Overview of Class

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Conceptual Questions

1. How common are other solar systems, and are they similar to ours?

2.       Is there life elsewhere in our solar system? Beyond our solar system? If so, could this be intelligent life?

Objectives

1. Understand the difference between rotation and revolution.
2. Understand the forces involved with stellar formation and solar origin. 

DPI Competency

The learner will acquire an understanding of the Earth in the solar system and its position in the universe.

Introduction

Our solar system consists of the Sun, nine planets, about 70 satellites of the planets, and many smaller bodies including comets and asteroids (meteorites). The inner planets are those that are relatively close to the Sun: Mercury, Venus, Earth and Mars. The planets of the outer solar system are Jupiter, Saturn, Uranus, Neptune and Pluto. Thus Earth is the third planet from the Sun, and our position in the solar system helps to account for many of the characteristics of the Earth (e.g., chemical composition and density of Earth's rocks, our atmosphere, temperatures at the Earth's surface).

To address this Competency, we first consider the characteristics and description of the solar system, and its formation. Today, astronomers generally believe that the bodies in the solar system formed from a gigantic cloud of gas and dust; this is the nebular model or hypothesis. Then we investigate tools, including telescopes and spacecraft, used by astronomers to study the solar system and space beyond our solar system. For the second class covering this Competency, we study energy produced by our Sun and other stars, and consider use of stellar spectra to indicate motion in space, and the life-cycle of stars. With this overview of our solar system and space, we will look at current thoughts on the origin of the universe.

Review

In addition to the BP reading, we will look at Internet sites that provide good photographs, drawings, and animations of the solar system. They also include text describing the planets and other bodies. It makes sense to understand the characteristics of the solar system, including motion of planets, etc., before considering the formation of the solar system. Thus, we defer consideration of the solar system's formation until the end of this section ("1. d.")

More sites describing the solar system are listed than you need visit. The extra sites are useful for 1) student assignments, 2) alternate sites in case those sites we especially recommend are not accessible (or might be slow in downloading), and 3) sources of additional information.

Descriptions of solar system:

The nine planets: Overview with tour of the solar system. Includes some great images, specific information about the Sun and each planet, plus the smaller bodies in the solar system. New and recent discoveries; many good and interesting links. There is an express tour, and one that is more detailed.

Question: Why is there some debate as to whether or not Pluto should continue to be considered a planet?

 Scale model of solar system: Shows distances between bodies as well as relative size of bodies in the solar system Very good, concise information about the planets, excellent images

Question: Why do distances between planets (e.g., Jupiter and Earth) vary from day-to-day and from year-to-year?

 Planetary tour: Scientific American website with good overview and good illustrations; provides tables with data for each planet.

 Good overview of entire solar system with beginner, intermediate and advanced levels of descriptive information; provides access to much information. Click on "Enter the Site." Then on "Our Solar Sysem," then on "Solar System Information." (Or whatever is of interest!)

 Simple, easy to understand information about the planets with good graphs and tables with comparative information on size, density, mass, length of day, etc.

Sol ar System Live: This is a drawing of an orrery that shows the positions of the planets today. By changing from "Time" to "Now" you can change the date to future or past, click on "Update," and see the planets change positions. Useful for seeing how the planets move with respect to one-another.

The planets revolve about the Sun in orbits. These orbits are nearly in a plane with the Sun at the center; this plane is called the ecliptic and is defined by the plane of the Earth’s orbit. The planets all revolve in the same direction (counter-clockwise looking down from above the Sun’s north pole). The orbits of the planets are ellipses with the Sun at one focus, although all of the orbits except those of Mercury and Pluto are very nearly circular. Pluto’s orbit deviates the most from the plane of the ecliptic with an inclination of 17 degrees. Planets and the Sun rotate about an axis (e.g., through the north and south poles of Earth). Planets generally rotate in the same direction that they revolve, but Venus, Uranus, and possibly Pluto are exceptions. Most of the rotation axes are nearly perpendicular to the ecliptic plane.

Kepler's Laws describe most aspects of planetary motion. Newton’s Law of Gravitation basically explains why the planets and other bodies in space move as they do. The following websites provide information about these laws, as well as very good graphics. View the 1st site on Kepler's Laws and the first one on gravity (i.e., view the 1^st and 3^rd sites below):

 Kepler’s Laws of Planetary Motion: Very good graphics and explanation of terms, brief history of debate regarding planetary motion

Question: Why was the Earth once considered to be at the center of the solar system?

 Kepler’s Laws of Planetary Motion: Very good animations provided by Java applets. Not much explanation, so it is best not to view this site unless you first look at the one above

Question: The apparent motion of our Sun relative to Earth can easily be seen. How? Why is this apparent motion and not real motion?

 Newton’s Universal Law of Gravitation: Very good graphics and explanation of terms; includes discussion of the difference between weight and mass

Question: What determines the amount that we weigh?

 Gravity and planetary motion: Simple but very good animated site that shows how gravity affects both the orbiting body (planet or moon), and the body being orbited (moon or sun).

Some of the relatively small bodies in the solar system, such as asteroids and comets, move in orbits that are much different than those of the planets. The following website provides information on Near Earth Objects (NEO's), which are asteroids with orbits that periodically bring them relatively close to Earth.

NASA’s Near Earth Object (NEO) Program home page. News, listings and images of NEO’s (asteroids). Link to "Near Earth Objects" provides a good overview of these asteroids and why they could be a hazard. Also try the link to "Potentially Hazardous Asteroids"

Question: What might cause a body in the solar system to have an unusual orbit or rotation?

Earth's characteristics reflect the distance our planet is from the Sun. Earth's size and density (mass), composition (lithosphere, hydrosphere, atmosphere), biosphere, and energy sources all can be attributed to our position in the solar system. Earth would be quite a different place if, for example, it were between Saturn and Uranus! The following websites provide information about the Earth as it relates to other members of the solar system. View the 1st website (you may have visited this one earlier).

 Earth: This is part of the very comprehensive site on the solar system that is recommended in part "1. a" above. This portion of the site provides specific, concise information about Earth as it relates to other bodies in our solar system.

Question: Our neighbor in space, the moon, has a surface covered with craters made by impacting asteroids (meteorites). Why are impact craters relatively rare on the Earth's surface?

 NASA website about solar eclipses. Includes some potentially useful links

 Lunar eclipses; also includes information and graphics on the phases of the moon

Lunar perigee and apogee: Explanation with good illustrations as to why the full moon appears to be of different size depending upon when it is viewed.

A successful hypothesis for the origin of the solar system needs to explain each of the following characteristics, most of which have been covered in your reading or on the websites:

1. All planetary orbits are in about the same plane
2. Sun's rotational equator is in about the same plane as planetary orbits
3. Planets and Sun move (revolve, rotate) in same direction (counter-clockwise if viewed from above the Sun's north pole)
4. Planets generally have nearly circular orbits; all orbits are counter-clockwise
5. Most planets (except Venus and Uranus) rotate in same direction as the Sun (counter-clockwise); Pluto's rotation is uncertain
6. There in an angular momentum (measure of velocity, size, mass) discrepancy between the Sun and planets: Planets have <1% of mass of solar system, but 99% of its angular momentum; Sun has >99% of mass of solar system, but only 1% of angular momentum; i.e., it is rotating more slowly than expected
7. All solar system bodies are composed of the same chemical elements, but in different proportions
8. Planet composition generally varies systematically with distance from the Sun
9. Distances between planets generally follow a regular pattern
10. Planet-satellite systems are similar to miniature solar systems

Historically, there are two main groups of hypotheses for solar system origin:

1. Sun formed first, planets (etc.) formed later and independently. This is called the Catastrophic or Encounter Hypothesis
2. Sun, planets, etc., formed at same time by same process: This is named the Protoplanet or Nebular Hypothesis

Catastrophic or Encounter Hypothesis:

The catastrophic or encounter hypothesis basically states:

1. Our Sun existed before the other objects in our solar system
2. A second star passed closed to the Sun
3. Gravitational attraction between the two stars pulled material from the Sun
4. The material from the Sun coalesced due to gravitational attraction, and eventually became the planets, etc.

This scenario would explain some of the information about the solar system, but there are many problems including: 1) There is a very low probability of two stars coming close together; 2) the hot gas and dust likely would escape into space, or, if not, orbits would be very eccentric; 3) the planet-satellite systems resemble miniature solar systems and this mode of solar system formation leaves them unexplained.

Protoplanet or Nebular Hypothesis

1. Rotating, disk-shaped cloud of "gas" and "dust": i.e., nebula
2. Within the nebula, condensation of gas results in more solid material, forming dust (planetary material) and ices
3. Gravitational attraction within the central portion of this "cloud" eventually forms protosun; collision of particles within it produces heat
4. Elsewhere in the nebula, dust also undergoes gravitational and electrostatic attraction, forming aggregates of material: Large aggregates are protoplanets, smaller ones are planetesimals
5. Some planetesimals are attracted by gravitational attraction to protoplanets, some become asteroids/meteorites
6. Protosun undergoes (gravitational) collapse, increasing temperatures to the point that nuclear reactions begin, creating the Sun and solar energy
7. Heat from Sun drives all or much gas (atmosphere) from protoplanets, especially those close to Sun; protoplanets become new planets
8. Early planets become hot due to impact of planetesimals plus radioactive decay, and temporarily melt. The most dense material is concentrated (gravity again!) at the center (core) of the planet

The nebular or protoplanet hypothesis explains most of the compositional, size, spacing, and motion characteristics of the bodies in the solar system. The websites below provide additional information and useful graphics. Visit both of the following websites, although the 1^st site was used in Competency 3 and thus you already may be sufficiently familiar with it::

 Origin of the solar system: Good diagrams and discussion about the encounter hypothesis and the protoplanet hypothesis.

Question: How does a protoplanet differ from the planet that it eventually becomes?

 Behavior of nebula: Good diagrams showing the change from a nebula (gas and dust cloud) to protoplanets and protosun.

Ancient peoples apparently oriented structures like Stonehenge in Great Britain and the Egyptian pyramids according to the positions of stars or other bodies in space. It has been suggested that some early structures were used to make astronomical observations. Instruments used today to study objects in space include spacecraft and telescopes. We will consider these and other tools in the sections that follow. View the following website which gives a good and concise summary of the study of space:

 Concise history of the study of space from before 1600 to the present, with good links and photographs

Questions: How many stars can be seen? What is a galaxy?

Visit the spacecraft section of the 1^st website below; most of the other websites below describe specific missions in space (3^rd, 4^th, 5^th sites below). The extra sites provide additional good information about space exploration should you wish to look at them in the future:

Welcome to the Planets: Good images of the planets. The section entitled "The Explorers" has good information and photographs about spacecraft that have studied our solar system.

Question: Travelling at the velocity necessary to escape Earth's gravitational field (11,200 meters/second), how long would it take to get to Mars? To Pluto?

Past, present, and future USA spacecraft missions to bodies in our solar system. Includes overview and objectives of each mission; good photographs.

Space shuttle: Explanations of the space shuttle and how it is used. Click on the space shuttle itself. Good links

Near Earth Asteroid Rendezvous (NEAR) Mission: this spacecraft was the first to orbit an asteroid 433 (Eros)

Voyager Mission to outer solar system: Voyager I and II spacecraft will continue their exploration for about 20 more years, in the outer parts of our solar system

The optical telescope made it possible to study objects in space in detail. It is speculated that a manufacturer of eye glasses or spectacles may have made the first telescope. Spectacles apparently existed by about 1350. The first known telescope was made in 1608. A telescope is simply a tool for gathering light, resolving fine detail, and magnifying the size of objects. This light provides information about distant stars, nebula, supernova, and other objects or events in space. Early optical telescopes displayed distracting colors at the margins of the lenses. In studying the behavior of light to try to understand how light was producing these unwanted colors, it was eventually discovered that visible light is only one part of the energy or electromagnetic radiation (see p. 48-49, BP) that reaches Earth from space. These types of energy, listed in order of increasing wavelengths, include gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. Instruments to detect the non-visible wavelengths are attached to modern telescopes.

One of the major problems with using optical telescopes is visual interference caused by the Earth’s atmosphere. Even from mountain peaks, the atmosphere makes it impossible to obtain detailed images of distant objects. To study space without problems caused by our atmosphere, the Hubble Space Telescope was launched in 1990 using the Space Shuttle. This telescope has obtained magnificent images of distant objects, as well as other data. The Hubble Telescope does not study the Sun or moon, because the intensity of the light from these bodies would damage the telescope.

A spectroscope is a device that uses a prism to separate white light into its component wavelengths (represented by different colors). These wavelengths are determined by the chemical composition of the source of the light. Once this was understood, it was possible to determine the composition of the Sun and other stars without having to visit them! It now is common to attach a spectroscope to a telescope.

Radio astronomy is the study of space using radio waves that reach Earth from bodies in space. Radio telescopes are used to collect this form of energy. These waves come from the Sun and from other stars, and provide a different way of mapping and studying space. Some stars not visible with ordinary telescopes have been found by the radio signals they emit. The planet Jupiter also is a source of radio waves.

 History of early telescopes: Very good information on the development and use of early telescopes, as well as links to important early astronomers.

 Hubble Space Telescope: This site provides access to photographs taken by the Hubble Space Telescope, technical information about it, and links to many sources including educational activities and resources.

Exploring the Solar System Using Instruments from the Hubble Space Telescope: This site requires that you download a 4.4 MB file that then would reside on your computer. Once downloaded (which could be done when you do not need to use your computer), it provides excellent images, questions and comparative information about the planets based on Hubble telescope data. This software is set up as a tutorial with questions, answers, and scorekeeping.

Sky and Telescope Magazine site. Includes list of upcoming and recent astronomical events, good photos, links. Information on use of telescopes and cameras to study space

Review

1. How common are other solar systems, and are they similar to ours?
2. Is there life elsewhere in our solar system? Beyond our solar system? If so, could this be intelligent life?

1.  Understand the difference between rotation and revolution.
2. Understand the forces involved with stellar formation and solar origin. 

DAILY QUIZ