ASTR178 Other Worlds A/Prof. Orsola De Marco ts/ASTR178/

Announcements Use the undergraduate computer laboratories. I have posted pdf files of all the lecture notes (weeks 1 and 2) – 4 slides to a page. This is the website of the book, which contains a lot more than the book: Help questions (For this week) 1-28, page 232, 233. Most of the questions in this chapter are relevant since I covered this chapter pretty thoroughly.

Planet conjunction! August 13 th, look to the West to see a great planet conjunction. You will also see the Moon. This can be the first data point for your practical. You should be able to draw the ecliptic on this picture. Where is the Sun in this picture?

In last class A few words on the Sun to start a tour of the Solar System. What is light. Comparing the planets. The density of the planets. The largest “satellites”. What are planets made of. The planetary atmospheres The outer solar system. Craters, volcanos and magnetic fields.

In this class A quick wrap up of the magnetic fields in the Solar System. Earth’s energy sources The Greenhouse effect Earth’s layers: crust, mantle and core

Planetary magnetic fields (from last week)

Magnetic fields Mercury, 1% that of Earth’s Venus, none Mars, only in the highlands Jupiter, 14 times Earth’s Saturn, a little less than Jupiter Uranus and Neptune, have magnetic field WHY?

Earth

Earth’s sources of energy Internal heat The Sun

Dating rocks: radioactive dating. Some elements spontaneously change to other elements, taking a known time to do so. If you know the original amount of the parent and child element in a rock, you can measure the current amount of child isotope to determine the age of the rock, or how long since it solidified. Example: 235 U decays to 207 Pb with a half life of 704 million years.

The green-house effect

The green-house effect: in depth Sun hits Earth, some energy reflected, some energy is absorbed and then re-radiated, balance is reached – we know that the balance is reached because the temperature on Earth is stable. NOTE: the energy that reaches Earth, heats Earth; warm Earth radiates (all warm bodies radiate). Earth radiates in the infrared. We know how much energy reaches us from the Sun and we know how much is reflected from clouds etc., so we know how much Earth radiates. Earth’s radiation allows you to calculate Earth’s average temperature. It urns out that if Earth really radiated all the energy it receives, it would have an average temperature of -19 C. Earth’s actual average temperature is 14 C. What is wrong with this calculation? Green-house gases, H 2 O and CO 2 trap infrared radiation from Earth, keeping the atmosphere warmer than it would be otherwise.

Richard Dixon Oldham (Irish) Hypothesized the existence of a molten core. Inge Lehmann (Danish) Hypothesized the existence of the inner core

Key Ideas Magnetic Fields and Planetary Interiors: Planetary magnetic fields are produced by the motion of electrically conducting liquids inside the planet. This mechanism is called a dynamo. If a planet has no magnetic field, that is evidence that there is little such liquid material in the planet’s interior or that the liquid is not in a state of motion. The magnetic fields of terrestrial planets are produced by metals such as iron in the liquid state. The stronger fields of the Jovian planets are generated by liquid metallic hydrogen or by water with ionized molecules dissolved in it.

Key Ideas The Earth’s Energy Sources: All activity in the Earth’s atmosphere, oceans, and surface is powered by three sources of energy. Solar energy is the energy source for the atmosphere. In the greenhouse effect, some of this energy is trapped by infrared absorbing gases in the atmosphere, raising the Earth’s surface temperature. Tidal forces from the Moon and Sun help to power the motion of the oceans. The internal heat of the Earth is the energy source for geologic activity.

Key Ideas The green house effect: green-house gases (e.g., CO 2 and H 2 O) are those that let visible radiation through but not infrared. This means that they trap heat into Earth’s atmosphere, keeping the air warmer than it would be otherwise. The Earth’s Interior: Studies of seismic waves (vibrations produced by earthquakes) show that the Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin low-density crust. Seismologists deduce the Earth’s interior structure by studying how longitudinal P waves and transverse S waves travel through the Earth’s interior. The Earth’s inner and outer cores are composed of almost pure iron with some nickel mixed in. The mantle is composed of iron rich minerals. Both temperature and pressure steadily increase with depth inside the Earth.