Structure and Composition of the Universe

big bang questions

-Before the big bang, what was the universe like? Prior to the big bang, the universe was an extremely hot, dense core. -What happened to the temperature of the universe as it expanded after the big bang? During the big bang, the universe expanded rapidly while cooling considerably. think icon -What were the first atoms to form after the big bang? As the big bang continued, protons, electrons and neutrons formed. Eventually, these particles organized to form the first atom of hydrogen. think icon -Is the universe still expanding today? How do we know? In 1929, Edwin Hubble observed that the galaxies in our universe appear to be expanding outward at speeds proportional to their distance. This observation later became known as "Hubble's law." Hubble's law supports the idea that the universe is expanding. If the universe is continually expanding, it is logical to assume that it was once much more compacted than it is now. think icon -What evidence supports the big bang theory? In 1965, astronomers discovered cosmic microwave background radiation that is thought to be left over from the extremely hot dense core that preceded the big bang. The existence of this background radiation supports the big bang theory.

an expanding universe

A strong line of evidence in support of an expanding universe is something called the cosmological redshift. This has to do with the way we perceive radiation from other objects in the universe. Light waves are a form of electromagnetic radiation. Because the universe is expanding, the travelling light waves become stretched out. Their color appears to move from the blue end to the red end of the light spectrum. Scientists call this a redshift. The light we see from far away galaxies appears reddish rather than white. The farther away galaxies are, the redder they appear.

irregular galaxies

All other types of galaxies are collectively called irregulars. They have irregular shapes or peculiar morphologies

3rd century BC Aristotle

Aristotle believed that knowledge about the universe should come from observation and experience. He believed that all regions of the universe, from Earth to the Moon, were made only of one of four possible materials. These materials are earth, air, water, or fire, and each type of matter was perishable. Aristotle believed the other bodies in the universe, such as the stars and the planets, were made of a type of permanent, nonperishable material he called aether. He also believed that the motions of the planets were eternal and perfect, and since philosophers of his day believed that the circle was the perfect shape, Aristotle believed that objects in the universe must therefore move in perfect circles.

A star's parallax angle is found to be 0.77. How far away is the star in parsecs? In light-years?

Distance is 1/p, so the star is 1/0.77 = 1.30 parsecs away. This is 4.23 light-years away

dark energy/the composition of the universe

Everything on Earth is made of ordinary atoms—like atoms of carbon or oxygen or hydrogen. Most things are made of compounds of atoms, when two or more atoms of different types combine. Water, for example, is a compound that forms when atoms of hydrogen combine with atoms of oxygen. Anything made up of ordinary atoms is called baryonic material. Your body and all of your surroundings are made of baryonic material. Slide 2 For many years, scientists believed that the universe was made of baryonic material. But evidence shows that it is not. What scientists have noticed is that there are gravitational effects on visible matter. Because the matter acts like something is pulling it, scientists have come up with theories to explain it. Scientists believe there must be some type of energy and matter that are causing these effects. They call them "dark energy" and "dark matter" because we cannot see them. Dark matter cannot be detected because dark matter does not emit or absorb light. Dark energy is the source of the energy needed to keep the universe expanding. This hypothetical type of energy, called dark energy, makes up 70 percent of the universe. Twenty-three percent of the universe is made up of dark matter. Of the very small percentage of the universe that is made up of baryonic material, the most abundant element is hydrogen. Helium is the second most abundant. All of the stars and planets and the gases in outer space are baryonic material. These only account for about three to four percent of the inferred mass of the universe. Slide 3 In this picture, you see a telescopic image of distant stars and galaxies. Notice arcs of blue light in some parts of the picture. The arcs show places where light is being bent by the influence of gravity from matter that cannot otherwise be detected—evidence scientists use to explain their dark matter and dark energy theories.

1500s Copernicus

In the 15th century, Nicholaus Copernicus challenged the geocentric view of the universe with the heliocentric view. The word heliocentric means sun-centered. Copernicus argued that the sun is the center of the universe and that the earth and other planets make regular movements around the sun in perfect circles.

15th century BC Ancient Hindus

In the 15th to 8th centuries BC, the ancient Hindus put together some of humanity's first written discussions of the universe. This group of people from ancient India believed that the universe goes through cycles of creation, destruction, and rebirth, with each cycle lasting more than four million years. Their ideas are recorded in the Vedas, the sacred texts of ancient Hinduism. Sanskrit

2000s Today

It has been hundreds of years since Copernicus, Kepler, and Newton developed their ideas about the universe. In modern times, we can use high-tech telescopes and actual space travel to expand our knowledge of the universe

light years

One common unit of distance used in astronomy is the light-year. A light-year is defined as the distance that light travels in one Earth year. It is equal to just under 10 trillion kilometers. But scientists do not usually convert light-years to kilometers or miles; they simply speak in terms like "3.6 light-years away," or "12.8 light-years from Earth," etc. In this picture you see that Alpha Centuri, the closest star to Earth besides our Sun, is 4.3 light-years away from us. This is the same as 23,462,794,000,000 miles away.

how many light years are in 5 parsecs

One parsec is 3.26 light-years. So five parsces (5 x 3.26) = 16.3 light-years.

1st century AD Ptolemy

Ptolemy lived in the first century AD. He had what is called a geocentric view of the universe. The word "geocentric" means Earth-centered. Ptolemy believed that the Earth is the center of the universe, and that the other heavenly bodies move around the Earth.

1600s Johannes Kepler

Shortly after the work of Copernicus, work by Johannes Kepler used math to show that the planets move not in perfect circles but in ellipses, or elongated stretched out circles, around the sun. By the 1600's we had a view of the universe that included a sun with planets moving around it in elliptical paths.

parallax

There is an apparent shift in the position of the stars due to a change in Earth's location. This is referred to as the parallax of the stars. The amount that the stars appear to move during that 6 month time is called their parallax angle. Scientists have worked out mathematically that the distance from Earth to a star is 1 over the parallax angle, or d = 1 over p. This equation gives us a distance in units of parsecs, which we can convert to light years if we want to. Scientists have been carefully determining the parallax angle values for individual stars for hundreds of years. With this data, they have been able to calculate the distance to those stars from Earth. Parallax works well for measuring stellar distances for stars that are no more than a few thousand light years away. For stars that are farther away, parallax values become too small to be of much worth, and we have to use other methods of determining their distance. One of these methods relies on the apparent and the absolute magnitudes of stars.

bingo questions

True Feedback: The big bang model says that the universe is still expanding today. 2. False Feedback: The big bang model says that the universe was originally hot and dense and has subsequently been expanding and cooling. 3. False Feedback: We observe that the distance between galaxies is expanding. 4. False Feedback: According to the big bang model, the universe has been expanding outward for billions of years. 5. True Feedback: The big bang model asserts that the fabric of space is expanding outward. 6. True Feedback: The background of space is filled with radiation that does not come from any object. 7. True Feedback: Light waves become redshifted as they move away from us in space. 8. False Feedback: As distant galaxies move away from us, the radiation that comes from them approaches the red end of the electromagnetic spectrum.

1600s Issac Newton

With calculus Newton was able to describe the motions of planets better than anyone before him. His calculations showed that the same force of gravity that makes objects on Earth fall downward also works on planetary objects to keep them in their orbits. Newton's universal law of gravitation states that all objects exert a force on all other objects; and that the strength of that force is dependent on the mass and the distance between them.

parsecs

You may also see stellar distances measured in units called parsecs. The galaxy you see in the picture is about 17,000 parsecs in diameter. A parsec is a unit of length used in astronomy and is equal to about 31 trillion kilometers (or 19 trillion miles). So this galaxy is 17,000 x 31 trillion kilometers in diameter. A parsec is also equal to 3.26 light-years. The parsec is an SI (International System of Units) unit of measurement. Like other SI units, we can add prefixes to it to increase its value. Just like we can add the prefix "kilo" to "meter" to mean 1,000 meters or one kilometer, we can add the prefix "mega" to "parsec" to mean one million parsecs or one megaparsec. Parsecs are most appropriate for measuring distances within our galaxy; the megaparsec is best for measuring the much more immense distances between galaxies.

parsec

a unit of astronomical distance equal to about 3.26 light years, or 19 trillion miles

redshift

an increase in the wavelength of radiation emitted by a celestial body

stars

are massive luminous balls of plasma held together by their own gravity. Our Sun is a star and is the closest star to Earth. We see millions of other stars in the night sky that are farther away than the Sun.

spiral galaxies

consist of a rotating disk of stars, gas, and dust around a central mass of older stars. Spiral galaxies are named for the spiral arms that extend from the center of the disk. These arms are areas where stars are formed. The arms are brighter than the central part of the disk because of the young, hot bright stars that are found within them. Our own Milky Way galaxy is a spiral galaxy.

elliptical galaxies

have elliptical shapes, but may vary in just how elliptical they are; they may be highly elongated or nearly spherical. These galaxies can grow to enormous sizes and are generally dominated by older stars that orbit a common center of gravity in random directions. Elliptical galaxies are made of very little dust and gas, and so there is little formation of new stars in these galaxies. They make up about 10 to 15 percent of the galaxies in the universe

nebula

is a cloud of dust and gas. Nebula may become big enough to collapse under their own gravity and form stars.

blackhole

is a massive object in space. It has such an intense gravitational field that it prevents any object or form of radiation from escaping it. Because even light cannot escape their gravitational hold, they are invisible and cannot be seen, hence the name, "black" holes. Black holes have not been directly observed but scientists believe they exist because of the effects they have on their environment.

galaxy

is a system of stars, gas, dust, and other planetary objects held together by gravity. Our solar system is part of a galaxy called the Milky Way Galaxy. There are billions of galaxies in the universe, each containing billions of stars.

planetary system

is made of a central star and various other non-star objects orbiting around it. Our Sun and all the planets that orbit it make up a planetary system called our solar system. Several other planetary systems have been identified across the universe.

parallax

the apparent shift in position of an object when viewed along different lines of sight

big bang

the big bang model is based on evidence and observation. It is based on the idea that, initially, the universe was a hot dense sphere, and that it has expanded, and is still expanding today. This theory states that at some very ancient time—at a moment known as the big bang—the sphere exploded and space itself began expanding. And like the dust on the surface of an inflating balloon, all matter simply rode along on the expanding space.

light year

the distance that light travels in one year

absolute magnitude

the magnitude, or brightness, a star would have if viewed from the same distance as all other stars

apparent magnitude

the magnitude, or brightness, we perceive from a star based on its distance away from us