The Sun-Earth-Moon SystemChapter 28

28.1 Tools of Astronomy

The best tool astronomers have to learn about the universe is the light that comes to Earth from distant objects.

Aside from fragments that come to the Earth’s surface, the only way that we can study the universe is to understand the radiation.

Radiation

The type of radiation that is studied consists of electric and magnetic disturbances that travel through space as waves. This is referred to as electromagnetic radiation.

Electromagnetic radiation includes visible light, infrared and ultraviolet radiation, radio waves, microwaves, X rays, and gamma rays.

Electromagnetic radiation is classified by its wavelength (the distance between the peaks on the wave) and its frequency (the number of waves or oscillations occurring per second.)

Objects in space emit radiation in all portions of the electromagnetic spectrum.

Telescopes

Benefits of using a telescope: We can modify them with different mirrors and

detectors to observe all wavelengths, especially those the human eye cannot detect

A telescope collects electromagnetic radiation from a distant object and focuses it at a point where the image can be studied or recorded.

They allow astronomers to use specialized equipment.

Telescopes can be used to make time exposures with the aid of cameras or other imaging devices.

Types of Telescopes

REFRACTING TELESCOPES Visible light telescope The first type of

telescope Invented around 1600 Uses lenses to bring

visible light to a focus Largest lens is called

the objective lens

REFLECTING TELESCOPES Visible light telescope Invented in 1668 Uses mirrors to bring

visible light to focus Majority of telescopes

used today

Telescopes at other wavelengths Astronomers must observe the universe at

wavelengths that the human eye cannot detect

The goal of all telescopes is to bring as much visible light into focus

X rays and Gamma rays cannot be focused, so specially designed telescopes must be used

Interferometry is the process of linking separate telescopes together to act as one telescope

Additional means of collecting data

Earth’s atmosphere blocks infrared radiation, ultraviolet radiation, X rays, and gamma rays

Earth’s atmosphere does allow certain wavelengths to pass through; however, images are blurred

As result, we must send objects into space to make close-up observations

We rely on satellites, probes, and space-based astronomy conducted from space stations

Spacecraft

Space-based exploration can be achieved by sending spacecraft directly to the bodies being observed.

Robotic probes make close-up observations, sometimes landing to collect direct information.

Probes are practical only for objects within our solar system, because the stars are too far away.

Below, NASA’s Mars Expedition Rover is shown on a simulated Martian surface on Earth during one of its tests.

Human Spaceflight

Exploring objects and effects in space has been a top priority for scientists.

As result, the Space Shuttle Program was launched in 1981.

•Pro: Allows a place to study space •Cons: Most shuttle missions last only 17 days so long-term effects cannot be studied here

To “address” the short-term mission trip concerns of space shuttles, space stations have been built.

•Multi-country station, the International Space Station, began in 2000 and provides an ideal environment to conduct research

Spinoffs

Space exploration programs have benefitted our society far beyond our increased understanding of space.

Many technologies originally developed for space programs are used by people all over the world. Space shuttle fuel pumps led to the development of

pumps in artificial hearts The Apollo program led to the development of cordless

tools More than 1400 NASA technologies have been passed

on to commercial industries and are commonly called spinoffs

Hubble Space Telescope

Since the earliest days of astronomy, astronomers have shared a single goal — to see more, see farther, see deeper.

The Hubble Space Telescope is one of NASA's most successful and long-lasting science missions. It’s launch in 1990 has become one of humanity’s greatest advancements.

Hubble orbits Earth, positioning itself above the atmosphere, which ultimately distorts and blocks light that reaches our planet. This enables Hubble to get a view of the universe that cannot be given to ground-based telescopes.

Since 1990, Hubble has been “beaming” hundreds of thousands of images back to Earth, shedding light on the many great mysteries of astronomy.

To date, more than 6,000 scientific articles have been published based on data received from Hubble.

~ www.hubblesite.org ~

The Hubble Space Telescope is launched into space aboard Space Shuttle Discovery on April 24, 1990.

How it Works

Every 97 minutes, Hubble completes a spin around Earth, moving at the speed of about five miles per second (8 km per second). (This is fast enough to travel across the United States in about 10 minutes.)

Hubble is a type of reflector telescope, which means that light is hitting the telescope's main mirror, or primary mirror, and bouncing off the primary mirror onto a secondary mirror. The secondary mirror then focuses the light through a hole in the center of the primary mirror that leads to the telescope's science instruments.

The larger a telescope's mirror, the more light it can collect, and the better its vision. Hubble's primary mirror is 94.5 inches in diameter.

Each instrument is designed to examine the universe in a different way.

~ www.hubblesite.org ~

Hubble’s Data Pipeline

Orion’s Nebula

Jupiter’s Moons cast shadows

Infrared picture of Saturn

Mystic Mountain

A mountain of dust and gas rising in the

Carina Nebula.

The top of a three-light-year tall pillar of cool hydrogen is being worn away by

the radiation of nearby stars, while

stars within the pillar unleash jets of

gas that stream from the peaks.

Star forming region

Merging Galaxy Cluster

CassiopeiaShredded remains of an old supernova

This youngest-known supernova remnant in our galaxy lies 10,000 light years away in the constellation Cassiopeia.

The light from this exploding star first reached Earth in the 1600s.

Crab NebulaCombined images (X-Ray and

Optical)

All Good Things Must Come to an End…

Eventually, Hubble's time will end. As years pass, Hubble’s components will slowly degrade to the point at which the telescope stops working.

When that happens, Hubble will continue to orbit Earth until its orbit decays, allowing it to spiral toward Earth.

Because Hubble’s prolonged lifespan is beyond the date for the retirement of the space shuttle program, a robotic mission is expected to help de-orbit Hubble, guiding its remains through a plunge through the atmosphere and into the ocean, though NASA originally hoped to bring Hubble back to Earth for museum display.

~ www.hubblesite.org ~

The Sun-Earth-Moon System

Relationship of the Sun, Earth and Moon are important to us in several ways:

1. Sun provides light and warmth and is the source of most of the energy that fuels our society.

2. Moon raises tides in our oceans and illuminates our sky with its monthly phases.

3. Every society from ancient times to the present has based its calendar and its timekeeping system on the apparent motions of the Sun and the Moon.

Daily Motions

The most obvious pattern in the sky is the daily rising and setting of the Sun, the Moon, the stars, and everything else visible in the sky.

The Sun rises in the EAST and sets in the WEST, as do the Moon and stars. This is referred to as one solar day, which is the basis of our

timekeeping method.

These daily motions result from rotation of the Earth. The Earth rotates once every day, or 150 per hour. The length of a day as we observe is a little longer than the time

it takes Earth to rotate once on its axis because as Earth rotates, it also orbits and has to turn a bit farther.

How do we know the Earth rotates?

Coriolis Effect

Flowing air and water on Earth are diverted from a north-south direction to an east-west direction as result of the Earth’s rotation. (Chapter 12)

Annual Motions

The length of day and the temperature vary depending on the latitude in which you live as well as the annual orbit of the Earth around the Sun.

The plane in which the Earth orbits about the Sun is called the ecliptic.

The Earth is tilted relatively to the ecliptic, at 23.5o

As the Earth orbits the Sun, the tilt remains fixed. This causes the northern hemisphere to be tilted toward the Sun at one point and away from the Sun six months later. As result, we experience seasons.

Due to the tilt and the motion around the Sun, the Sun changes altitude in the sky. This is measured in degrees from the observer’s horizon to the object (Sun). There are 90o from the horizon to the point directly overhead, which is referred to as the zenith.

Solstices and Equinoxes

SOLSTICES (NORTHERN HEMISPHERE)

Summer Solstice June 21 Tilted toward the Sun Maximum amount of daylight hours Sun is directly overhead at the Tropic of

Cancer (23.5oN) Sun does not set in the region within

the Arctic Circle and does not rise within the Antarctic Circle

Winter Solstice December 21 Tilted away from the Sun Sun is directly overhead at the Tropic of

Capricorn (23.5oS) Minimum amount of daylight hours Sun does not rise within Arctic Circle

and does not set within Antarctic Circle

EQUINOXES

Means “Equal Nights”

Midway through Summer and Winter solstice, the Earth’s axis is not pointed at the Sun. As result, both hemispheres receive equal amounts of sunlight

Sun is directly overhead at the equator

At the Tropic of Cancer and Tropic of Capricorn, the Sun is 23.5ofrom the point directly overhead

Position of the Sun affects how directly sunlight strikes the Earth. The lower the altitude, the larger the area of sunlight

Solar Eclipses

When the Moon passes directly between the Sun and Earth, blocking out our view of the Sun.

Because we are so far away from the Sun, on Earth it appears that the Sun and Moon are similar in size… NOT TRUE!!

When the Moon blocks the Sun, we only see the dim, outer gaseous layers. This is called a total solar eclipse. (A partial is when only a portion of the Sun is blocked.)

The shadow cast upon the Earth by the Moon has two portions. The inner portion does not receive

direct sunlight and is called the umbra. The outer portion of the shadow

receives some light and is referred to as the penumbra.

The Effects of Orbits

Although the Moon passes between the Sun and Earth every month, we do not experience solar eclipses this often.

This is because the Moon’s orbit is tilted 5o relative to the ecliptic. Usually, the Moon passes north or south of the Sun (as seen from the Earth).

The Moon not only moves above and below the plane of the Earth and the Sun, but it also increases and decreases distance from Earth in its elliptical orbit.

The closest point in orbit to Earth is called perigee and the furthest point in orbit to Earth is called apogee.

At apogee, the Moon appears smaller from Earth and creates an annular eclipse, because the disk of the Sun is not completely blocked.

Lunar Eclipses

Occurs when the Moon passes through Earth’s shadow.

Can happen only at time of Full Moon, when the Moon is in the opposite direction of the Sun.

The Earth’s shadows are similar to the Moon, so there is an umbra and a penumbra.

A total lunar eclipse occurs when the entire Moon is within the Earth’s umbra (as shown). This lasts for approximately 2 hours. The Moon is faintly visible because sunlight that has passed near Earth has been refracted by Earth’s atmosphere. This light gives the Moon a reddish color.

Lunar eclipses do not occur every Full Moon because the Moon in its orbit usually passes above or below the Sun as seen from the Earth.

Did You Know?

Solar and lunar eclipses occur in almost equal numbers, with slightly more lunar eclipses.

The maximum number of eclipses, combined, that can be seen in a year is 7

The last time this occurred was in 1982, it won’t happen again until 2038

The Moon

Astronomers have learned much about the Moon from telescopic observations

The first steps taken to reach the moon were made by the Soviets in 1957, with the launch of the satellite Sputnik I

In 1961, Yuri Gagarin (Soviet) became the first human in space

The first American in space was Alan Shepard, in 1961, through Project Mercury

Project Gemini launched two-person crews into space

On 07-20-69 the Apollo program landed Neil Armstrong and Buzz Aldrin on the Moon during Apollo 11

History of the Moon

The lunar surface is very old, with an age between 3.8 and 4.6 billion years.

It is believed that the Moon was bombarded during its first 800 million years, which formed a loose layer of ground up rock called regolith.

Between 3.1 and 3.8 billion years ago, lava welled up from the Moon’s interior and filled in large impact basins to form maria. The lava often did not fill the basins completely, leaving the rims of the basins above the maria to form mountain ranges on the Moon.

As the crust on the far side of the Moon is twice as thick as the near side, there are virtually no maria formations there.

Formation Theories…

There are three major theories as to how the Moon formed, only one being commonly accepted:

1. Capture Theory▪ States that a large object ventured too near Earth as the solar system was

forming and became trapped in its gravitational pull, forming the Moon

2. Simultaneous Formation▪ States that the Moon and Earth formed at the same time, in the same general

area, so materials forming them were relatively the same. States that because they formed in the same general area, the Moon did not have to slow down to become gravitationally trapped.

3. Impact Theory▪ States that the Moon formed as result of a giant collision between Earth and a

Mars-sized object about 4.5 billion years ago, when the solar system was forming. As result, materials from the incoming body and the Earth’s outer layer were ejected into space and merged together to form the Moon. This model accounts for why the Moon is so similar to the Earth in composition.

What are the problems with the first two theories?

Capture Theory

Something would have had to slow down the passing object to allow it to become trapped

If the Moon had been captured, wouldn’t it have different composition from the Earth?

Simultaneous Theory

What about the amounts of iron on Earth and on the Moon? The Earth is iron rich and the Moon is iron poor

Lunar Properties

The Earth’s moon is unique within the solar system.

It is one of the largest, with a radius about 27% of Earth’s and a mass of more than 1% of Earth. (Most moons are much smaller in relation to the planets they orbit.)

The orbit is unusual in that it is relatively further from its planet than most moons in the solar system

Earth’s moon is the only large moon among the inner planets

Lunar Surface

Solid, rocky surface made of minerals similar to those on Earth (primarily silicates)

There is no erosion due to a lack of atmosphere or flowing water

Small amount of albedo, or the amount of sunlight that its surface reflects

Several features are found on the moon…

Features of the Moon

Highlands - light in color, mountainous, heavily covered with craters

Maria – dark, smooth plains, average 3km lower than highlands

Impact craters – formed when objects from space crashed into the lunar surface

Ejecta – material blasted out during impacts that fell back to surface of Moon

Rays – long trails of ejecta that radiate outward. Visible as light-colored streaks

Rilles – meandering, valley-like structures

Composition of the Moon

Scientists infer that the Moon has a layered structure, like the Earth, which consists of the crust, upper mantle, lower mantle, and core.

Made up of minerals similar to those of Earth – mostly silicates.

Highlands are primarily lunar breccias, which are rocks formed by fusing together smaller rocks during impacts.

Most lunar breccias are composed of plagioclase feldspar.

Maria are primarily basalts that differ from those on Earth as they contain no water.

Tectonics on the Moon

Mountain ranges found on the moon were formed by impact craters, not tectonic motions as formed on Earth.

Seismometers measure moonquake strength strong enough to cause damage once per year; however, scientists theorize the Moon is not tectonically active.

The fact that the Moon has no active volcanoes or significant magnetic field supports the scientific theory.

Phases of the Moon

Like the Sun, the Moon appears to change its position in the sky as result of the movement of the Moon around the Earth.

The sequential changes in the appearance of the Moon are called lunar phases.

The Moon does not emit visible light. What you “see” is the Moon’s reflection of the Sun’s light.

When the Moon is between the Earth and Sun, we cannot see it as the sunlit side is facing away from us. This is referred to as a New Moon.

From the New Moon phase, the amount of sunlight we see increases (waxing) to the time in which the Moon reaches a Full Moon phase, where we see the entire Moon. From there, the amount of sunlight we see decreases (waning) to the time in which it again reaches total darkness at the New Moon Phase.

Lunar Phases: New Moon Waxing Crescent First Quarter Waxing Gibbous Full Moon Waning Gibbous Third Quarter Waning Crescent

Motions of the Moon

The amount of time it takes for the Moon to go through a complete cycle of phases is called a lunar month.

A lunar month is about 29.5 days, which is longer than the 27.3 days it takes for one revolution around the Earth.

The Moon rises and sets 50 minutes later each day due to its movement in orbit.

TIDES

The Moon’s gravity pulls on Earth along an imaginary line connecting Earth and the Moon, which creates bulges of ocean water on both the near and far sides of the Earth.

As the Earth rotates, the bulges remain aligned with the Moon, so a person at shoreline on the Earth’s surface would observe that the ocean level rises and falls every 12 hours.

The Sun’s gravitational effect is different because it is further away; however, when the Sun and Moon align along the same direction the tides are higher than normal (Spring Tides). When the Moon is at a right angle to the Sun-Earth Line the tides are lower than normal (Neap tides).