Gravity & Orbital Motion

Gravitation

Law of Universal Gravitation
Inverse Square Relationship
All objects with mass attract each other

Newton's 1st Law

Linear vs Circular Motion

Relative Motion

Circular Motion

Rotate

Revolve

Period/Rotation Speed

Tangential Velocity

Rotational Mechanics

Centripetal Acceleration

Centrifugal Force

Orbits

Circular

Elliptical

Orbital Radius

Orbital Speed

Conservation of Orbital Energy

Astronomical Dimensions

Units of Measure

the AU - Astronomical Unit

Light Years, Parsecs, Eons

Relative to Things Familiar

How Many?

Galaxies

Stars

Solar Systems/Planets

How Big?

The Universe

Galaxies

The Milky Way

Our Sun

Earth & the Other Planets

Asteroids

Comets

How far?

to the Sun

to the Moon

to the Other Planets

to the Nearest Star

to the Nearest Solar System

to the Center of the Milky Way

to the Nearest Galaxy

How Old?

the Universe

the Stars

Our Sun

Our Solar Sytem

The Earth, Moon, and Planets

Chemical Composition

of the Universe

Galaxies

Stars

Interstellar Space

Dark Matter

of Our Solar System

Sol - the Sun

Terra - the Earth

Luna - the Moon

the Planets

Asteroids

Comets

Sources of Light & Energy

Temperature

Heat

Heat Transfer in Space

Visible

Infrared

Formation, Evolution, & Age

of the Universe

Before

Big Bang

Universal Expansion

The Center

The End

Galaxies and Stars

Interstellar dust

Nebulae

Our Solar System

the Sun

The Earth & Moon

The Planets

Asteroids

Comets

 Standard Set 4 The structure and composition of the universe can be learned from studying stars and galaxies and their evolution. As a basis for understanding this concept: a. Students know galaxies are clusters of billions of stars and may have different shapes. b. Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature, and color. c. Students know how to use astronomical units and light years as measures of distances between the Sun, stars, and Earth. d. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light. e. Students know the appearance, general composition, relative position and size, and motion of objects in the solar system, including planets, planetary satellites, comets, and asteroids originally thought to be stars are now known to be distant galaxies.

4.a. Galaxies them-selves appear to form clusters that are separated by vast expanses of empty space. As galaxies are discovered they are classified by their differing sizes and shapes. The most common shapes are spiral, elliptical, and irregular. Beautiful, full-color photo-graphs of astronomical objects are available on the Internet, in library books, and in popular and professional journals. It may also interest students to know that astronomers have inferred the existence of planets orbiting some stars.

4.b The Sun is a star located on the rim of a typical spiral galaxy called the Milky Way and orbits the galactic center. In similar spiral galaxies this galactic center appears as a bulge of stars in the heart of the disk. The bright band of stars cutting across the night sky is the edge of the Milky Way as seen from the perspective of Earth, which lies within the disk of the galaxy. Stars vary greatly in size, temperature, and color. For the most part those variations are related to the stars’ life cycles. Light from the Sun and other stars indicates that the Sun is a fairly typical star. It has a mass of about 2 × 1030 kg and an energy output, or luminosity, of about 4 × 1026 joules/sec. The surface temperature of the Sun is approximately 5,500 degrees Celsius, and the radius of the Sun is about 700 million meters. The surface temperature determines the yellow color of the light shining from the Sun. Red stars have cooler surface temperatures, and blue stars have hotter surface temperatures. To connect the surface temperature to the color of the Sun or of other stars, teachers should obtain a “black-body” temperature spectrum chart, which is typically found in high school and college textbooks.

4.d The energy from the Sun and other stars, seen as visible light, is caused by nuclear fusion reactions that occur deep inside the stars’ cores. By carefully analyzing the spectrum of light from stars, scientists know that most stars are composed primarily of hydrogen, a smaller amount of helium, and much smaller amounts of all the other chemical elements. Most stars are born from the gravitational compression and heating of hydrogen gas. A fusion reaction results when hydrogen nuclei combine to form helium nuclei. This event releases energy and establishes a balance between the inward pull of gravity and the outward pressure of the fusion reaction products.

Ancient peoples observed that some objects in the night sky wandered about while other objects maintained fixed positions in relation to one another (i.e., the constellations). Those “wanderers” are the planets. Through careful observations of the planets’ movements, scientists found that planets travel in nearly circular (slightly elliptical) orbits about the Sun.

Planets (and the Moon) do not generate the light that makes them visible, a fact that is demonstrated during eclipses of the Moon or by observation of the phases of the Moon and planets when a portion is shaded from the direct light of the Sun.

Various types of exploratory missions have yielded much information about the reflectivity, structure, and composition of the Moon and the planets. Those missions have included spacecraft flying by and orbiting those bodies, the soft landing of spacecraft fitted with instruments, and, of course, the visits of astronauts to the Moon

If feasible, teachers should have students observe the motion of Jupiter’s inner moons as well as the phases of Venus. Using resources in the library-media center, students can research related topics of interest.

Copyright © 2005 -  S. B. EglI