Astrophysics-I Fiz463e CRN Thursday / Y5 There will be 1 midterm Many quizes Many reading material Follow the website.

Contents of Astrophysics I Basic concepts in astrophysics Astronomical distance scale Observational instrumentation Solar system (Sun, Moon, Planets, Comets and asteroids) Stellar structure and evolution

Contents of Astrophsics II Compact objects (white dwarfs, neutron stars and black holes) Magnetohydrodynamics (MHD) and plasma physics Galactic dynamics Cosmology Accretion processes around compact objects

Lecture I- History of Astronomy Celestial Sphere=Gökküre=Felek (Çoğ:Eflak) Planets (=Gezegen=Seyyare) and Their Retrogade Motion Aristotelian World View Ptolemian Astronomy The Copernican Revolution-The Earth is a Celestial Object! Galileo-The First (or the second after Gilbert) Scientist Universal Law of Gravity The Chemistry of Stars-How the spectroscopy challenges Aristotle.

Diurnal Motion Apparent Daily Motion of Stars Around the Earth

Stars move East to West as the Earth rotates West to East. They cover 15 degrees per hour which amounts to 360 degrees per day! Diurnal Motion

Ancient World View Ancient people have been observing the sky and were well aware this circular trajectory of the stars. Ancient people believed that the Earth was at the center of the Universe, motionless and non-rotating. For the ancient people the circular trajectories of the stars were not just an apparent motion but was real, the stars were indeed rotating around the Earth.

Star Trails on the Equator (Kenya)

Constellations Preserve Their Form Ancient people also noticed that the constellations (e.g. Ursa Major=büyükayı) preserve their form during diurnal rotation, hence they concluded that... The stars are not rotating by their own but they are fixed onto a sphere and the diurnal rotation of the stars is due to the rotation of this sphere. This sphere is called the celestial sphere.

Constellations Constellation=takımyıldız The stars in the constellations are not physically close but their projections onto the celestial sphere appear to be close. Constellations help to locate objects on the sky.

Globular Cluster These are stars physically close to each other.

Celestial Sphere is still a useful concept because we only see the projections of celestial objects on such a fictitious sphere. Measuring the distances is a hard problem of astronomy (see Next Weeks lesson). Celestial Sphere=Gökküre=Felek (Çoğ:Eflak)

Seven Objects not Fixed to the Celestial Sphere For the ancient people the celestial sphere was a real object! All stars were fixed onto this sphere but there were 7 objects moving independent of the celestial sphere. These are the 5 planets that can be identified by the naked eye (Mercury, Venus, Mars, Jupiter, Saturn), the Moon, and the Sun. These objects are all located along the ecliptic and appear to be not fixed on the celestial sphere.

Retrogade Motion of Mars

Understanding the Retrogade Motion

Modern Science, to a large extend, was born out of the human desire to explain the retrogade motion of the planets.

Planets Planetes means wanderers in Greek. Planet = Gezegen = Seyyare Notice they all carry the same meaning referencing their apparent wandering with respect to the “fixed” stars. For the ancient people planets were gods and they gave their name to each day of the week.

Days of the Week SaturdaySaturn SundaySun MondayMoon Tuesday Tiw  Mars Wednesday Odin  Mercury Thursday Tor  Jupiter Friday Frie  Venus Astronomical Names for the Days of the Week, Falk, M.., 1999, J. of the Royal Astron. Soc. of Canada, Vol. 93, p.122

Aristoteles (M.Ö ) The Earth is a sphere at the center of a spherical universe The Moon, Merkury, Venus, the Sun, Mars, Jupiter, Saturn and fixed stars each rotate around their own spheres. These spheres are made of crystal (so that they are not seen)

7 katlı gök The 7 Spheres Above the Earth Below the Celestial Sphere

Felek Feleğin tekerine çomak sokmak Felekten bir gün çalmak Feleğin çemberinden (çeperinden?) geçmek.

Aristoteles... Dominated the philosophy all throughout the medieval ages. The research at that time simply meant finding out what Aristoteles said about that research topic. No experiment, no questioning.

Today... There can be different models on any observed phenomena but there is no a priori authority accepted to be true without question. The validity of models is checked by experiment and/or observation whoever the proposer of the model is. The reference of truth is expriment. Hence we select between the models by asking the nature.

Aristoteles: Objects on Earth and Celestial Objects are composed of Different Elements Objects on Earth (everything below the sphere of the Moon) are a mixture of 4 elements: Earth, Water, Air and Fire. Such objects are subject to change, decay and/or death and are defected. Celestial Objects are made from a fifth element (Ether). Such objects are defectless/perfect, and eternal. They are not subject to any change. Aristoteles was a student of Platon and envisaged the world of ideas in the sky.

Aristoteles: Objects on the Earth and the Celestial Objects Obey Different Laws Each element has a natural place determining its natural motion: Earth belongs to the Earth. The natural place of Water is arround earth. Natural place of Air is above Earth & Water. And Fire is to be above the Air. A stone falls down because it belongs to the Earth. Fire tends to rise up because it wants to reach the greatest fire (the Sun), the bubbles in water rise up because air is to be above water, etc. Apart from the natural motions there are forced (violent) motions. One has to apply force in order to keep objects in motion: The card stops when the horse stops. Heavier objects fall more rapidly than the lighter objects. Celestial objects eternally follow circular trajectories. They do not change their speed during this motion. Each celestial object rotates around the Earth.

Comets According to Aristoteles The celestial objects are eternal and the sky is not subject to change. Hence comets must be inside the sphere of the Moon, i.e. they are atmospheric events.

Aristarchus of Samos ( BC) Proposed the heliocentric model This was not widely accepted because… …the parallax can not be measured with naked eye. …the rotation of the Earth would throw us away. …the Earth would leave behind the Moon

Summary: For the Ancient People... Objects on the Earth and the Celestial Objects have different structures. Celestial objects are perfect while the objects on the Earth are defected and are subject to decay. Different laws in the sky and on the Earth. The Earth is at the center of the Universe (obviously!) Force is needed to keep objects in motion.

The Universe of the ancient people was very small Though this picture is misleading because humans have been believing that the Earth is spherical since long time. It is a 19 th century misconception to think that the ancients believed the Earth was flat. Flat Universe?

Hipparchus & Epicycles Retrograde motion of planets could be explained by a combination of circular motions; the planet moves in a small circle called an epicycle the centre of the epicycle moves around a larger circle called the deferent If the planet moves around the epicycle faster than the epicycle moves around the deferent, retrograde motion will occur in some regions of the orbit

Ptolemy=Batlamyus (Claudius Ptolemaeus-140AD) Ptolemy expanded upon Aristotles geocentric model to predict the motion of planets accurately. Following Hipparchus, he assumed that planets moved around circular epicycles. The centres of the epicycles moves around the Earth in circular deferents. He added a number of refinements to the old model to obtain better agreement with observations. In particular, he offset the centre of the deferent from the centre of the Earth!

Ptolemy’s Epicycles

Ptolemaic System Mathematike Syntaxis (13 Volume book of Ptolemy) Arabic Scientists loved the book and named it al-kitabu-l-mijisti, i.e. "The Great Book" Today this book is called “Almagest” because of this.

Ptolemaic Model of the Universe

The Ptolemaic Model Ptolemy was able to predict the motions of the seven celestial objects to great accuracy by introducing more and more epicycles (equivalent to Fourier analysis) Ptolemy’s model had been used nearly for 1500 years by the western and eastern astronomers.

Nasir al-Din TusiNasir al-Din Tusi (1201–1274) Resolved significant problems in the Ptolemaic system by developing the Tusi- couple as an alternative to the physically problematic equant introduced by Ptolemy.Tusi- couple equant

Tusi-Couple A mathematical device in which a small circle rotates inside a larger circle twice the radius of the smaller circle. Rotations of the circles cause a point on the circumference of the smaller circle to oscillate back and forth along a diameter of the larger circle. Tusi's diagram of the Tusi couple (Vatican Arabic ms 319, fol. 28v; 13th. c.)

The rest of the Universe was comparable to the size of the Earth. Size of the Earth Comparable to the size of the Heavens

Nicolaus Copernicus ( ) “Who in this most beautiful of temple would put his lamp at a better place than from where it can illuminate them all?. Thus the Sun sitting as on a Royal throne, leads the surrounding family of stars!”

Copernican Model The Sun is at the center of the Universe (not just the Solar System) The orbits are circular (and still there are epicycles though they are significantly less than the geocentric model) The crystal spheres are still there.

Tycho Brahe ( ) Observed a supernova explosion (1572). He thought this was a new star. Surprised because he thought the celestial objects are eternal and the sky does not change.

Stella Nova The image in this page is from Tycho Brahe's "Stella Nova“.

Tycho Brahe and Comets Observed a comet Made collaborations with an observer at a different location to find that the comet was nearly in the same position with respect to the background stars for both observers (i.e. no parallax). Concluded that the comet was at least six times farther away than the Moon.

Tycho Brahe and the Crystal Spheres Tycho Brahe also understood that the comet must have passed through the spheres. So the crystal spheres of Aristoteles can not be real!

Around the Same Time in Istanbul! Takiyuddin founded the Istanbul Observatory in Tophane (1577) He had similar instruments as with Tycho Brahe. Some of the measurements of Takiyuddin are even more precise. However, Takiyuddin wasn’t able to continue his observations as long as Tycho did.

Galileo ( ) The Second Scientist after Gilbert A strong refuter of the Aristotelian world view.

Galilei Supernova In 1604 he observed the SN studied by Kepler. He thought this was a new star. The new star showed no motion accross the sky compared with the other stars (i.e. No parallax) Gave series of well recieved lectures arguing that it must be as far away from the Earth as the other stars. This refutes the Aristotelian notion of an unchanging celestial sphere.

Galileo’s Poem for the New Star No lower than the other stars it lies And does not move in other ways around Than all fixed stars-nor change in sign or size. All this is proved on the purest reasons ground; It has no parallax for us on Earth By reason of the sky’s enormous girth.

A Celestial Object Defected? Directed his telescope to the sky (1609). The Moon is not perfect! It has craters which are defects.

...Galileo Discovered Jupiter’s moons. This implies that (independent of whether the geoentric or heliocentric model is true) not every celestial object rotates around the Earth. This also obviates the argument against the Copernican sytem that if the Earth rotated around the Sun then the Earth and the Moon would get separated from one another.

Galilei observed the Phases of Venus Heliocentric Model: All phases should be visible Geocentric Model: Only crescent and new phases would be seen

Galilei and the Milky Way As seen with the telescope Milky Way is a myriad of individual stars.

Aristotelian Response Aristotelians refused to accept that what was seen through the telescope was real. (Some of them even refused to look through the telescope saying it is simply a nonsense device). Galileo himself tested the possibility by observing hundreds of objects to see if the instrument does anything except magnify.

The Sun also is not Perfect (Galilei 1613)

–falling bodies: according to Aristoteles, heavy bodies (contain more earth element) fall faster than lighter bodies observation: fall equally fast if they have same shape and size Galilei: difference in speed of differently shaped falling bodies due to air resistance –thought experiment about two falling bodies - “reductio ad absurdum”: consider two bodies, one light (L), one heavy (H) Aristoteles: L falls more slowly than H  L put under H should slow down fall of H;  H with L under it should fall more slowly than H alone; but (L + H) heavier than H alone  should fall faster than H alone  contradiction. –ball rolling on inclined plane: ball rolling down inclined plane speeds up; ball rolling up slows down; rate of slowing down depends on steepness of incline: less steep  longer distance travelled; extrapolation to zero slope of incline: ball will go on forever Galileo's thought experiments and real experiments:

Achievements of Galileo founder of modern science; –new methods introduced by Galilei include: controlled experiments designed to test specific hypotheses idealizations to eliminate any side effects that might obscure main effects limiting the scope of enquiry - consider only one question at a time; quantitative methods - did careful measurements of the motion of falling bodies. –from observations and thought experiments, generalizes to two new laws: LAW OF INERTIA: –without external influence (force) acting on it, a body will not change its speed or direction of motion; it will stay at rest if it was at rest to begin with. –inertia = property of bodies that makes them obey this law, their ability to maintain their speed (or stay at rest) About FALLING OBJECTs: –if air resistance is negligible, any two objects that are dropped together will fall together; speed of falling independent of weight and material.

Three Quotations from Galileo In questions of science the authority of a thousand is not worth the humble reasoning of a single individual. Instead of philosophical arguments, I prefer to discover a single fact. What has philosophy got to do with measuring anything?

Kepler If the celestial objects are not perfect their orbits also may not be perfect. Then introduce elliptic orbits into the Copernican system. Kepler’s laws for the motion of planets.

Newton (1687) Gravitational attraction is between all bodies. The force that keeps the Moon in orbit is the same force that causes the apple to fall down. Objects on the Earth and the objects in the sky obey the same laws.

New Mechanics Aristotelian view: forces cause velocity (force necessary to maintain uniform motion). Newtonian view: forces cause acceleration (force necessary to change motion)

Bessel (1838) Successfully measured the parallax of the star 61 Cygni.parallax61 Cygni This was considered conclusive evidence that the Earth was in motion.

Objects on the Earth and Celestial Objects are made of same kind of elements Spectroscopy discovered in the 19 th century Using spectroscopy astronomers understood that stars are made of mainly hydrogen and some other elements like Carbon and Oxygen that also make up the Earth. This is the last blow to the Aristotelian World View.

Short History Tycho Brahe supplied the accurate data about the motion of the planets. Kepler analysing the data arrived at the Kepler’s Laws. Newton, trying to explain Kepler’s laws found the general laws of motion which are not only valid in the solar system but can also be applied to many different phenomena. This was the physics behind the industrial revolution which took the Western civilization ahead of the Eastern world. The history unfolded differently in the Eastern world.

The Fate of Takiyuddin’s Observatory in Istanbul Takiyuddin ( ) came to Istanbul in 1570 Convinced the Ottoman King (III.Murat) to build an Observatory. By observations Takiyuddin was to prepare a “zic” in the name of the King. With this renewed catalogue whorshipping times would be more accurately determined.

Istanbul Observatory (1577)

A comet at November 1577

Black Death in 1578 Gossip that all this evil arising because they have been observing the legs of the angels in the observatory Şeyhülislam (Ahmed Şemseddin Efendi): Observing the legs of the angels from the ground with pipes is a grand sin.

Black Death and the Şeyhülislam continues Şeyhülislam:İhrac-ı Rasad meş'um perde-i esrarı felekiyeye küstahane itlak-ı cür'etin vehamet ve akibeti meczumdur. Hiçbir mülkde mübaşeret olunmadı ki ma'mur iken harap ve bünyan-ı devleti zelzelenak-i inkilab olmaya. Observation brings illomens. The serious danger in attempting to understand the secrets of the celestial spheres should be obvious. In no country where observation is conducted there has ever been a case that the strong state had not been destroyed and the structure of the state was not shaken.

The End of the Observatory The king was scared and wanted the observatory to be broken down. This was done by Kılıç Ali Paşa in 1580 just after 3 years that the observatory started working. The second attempt to build a telescope in Ottoman Empire was in 1873 afer about 300 years. This also was broken down by the softas in 31 Mart event in Kandilli observatory was built in 1911 by Fatin Gökmen.

End of the Lecture Be sure to read some of the material on the web. o463/astro463.html