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Christopher Ervin

on 1 May 2015

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Transcript of Astronomy

Introduction to Astronomy
Earth in Space
What is Astronomy?
Astronomy is the study of the moon, stars and other objects in space.
Earth Movements
Earth moves through space in two (2) major ways; Rotation and Revolution.
Rotation is defined as the Earth turning about on its axis.
Revolution is the movement of one object in space around another in space.
Earth also has a minor movement, called axial wobble. A process much like a spinning top where, toward the end of its spinning begins to wobble about its axis.
Earth in Space
How long does it take Earth to make one rotation? How long does it take Earth to make one revolution?
A calendar is a system of organizing time that defines the beginning, length and divisions of a year.
Who are the people given credit for the first calendars?
The ancient Egyptians are the people who are given credit for the first ever calendars.
The Egyptian calendar was based on the first appearance of the star Sirius in the morning, astronomers counted the days between each first appearance of the star. This method of using Sirius led to the discovery that there are 365 days in a year.

Earth in Space
Most cultures borrowed from the Egyptians and made the calendars fit their needs. Technically it takes 365 ¼ days to revolve around the sun.
Most places outside the tropics and the polar regions have four (4) distinct seasons.
Because the Earth is tilted on its axis 23.5 degrees sunlight does not strike the Earth in equal amounts on all surfaces.
In the tropics the Earth receives more direct sunlight whereas nearer the poles the sunlight strikes the Earth at much sharper angles. As a result of these steep angles, sunlight is spread out over a much greater area.

Earth in Space
For these reasons, is why its warmer near the equator than it is near the poles.
Earth has seasons because of its
on its axis of 23.5 degrees as it
around the sun.
The changes in the seasons are not caused by changes in Earth’s distance from the sun. In fact, Earth is farthest from the sun when it is summer in the northern hemisphere.
Earth in June
In June in the northern hemisphere, or the north end of Earth, earth’s axis is pointed/tilted toward the sun. In the northern hemisphere the noon sun is high in the sky and there are more hours of daylight than darkness. The combination of direct rays and more hours of sunlight heat the surface more in June than any other time of the year.

Earth in Space
In the southern hemisphere the sun’s energy is spread out over a larger area.
The sun is low in the sky and the days are shorter than the nights. This combination of less direct rays and shorter/fewer hours of sunlight heats the Earth’s surface less than at other times in the year.
Earth in December
The southern hemisphere now receives the most direct sunlight, so it is summer there and winter for us here in the northern hemisphere.

Earth in Space
The sun reaches its greatest distance north or south of the equator twice each year. Each of these days, when the sun is farthest north or south of the equator, are known as a solstices.
The day when the sun is farthest north of the equator is the summer solstice in the northern hemisphere. Opposite in the southern hemisphere. This solstice occurs around June 20th or 21st annually. And theses are the longest days of the year in the northern hemisphere and the shortest in the southern hemisphere.

Earth in Space
December 21st, the sun is farthest south of the equator, so winter in the northern hemisphere and summer in the southern hemisphere.
Halfway between the solstices, neither hemisphere is tilted toward or away from the sun. This also occurs twice a year, when the noon sun is directly over head at the equator. Each of these days is known as an equinox.
Equinox actually means “equal night”. During the vernal equinox both day and night last about 12 hours each everywhere on Earth.
Equinoxes occur twice a year just as solstices. The vernal equinox marks the start of spring and occurs around march 21st in the northern hemisphere. The autumnal equinox occurs around September 22nd and marks the beginning of fall in the northern hemisphere.

Gravity and Motion
As we already know the Earth revolves around the sun and the moon revolves around the Earth. What keeps them revolving? Why don’t they just fly off into space?
Sir Isaac Newton was the first person to answer these questions, Newton realized that there must be a force acting on both the Earth and moon that kept them in orbit.
Force is simply defined as a push or a pull. Most everyday forces require objects to be in contact with each other. Newton realized that the force that holds the moon in orbit is different in that it acts over long distances between objects that are not in contact.
Newton hypothesized that the same force that pulls the apple to the ground must also pull the moon toward the Earth, keeping it in orbit.

Gravity and Motion
This force, called gravity, attracts all objects toward each other.
Newton did not discuss gravity but he was the first to realize that gravity occurs everywhere and acts on ALL objects.
Newton’s law of Universal Gravitation states that every object in the universe attracts every other object.
The strength of the force of gravity between two objects depends on two factors;
of the objects and the
between those objects.

Gravity, Mass, and Weight
According to Newton’s Law of Universal Gravitation, all of the objects around you are pulling on you right now, just as you are pulling on them.
If that’s true why then don’t we feel or notice a pull on us all of the time? The answer is quite simple, the strength of gravity depends on the masses of each object. Are mass and weight the same thing?
Mass is the amount of matter in an object.
Weight is the force of gravity on an object.
Unlike mass, which does not change, an objects weight can change depending on its location.
Gravity and Distance
The strength of gravity is affected by the distance between two objects as well as their masses. Gravity goes down if distance goes up! An inversely proportional ratio.
Inertia and Orbital Motion
If the Earth and sun are constantly pulling on each other because of gravity, why doesn't the Earth fall into the sun? Or, why doesn't the moon crash into the Earth?
The fact that such collisions have not occurred shows that there must be another force at work.
What force do you think keeps objects apart in space preventing such collisions?

Inertia is the tendency of an object to resist a change in motion.
Mass and inertia are directly proportional.
The more mass an object has the greater its inertia will be.
What is Newton’s first law of motion?
Newton's first law of motion states that an object in motion will stay in motion and an object at rest will stay at rest unless acted on by an outside force.

Orbital Motion
Why do the moon and the Earth remain in orbit if gravity is always acting on them?
Newton concluded that 2 factors – inertia and gravity, combine to keep the Earth in orbit around the sun and the moon in orbit around the Earth.
If not for Earth’s gravity the moon would just fly off into space in a straight line.

Phases, Eclipses, and Tides
Motions of the Moon
Like the Earth, the moon moves through space in 2 ways. The moon revolves around the Earth, the relative positions of the Earth, moon and sun change. The changing relative positions of all 3 cause the phases, eclipses and the tides.
The moons “day” and “year” are the same length. The moon rotates once on its axis in the same amount of time it takes it to revolve around the Earth.
The bright light we see from the moon is a reflection of the sun’s light off of the moon.
The different shapes of the moon we see are called phases.
Phases are caused by the relative positions of the moon, Earth and sun.

Christopher A. Ervin
Vista Grande
Earth Science
An eclipses occurs when the shadow of one body in space falls on another body in space.
There are 2 types of eclipses, Solar eclipses and Lunar eclipses.
During a new moon the moon is between the Earth and sun.
A solar eclipse occurs when the moon passes directly between the sun and Earth blocking the sunlight from Earth. The moons shadows falls on the Earth.

A lunar eclipse occurs when Earth blocks the sunlight from reaching the moon. This occurs during a full moon when the Earth is directly between the sun and moon.
Neap Tides
During the first quarter and third quarter moon phases the line between the Earth, sun and moon are at right angles to each other.
That is the sun’s pull of gravity is at right angles to the moons gravitational pull, this produces a neap tide, a tide with the least difference between consecutive low and high tides. These also occur twice a month.
Earth’s Moon
In 1609, the Italian scientist Galileo heard about a telescope, a device built to observe distant objects by making them appear closer.
The Greeks thought the moon was a perfect sphere. It wasn’t until Galileo built his own telescope and looked at the moon that we knew it had an irregular surface.

Earth’s Moon
The moon’s surface
The moon has several different distinctive features on it’s surface, they include; maria, craters and highlands.
Maria – The moons surface has large flat areas which Galileo maria. Maria is a Latin word for seas.
Galileo incorrectly thought those areas were oceans. The maria are actually large areas of hardened rock formed from huge lava flows that occurred on the moon between 3 and 4 billon years ago.
Craters – Large round pits on the moon called craters. Some of the moons craters are 100’s of kilometers across. For many years scientists thought that these craters were caused by volcanoes. Scientists now know that the moon’s craters were caused by meteor impacts. Most of the moons craters are older than the maria. There are a few craters in the maria. Earth had many of the same types of craters as the moon but over time, through the process of erosion the Earth’s craters have disappeared.

Stars, Galaxies, and the Universe
Light is a form of electromagnetic radiation, or energy that can travel through space in the form of waves.
Forms of Radiation
Scientists call the light you can see visible light. Visible light is just one type of many type of electromagnetic radiation. Many objects give off radiation that you can’t see. An example is the heater’s glowing coils that are giving off infrared radiation, which you feel as heat.
Radio transmitters produce radio waves that carry signals to radios and televisions. Objects in space give off all types of electromagnetic radiation.

Electromagnetic Radiation
The Electromagnetic Spectrum
As seen in the figure below, the distance between the crest of one wave and the crest of the next wave is called wavelength.

Electromagnetic Radiation
Visible light has very short wavelengths, less than one millionth of a meter.
The spectrum of visible light is made of the colors red, orange, yellow, green blue and violet.
The electromagnetic spectrum includes the entire range of radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
These are images of the M81 galaxy as seen with various telescopes that are able to see the different wavelengths in the electromagnetic spectrum
Characteristics of Stars
Color and Temperature
Like objects here on Earth, a star’s color reveals its surface temperature. When a toaster heats up the wires the glow red. The wires inside a light bulb are even hotter and glow white. Similarly, the coolest stars – with a surface temperature of about 3,200 degrees Celsius – appear reddish in the sky. With a surface temperature of about 5,500 degrees Celsius, the sun appears yellow. The hottest stars in the sky, with surface temperatures of over 20,000 degrees Celsius, appear bluish.

Characteristics of Stars
When you look at stars in the sky they all appear to be points of light of the same size. Many stars are actually about the size of the sun, which is a medium size star. Some stars are much larger than our sun, very large stars are called giant stars or super giant stars. If a super giant star were located where our sun is, it would be large enough to fill the solar system out as far as Jupiter.

Characteristics of Stars
Chemical Composition
Stars vary in their chemical composition. The chemical composition of most stars is about 73% hydrogen, 25% helium and 2% other elements by mass. This is similar to our sun’s composition.
Astronomers use spectrographs to determine the elements found in stars.
A spectrograph is a device that breaks light into colors and produces an image of the resulting spectrum.

Brightness of Stars
The brightness of a stars depends upon both its size and its temperature.
Apparent Brightness – A star’s apparent brightness is the brightness as seen from Earth.
Absolute Brightness – A star’s absolute brightness is the brightness the star would have if it were at standard distance from Earth.

Measuring Distance to Stars
If we could travel to our star, the sun, at the speed of light, it would take us only 8 minutes. That is a pretty short trip for such a long distance.
The next nearest star, Proxima Centauri, is much farther away. A trip to our neighbor, Proxima Centauri, at the speed of light would take us 4.2 years.
Light travels at a rate of about 300,000 km/sec.
A light-year is the distance that light travels in one year, about 9.5 million million kilometers.
Astronomers use parallax to measure the distance to star. Parallax is the apparent change in position of an object when you look at it from different places.

The Hertzsprung-Russell Diagram
In the early 1900’s, two astronomers working independently, Ejnar Hertzsprung and Henry Russell, made a similar observation. Both discovered that stars can be classified by locating them on a graph showing two easily determined characteristics.
An H-R diagram is a graph of the surface temperature, or color, and absolute brightness of a sample of stars.
H-R diagrams are used to estimate the sizes of stars and their distances, and to infer how stars change over time.

The Hertzsprung-Russell Diagram
The H-R Diagram
Main Sequence Stars
Main sequence stars are the stars on the H-R diagram that fall in that middle band.
About 90% of all stars are found on the main sequence. Our sun lies near the middle of this band.
Giants and dwarfs
The very bright stars in the upper right hand corner of the H-R diagram are called super giants. Super giants are much brighter than main sequence stars of the same temperature.
Super giants range in size from about 100 to 1000 times the diameter of the sun.
Below the main sequence stars in the lower portion of the H-R diagram are the white dwarfs. A white dwarf is the small, dense remains of a low or medium-mass star.

Life Cycle of Stars
Birth of a Star

Life Cycle of Stars
How stars Form
The space around stars contain gas and dust. In some regions this matter is spread thinly; in others it is packed densely.
A nebula is a large cloud of gas and dust spread out over a large volume of space.
Star form in the densest regions of nebulae.
Stars are created by gravity. Gravity pulls a nebula’s gas and dust into a denser cloud. As it contracts, it heats up. A contracting cloud of dust and gas with enough mass to form a star is called a protostar.
A star is formed when a contracting cloud of gas and dust becomes so dense and hot that nuclear fusion begins.

Life Cycle of Stars
Adult Stars
Stars spend about 90% of their lives on the main sequence. In all main-sequence stars, nuclear fusion converts hydrogen into helium at a stable rate. There is an equilibrium between the outward thermal pressure and gravity’s inward pull. A star’s mass determines the star’s place on the main sequence and how long it will stay there.
The amount of gas and dust available when a star forms determines the mass of the young star.
The most massive stars have large cores and therefore produce the most energy.

Life Cycle of Stars
Adult Stars
High mass stars become the bluest and brightest main sequence stars. Typically these stars are about 300,000 times brighter than the sun.
These stars pay a great price for being so bright. Because blue stars burn so brightly, they burn up their fuel relatively quickly and last only a few million years.
Stars similar in size to our sun occupy the middle of the main sequence. A yellow star like our sun has a surface temperature of about 6000 K and will remain stable on the main sequence for about 10 billion years.
A star can have mass as low as one tenth of that of our sun. The gravitational force in such a low-mass star is just string enough to create a small core where nuclear fusion takes place. The lower energy production results in red stars, which are the coolest and least bright of all visible stars.
A red main sequence star, with a surface temperature of about 3500 K, stay on the main sequence for more than 100 billion years.

Death of a Star
When a star’s hydrogen supply begins to run out gravity gains the upper hand and the star’s days are numbered.
Death of a Star
The collapsing core will grow hot enough for helium fusion to occur. In the process of helium fusion a number of heavy elements are produced. The production of carbon, oxygen and heavier elements immediately dooms the dying star. Carbon production spells the end of the star’s life.
The dwindling supply of fuel in a star’s core ultimately leads to the star’s death as a white dwarf, neutron star, or black hole.
Low and Medium Mass Stars
These stars, which can be as much as eight times the size of the sun, eventually turn into white dwarfs. These stars stay in the giant stage until their hydrogen and helium supplies are low enough for fusion to stop. With less outward pressure gravity wins and the star collapses. The dying star is surrounded by a glowing cloud of gas. This cloud of gas is known as a planetary nebula. As the dying star blows off much of its mass, only its hot core remains. The dense core is the white dwarf.

Death of a Star
Death of a massive star, a star more massive than our sun, begins its life in the same way as other stars, but in dying it can become a little different. Because they are so big, they undergo many more reactions than a smaller star. This process burns its fuel much quicker than smaller stars. Massive stars do not make it to the white dwarf stage, they become neutron stars and explode as a supernova, or may continue its collapse and become a black hole.
When you look up into the sky at night, and gaze at the stars, you are viewing the Milky Way galaxy from the inside. Our galaxy is just one that makes up the vast universe. Our sun is just one of maybe over 100 billion stars that can be found in our galaxy. The shape of our galaxy, discovered through the use of radio waves as well as infrared radiation, has a nuclear bulge at the center, sort of like the yoke of an egg, around the nuclear bulge there is a halo, extending outward toward space there are spiral arms.
'Red shift' is a key concept for astronomers. The term can be understood literally - the wavelength of the light is stretched, so the light is seen as 'shifted' towards the red part of the spectrum. Something similar to this is the doppler effect, when a noise becomes louder as it approaches and then begins to fade as it moves away from you again. However, to be accurate, the red shifts observed in distant objects are not exactly due to the Doppler phenomenon, but are rather a result of the expansion of the Universe. A convenient analogy for the expansion of the Universe is a loaf of unbaked raisin bread. The raisins are at rest relative to one another in the dough before it is placed in the oven. As the bread rises, it also expands, making the space between the raisins increase.
This is the concept that scientists have used to determine that our universe is expanding at a pretty constant rate.
The moon’s gravity pulls the water toward the moon on the side of the Earth closest to the moon. There are 2 high tides and 2 low tides on Earth at all times.
Spring Tides
Spring tides occur during new and full moon phases.
That is when the Earth, sun and moon all line up to produce the strongest gravitational pull on the Earth causing unusually high tides.

Solar Eclipse
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