formation the majority of this gas is hydrogensome outside force causes the cloud of gas and dust to be pushed togetheras the gas and dust get closer, friction between the particles causes the temperature to increasethe attraction of gravity between the particles causes them to continue to move together, and density also increases
29 In a nuclear reactor like Indian Point, nuclear fission takes place friction increases and temperature increases until the center becomes so hot that nuclear fusion takes placehydrogen atoms are forced together to form helium atoms, and a tremendous amount of energy is releasedIn a nuclear reactor like Indian Point, nuclear fission takes placeThis is when radioactive atoms are split apart to release energy
31 OK, so stars form from hydrogen gas and dust, but where does that gas & dust come from????
32 SUPERNOVAS One of the most energetic explosive events occur at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energyIf the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energyThis will cause a blast wave that ejects the star's gas envelope into interstellar space
35 SUPERNOVA 1987 – right image is the star that became the left image after going supernova – shone brighter than most galaxies for a few months!
36 Here are some images of nebulae, courtesy of our friend Hubble… Clouds of dust & gas (supernova remnants?)2 Main Types:Diffuse Nebula – nearby star illuminates the gas/dust cloudDark Nebula – Dark patch against more-distant stars (dust/gas is blocking the light from stars behind it)Here are some images of nebulae, courtesy of our friend Hubble…
48 LIFE CYCLE OF STARSVIF!!!! - A star’s life cycle is determined by its MASSThe larger the star, the faster it burns out!A star’s MASS is determined by the MATTER available in the nebula of formation
49 LIFE CYCLE OF STARS SUN-LIKE STARS RED GIANT PLANETARY NEBULA (NOVA) (UP TO 1.5 X MASS OF OUR SUN)RED GIANTPLANETARY NEBULA (NOVA)WHITE DWARFBLACK DWARFSTELLAR NURSERYMASSIVE STARS(1.5 – 3 X OUR SUN)RED SUPERGIANTSUPERNOVANEUTRON STARSTARS FORM IN A NEBULA OF GAS & DUSTSUPERMASSIVE STARS> 3 X OUR SUNRED SUPERGIANTSUPERNOVABLACKHOLE
50 DEATH OF A SUN-LIKE STAR RED GIANTNEBULAWHITE DWARFBLACK DWARFSTAR COOLS ARE SHRINKS BECOMING ONLY A FEW THOUSAND MILES ACROSS!NO NUCLEAR REACTIONLONGEST, MOST STABLE PERIOD OF A STAR’S LIFE – CONVERTS HYDROGEN TO HELIUM, RADIATING HEAT & LIGHTSTAR LOSES ALL HEAT TO SPACE AND BECOMES COLD AND DARK CARBON BALLNUCLEAR FUEL DEPLETES, CORE CONTRACTS, SHELL EXPANDSOUTER LAYERS DRIFT OFF INTO SPACE IN SPHERE-LIKE PATTERN
51 GIANTS/SUPERGIANTS the brightest & largest kind of star luminosities of 10,000 to 100,000radii of 20 to several hundred solar radii (they are about the size of Jupiter's orbit!!!!)two types are red supergiants (Betelgeuse and Antares) and blue supergiants (Rigel)
52 Betelgeuse a red supergiant, with about 20 times the mass and 800 times the radius of the Sun, so huge that it could easily contain the orbits of Mercury, Venus, Earth, Mars & Jupiter. It will probably explode as a supernova at some point within the next 100,000 years. Even at its relatively remote distance, it normally ranks as the tenth brightest star in the sky.Rigel, a blue supergiant, has a diameter of about 100 million kilometers, some seventy times that of the Sun. Within a few million years, it will probably evolve to become a red supergiant like its neighbor in Orion (though not in physical space), Betelgeuse.
53 Dwarf StarsA term used, oddly enough, to describe any star that is of normal size for its massThe Sun, for example, is classified as a yellow dwarfIn general, dwarf stars lie on the main sequence and are in the process of converting hydrogen to helium by nuclear fusion in their cores
55 White DwarfsA medium sized star that has exhausted most or all of its nuclear fuel and has collapsed to a very small sizeTypically part of a planetary nebulaEventually cools into a BLACK dwarf (lump of carbon)This takes BILLIONS of years!This is the fate of OUR SUN!
56 Neutron StarThe imploded core of a massive star produced by a supernova explosionThe most dense known objects in the universe!A sugar cube size of neutron star material weighs 100 million tons!!!!!!!
60 3,700 LY wide dust-disk encircling a 300 million solar mass blackhole in the center of an elliptical galaxy.The disk is a remnant of an ancient galaxy collision and could be “swallowed” up by the blackhole in a few billion years.
62 Big Bang TheoryThe Big Bang Theory is the dominant scientific theory about the origin of the universeAccording to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions
63 Galaxy FormationThe formation of all the galaxies is explained by the Big Bang TheorySimply put, it states that the universe was a big ball of hydrogen gas that exploded outwardThe expanding cloud had areas that condensed into galaxies that are still expanding out from the center (the universe is getting larger)We can see this via RED SHIFT!
66 Galaxies system containing millions to billions of stars Ex. the Milky Way galaxy contains over 500,000 million starsMilky Way galaxy is a spiral shaped galaxy with a large central cluster of stars, and thinner “arms” radiating out from the centerThe solar system is located on one of the arms of the Milky Way galaxy about 2/3 away from the center
67 Origin of the Milky Way Formed 10-12 billion years ago Possibly collided with smaller galaxiesGlobular star clusters formedStars and solar systems formed roughly 5 billion years ago