Unified Science Chapter 13 (Stars and Galaxies), Section 4: Galaxies and the Universe, pp. 386-391.

la Vía Lactea (imagen)

(the Milky Way)

What is an irregular galaxy?

A galaxy that does not have a regular shape such as a spiral or an ellipse. Irregular galaxies are SMALLER than the other types of galaxies. 2 irregular galaxies called the Clouds of Magellqan orbit the Milky Way.

What is a galaxy?

A large group of stars, gas, and dust held together by gravity. Note that a NEBULA is a large cloud of gas and dust held together (& pulled!) by gravity...a galaxy is different because it also has STARS.

Like many galaxies, what does the Milky Way have at its center?

A supermassive black hole that may be more than 2.5 million times as massive as the Sun. Evidence comes from X-ray emissions and from observing the orbit of a star near the galaxy's center.

What is an elliptical galaxy?

An elliptical galaxy is shaped like a large, 3-dimensional ELLIPSE (círculo "aplastado" o en forma de óvalo) ...many are (American) football-shaped, but others are so large that several Milky Way-sized galaxies could fit (podrían caber) inside them.

Doppler Shift effect for light (image)

As light moves closer, light shifts to the red end of the spectrum (elongated wavelengths appear); as light moves closer, light shifts to blue end of spectrum (compressed wavelengths appear).

What is Red Shift and why is it important?

Edwin Hubble observed that in light coming from most galaxies beyond our Local Group galaxies, a red shift occurs in the light (a change to more red light). Because all galaxies beyond the Local Group show this Red Shift in the light spectrum, they must be moving away from Earth, i.e., the entire universe is expanding. (NOTE: In image, approaching=que se acercan; receding=que se alejan)

How are galaxies grouped? (¿Cómo se agrupan las galaxias?)

Galaxies are grouped in clusters (bonches) like stars.

Is the Milky Way a normal spiral galaxy or a barred spiral galaxy?

It is unclear which one it really is. It is often classified as a normal spiral galaxy, but recent evidence suggests the Milky Way may be a barred spiral galaxy.

What is the name of the cluster that the Milky Way is part of?

It's called the Local Group. It contains 45 galaxies of different types & sizes.

Big Bang theory vs. Oscillating (Big Crunch) theory

Some supporters of the Oscillating theory agree with the Big Bang theory that the universe has been expanding, BUT they say that it will eventually start to contract again over time to a single point (resulting in a Big Crunch or reduction)and will not continue to expand continually. They think this will happen because of the forces of gravity (if enough matter exists).

What 2 categories of spiral galaxies exist?

Spiral galaxies can be normal or barred. In a NORMAL spiral galaxy, arms in a normal spiral start close to the center of the galaxy. In a BARRED spiral galaxy, spiral arms extend (se extienden) from a large bar of stars and gas (de una larga barra / banda de estrellas y gas) that passes through the center (que atraviesa el centro) of the galaxy. (NOTE: The arms in the BARRED galaxy in the picture do not start in the center; they start or connect at the end of the central bar of light / stars)

What is a third theory or model to explain the origin of the Universe?

The Big Bang Theory says that the universe started with a big bang or explosion and has been expanding ever since then (continuamente desde entonces).

When scientists discovered the universe was expanding because of the Red Shift beyond the Local Group of galaxies, what theory about the origin of the universe did they develop?

The Big Bang Theory. It says that approximately 13.7 billion years ago, the universe began with an enormous explosion & the entire universe began to expand everywhere at the same time.

Why can't we see the shape of the Milky Way (la Vía Lactea)?

We can't see the shape of the Milky Way (la Vía Lactea) because we are located inside one of its spiral arms. We can see the Milky Way stretching across the sky as a band of faint light (luz tenue)---see image. NOTE: Technically, all the stars you can see in the night sky are part of the Milky Way.

Do other galaxies exist? How distant are they from each other?

Yes, countless (un sin número de) other galaxies exist. Galaxies are separated by (se separan por) enormous distances...often millions of Light Years.

pinwheel (image)

molinete

What are the 3 major types of galaxies?

spiral, elliptical, and irregular

What cluster of galaxies to the Magellanic Clouds, or Clouds of Magellan (irregular galaxies) form part of?

the Local Group of galaxies, the same group that the Milky Way is in.

Clouds of Magellan or Magellanic Clouds in night sky (image)

Magellanic Clouds are purple or violet in color in this picture.

What is a spiral galaxy?

Spiral galaxies are galaxies that have spiral arms that spin outward from the center like a pinwheel (molinete). The arms consist of (consiste en) bright stars, dust, and gas. The Milky Way is a spiral galaxy.

What is the Doppler Shift?

The Doppler Shift effect occurs with light and with sound; it causes changes in the wavelengths (longitud de onda) to occur as the source (la fuente) comes closer or moves farther away (se acerca o se aleja). If a star moves closer to earth, its wavelengths of light are compressed (se comprimen); if a star moves away from earth, its wavelengths are stretched (se alargan, se estiran).

What is the name of the galaxy where our Earth and solar system are? How many stars might it contain?

The Milky Way; it might contain up to one trillion stars.

What is another theory or model to explain the origin of the Universe?

The Oscillating Model (modelo oscilante) says the universe began with expansion, but then expansion slowed and contraction began. Then, expansion began again and later contracted again i.e., oscillated, going back and forth between expanding and contracting. Some scientists still think the universe may expand and contract in a cycle. (Don't worry about the balloon in the slide!)

What is one theory or model to explain the origin of the Universe?

The Steady State theory (teoría Estado Estable o Estado Estacionario) says the universe has always been the same as it is now; that it always existed and always will. As the universe expands, new matter (materia) is created (se crea) to keep the overall density the same, or steady (estable, estacionario).

Where is the Sun in our Milky Way galaxy?

The Sun is about 26,000 Light-Years from the center of the galaxy in one of the spiral arms; it takes about 225 million years for the Sun to orbit the center of the Milky Way. NOTE: In a galaxy, all stars orbit around a central region, or core.

Where is the Sun in our Milky Way galaxy? (image)

In one of the spiral arms, ~26,000 Light-Years from the center of the galaxy.