Notes PDF

Preview

Summary

Exam 1 notes...

Description

Astronomy 

The order of the planets

   

Moon can be interchangeable with satellite because a satellite is something that orbits an object Saturn’s Moon is Tethys Venus is closest in size to Earth Mars is the closest in regards to ecosystem and environment (if we were able to set up a functional living system that would be the only planet to do son) The Sun takes up around 99% of the solar system Order of universe

 

Planets  

 

 



Solar System

Galaxy Satelite Galaxy

Universe

o Satellite Galaxy – orbits another galaxy Galaxies come in different shapes and sizes but since we are so far away we are unable to communicate with them even if they did have intelligent life forms Astronomy uses standard units of time but metric for distance  1 meter  3.28 feet  1 Kilometer  .062 miles  1 kiolgram  2.205 lbs Time o 365.24 days = 1 year Scientific Notation  1  1 x 10^0  10  10^1  100  10^2  1,000,000  10^6  1700  1.7 x 10^3  17E^3  1  10^0  .1  10^-1  .01  10^-2  .000001  10^-6  .046  4.6 x 10^-2   4.5E^-2 One meter can be written also as 10 cm or 100 cm Astronomical Unit (Au) – average unit between Sun and Earth o 1 AU = 93,000,000 miles  150,000,000 Km  1.5 x 10 ^8 km  8.3 light minutes Light year (ly) – distance light travels in 1 year o 1 ly = 9.46 x 10^12 km





  

 .307 parsecs (pc)  63,000 AU When we talk about distances o on Earth talk in Kilometers o outside the Earth use AU o stars use light years o between two galaxies use Million light years (Mly) o across the universe use billions of light years (Gly) Helpful websites o www.powersof10.com/film o www.haydenplanetarium.org/blog/tags/the-known-universe o Distances described in terms of AU

The order from smallest to largest in width: o Planet, Star, Solar System, Galaxy, Universe Observations of the night sky o Philosophical ideas of the ancient greeks  The heavens represent perfection  The heavens are immutable (changing)  The circle is the perfect shape  Ptolemy  In 2nd century AD, Ptolemy tried to build a comprehensive model of the solar system – it was in his book Almagest (only surviving ancient comprehensive book on astronomy)  His model was based on the Greek ideals o The Earth was at the center and did not move o Everything in the sky goes around the earth o The stars were all fixed to the celestial sphere, which is the farthest from Earth

o Why did the Greeks believe this? o What happens to the sun, stars, moon, and planets, over the course of one day?  Everything seems to move around us: sun rises and sets, moon rises and sets, stars go across night sky, etc.  However they were wrong – The Earth’s rotation makes everything appear to move across the sky  Evidence – European Southern Observatory (Chile)  VLT – Very Large Telescope – give time lapse videos of the night sky (www.youtube.com/watch?v=wFpeM3fxJoQ) o Review Questions:  In general, stars, planets, the sun, and the moon rise in the --- and set in the -- During the day the stars --o Circumpolar – stars that appear to move in a circle around either the north or south pole rather than rising and setting  As you move from the equator to the pole the number of circumpolar stars:  Associated reading o Ch. 2 Motions of the sky o Worksheet in binder o www.josefrancisco.org o www.astrosurf.com/sguisard/ Constellations, Astrology, and Seasonal Stars o What are Constellations  There are 88 not very rectangular regions on the sky  Convenient to find other stars 





 o Origin of Constellations  48 of 88 modern constellations listed in Almagest  Oldest direct evidence (cuneiform tablets) date to 700 B.C.  Observations likely from Assyria (northern Mesopotamia in 1300 B.C.  Old worlds and new had similar stories about Bear and hunters (Big Dipper)  Story likely carried across Bering Strait land bridge (Russia/ Alaska connection) about 14000 years ago  First Constellation Discovery (evidence)  Lascaux Paleolithic cave paintings date back – 17,300 years ago  Mostly large animals  Some believe the scenes represent Orion’s belt, Taurus the bull, and the Pleiades o Ancient Uses  Mythology/ storytelling  Calendar  Constellations in general are seasonal – whatever time period you were born in would be represented by that constellation  Navigation  Polaris points north and gives you latitude  Constellations overhead give you longitude  Astrology  Not real  The only star that can alter are lives is the sun, it gives us heat and without it we would die  The Constellations are not physically connected in any way, so there arrangement is coincidental not destiny. Also the physical distance between the

stars is so great there is no way that one star that is 240 light years away is predicting our life  Sign – Your sign is roughly the constellation that the sun was in front of on the day that you were born  Zodiac Calendar o Tropical Zodiac – 12 constellations, used in astrology. Defined 2000 years ago o Sidereal Zodiac – tropical zodiac, updated for precision of Earth’s axis o IAU “Zodiac” – 13 constellations that the sun currently passes through over the year  The Calendar is updated because it takes in account the change in position of the North Celestial Pole over the 26,000 year wobble of Earth’s axis o Evening sky map  When looking at a sky map, east and west flip directions because you are looking at it from above. On Earth, our directions are oriented with our position on earth o Solar vs. Sidereal day  Over the course of one day, the sun moves with the stars across the sky  Longer periods of time, change that  Sidereal day – how long it takes for the stars to return to the same position as they were on the previous night  23 h 56m 4.091 s  Depends on Earth’s rotation  Solar Day – how long it takes the Sun to return to the same position in the sky  24 hours  Depends on rotation and Revolution

 

More Practice  Lecture Tutorials – p. 11 – 12 o Review Questions  Which takes longer to complete: sidereal or solar?  On one night you see Sirius, the brightest star in the night time sky, rise exactly at 7:36 pm. What time does it rise the next night?

N o rth S ta r A q u a riu s P isc e s

C a p ric o rn u s

A rie s 1 day

T au ru s

S a g itta r iu s

S c o rp iu s

365 days

L ib ra

G e m in i V irg o



C ancer L eo   What does this observer’s sky look like? o More work  Tutorials: p. 7 – 9 o Suggested Reading  Ch. 2 Constellations and Astrology  PDF on moodle about astrology Path of the Sun and Seasons o Is the sun always in the same position relative to the constellations throughout the year? o Everyday at noon, does the sun have the same altitude and azimuth?  Altitude – the distance an object appears above the horizon. The angle is measured up from the closest point on the horizon  Azimuth – what direction you are facing  The azimuth of an object is the angular distance along the horizon to the location of the object. By convention, azimuth is measured from north towards the east along the horizon  Measured the degrees from north to the position of that object  Does the amount of sunlight at a given location change over the year?  Yes, shadows  The bigger shadow occurs in December when the sun is lower in the sky  How does the tilt of the Earth’s axis affect the sun’s path across the sky?

o

o o Important Dates  Summer Solstice  June 21  Winter Solstice  December 21  Vernal (Spring) Equinox  March 21  Autumnal Equinox  September 21  Equinox – the sun is equal in the sky so the earth receives 12 hrs. of daylight and 12 hrs. of night time o Facts  In the summer, the sun is high and we get more hours of direct sunlight  The sun is lower in the winter thus receiving fewer hours of indirect sunlight  The tilt of the axis of rotation causes more (or fewer) hours of more (or less) direct sunlight  The seasons respond to which hemisphere we are in; they are opposite in the southern hemisphere than in the northern hemisphere



o o Additional Info  Tutorials – p. 91 – 96  Ch. 2 – Seasons Changing the Views of the Universe o Philosophical ideas of the ancient Greeks  The heavens represent perfection  The heavens are immutable (unchanging)  But the earth is changing and imperfect  The circle is the perfect shape

These ideas lead to the geocentric model, with everything in the heavens moving around the Earth  The problem with this  There were “stars” that appeared to move across the sky without staying with their constellation  The Greeks called these objects “wandering stars” and gave them the name “planete” which means wanderer  Planets also had retrograde motion, which complicated things even more o The east-to-west motion of an object relative to the stationary background stars o Prograde motion – the apparent west-to-east motion (over the course of many nights) of an object (like the sun) relative to the stationary background stars Ptolemaic Model  Ptolemy’s geocentric model couldn’t immediately explain the retrograde motion of planets  He developed epicycles to deal with planets  Philosophical problem (known as Occam’s Razor)  Ptolemy’s model treated each planet independently; there was no single law governing the motion of all the planets Nicolaus Copernicus  Born in Poland, 1473-1543 AD  In his time, the geocentric view was main-stream; it was standard curriculum in universities  Copernicus developed the details of a heliocentric (sun-centered) model in which the Earth and other planets orbit the sun  Aristarchus proposed this idea in the 3rd century BC  This model easily explains things Ptolemy couldn’t Tycho Brahe  Born in Denmark, 1546 – 1601 AD  Lost part of his nose in a duel with a fellow student (he had a silver and wooden fake noses)  He was credited as being the world’s best naked eye astronomer  Made extremely accurate observations without a telescope  He used parallax and Supernova 1572 to show that the heavens change o Parallax - An apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight  Distant objects have a smaller parallax than objects closer to the eye Johannes Kepler  German, 1571-1630 AD  Worked with Brahe  He actually hated Brahe, but was in it for Brahe’s data  He created a theoretical model to explain planetary motion  Now known as Kepler’s three laws of Planetary Motion  Kepler’s laws of Planetary Motion  The orbit of every planet is an ellipse, with the Sun at one of the two foci o Eccentricities – when the e (eccentricities) is closer to 0, that means its closer to a perfect orbit of a circle o Earth has an eccentricity of 0.016 

o

o

o

o



 



A line joining a planet and the Sun sweeps out equal areas during equal intervals of time

The square of the orbital period (p) of a planet is directly proportional to the cube of the semi-major axis (a) of its orbit o P2∝ a3 o Planets that orbit near the sun have shorter periods than planets that orbit far from the sun o Mass has no effect on how fast an object rotates around the sun o Suggested practice  Universe Revealed: Ch. 3, Ptolemy through Kepler’s Laws  Tutorials: p. 25-27 Phases of the Moon o Common Misconceptions about the Moon  The Moon can only be seen at night  The Moon makes its own light, instead of reflecting sunlight  The Moon’s phases are caused by the Earth’s shadow  The Moon’s phases are caused by clouds  The Moon’s phases are caused by Earth’s rotation on its axis  The Moon’s phases are caused by the Moon’s rotation on its axis  The Moon takes one day to orbit the Earth  The Moon orbits the Sun instead of the Earth o The Phases of the Moon





 This cycle takes 29.5 days or just shy of one month! o Suggested Reading  Universe Revealed: Ch. 5 Earth-Moon Section  Tutorials: p. 79-81 Eclipses o An astronomical event that occurs when one celestail body is temporarily obscured by either another object or that object’s shadow o Different types of Eclipses  Total Lunar  The moon passes through the Earth’s shadow to where the moon doesn’t receive all of the sun’s light o Only occurs at the full moon o Turns redish color because of when light enters through Earth’s atmosphere, it scatters in all directions, but Red light doesn’t enter easily so it refacts off the Earth and onto the moon  Partial Lunar  Total Solar  The moon is closer to earth to where it blocks out the Earth’s light  Can only happen at noon  You have to be directly underneath the moon’s Umbria (shadow) to see it  Only at a new moon  Partial Solar  Annular Solar  Little ring of sunlight on the outside of the moon, Not completely blocked from the sun  Why don’t we have two eclipses per month?  The moons orbit around the Earth is inclined % degrees relative to the orbit of the Earth around the sun  Eclipese occur when the line of nodes points towards the Sun and we have a full moon or new moon o Line of Nodes – when Earth, moon, and sun are lined up together...