ASTRO 101

1. ASTRO 101 Principles of Astronomy

2. Instructor: Jerome A. Orosz (rhymes with “boris”)Contact: • Telephone: 594-7118 • E-mail: orosz@sciences.sdsu.edu • WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ • Office: Physics 241, hours T TH 3:30-5:00

3. Text: “Discovering the Essential Universe, Fifth Edition”by Neil F. Comins

4. Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html Note the underline: … ast101_fall2012.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/

5. Homework/Announcements • Homework due Thursday, October 25: Question 6, Chapter 7 (What role did Charon play in enabling astronomers to determine Pluto’s mass?).

6. Next: Chapter 5 and Chapter 6: Other Planets and Moons.

7. Mercury • Mercury is the closest planet to the Sun. • It is never seen against a dark sky, and it is never far above the horizon.

8. Mercury as Seen From the Earth • Here is the best ground-based image of Mercury.

9. Mercury as Seen From Earth • Mercury is hard to study from the ground since it is close to the Sun. • We can measure its average density. We find the density is 5.4 grams/cc, much like the Earth. • We can measure the albedo, and we find it is about 10%, much like the Moon. • Mercury mass is 5.5% of the Earth’s mass, and its gravity is 38% of the Earth’s. • We expect Mercury to be similar to the Moon.

10. Mercury Seen up Close • In 1974 NASA sent a probe to Mercury. • It really does look like the Moon.

11. Mercury Seen up Close • In many cases you can see rays of material ejected by the impacts.

12. Mercury’s Interior • Mercury has a large iron core. • This core is relatively cold. • There is very little evidence of present-day geological activity.

13. Mercury’s Interior • Mercury has a large iron core. • It is possible that a collision early in the history of Mercury could have stripped off less dense material near the surface, leaving behind the heavier material.

14. Mercury’s Rotation • Since Mercury is so close to the Sun, tidal forces have forced it into a 3-to-2 spin-orbit coupling. • As a result, a day on Mercury is 2 Mercury years long!

15. Mercury • Mercury has a very thin atmosphere. • There is no water. • There is essentially no erosion. • It is relatively hot on the day side (up to 800oF) since it is near the Sun. However, on the night side it can be as low as -280oF • It looks a lot like the moon on the surface, but it is different in its interior.

16. Venus • Venus has a mass and radius similar to that of the Earth.

17. Venus • Venus has a mass and radius similar to that of the Earth. Its gravity is strong enough to retain a substantial atmosphere.

18. Venus • Venus has a mass and radius similar to that of the Earth. Its gravity is strong enough to retain a substantial atmosphere. • The albedo is very high, more than 75%.

19. Venus • Venus has a mass and radius similar to that of the Earth. Its gravity is strong enough to retain a substantial atmosphere. • The albedo is very high, more than 75%.

20. Venus • Venus has a mass and radius similar to that of the Earth. Its gravity is strong enough to retain a substantial atmosphere. • The albedo is very high, more than 75%. We do not see the surface, but rather the tops of the clouds.

21. Venus • Venus is the second closest planet to the Sun. • It is never seen against a very dark sky, and it is never far above the horizon.

22. Venus • No surface features are seen from Earth.

23. Venus • The cloud patterns are changing over several hours.

24. Venus • The surface temperature is about 475o C, compared to about 25o C for Earth.

25. Venus • The temperature at the surface of Venus is high.

26. Venus • The surface temperature is about 475o C, compared to about 25o C for Earth. • The atmospheric pressure at the surface of Venus is 90 times that of the Earth.

27. Venus • The surface temperature is about 475o C, compared to about 25o C for Earth. • The atmospheric pressure at the surface of Venus is 90 times that of the Earth. • The composition of the atmosphere is about 96% CO2, compared to mostly N and O on the Earth.

28. Venus • The surface temperature is about 475o C, compared to about 25o C for Earth. • The atmospheric pressure at the surface of Venus is 90 times that of the Earth. • The composition of the atmosphere is about 96% CO2, compared to mostly N and O on the Earth. • ??????

29. The Greenhouse Effect • Venus has a “runaway” greenhouse effect that heats the planet an extra 375o C.

30. The Greenhouse Effect

31. The Greenhouse Effect • Venus has a “runaway” greenhouse effect that heats the planet an extra 375o C. • Some visible light from the Sun reaches the surface and heats it.

32. The Greenhouse Effect • Venus has a “runaway” greenhouse effect that heats the planet an extra 375o C. • Some visible light from the Sun reaches the surface and heats it. • The surface radiates the energy in the infrared, which the CO2 in the atmosphere absorbs.

33. The Greenhouse Effect • Some visible light from the Sun reaches the surface and heats it. • The surface radiates the energy in the infrared, which the CO2 in the atmosphere absorbs. • The extra heat “bakes out” more CO2 from the rocks.

34. The Greenhouse Effect • The surface radiates the energy in the infrared, which the CO2 in the atmosphere absorbs. • The extra heat “bakes out” more CO2 from the rocks. • The extra CO2 leads to more trapping of the surface infrared radiation.

35. The Greenhouse Effect • The extra heat “bakes out” more CO2 from the rocks. • The extra CO2 leads to more trapping of the surface infrared radiation. • The extra trapped heat bakes out more CO2, and so on…

36. The Surface of Venus • Soviet spacecraft have landed on Venus and recorded close-up pictures. • These images show basalt, which is quite similar to lava rock.

37. The Surface of Venus • The Venusian surface has been mapped with radar by the Magellan spacecraft. • These maps reveal gently rolling hills, two “continents”, and many volcanoes.

38. The Surface of Venus • The Venusian surface has been mapped with radar by the Magellan spacecraft. • There are relatively few impact craters. Perhaps melting of the surface has erased earlier craters.

39. Venus Summary • Although Venus has a similar mass and radius as the Earth, it is a very different place owing to the runaway greenhouse effect: • The temperature at the surface is about 475 oC. • The atmospheric pressure is about 90 times that on the Earth. • The atmosphere is mostly CO2.

40. NEXT:

41. Mars • Named for the Roman god of war, owing to its red color. • Its mass is 10% of the Earth’s mass, its radius is 50% of Earth’s radius, and its gravity is 38% of Earth’s gravity. • Mars has usually been considered to be the place to look for extraterrestrial life.

42. Mars • In some ways, Mars is a bit like Earth: • Its rotation rate is 24 hours and 37 minutes. • The inclination of the axis is 25.2o. • The seasonal variations of the solar heating are similar to that on Earth.

43. Mars • Mars is different from the Earth in some important ways: • The surface temperature ranges from about -125 oC to 25 oC, with typical temperatures below 0 oC. • The atmospheric pressure is about 1% of that on the Earth, which is too thin to maintain a significant greenhouse effect.

44. Why the Interest in Mars? • Every few years Mars passes relatively close to Earth. • During these close passages, it is possible to see surface features through a good telescope.

45. Early Observations of Mars • Early observations were by eye (through a telescope). The observer had to draw what he saw. • Here is drawing from 1800 (image from William Sheehan, http://www.uapress.arizona.edu/online.bks/chap03.htm)

46. Early Observations of Mars • Here is drawing from 1877. (image from William Sheehan, http://www.uapress.arizona.edu/online.bks/chap05.htm)

47. Early Observations of Mars • The Italian astronomer Schiaparelli made detailed observations in the 1870s. • He noted the presence of “canali.” (image from William Sheehan, http://www.uapress.arizona.edu/online.bks/chap05.htm)

48. Early Observations of Mars • Schiaparelli meant “channels.” • English translations used “canals,” implying that they are of intelligent design. Note, however, that beavers dig canals too.

49. Early Observations of Mars • Schiaparelli meant “channels.” • English translations used “canals,” implying that they are of intelligent design. Note, however, that beavers dig canals too. • Near the turn of the 20th century, many people were convinced that there was life on Mars.

50. Life on Mars • This famous movie made in 1953 was based on H.G. Well’s classic novel of 1898. • On Oct 30, 1930, Orson Wells broadcast a fake news report of invading Martians, causing widespread panic.