Chapter 28 – The Sun-Earth-Moon System
28.1 – Tools of Astronomy
- the best tool that astronomers can use to learn about the universe is the light that comes to Earth from distant planets
Radiation
- light is the common term for electromagnetic radiation
- the human eye can only see a limited range of all the various wavelengths of electromagnetic radiation
- electromagnetic radiation includes not just visible light, but also infrared and ultraviolet radiation, radio waves, microwaves, X rays, and gamma rays
- fig 28-1
Telescopes
- objects in space emit radiation in all portions of the electromagnetic spectrum
- a benefit of the telescope is that detectors can be attached that see wavelengths the human eye cannot see
- it also brings more light to focus than the human eye
- a 3rd benefit is it allows astronomers to used specialized equipment
Refracting and Reflecting Telescopes
- refracting telescopes were invented around the year 1600
- fig 28-2
- in 1668 the reflecting telescope was invented and uses mirrors
- both are used today, but most of these are reflecting telescopes
Telescopes at Other Wavelengths
- Fig 28-3
Satellites, Probes, and Space-Based Astronomy
- these items are put in space because the Earth’s atmosphere does not allow all of the electromagnetic waves through the atmosphere
o this causes some of the images to blur
- the best known is the Hubble telescope
o this was launched in 1990 and is expected to work until 2010
Spacecraft
- robotic probes get close-up views and sometimes land on planets
- these type of robotic probes landed on Mars (fig 28-5)
Human Spaceflight
- the space shuttle program began in 1981
o a big experiment here is to study the effects of weightlessness on humans and other living objects
o these flights last a maximum of 17 days, so studying the long term effects of weightlessness also is done
- the International Space Station has had astronauts living in it since 2000 (fig 28-6)
o construction on it is not totally complete
Spin-Offs
- the fuel pumps on the space shuttle led to development of artificial heart pumps
- the Apollo program lead to cordless tools
28.2 The Moon
Reaching for the Moon
- most of our knowledge about the Moon comes from space probes
- 1957 was the year that the Russians launched the first satellite, Sputnik I
- in 1961, a Soviet cosmonaut Yuri A. Gagarin became the first human in space
- Alan B. Shepard Jr., was the first American in space – May 5th, 1961
- Neil Armstrong and Buz Aldrin landed on the Moon on July 20th, 1969, during Apollo 11
Lunar Properties
- Earth’s moon is one of the largest moons especially compared to the size of the planet it borders
- the Moon’s radius is 27% that of Earth’s and it is more than 1% of Earth’s mass
- the orbit of the Moon is relatively farther away than other moons around other planets
- Earth’s moon is solid, rocky body
o the moons of Jupiter, Saturn, Uranus, Neptune, and Pluto are more of an icy composition
- Earth’s moon is the only large one of the inner planets
o Mercury and Venus have no moons and the moons of Mars are tiny chunks of rock
The Lunar Surface
- the lunar surface is a very dark place
o it’s albedo, the amount of light the surface reflects, is very small
o the Moon has no atmosphere so temps can range from 127 degrees Celsius (260 F) to –173 degrees Celsius (-343 F) where the sun is not shining
- there is no erosion on the Moon except for creep and wear caused by recent impacts
- Vocab:
o highlands – light in color, mountainous, and heavily covered in craters
o maria – dark, smooth plains
o impact craters – formed when objects from space crashed into the moon
o ejecta – material blasted out by the impacts
o rays – long trails of ejecta
Composition
- the Moon is made of minerals similar to those that make up Earth
History of the Moon
- the Moon is between the age of 3.8-4.6 billion years
- scientists theorize that the Moon was heavily hit by other objects for the first 800 million years of its’ existence
- all of these collisions caused regolith, which is a thick layer of loose, ground-up rock
- the maria are slightly younger than the highlands – between 3.1 and 3.8 billion years old
- the highlands formed during the period of time when there was intense bombardment on the moon
o after this lava came up from the Moon’s interior and filled the large impact craters to form the maria
o they are without craters because not much has hit the moon since they have been created
o fig 28-9
Tectonics on the Moon
- fig 28-10
- scientists believe that the Moon has a layered structure somewhat like the Earth
o it consists of the crust, the upper mantle, the lower mantle, and the core
o the crust varies in thickness and is thickest on the far side
o the upper mantle is solid and the lower mantle is partially molten, and the core is made of solid iron
Formation Theories
- Theory 1 – The Capture Theory
o this proposes that when the solar system was forming, a large object came too close to the Earth and was trapped in the Earth’s gravitational pull and formed the Moon
o Problems: the object would have had to slow down and the Moon and Earth are made of similar elements
- Theory 2 – The Simultaneous Formation Theory
o this proposes that the Earth and Moon were formed at the same time in the same general area
o Positives: would show why the Earth and Moon are made of the same general elements and the object would not have had to slow down
o Problem: does not account for different amounts of iron – Moon is generally iron deficient
- Theory 3 – The Impact Theory (Most commonly accepted)
o computer models indicate that Earth was hit by a Mars-sized object about 4.5 billion years ago
o because of this collision, materials from that large object and from Earth’s outer layers were ejected into space, forming the Moon
o Positives: this accounts for similar composition, heat from the collision would have evaporated any water that could have been on the Moon
o Fig 28-11