Astronomy - Purdue Universitybraile/eas100/AstroNotes.pdf · Astronomy 1. Introduction and Observations 2. Sun and Solar System 3. Stars (Stellar Evolution) 4. Galaxies 5. Universe

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Astronomy1. Introduction and

Observations

2. Sun and Solar System

3. Stars (Stellar Evolution)

4. Galaxies

5. Universe (Deep Space, Expanding Universe, Hubble

Red Shift, Cosmology)

An excellent book on astronomy by

Timothy Ferris (1988, 2003)

Also, there are two ,excellent periodicals related to astronomy

– Astronomy and Sky and Telescope

Astronomy – Significance

1. Earth’s position in the solar system and Universe2. Origin of the Universe3. Natural interest in observing the night sky

Problems in understanding astronomyProblems in understanding astronomy concepts:

1. Scale (distance and time)2. Frame of reference (changing and 3-D)3. Vast distance and time (large numbers and

unfamiliar units/terminology)

1. Scale of the UniverseEarth orbit 300 million km (diameter)

~1 billion km (orbital path)Solar System 12 billion km across

(~ 10-3 light years*)Nearest Star 4.27 light yearsMilky Way Galaxy 105 light yearsLocal Group of Galaxies 2 5 million light yearsLocal Group of Galaxies 2.5 million light yearsObservable Universe 13.3 billion light years* One light year ~1013 km, or ~10 trillion km (It takes about 1/1000 of a year, or about 9 hours for light to travel across the solar system; 4.27 years for light from the nearest star to reach Earth; 434 years for light from Polaris (the North star) to reach Earth; ~100,00 years for light from the most distant stars in the Milky Way, our galaxy, to reach Earth, and ~13.3 billion years for light from the most distant galaxies in the universe to reach Earth!)

Light Year – A unit of distance - “how far light travels in one year”

Calculate a light year (you could do this calculation!):

~300,000 km/s the “speed of light” (start here, x60 s/min note units)

~18,000,000 km/min note that units cancel/changex60 min/hr at each calculation

1 080 000 000 k /h~1,080,000,000 km/hrx24 hr/day

~25,920,000,000 km/dayx365 days/yr

~9,460,800,000,000 km/yr speed of light in km/yr)~9,460,800,000,000 km One light year (units = km)

So, one light year is approximately 10,000,000,000,000 km, or,… 1013 km or,… 10 trillion km

http://hubblesite.org/newscenter/archive/releases/2004/07/(~60 MB jpeg file; deep space photograph, all of the bright dots or images are distant galaxies)

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Close-up of area in lower right corner of previous slide –these are all galaxies

Hubble Space Telescope (HST)Ultra Deep Field Image (2003-04)

Can image 30th magnitude objects.

Required 400 orbits, 11.3 days or recording.

Image contains about 10,000 galaxies.

Area covers 1/12.7 million of the entire sky. Area covers 1/12.7 million of the entire sky.

Like looking through an 2 ½ m (8 ft) long soda straw. With this view, astronomers would need about 50 Ultra Deep Fields to cover the entire Moon.

Hubble's keen vision (0.085 arc seconds) is equivalent to standing at the U.S. Capitol and seeing the date on a quarter 400 m (1/4 mile) away at the Washington monument.

http://news.discovery.com/space/zooms/oldest-galaxy-universe-hubble-110126.html

2011 Deep space image (after repair/upgrade of Hubble Space Telescope (HST)

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http://news.discovery.com/space/zooms/oldest-galaxy-universe-hubble-110126.html

Close-up of upper left of previous slide

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USAToday, December 2, 2010

Stars in Milky Way (spiral) galaxy (left) and in an elliptical galaxy (right) which contains large numbers of red dwarf stars.

2. Frame of Reference – 3D and constantly changing (due to Earth’s rotation and seasons caused by tilt of axis of rotation)

North star (Polaris)

http://antwrp.gsfc.nasa.gov/apod/ap991006.html

Meteor

Time lapse photo

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North star (Polaris)

http://en.wikipedia.org/wiki/North_Star

Time lapse photo

http://www.opencourse.info/astronomy/introduction/02.motion_stars_sun/northpole_malin.html

Time lapse photo centered on Polaris

(~ 8 hours)

The Universe's Most Ancient Object

The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope. This is the deepest infrared image taken of the universe. Based on the object's color, astronomers believe it is 13.2 billion light-years away.

The most distant objects in the universe appear extremely red because their light is stretched to longer, redder wavelengths by the expansion of the universe. This object is at an extremely faint magnitude of 29, which is 500 million times fainter that the faintest stars seen by the human eye.

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The dim object is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe's current age. It is tiny and considered a building block of today's giant galaxies. Over one hundred such mini-galaxies would be needed to make up our Milky Way galaxy.

The Hubble Ultra Deep Field infrared exposures were taken in 2009 and 2010, and required a total of 111 orbits or 8 days of observing. The new Wide Field Camera 3 has the sharpness and near-infrared light sensitivity that matches the Advanced Camera for Surveys' optical images and allows for such a faint object to be selected from the thousands of other galaxies in the incredibly deep images of the Hubble Ultra Deep Field.

Credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), R. Bouwens (University of California, Santa Cruz and Leiden University), and the HUDF09 Team 16

OBSERVINGYEAR Looking Back in Time (after the Big Bang)

3. Vast Distances and Large Numbers…Number of stars in the universe (just recently updated), in at least 3 trillion galaxies:

300 sextillion

(300 x 1021 or,… 3 trillion times 100 billion)

106 1,000,000 Million109 1,000,000,000 Billion1012 1,000,000,000,000 Trillion1015 1,000,000,000,000,000 Quadrillion1018 1,000,000,000,000,000,000 Quintillion1021 1,000,000,000,000,000,000,000 Sextillion

3. Units of distance in astronomy:

km - not usually used except within the solar system.

A.U. - Astronomical Units, equals distance from the Earth to the Sun, about 150 million km.

Parsec angle - used when distances are d t i d b th ll th d lldetermined by the parallax method; a parallax angle of 1 second of arc (1/3600 degrees angle) corresponds to a distance of 3.09 x 1013 km and is called one Parsec. Distant stars are measured in MegaParsecs (106 Parsecs).

Light Year - distance that light travels in one year, ~9.5 trillion km, usually used for distance to galaxies and size of the known universe.

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3. Vast Distances and frame of reference

Distant star

View from EarthNames of Stars

Pointer StarsTo North Star

We view the stars in the sky as if they were all equal distance from Earth (as on a flat or spherical surface). However, the distance to stars varies greatly.

Ursa Major (the big bear, or the big dipper, perspective view)

Sun and Earth

Closer stars

All of the objects that

3. Vast Distances and frame of reference

Distant stars

View from Earth

Names of Stars

The constellation Vega, perspective view.

we see with the naked eye in the night sky are within the Milky Way galaxy (can see two other galaxies with excellent viewing or binoculars and many galaxies with a telescope)

Closer stars

Jupiter

Moons

The Solar System

Galileo Galilei

Galileo’s observations of Jupiter’s moons demonstrated that moons revolved (orbited) about a planet providing support for the Copernican theory that the Sun was the center of the solar system.

JupiterEuropa

Callisto

Jupiter and the Galilean Moons as viewed through a modern amateur telescope (25 cm Meade).

IoGanymede

p

http://en.wikipedia.org/wiki/Moons_of_Jupiter

Jupiter has at least 63 moons. The largest (and mostly closest to the planet) were discovered by Galileo in 1610 and are called the Galilean moons

Io Europa Ganymede Callisto

http://en.wikipedia.org/wiki/Moons_of_Jupiter

Kepler’s 3rd law:P2 ~ D3

Period squared is proportional to Diameter cubed. The exact equation can be used to calculate the mass of a planet:

Period (days)

Ganymede

Jupiter

http://kepler.nasa.gov/files/mws/OrbitsOfJupitersMoons.pdf

JohannesKepler

Diameter (km)

Nig

hts

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Sky and Telescope javascript Jupiter’s moons orbit calculator: http://www.skyandtelescope.com/wp-content/observing-tools/jupiter_moons/jupiter.html#

Sky and Telescope javascript Jupiter’s moons orbit calculator: http://www.skyandtelescope.com/wp-content/observing-tools/jupiter_moons/jupiter.html#

Close-up of Galilean Moons positions relative to Jupiter on the date and time shown (C = Callisto, E = Europa, I = Io, G = Ganymede). With the calculator (below) you can step through time (use 10 minute or 1 hour time steps) to see the orbits of the moons about Jupiter (viewed from Earth, approximately along the plane of the ecliptic.

Moon rotating (animation from multiple images from the NASA LRO (Lunar Reconnaissance Orbiter): http://www.youtube.com/watch?v=sNUNB6CMnE8. The moon does rotate about once every 27 days so that we always see the same “side” of the Moon from Earth. The rotation rate is caused by gravitational “locking” of the Moon to the Earth. It tool 4 years of observations to gather the images for the animation.

Here’s our view of the Moon. The Moon as it appears from Earth (northern hemisphere): http://en.wikipedia.org/wiki/Moon

The Solar System (Sun and planets not to scale; Figure 15.17, text)

Orbits to scale

Orrery

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An excellent online Orrery (for viewing the planets in orbit) can be found at: http://gunn.co.nz/AstroTour - main controls are speed, orbit brightness, planet size and zoom. (also: http://www.pbs.org/wgbh/nova/space/tour-solar-system.html)

Solar system model (Orrery, named after Boyle, Charles, fourth earl of Orrery (1674–1731) – note that it is not at true scale in distances or diameters!

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Orrery

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An excellent online Orrery (for viewing the planets in orbit) can be found at: http://www.gunn.co.nz/astrotour/?data=tours/retrograde.xml - main controls are speed, orbit brightness, planet size and zoom. (also: http://www.pbs.org/wgbh/nova/space/tour-solar-system.html)

A Brief Tour of the Solar System

The Sun and planets drawn to scale (orbital positions not to scale) Figure 15.18, text)

Another view of the Solar System

33The Sun and planets, diameters drawn to scale. Orbital position not to scale. (http://en.wikipedia.org/wiki/Planet).

The terrestrial planets

34The Sun and planets drawn to scale (orbital position not to scale) (http://en.wikipedia.org/wiki/Planet).

The gas giant planets (Jovian planets)

Note sunspots

35The Sun and planets drawn to scale (orbital position not to scale) (http://en.wikipedia.org/wiki/Planet).

Sunspot (and image of Earth for scale). “Today [May 19, 2016], sunspot AR2546 is directly facing E th J PEarth. J.P. Brahic photographed the behemoth active region from his backyard observatory on Uzès, France.”ttp://spaceweathergallery.com/indiv_upload.php?upload_id=125887

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Figure 15.19, text

Earth’s Moon (Figure 15.23, text)

Mars (Figures 15.29 and 15.30, text)

Olympus Mons (and outline of Arizona for scale) Jupiter (and great red spot) (Figure 15.33, text)

Saturn (and rings) (Image from Hubble Space telescope; Figure 15.36, text)

“On July 19, 2013, in an event celebrated the world over, NASA's Cassini spacecraft slipped into Saturn's shadow and turned to image the planet, seven of its moons, its inner rings -- and, in the background, our home planet, Earth.” (http://www.nasa.gov/mission_pages/cassini/whycassini/jpl/cassini20131112.html#.UoTHPD8wLpf)

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Moon

Zoom in to see Earth and Moon

Neptune (and great dark spot) (Figure 15.40, text)

Asteroid Eros (Figure 15.42, text)

Comet (dust and ion tail) orbiting the Sun (Figure 15.43, text)

Planets and Solar System Websites

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http://www.nasa.gov/worldbook/planet_worldbook_update.html

http://en.wikipedia.org/wiki/Planet

http://pds.jpl.nasa.gov/planets/

http://www.space.com/planets/

http://science.nationalgeographic.com/science/space/solar-system

http://www.buzzfeed.com/daves4/the-universe-is-scary

Viewing the Night SkyObserving Stars – Apparent Magnitude (brightness; what we see without adjusting for distance to the star) and Absolute Magnitude (brightness adjusted for distance).

The Sun has a brightness (apparent magnitude of 27; note that smallermagnitude of -27; note that smaller magnitudes are brightest).

Faintest stars: Apparent Magnitude*Naked Eye viewing 6Binoculars 10Amateur Telescopes 15Modern Large Telescopes >25Hubble Space Telescope 31* Larger numbers are dimmer stars

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The star magnitude scale is logarithmic

Difference of a factor of 2 in magnitude

Difference of a factor of 10,000 in brightness

Measuring Distance to Stars: 1. The Stellar Parallax method

Stellar Parallax – distance determined from parallax angle, the smaller the parallax angle the greater the distance to the star. A parallax angle of 1 second of arc (1/3600 degrees angle) corresponds to a distance of 3.09 x 1013 km and is called one Parsec. Distant stars are measured in MegaParsecs.

(Figure 16.2, text)

Example of lunar parallax: Occultation of Pleiades by the MoonThis is the method referred to by Jules Verne in From the Earth to the Moon:

http://en.wikipedia.org/wiki/File:Stellarparallax2.svg

Another method is to take two pictures of the Moon at exactly the same time from two locations on Earth and compare the positions of the Moon relative to the stars. Using the orientation of the Earth, those two position measurements, and the distance between the two locations on the Earth, the distance to the Moon can be triangulated:

This is the method referred to by Jules Verne in From the Earth to the Moon.

Measuring Distance to Stars: 1. The Stellar Parallax method

Stellar Parallax – Animation available at: http://www.astro.ubc.ca/~scharein/a311/Sim.html

(Figure 16.2, text)

Measuring Distance to Stars: 2. Brightness method

Light spreads out with distance such that the brightness varies by 1/r2, where r is the distance. For example in the diagram above, the brightness at 4 m distance would be only 1/16th of the brightness at 1 m.

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Brightness Demo… Absolute Brightness = 1, Absolute Brightness = 4

Observer Distant Stars o

Example 1 Star A Star B

Star B is twice as far as A

The apparent brightness of A and B will be the same


Brightness Demo… Absolute Brightness = 1, Absolute Brightness = 4

Observer Distant Stars o

Example 2 Star C Star D

Star D is twice as far as C

The apparent brightness of C will be 16 times as great D

Measuring Distance to Stars: 3. Brightness methodVariable Stars – Certain stars that have used up their main supply of hydrogen fuel are unstable and pulsate. RR Lyrae variables have periods of about a day. Their brightness doubles from dimest to brightest. Cepheid variables have longer periods, from one day up to about 50 days. Their brightness also doubles from dimest to brightest.

Period ~3 days

http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html

Measure the period of the variable star, then … see next slide

Period ~3 days

Empirical relationship (determined by observations of stars having a known distance) between period of pulsation for variable stars and luminosity. Absolute magnitude for a star whose distance is unknown can be calculated from the determined luminosity and then the distance to the star calculated from the brightness method using the absolute and apparent magnitude and 1/r2 relationship.

yindicates a luminosity (proportional to absolute magnitude) of about 500.

Period ~3 days

American astronomer Henrietta Leavitt observed many Cepheid variables in the Small Magellanic Cloud (a satellite galaxy to ours). She found the period-luminosity relation (below; reported in 1912). (http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html )

yindicates a luminosity (proportional to absolute magnitude) of about 500.

The Sun – A Typical Star

Hydrogen 73.46%

Helium 24.85%

Oxygen 0.77%

Carbon 0.29%

Iron 0.16%

Spectacular loops and prominences are often visible on the Sun's limb.

http://nineplanets.org/sol.html

Main composition of the Sun

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The sun is a star with a diameter of approximately 1,390,000 km, about 109 times the diameter of Earth. The largest stars have a diameter about 1,000 times that of the sun

The sun is one of over 300 billion stars in the Milky Way Galaxy. It is about 25,000 light-years from the center of the galaxy, and it revolves around the galactic center once about every 250 million years.

that of the sun.

http://www.nasa.gov/worldbook/sun_worldbook.html

Fewer than 5 percent of the stars in the Milky Way are brighter or more massive than the sun. But some stars are more than 100,000 times as bright as the sun, and some have as much as 100 times the sun's mass. At the other extreme, some stars are less than 1/10,000 as bright as the sun, and a star can have as little as 7% of the sun's mass. There are hotter stars, which are much bluer than the sun; and cooler stars, which are much redder.

Comprising about 99.8632% of the total mass of the Solar System –most of the remainder is Jupiter.

http://en.wikipedia.org/wiki/Sun

Sun and planets – diameters shown to same scale (http://nineplanets.org/sol.html)

Adapted from: http://missionscience.nasa.gov/sun/MysteriesOfTheSun_Book.pdf

Radiative

The CoronaThe ionized elements within the corona glow in the x-ray and extreme ultraviolet wavelengths. NASA instruments can image the Sun’s corona at these higher energies since the photosphere is quite dim in these wavelengths.

The Convection ZoneEnergy continues to move toward the surface through convection currents of heated and cooled gas in the convection zone.

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Photosphere~5800 K

Zone ~2 million K

Core~15 million K

The Radiative Zone Energy moves slowly outward –taking more than 170,000 years to radiate through the layer of the Sun known as the radiative zone.

Sun’s CoreEnergy is generated by thermonuclear reactions (fusion) creating extreme temperatures deep within the Sun’s core.


Radiative



Most Important!

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Photosphere~5800 K

Zone ~2 million K

Core~15 million K


Sun’s CoreEnergy is generated by thermonuclear reactions (fusion, see next slides) creating extreme temperatures deep within the Sun’s core.

K is Kelvin (= oC + 273.15), sometimes listed incorrectly as “degrees Kelvin”

Nuclear Fusion in the Sun (and other stars) – the proton-proton chain reaction:

Note that the process starts with 4 protons and ends with one atom of helium-4 (4 protons are fused into one

http://en.wikipedia.org/wiki/Nuclear_fusion

helium-4 atom) plus large energy release – the gamma particles that eventually convert to photons (electromagnetic radiation, or light).

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The decrease in mass (from 4 protons to 2 protons and 2 neutrons) is only 0.7% but the energy release is large because of the equation


because of the equation e=mc2.

Also note that at the end of the reaction, there are still two protons remaining, so the reaction continues as a chain reaction always releasing energy.


The proton–proton chain reaction occurs around 9.2×1037 times each second in the core of the Sun. The Sun releases energy at the mass-


releases energy at the mass-energy conversion rate of 4.26 million metric tons per second, (3.846×1026 W) or 9.192 × 1010 megatons of TNT per second. (http://en.wikipedia.org/wiki/Sun)


Reaction continues until the Hydrogen (source of the protons) is nearly all converted to Helium


converted to Helium.

Energy from nuclear fusion in stars larger than the Sun (hotter and higher pressure core) is generated by the Carbon-Nitrogen-Oxygen (CNO), or other, chain reactions.

The “holes” (absorption bands) in the spectrum are due to absorption by compounds in the atmosphere

http://en.wikipedia.org/wiki/File:Solar_Spectrum.png

Life Cycle of the Sun


In about another 5 billion years, the hydrogen will be nearly depleted and the Sun’s core will collapse and heat up resulting in helium fusion and the Sun will become a Red Giant with a size that will probably extend out to the present orbit of Mars.

Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surroundingsurrounding regions. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature.

http://en.wikipedia.org/wiki/Sunspot

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Note 11 year cycle of sunspots


http://csep10.phys.utk.edu/astr162/lect/sun/spectrum.html

Very bright stars have more shorter-wavelength radiation and higher temperatures. These measurements are from spectrometers.

Galaxies – Typically consist of 1 billion to over 100 billion stars. Most are relatively flat. Stars in the galaxy revolve around a central area, and thus don’t collapse (at least not quickly) from gravity (similar to the solar system). Most galaxies (including the Milky Way) probably have black holes in the center of the galaxy accounting for a substantial part of its mass.its mass.

Types of Galaxies: Elliptical, Spiral, Irregular, Dwarf

A tour of some galaxies…

Spiral Galaxy M81 (NASA)

(Chapter 16, text)

Above: The Milky Way (panorama from

(Chapter 16, text)

y (pEarth).

Right: Spiral galaxy NGC 2997 (similar to Milky Way).

(Chapter 16, text)

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(Figure 16.17, text)


Panoramic Photo (seven frames stitched together; time lapse exposure; a quarter Moon provided the light to illuminate the mesas and foreground) of the Milky Way galaxy above Monument Valley, AZ (from Dec./Jan. 2012 issue of National Wildlife, www.nwf.org; http://www.nwf.org/News-and-Magazines/National-Wildlife/PhotoZone/Archives/2011/2011-National-Wildlife-Photo-Contest-Winners.aspx)

Spiral Galaxy Andromeda

(Figure 16.2, text)

The Barred spiral galaxy


Stellar Evolution, Galaxies, and the UniverseThe Sun – A Typical Star

Spectacular loops and prominences are often visible on the Sun's limb.

The mass of the Sun is large enough to cause high

pressure and temperature

in the core,resulting

in nuclearfusion!

Hydrogen is being converted to Heliumin the Sun. Thereis a large amount of H d i i

It is important to know about the Sun! Not only is it the center of our solar system, it is also an important source of energy for the Earth, and the closest star that we can study to better understand stars, galaxies and the universe! Adapted from: http://nineplanets.org/sol.html

Main composition of the Sun:Hydrogen 73.46%Helium 24.85%Oxygen 0.77%Carbon 0.29%Iron 0.16%

Hydrogen remaining, so the Sun will exist for a long time.

The sun is a star with a diameter of approximately 1,390,000 km, about 109 times the diameter of Earth. The largest stars have a diameter about 1,000 times that of the sun

The sun is one of over 100 billion stars in the Milky Way Galaxy. It is about 25,000 light-years from the center of the galaxy, and it revolves around the galactic center once about every 250 million years.

that of the sun.

http://www.nasa.gov/worldbook/sun_worldbook.html

Fewer than 5 percent of the stars in the Milky Way are brighter or more massive than the sun. But some stars are more than 100,000 times as bright as the sun, and some have as much as 100 times the sun's mass. At the other extreme, some stars are less than 1/10,000 as bright as the sun, and a star can have as little as 7% of the sun's mass. There are hotter stars, which are much bluer than the sun; and cooler stars, which are much redder.

Comprising about 99.8632% of the total mass of the Solar System –most of the remainder is Jupiter.


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85Adapted from: http://nineplanets.org/sol.html

Sun and planets (enlarged) – diameters shown at same scale (Adapted from: http://nineplanets.org/sol.html)

)

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Radiative



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Photosphere~5800 K

Zone ~2 million K

Core~15 million K


Sun’s CoreEnergy is generated by thermonuclear reactions (fusion) creating extreme temperatures deep within the Sun’s core.



Radiative



Most Important!

88

Photosphere~5800 K

Zone ~2 million K

Core~15 million K


Sun’s CoreEnergy is generated by thermonuclear reactions (fusion, see next slides) creating extreme temperatures deep within the Sun’s core.



Note that the process starts with 4 protons and ends with one atom of helium-4 (4 protons are fused into one


protons are fused into one helium-4 atom) plus large energy release – the gamma particles that eventually convert to photons (electromagnetic radiation, or light).


The decrease in mass (from 4 protons to 2 protons and 2 neutrons) is only 0.7% but the energy release is large because of the equation


of the equation e = mc2.

Also note that at the end of the reaction, there are still two protons remaining, so the reaction continues as a chain reaction (requiring very high temperature and pressure) always releasing energy.

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The proton–proton chain reaction occurs around 9.2×1037 times each second in the core of the Sun. The Sun releases energy at the mass-


releases energy at the mass-energy conversion rate of 4.26 million metric tons per second, (3.846×1026 W) or 9.192 × 1010 megatons of TNT per second.

(http://en.wikipedia.org/wiki/Sun)


Reaction continues until the Hydrogen (source of the protons) is nearly all converted to Helium


converted to Helium.

Energy from nuclear fusion in stars larger than the Sun (hotter and higher pressure core) is generated by the Carbon-Nitrogen-Oxygen (CNO), or other, chain reactions.

Tools of Astronomy:

1. Samples – meteorites (abundance of elements).2. Photography – telescopes (Earth-based and

satellite; visible and invisible wavelengths)3. Distance measurement – stellar parallax,

brightness method (variable stars) Hubble red shift

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brightness method (variable stars), Hubble red shift.4. Brightness – absolute and apparent magnitude

(classification).5. Spectroscopy – continuous spectrum (amount of

radiation at different wavelengths; provides temperature of surface of star), bright line and dark line spectra (provides composition).

http://en.wikipedia.org/wiki/File:Solar_Spectrum.png

Life Cycle of the Sun


In about another 5 billion years, the hydrogen will be nearly depleted and the Sun’s core will collapse and heat up resulting in helium fusion and the Sun will become a Red Giant with a size that will probably extend out to the present orbit of Mars.

Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surroundingsurrounding regions. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature.http://en.wikipedia.org/wiki/Sunspot

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http://en.wikipedia.org/wiki/SunNote 11 year cycle of sunspots


http://csep10.phys.utk.edu/astr162/lect/sun/spectrum.html

Very bright stars have more shorter-wavelength radiation and higher temperatures. These measurements are from spectrometers.

The Hertzsprung-Russell (H-R) Diagram

Sun

y (S

un =

1)

Mag

nitu

de

(Figure 16.4, text)

Lum

inos

ity

Abs

olut

e M

Surface Temperature (K)

The Hertzsprung-Russell (H-R) Diagram

Hotter stars have shorter wavelength radiation and shorter lifetimes

Sun

y (S

un =

1)

Mag

nitu

de

(Figure 16.4, text)

Cooler stars have longer wavelength radiation and longer lifetimes

Lum

inos

ity

Abs

olut

e M

Surface Temperature (K)

“Classification of Stars” (Figure 16.5, text)

H-R diagram illustrating life cycle of a main sequence star (such as the Sun). Most of lifetime, star is on Main Sequence, then in dwarf stage.

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(Figure 16.12, text)Low Mass

Medium Mass

103Life cycle of stars

High Mass


Medium Mass

104

Life cycle of stars – National Geographic, March 2014

High Mass


Medium Mass

105

High Mass



Medium Mass

106

High Mass


Supernova remnant Cassiopeia A, located about 10,000 light years from Earth.

Neutron Star

(also, Figure 16.9, text)

Trifid Nebula (birthplace of Stars, mostly H and He gases illuminated by hot young stars).

(Figure 16.1, text)

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Horsehead (mostly dark) Nebula in constellation Orion.

The Helix Planetary Nebula (formed during a star’s collapse from a red giant to a white dwarf).

(also, Figure 16.8, text)

The Crab Nebula (in the constellation Taurus; the remains of the supernova explosion of A.D. 1054).


The Veil Nebula (in the constellation Cygnus; the remains of a supernova implosion).


Galaxies – Typically consist of 1 billion to over 100 billion stars. Most are relatively flat. Stars in the galaxy revolvearound a central area, and thus don’t collapse (at least not quickly) from gravity (similar to the solar system). Most galaxies (including the Milky Way) probably have black holes in the center of the galaxy accounting for a substantial part of its mass.

Types of Galaxies: Elliptical, Spiral, Irregular, Dwarf

A tour of some galaxies…

Spiral Galaxy M81 (NASA)

(Chapter 16, text)

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Above: The Milky Way (panorama from

(Chapter 16, text)

y (pEarth).

Right: Spiral galaxy NGC 2997 (similar to Milky Way).

(Chapter 16, text)



Panoramic Photo (seven frames stitched together; time lapse exposure; a quarter Moon provided the light to illuminate the mesas and foreground) of the Milky Way galaxy above Monument Valley, AZ (from Dec./Jan. 2012 issue of National Wildlife, www.nwf.org; http://www.nwf.org/News-and-Magazines/National-Wildlife/PhotoZone/Archives/2011/2011-National-Wildlife-Photo-Contest-Winners.aspx)

Spiral Galaxy Andromeda

(Figure 16.2, text)

The Barred spiral galaxy


Elliptical galaxy ESO 325-G004. Most elliptical galaxies are very old and probably result from two galaxies colliding.

119http://en.wikipedia.org/wiki/Elliptical_galaxy

Cosmic Web (structure of the universe, how the galaxies are distributed in the universe) Videos –

Where the Galaxies Are – Margaret Geller, 1991

NASA /Goddard Space Flight Center Scientific Visualization Center:

Cosmic Origins Spectrograph: Large Scale Structure of the Universe

http://svs.gsfc.nasa.gov/vis/a010000/a010200/a010223/index.html

Journey Through the Cosmic Web

http://svs.gsfc.nasa.gov/vis/a010000/a010100/a010118/index.html

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How to find a galaxy, Margaret Geller.View of a slice of the universe,each yellow dot is agalaxy. Note patternof empty space and closespacing.

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NOVA, https://www.youtube.com/watch?v=gAyZbpSW15U

Moving object emitting radiation

Motion

Measuring Distance to Stars (and Galaxies): 3. The Hubble Red Shift (a Doppler Effect)

Doppler Effect (and Red Shift) – Animation available at: http://www.astro.ubc.ca/~scharein/a311/Sim.html

MotionObserver here sees longer wavelength radiation (red shifted)

Observer here sees shorter wavelength radiation (blue shifted)


Example of Doppler Effect – Observer senses different wavelengths (hears different sounds) from approaching and receding ambulance. Note that the ambulance moving away results in longer wavelengths. The faster the ambulance is moving away, the longer the wavelength (lower frequency sound).

Moving object emitting radiation

Motion

Measuring Distance to Stars (and Galaxies): 3. The Hubble Red Shift (mostly a Doppler Effect)

Doppler Effect (and Red Shift) – Animation available at: http://www.astro.ubc.ca/~scharein/a311/Sim.html

MotionObserver here sees longer wavelength radiation (red shifted)

Observer here sees shorter wavelength radiation (blue shifted)

Hubble, 1929

Hubble’s Law

Hubble's law is a statement of a direct correlation between the distance to a galaxy and its recessional velocity as determined by the red shift. It can be stated as:

H0 is the slope of the linehttp://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html

Hubble’s Law

slope ~ 500 km/sMpc

The reported value of the Hubble parameter has varied widely over the years, testament to the difficulty of astronomical distance measurement. But with high precision experiments after 1990 the range of the reported values has narrowed greatly to values in the range of:

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html

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1) Virtually all galaxies are moving away from us, e.g. they are redshifted.

2) The more distant the galaxy, the larger

Modern Hubble’s Law Data

g y, gits redshift, that is the faster it is moving away.

http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/bigbang.htm

One MegaParsec (Mpc) = 3 million light years = 3 x 1019 km

Hubble’s original 1929 data

At all locations, objects are moving away and more distant objects have higher recession velocity.

http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/bigbang.htm

Expanding Universe – As the universe expands, the galaxies get farther apart (although some are gravitationally connected and collide/merge) and increase their red shift.

129 130

131http://www.youtube.com/watch?v=oAVjF_7ensg

Hubble Ultra Deep Field 3D

Expanding universe modeled as the surface of a balloon - Imagine a balloon with points A, B and C labeled. After expanding the balloon, the distances change.

Time 1

A

A

B

B

C

1

2

2From Time 1 to Time 2,

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Time 2

B

C

4

,increase in distance A to B is 1, A to C is 2. So, velocity for A to C is twice is large as from A to B. More distant objects have higher recession velocity. This is true for all locations on the surface. Distances in Red

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Cosmic Microwave Background Radiation

Observations of background radiation of the universe from the 1990 NASA COBE (Cosmic Background Explorer) satellitehttp://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation


With a traditional optical telescope, the space between stars and galaxies (the background) is pitch black. But with a radio telescope, there is a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum, hence the name cosmic microwave background radiation. The CMB's serendipitous discovery in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned them the 1978 Nobel Prize.

http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation


The CMBR is well explained as radiation left over from an early stage in the development of the universe, and its discovery is considered a landmark test of the Big Bang model of the universe. When the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, stable atoms could form. These atoms could no longer absorb the thermal radiation, and the universe became transparent instead of being an opaque fog. The photons that existed at that time have been propagating ever since, though growing fainter and less energetic, since exactly the same photons fill a larger and larger universe. This is the source for the term relic radiation, another name for the CMBR.http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation

Two of COBE's principal investigators, George Smoot and John Mather, received the Nobel Prize in Physics in 2006

http://www.astro.ucla.edu/~wright/CMB.html

Nobel Prize in Physics in 2006 for their work on precision measurement of the CMBR.

The Cosmic Microwave Background Radiation measured by the COBE satellite almost precisely fits the backbody radiation curve corresponding to 2.725 K (-270.425 oC) – a very cold temperature due to cooling of the universe (in the space between galaxies and stars) and the red shift.

The scale of the Universe – Earth and the Solar System

Logarithmic Scale

137 138

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The scale of the Universe – Beyond the Solar System

Logarithmic Scale

Evidence for Big Bang Theory

1. Red Shift, universe expanding

2. Distant galaxies receding faster

3. Cosmic background radiation

4. Abundance of elements in the universe is consistent with mathematical models and nuclear physics of Big Bang evolution of the universe

5. Einstein’s general theory of relativity predicts expanding universe

6. Formation of galaxies and large scale structure of the universe

Black Holes

A black hole is a region of space whose gravitational force is so strong that nothing can escape from it. A black hole is invisible because it even traps light. The fundamental descriptions of black holes are based on equations in the theory of general relativity developed by the German-born physicist Albert Einstein. The theory was published in 1916.

Characteristics of black holes

http://www.nasa.gov/worldbook/blackhole_worldbook.html

Characteristics of black holesThe gravitational force is strong near a black hole because all the black hole's matter is concentrated at a single point in its center. Physicists call this point a singularity. It is believed to be much smaller than an atom's nucleus. The surface of a black hole is known as the event horizon. This is not a normal surface that you could see or touch. At the event horizon, the pull of gravity becomes infinitely strong. Thus, an object can exist there for only an instant as it plunges inward at the speed of light.

Black HolesFormation of black holes According to general relativity, a black hole can form when a massive star runs out of nuclear fuel and is crushed by its own gravitational force. While a star burns fuel, it creates an outward push that counters the inward pull of gravity. When no fuel remains, the star can no longer support its own weight. As a result, the core of the star collapses. If the mass of the core is three or more solar masses, the core collapses into a


singularity in a fraction of a second.

Galactic black holesMost astronomers believe that the Milky Way Galaxy -- the galaxy in which our solar system is located -- contains millions of black holes. Scientists have found a number of black holes in the Milky Way. These objects are in binary stars that give off X rays. A binary star is a pair of stars that orbit each other.

Black HolesSupermassive black holes Scientists believe that most galaxies have a supermassive black hole at the center. The mass of each of those objects is thought to be between 1 million and 1 billion solar masses. Astronomers suspect that supermassive black holes formed several billion years ago from gas that accumulated in the centers of the galaxies.

Th i t id th t i bl k h l li t th t


There is strong evidence that a supermassive black hole lies at the center of the Milky Way. Astronomers believe this black hole is a radio-wave source known as Sagittarius A* (SgrA*). The clearest indication that SgrA* is a supermassive black hole is the rapid movement of stars around it. The fastest of these stars appears to orbit SgrA* every 15.2 years at speeds that reach about 3,100 miles (5,000 kilometers) per second. The star's motion has led astronomers to conclude that an object several million times as massive as the sun must lie inside the star's orbit. The only known object that could be that massive and fit inside the star's orbit is a black hole.

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Because black holes are invisible, they are mostly detected (inferred) form the gravitational forces required for objects which revolve around them and from radiation from nearby regions (outside the event horizon) that are energized by the


Some useful references: Chaisson, E., Relatively Speaking: Relativity, Black Holes, and the Fate of the

Universe, W.W. Norton & Company, New York, 254 pp., 1988.Ferris, T., Coming of Age in the Milky Way, Anchor Books, New York, 495 pp.,

1988.

rapid motion of objects and gases and emit x-ray radiation.

The following slides are just for interest (if you are in Houston, I highly recommend visiting these locations)

1. From tour of NASA Johnson Space Center (JSC) in Houston, Texas (seven slides)

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slides)

2. Saturn 5 Rocket displayed in building near JSC entrance gate (5 slides)

3. Paleontology and Gem and Mineral display at Houston Museum of Natural Science (11 slides)

1. NASA and Purdue astronaut, Drew Feustel, landed back on Earth on 10/04/2018, at about 7:45 a.m. EDT. NASA video of descent and landing on Soyuz MS-08: https://www.youtube.com/watch?v=pxaX7CtdGAg or https://www.youtube.com/watch?v=GWusG5EW3dU

Purdue Today Article (10/4/2018):https://www purdue edu/newsroom/https://www.purdue.edu/newsroom/releases/2018/Q4/astronaut-feustel-scheduled-to-return-to-earth-on-thursday.html

The Space Shuttle

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The Space Shuttle on a 747

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Astronaut suits –weighing 300 lbs

150

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40 ft deep weight-less training pool with Space Station modules. Astronauts in their space suits spend 6-hour training sessions in the pool. Drew Feustel’s training in the pool was for over 800 hours. 152

International Space Station (ISS) modules for training.

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Soyuz spacecraft. Upper left –module for returning to Earth from the ISS; two parts are jettisoned in the upper atmosphere before landing. Upper right – capsule holding the astronauts. Lower left – astronauts in the capsule.

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2. The Saturn V was an American human-rated expendable rocket (111 m long, 2,970,000 kg) used by NASA between 1967 and 1973. The three-stage liquid-fueled super heavy-lift launch vehicle was developed to support the Apollo program for human exploration of the Moon and was later used to launch Skylab, the first American space station. https://en.wikipedia.org/wiki/Saturn_V

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Space Capsule

Saturn V on launch pad

Capsule

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Propulsion Rockets

launch pad

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Neil Armstrong on the Moon, Apollo 11, July, 1969

158Neil Armstrong, Michael Collins and Buzz Aldrin – astronauts for Apollo 11 and Moon Landing, July, 1969.

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3. Fossils, gems and minerals displayed at the Houston Museum of Natural Science (http://www.hmns.org/ - some photos are also online here) 160

161 162

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163 164

165

Jaws of Giant Shark - 3 meter opening

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Gold

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Documents

Astronomy - Purdue Universitybraile/eas100/AstroNotes.pdf · Astronomy 1. Introduction and Observations 2. Sun and Solar System 3. Stars (Stellar Evolution) 4. Galaxies 5. Universe