How ideas of the universe have changed over time

1. How ideas of the universe have changed over time

2. Into the frontier of space • NASA • National Aeronautics and Space Administration • Pioneer and Voyager craft • Sent off on missions to transmit images of Jupiter, Saturn, and outer solar system • No communication from Pioneer craft anymore • Eventually it will be the same for Voyager craft • Voyager 1 is the most distant human-made object in space • Still transmits data! :o

3. Purpose of craft • not only transmission of data, also have plaques detailing a man and woman, the solar system, and other information showing where Earth is located • Each Voyager probe also has a “golden record” with recorded sounds and pictures of Earth

4. Quick lab – greetings from the people of earth • Each of the Pioneer space probes that have left the solar system carries the plaque from the previous slide. • It’s hoped that other planetary life forms that think enough like humans might find one of the probes and be able to use the plaque information, even millions of years from now, to locate Earth. • We are going to think about the implication of sending information about humans into space.

5. Quick lab – greetings from the people of earth • With your partner(s), discuss the following questions. Record your thoughts in point form. • What does our sending information like this out into space suggest about our own ideas of the universe? • What does the plaque information assume about the nature of any aliens who might acquire it? • If you were to design your own plaque, what would you like to put on it? Why? • If the plaque can last a million years, will it outlive the human race? Explain your answer. • Would aliens capable of finding the plaque already know about Earth because of our radio transmissions? • Is the most likely finder of the plaque going to be future human space travellers who have forgotten their early roots? Explain your answer.

6. Building on past knowledge • Our ancestors used astronomical phenomena to: • Mark the passage of time • Foretell the changing seasons • Indicate direction during travels • Aztecs and Mayans developed accurate calendars over generations of observation and recording • During the Renaissance (15thc.) relied heavily on knowledge gathered by Islamic astronomers for more than 800 years

7. solstices • Two important annual events for our ancestors: • Summer solstice (northern hemisphere) • Near June 21  start of summer • Longest day of the year • Winter solstice (northern hemisphere) • Near December 21  start of winter • Shortest day of the year • Solstices are opposite in southern hemisphere • Stonehenge was used to mark summer and winter solstices 4500 years ago • Ancient African cultures also used this method

8. equinoxes • It means a day when the hours of daylight and hours of night are of equal length. • Vernal/spring equinox • Around March 21 • Autumnal/autumn equinox • Around September 21 • Mayans built towers (1000CE) to celebrate these • Egyptians built pyramids and monuments to align with the seasonal position of certain stars • First Nations used large rocks to build medicine wheels • Key rocks were aligned with bright stars that rose at dawn (Aledebaran, Rigel, Sirius) • Also used to predict right time of year to plant/harvest crops or prepare for hunting and fishing

9. Models of planetary motion • Geocentric Model • 2000+ yrs ago, Earth was believed to be the centre of the universe • Using Plato’s work, Aristotle first described the earth-centred (geocentric) model • Stars didn’t move? They were attached to the outside sphere

10. Models of planetary motion • Geocentric motion • Ptolemy helped many astronomical phenomena to be forecasted (moon phases) • Retrograde motion: apparent reversal o the planets’ path relative to the starry backdrop

11. Retrograde motion

12. Models of planetary motion • Heliocentric model • Improvements in technology changed thinking • Proposed by Greeks in 500 BCE • Polish astronomer Nicholas Copernicus revived the idea • Sun is at the centre of our universe (Sun-centred) and planets orbited around SUN

13. Heliocentric model • Two key things about planetary orbit helped support the heliocentric (sun-centred) model • Orbital radius • A planet’s distance from the Sun • The shorter this is, the faster the planet moves in its orbit • Because of the Sun’s gravity being stronger when you’re closer to it • Earth is moving faster than Mars, Mars is faster thanJupiter • 100 yrs later, more solid evidence was brought on by the invention of the telescope (binoculars) • Galileo Galilei

14. Heliocentric model • Two key things about planetary orbit helped support the heliocentric (sun-centred) model • Elliptical orbits • This model could not predict planetary motion very accurately, just like the geocentric model • Kepler figured it out • Using much of the observations from his teacher, Tycho Brahe, found that the planets were ELLIPSES, NOT CIRCLES • Everyone supports this idea now, and we use it to study other star-and-planet systems

15. Learning checkpoint • In the northern hemisphere, what is the:(a) summer solstice and when is it?(b) winter solstice and when is it? • What is the main difference between the geocentric model and then heliocentric model? • Define retrograde motion and make a sketch to support the definition. • The orbits of the planets are not exactly circular. What shape are they?

16. Evolution of astronomy tools • Sundials • Used for more than 7000 years to measure time • Quadrant • Measures the stars’ height above the horizon • Astrolabe • Makes accurate charts of star positions • Cross-staff • Levi ben Gerson invented this to measure the angle between the moon and any given star

17. Optical telescopes • Telescope was invented in the late 16th cent. • Refracting telescope • Two lenses gather and focus starlight • Has a size limit (1m diameter)  glass warps • Reflecting telescope • Uses mirrors instead of lenses to collect visible light • Often located high on mountaintops to get the clearest view • Hubble Space telescope is one of these • Space-based is better than ground-based because they escape light and air pollution, weather,

18. Radio telescope • Use radio waves emitted by objects in space • Less affected by weather, can detect during day and night • Radio waves not distorted by clouds, pollution, or atmosphere like light waves • These telescopes helped establish the BBT by detecting CBR (microwave radiation leftovers) • Also detected enormously powerful energy sources at the edge of the visible universe • Called quasars • Put out as much energy as a WHOLE GALAXY, but may not be larger than a solar system • Don’t know too much about them yet – but we’re working on it