ASTRO 101

ASTRO 101

Principles of Astronomy

Instructor: Jerome A. Orosz (rhymes with “boris”)Contact:• Telephone: 594-7118

• E-mail: [email protected]

• WWW: http://mintaka.sdsu.edu/faculty/orosz/web/

• Office: Physics 241, hours T TH 3:30-5:00

Text:

“Discovering the Essential Universe, Fifth Edition”

by Neil F. Comins

Course WWW Pagehttp://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/

Homework/Announcements

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

Next:

Chapter 5 and Chapter 6: Other Planets and Moons.

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.

Mercury as Seen From the Earth

• Here is the best ground-based image of Mercury.

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.

Mercury Seen up Close

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

Mercury Seen up Close

• In many cases you can see rays of material ejected by the impacts.

Mercury’s Interior

• Mercury has a large iron core.

• This core is relatively cold.

• There is very little evidence of present-day geological activity.

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.

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!

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.

Venus

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

Venus

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

Venus


• The albedo is very high, more than 75%.

Venus


• The albedo is very high, more than 75%.

Venus


• The albedo is very high, more than 75%. We do not see the surface, but rather the tops of the clouds.

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.

Venus

• No surface features are seen from Earth.

Venus

• The cloud patterns are changing over several hours.

Venus

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

Venus

• The temperature at the surface of Venus is high.

Venus


• The atmospheric pressure at the surface of Venus is 90 times that of the Earth.

Venus



• The composition of the atmosphere is about 96% CO2, compared to mostly N and O on the Earth.

Venus



• The composition of the atmosphere is about 96% CO2, compared to mostly N and O on the Earth.

• ??????

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.




• The extra heat “bakes out” more CO2 from the rocks.




• The extra CO2 leads to more trapping of the surface infrared radiation.



• The extra CO2 leads to more trapping of the surface infrared radiation.

• The extra trapped heat bakes out more CO2, and so on…

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.


• The Venusian surface has been mapped with radar by the Magellan spacecraft.

• These maps reveal gently rolling hills, two “continents”, and many volcanoes.


• 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.

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.

NEXT:

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.

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.

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.

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.

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)


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


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)


• Schiaparelli meant “channels.”• English translations used “canals,” implying

that they are of intelligent design. Note, however, that beavers dig canals too.


• 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.

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.

Modern Views of Mars

• We know now that the early observations of “canals” were in error.

• There are no cities or civilizations.


• The surface of Mars has been mapped extensively by orbiting spacecraft.

• One sees plains, deep canyons, numerous craters, and volcanoes, which are extinct.







Searching for Life

• How do you detect primitive life remotely?

Searching for Life

• How do you detect primitive life remotely? Organisms on Earth breathe and have certain

metabolisms, so look for signs of respiration and other biological processes.

Searching for Life


metabolisms, so look for signs of respiration and other biological processes. What if life on Mars is different than that on Earth?

Searching for Life



Life on Earth is carbon-based, so look for organic compounds.

Searching for Life



Life on Earth is carbon-based, so look for organic compounds. What if life on Mars is different than that on Earth? Also, organic compounds can be made by other means.

Searching for Life

• In 1976 the Viking spacecraft landed on Mars. Soil was analyzed by three experiments, but no signs of life were found.

Searching for Life

• In 1984 a meteorite from Mars was discovered in Antarctica.

• Evidence for microscopic fossils in the meteorite was announced in 1996.

• Most scientists today remain unconvinced.

Recent Events: Mars Rover• Recently, NASA landed

twin rovers on Mars. These probes are vastly more superior than the Viking landers.

Recent Events: Mars Rover

• The cameras deliver extremely high quality images.

Recent Events: Mars Rover

• The cameras deliver extremely high quality images.

Evidence for Water on Mars

• These images and others suggest the presence of liquid water on Mars, at least in the past.

Evidence for Water on Mars

• These images and others suggest the presence of liquid water on Mars, at least in the past.

Life on Mars

• There is no evidence that there is currently life on Mars. The recent Mars rovers will perform additional experiments along these lines.

• It is possible that there was primitive life in the early history of Mars, but the only way to be sure would be to go there.

Comparing the Inner Planets

Next: The Giant Planets

ASTRO 101

Documents

mercury mass

mercury years

history of mercury

radius similar

mercurys rotationsince

earths mass

plutos mass

substantial atmosphere