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Introduction to ! AST0111-3 (Astronomía) ! ! ! ! ! ! ! ! ! ! ! ! Semester 2014B Prof. Thomas H. Puzia What is maximum/minimum observable altitude from Santiago for the following? ! DEC 33.4500° S 02h 32m +89d 15m 70.6667° W Crab / 05h 34m +22d 00m Nebula Large Magellanic 05h 23m -66d 45m Cloud (LMC) M42 (Orion 05h 32m -05d 23m Nebula) Southern Cross 12h 30m -60d 00m (Crux) Ω Cen 13h 26m -47d 28m

Fomalhaut 22h 57m -29d 37m

4h 4h 0h 8h

20h 12h 16h N?

What can you tell from this picture??? What of is it? Where is the ? Where would other lie? Where on could you be? How do we know when a celestial object will ? We define Local (ST) to be 0 hrs when the vernal (VE, which has RA=0) transits the observer's local . One later, the local (HA) of the equinox is +1h (by the definition of Hour Angle), and the Local Sidereal Time is 1h. A transiting now has RA~1h.

At any instant, Local Sidereal Time = Local Hour Angle of the VE. Alternatively, Local Sidereal Time ~ of any star currently transiting (I use ~ here because 23h 56m does not = 24h) ! Now, LST is different from , which defined as some variant of (GMT). To calculate the offset, roughly: Greenwich mean time of March 21 => vernal equinox and Sun transit Greenwich together, RA=0

Each day, Sun position moves +3.94min in RA, providing an offset between solar time and local sidereal time. Your location on the Earth relative to Greenwich, UK is not the same as the median location of your , so better to use your (Santiago=70.6667° W), which is equivalent to 4.71111 hrs. Then the offset between local time and LST: LST - local time = 3.94 min * days VE + (GMT/local diff - 4.7111h) Key Concepts:

What are the different coordinate systems and why are each potentially useful?

How do we use equatorial coordinates to gain a deeper understanding and intuition of the sky? Theme

• Time: Measures of time CALENDARS CALENDARS CALENDARS Importance of measuring the passage of time in various human civilizations. Example: Mayan , very advanced. ! Historically we impose the calendar of the Roman Republic: : 7 days, one for each + sun + • Sábado Saturno • Domingo Sol • Lunes Luna • Martes Marte • Miércoles Mercurio FASTI • Jueves Júpiter • Viernes ! : between 28 and 31 days, associated with the synodic period (phases of the Moon) ! : associated with the period of revolution of the Earth around the Sun and the repetition of : 12 = 52 CALENDARS General consensus to divide into months and days. Knowing the number of a day and the month's name can refer precisely to any day of the year. ! Difficulty: There are 365.2422 days in a year

12 months of 29.5 days do not make a year. An extra month was added every few years because of the gap. If we take 365 days in a year there is a lag of 0.2422 days per year. After 100 years would have 24 days of lag.

Early : 12 months of ~29 or 31 days, ends in February, occasional extra month of 27 days Julius Caesar (in 46 BC) tried fix things by adopting the strategy of the Alexadrian Sosigenes: ! It was known then that the solar/ lasted 365.25 days ! Established a convention that there would be three consecutive years of 365 days, then one year of 366 days ! Every 4th year, an extra day is added to February: . “last year of ! Realign so year begins on Jan. 1 (46 BC was 445 days long!) confusion” Greatly reduced the problem; now only a difference of ~1 day in 100 years. Julius Caesar died in 44 BC: July named in honor of birth month August renamed in 8 BC to honor Augustus Caesar. This calendar worked well up to 1582, by which point there was an appreciable discrepancy between the equinox, spring and Easter. " The discrepancy between the Julian and Solar year (365.242199 d) is 11m14s. By 1582 this had amounted to 10 days.

" Pope Gregorio XIII tried to improve the situation by:

# Abolishing October 5-14, 1582.

# Proposing to skip 3 days every four .

" In his reformed calendar, years that end in 00’s (e.g. 1900, 2000) skip leap years unless they are divisible by 400.

" This corrected the calendar to within ~1 day in 3300 years (1 yr = 365.2425 d)

" Catholic countries adopted this immediately, but Protestant and other countries did not until later epochs. From 1582 to 1923, dual dates were often listed to avoid confusion (Julian and Gregorian).

" In 1800s, Herschel proposed skipping leap years in 4000, 8000, etc. Such a calendar would only lose ~1 day only every 20000 years. Gregorian Calendar

Sometimes it is necessary to express the instant of an observation as a certain number of days plus some fraction of some fundamental time. Astronomer J. J. Scaliger chose noon of January 1, 4731 BC. The number of days from that is the Julian Day. Important: Each new day begins at 12h00m Julian GMT (UT), half- day gap with the calendar day. Example: the Julian day 2444606 began at noon on January 1, 1981. It is common to use the Julian calendar for astronomical events. GMT = Greenwich Mean Time, UT = Universal Time " Mean Solar time as observed from the meridian of Greenwich, UK (longitude = 0). Established in 1685, although disputed for 200+ yrs with Paris’ (and Belgium) meridian. " A countries’ local time is related to GMT and its time zone (e.g., UTC/GMT-4). " So time in a place refers to a time zone (can be somewhat arbitrary => up to 2 hrs “off”). Daylight Savings (summer time) " Controverisal (and complex) shift time of official “noon” to exploit sunlight after working . " Good: ~0.5% energy savings?, retailers, sports; Bad: farming, confusion. " Often attributed to Ben Franklin (satirically suggests Parisians rise early to conserve candles). " But, precise schedules not really required until rail and communication forced modern standardization of time (>1900s). " Modern version suggested by Hudson in NZ (also Willett in UK). However, not until WWI (1918) Time (ET)

• UT and (sidereal time) ST are related to the period of rotation of the Earth. • But this period is not constant. It shows irregularities on “short” time scales of order to , and is slowing down on longer time scales due to various factors. •For example, the day was lengthened 1 / 2000 sec per 100 years (0.000005 sec / yr) due to the gravitational action of the moon. ET-UT=51 sec (Jan. 1900 vs Jan. 1980) • need to measure time evenly. (ET) used from 1952 to ~1970, but phased out by atomic . •The ET is calculated by the motion of the Moon, which is assumed uniform. International Atomic Time (TAI)

• Atomic clocks use electronic transition as . • Current standard for civil timekeeping. Basis for (TT) and Coordinated Universal Time (UTC) systems • TAI is a weighted average of the time kept by over 200 atomic clocks in ~70 national laboratories worldwide, compared using . • The majority of the clocks are clocks (9192631770 cycles) • Definition of the International written in terms of caesium Leap Seconds Clocks throughout ~3500 BC ~350 BC ~2000 BC

~1960 AD Measuring Time (and rotation)

" The period of the common depends on the mass and longitude: can be used to measure time " Foucault’s Pendulum " Jean Foucault in 1751 suspended a mass of 25 kg from a 25m cord in the Pantheon of Paris " The pendulum made marks in the sand, demonstrating that its plane of oscillation was not permanent " Historically important " Affected by the rotation of the Earth " Can define the of a place " Period of revolution P = 23h56m / sinΦ" " Foucault’s Pendulum at the Pole " Foucault’s Pendulum at the Ecuador Measuring Time

" Using the Sun and Earth as in ancient is not so useful due to chaotic effects. We need very precise clocks today (e.g., GPS, guidance/control systems, synchronization, computing). " Example: have rotation periods of .

Clock (Time system) Precision Sun (UT), (ST) minutes ET-UT=51 sec Pendulum seconds (Jan. 1900 vs Jan. 1980) Mechanical 1s/yr Quartz 1s/10yrs Moon (ET) 1s/300yrs Atomic Cs (SI sec) 1s/6,000yrs Atomic H Maser (TAI) 1s/100,000yrs Quantum 1s/3,700,000,000yrs Measuring Time

It is one thing to measure a time interval accurately, but another to measure long time intervals in the past. ! Modern has developed several methods and accurate of time spent: ! Biology: tree rings Physical-chemical: C14 radioisotope decay Astronomy: stellar evolution Key Concepts:

History and Mechanics of calendars/time (origin, format, etc.). How do we “keep” time?

Accuracy and importance of time-keeping Why do we “keep” time? Theme

COSMOLOGY geocentric and heliocentric ! • Greek Astronomy • • Copernicus • Brahe • Galileo • Kepler • Kepler's laws • • Newton's Laws • Orbits, satellites A historical prespective segwaying into physics Greek Astronomy

" School in Alexandria (after Aristoteles) ! " Aristarchus of Samos (310-230 BC): " Explained the phases of the Moon " Tried to measure the distance to the Sun and Moon " Believed that the Sun was the center of the Universe " Eratosthenes (276-196 BC): " Measured the circumference of the Earth using the Sun’s shadow as seen from Alexandria and Asuan. " Hiparco (Hipparchus)... Greek Astronomy

" Hipparchus (190?-120? BC): • considered greatest astronomer of antiquity (but all original work lost) • built an astronomical observatory on Rhodes • made a star catalog, assigning coordinates to each star and defining their magnitudes • discovered that the moves slowly () • measured the distance to the Moon to be 59 times the Earth radius (60 is the correct value) • determined length of the year to ~6 minutes of accuracy • carefully measured the movement of the Sun, Moon and planets, which allowed him to predict eclipses • postulated that the Sun's orbit is eccentric • discovered that perihelion was in December (it's now early January) • thought to be first to postulate a heliocentric system, but theory was abandoned because orbits were not perfectly circular (a mandatory condition of the time). Theory of Geocentrism Theory of Geocentrism Ptolemy (140 BC??) presented a Geocentric Theory in his Almagest, wherein the Earth was the center of the universe. His theory retained the idea of circular orbits, which was very compelling to the Greek populace. Ptolemy convincingly explained that the Sun, Moon, planets and the heavens rotate around the Earth. In addition to the Moon and the Sun, five planets were known in antiquity: , Venus, Earth, Mars, and Saturn. Careful observers of antiquity realized that the planets move with respect to the in the sky. This movement is made along the plane. Planet = “Wandering Star” (aster planetes) Their movements on the ecliptic are not uniform: - Normal/direct movement: eastward - Retrograde motion: westward Retrograde Motion The planets move eastward around the Sun in nearly circular orbits in the plane of the ecliptic. However, sometimes their apparent movement slows and changes direction, making a loop to the west. This is called retrograde motion. Example: the loop of Mars with respect to distant stars below Theory of Geocentrism

• Ptolemy (140 BC??) Geocentric cosmology presented in the Almagest, with his theory of “deferents” and “epicycles” to explain the motions of the planets. • Ptolemy postulated that each planet moved in a larger circle around the earth (deferent), but describing a small orbit (epicycle) as shown in the diagram. • This would explain retrograde motion. Theory of Geocentrism Since the movements did not appear to be circular uniform, Ptolemy proposed that deferens were eccentric, and that the epicycles moved around equants. The system was very complex, but could explain the observations. The success in explaining the retrograde motion earned this theory acceptance until the seventeenth . Note the order of the planets. Theory of Geocentrism Theory of Geocentrism: Copérnico • Nicolás Copérnico (Mikolaj Kopernik, 1473-1543) studied law and medicine, but dabbled in astronomy. • In De Revolutionibus proposed that the Sun is the center of the system, and that the Earth was just one of the 6 planets revolving around the sun • This theory also explains the retrograde motion. • In addition, calculated the distances of planets from the Sun • His ideas were only accepted a hundred years after his death!

PLANET COPERNICO TODAY Mercurio 0.38 AU 0.387 AU Venus 0.72 AU 0.723 AU Tierra 1.00 AU 1.00 AU Marte 1.52 AU 1.52 AU Júpiter 5.22 AU 5.20 AU Saturno 9.18 AU 9.54 AU Retrograde Movement Theory of Heliocentrism

• Copernicus also recognized the difference between the synodic periods (seen from Earth) and sidereal periods (real) of the planets. • He realized which planets are closer to the Sun, and which are farther away (e.g. Mercury and Venus are always close to Sun.) ! • Configurations of the planets: ✴ Superior planets: - Conjunction - Opposition ✴ Inferior planets: - superior conjunction - inferior conjunction • Problem: orbits assumed circular, not elliptical. Theory of Heliocentrism Theory of Heliocentrism

Philosophically, the theory of Copernicus revolutionized the world of science: Earth is nothing special, it's just one of the planets. That's the Copernican cosmological principle. ! We are not the center of the universe! Observations Of Tycho Brahe ! Nobleman Tycho Brahe (1546-1601) made careful of the positions of the Sun, Moon and planets for ~40 years. ! • Using only his eyes as instruments, he measured sky positions with an accuracy of 1' (arcminute). • Determined the length of the year to ~1 second precision. • Although he did not believe his observations, they eventually proved that the heliocentric theory is correct. • Also observed several comets, and determined that they were more distant than the Moon and orbiting around the Sun • In addition, observed a supernova (Tycho’s SN) in 1572. • Incorrectly measured the sizes of stars. Observations of Tycho Observations of Tycho Galileo, The Scientist

Galileo Galilei (1564-1642) Galileo Galilei (1564-1642) studied medicine, but chose mathematics and astronomy. ! • His astronomical discoveries were published in the Star Nuncius (Sidereal Messenger) and the Dialogo dei Due Massimi Sistemi. • The dialogue was written in Italian, with 3 characters discussing the celestial movements. • Galileo profoundly influenced science. He was the father of mechanics, doing experiments on the movements of bodies (inclined plane, pendulum, etc.) ! Galileo! ! 30x magnification

Salviati, Sagredo y Simplicio Galileo’s Casa in Arcetri (Florencia, Italia) Galileo’s Casa in Arcetri (Florencia, Italia) Galileo was one of the most prolific scientists of human history, with important legacies: 1. His comments defended the heliocentric theory, which lead to being persecuted by the and condemned by the Inquisition. 2. Contributions to mechanics (e.g. Law of inertia). 3. He built his own refractor telescopes, the best was 3 and 30x lenses, and made numerous discoveries. 4. Discovered spots on the Sun, and concluded that Sun rotates. 5. Discovered seas, craters and mountains on the Moon. 6. Discovered 4 of Jupiter: a mini-. 7. Discovered the phases of Venus. 8. Found that nearby “fuzzy clusters” are composed of stars. 9. Discovered stars in the Milky Way. 10. Saturn was discovered to be “strange” Galileo (1695 Huygens discovered the rings). 11. He was eventually exonerated in 1992 by Pope John Paul II.

Sunspots and solar rotation Phases of Venus Since Venus is in various orientations (during its orbit) with respect to the Sun, we see it in various phases. What phases should we be able to see?

A. Crescent only B. Gibbous only C. Full and New only D. New and Crescent only E. All phases The Imperfect Moon Jupiter and its satellites: a mini-solar system Heliocentric Theory