Astronomy Unit

1. Astronomy Unit Started notes 5-22-14

2. 28.1 Information • Be familiar with the 7 types of electromagnetic radiation (visible light, radio waves, infrared radiation, ultraviolet radiation, x rays, microwaves and gamma rays) • Know that telescopes, satellites, international space station, and other instruments such as robots collect information to explore space.

3. Combustion vs. Fusion & Fission • Combustion – chemical reaction requiring fuel, a heat source, and oxygen • Remember burning coal releases CO2 into the atmosphere (adding to greenhouse effect) • Nuclear Fusion – collision of nuclei forming nuclei of heavier elements & producing enormous amounts of energy • Is the process that produces radiant energy of stars • Does not produce particulate air pollution or a radioactive product but we lack technology to maintain reactions as a viable energy source

4. Combustion vs. Fusion & Fission • Nuclear fission – a neutron is aimed at the nucleus of a large, unstable atom causing the nucleus to split apart and form lighter elements • Source of energy in core of Earth • Produces harmful radioactive elements

5. Earth’s motion • Origin of Earth’s galaxy and solar system: • 1929 Edwin Hubble noted that galaxies outside our own (The Milky Way Galaxy) were moving away from us at a speed proportional to the distance from us. v=Hd (v=speed, d=distance, H=Hubble’s constant) • https://www.e-education.psu.edu/astro801/content/l10_p4.html (to help you better understand Hubble’s law) • The Big Bang Theory – theory that the universe began as a point and is still expanding (it is an expansion of space and matter went along with it)

6. Earth’s motion • Our galaxy formed about 4.5 bya from a huge swirling cloud of dust and gas (nebula) • Something (perhaps a supernova explosion (star death)) caused dust particles to come together • As core of dust attracted more particles, it gained gravitational pull and eventually the cloud of gas collapsed on itself • Temperature increased with more particles together and eventually temperature was high enough to cause nuclear fusion and the sun was “born” • Evidence in using telescopes to watch birth of other stars

7. Earth’s motion • Stars: • Form when a cloud of gas collapses in on itself under the influence of gravity • Planets: • Form when material in the disk around a pre-existing star begins to condense around rock/ice cores • Can be mostly rock/ice/water – Earth or gas attracted to rock/ice core – Jupiter, Saturn

8. Earth’s motion • Earth’s role in the hierarchy of organization within the universe: • The universe is made of galaxies which is made of many stars • Some stars have planetary systems similar to our solar system • Earth is a satellite of the sun like the moon is a satellite of Earth • Satellite – object that moves around a larger object

9. Earth’s motion • History: • People used to think the Earth was the center of the solar system (geocentric) • 1543 Polish Nicolaus Copernicus suggested the sun was the center of the solar system (heliocentric) • 1576 – 1601 Danish Tycho Brahe made observations of planetary positions that supported the heliocentric model • German Johannes Kepler used Brahe’s data to demonstrate the planets orbit in an ellipse and not a circle (ellipse information: http://mathworld.wolfram.com/Ellipse.html) – this is Kepler’s First Law

10. Earth’s motion • Kepler’s second law: an imaginary line between the Sun and a planet sweeps out equal amounts of area in equal amounts of time • Kepler’s third law: the square of the orbital period (P) equals the cube of the semimajor axis of the orbital ellipse (a) so P2 = a3 • Translation: Larger orbits have longer orbital periods and average orbital speeds are slower for planets with larger orbitals • More information: http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html

11. Kepler’s Second Law • A planet moves fastest when closest to the sun and slowest when farthest from the sun; equal areas are swept out in equal amounts of time. http://howthingsfly.si.edu/flight-dynamics/kepler%E2%80%99s-laws-orbital-motion

12. Earth’s motion • Relative motion of the Earth: • Earth orbits sun • Sun orbits the solar system barycenter • More information here tomorrow!

13. Earth’s motion • Earth’s axis is tilted at 23.5° which creates our seasons (see pg. 370 for reminder picture) • Precession: change in direction of the axis without any change in the tilt (so still 23.5° ) which will cause the axis to point toward Vega by the year 14000 rather than Polaris (current) • This cycle occurs every 26,000 years • The gravitational pull that causes precession is from the moon • https://www.youtube.com/watch?v=qlVgEoZDjok

14. Earth’s motion • Nutation: wobbling around the precessional axis • Change in the angle ½ degree one way or the other • Occurs in an 18 year period and is due exclusively to the moon’s gravitational pull • This ½ degree change slightly increases or decreases the amount of seasonal effects

15. Earth’s motion • Barycenter: the common center of mass around which two or more celestial bodies revolve • Ex. When the moon orbits the Earth, it does not orbit exactly around the center of the Earth but instead it orbits around a point where their respective masses balance. Videos: http://www.youtube.com/watch?v=uGBANgbRkws http://www.youtube.com/watch?v=CnLwLF4e6uQ • Good website for better understanding: http://spaceplace.nasa.gov/barycenter/en/

16. Earth’s motion • Sun’s movement in our solar system: • The sun is not stationary in our solar system! • It moves as the gravitational pull of the planets pulls on it • It orbits the solar system’s barycenter due to these gravitational pulls

17. More websites to explore! • Planetary atmospheres: http://www2.astro.psu.edu/users/rbc/a1/lec29n.html • Moon’s movement: http://www.pbs.org/wgbh/nova/tothemoon/puz2n3.html • Astronomy notes on planets: http://www.astronomynotes.com/tables/tablesb.htm • Light Year information: http://www.cyberphysics.co.uk/topics/space/Lightyear/Lightyear.htm

18. Follow Up Planet Presentations • Vote on which planet you would like to go visit • How many planets are there in our solar system? • Which planet used to be a planet and is now a dwarf planet? • What is Kepler 186F? • Which planets are gas giants and which are terrestrial planets?