Week of November 5, 2018

Astronomy

THE DIFFERENT TYPES OF GALAXIES

OUR GALAXY CLASSIFICATIONS

As discussed in the section on galaxy classifications, Hubble found four distinct types of galaxies: elliptical, spiral, spiral barred and irregular. Although there are different types, we also learned that each galaxy contains the same elements, but these are arranged differently for each type. Just as every human is created with the same proteins that are configured uniquely, so are the galaxies uniquely configured with gasses, dust, stars and other elements.

SPIRAL GALAXY

Spiral galaxies are easily identified by observing three components common to all spiral galaxies. A spiral galaxy has a disk, a bulge, and a halo. The center of the galaxy is like a nucleus, containing a sphere shaped bulge that houses old stars and is devoid of dust and gas. The circular shape of the galaxy composes the disk. The arms of the spiral galaxy originate in the disk and are where new stars will form in a galaxy.

The sun in our galaxy is located in one arm and its stars are created in this portion of the galaxy, which contains the most gas in the galaxy. This area is rich in blue stars. The Halo is a spherical shaped collection of old stars and clusters known as globular clusters that is found in the outer edge of the galaxy. This stunning view of Spiral Galaxy Messier 74 from NASA taken with the Hubble telescope shows a bright bulge in the center with the arms spiraling outward.

When a spiral galaxy has no arms, S0, it is termed lenticular. These galaxies are so similar to E7 that identifying them can be tricky. Lenticular galaxies also occur with barred spiral and are classified as SB0. Spiral galaxies are the most common galaxy of the known universe, comprising about 77% of all known galaxies.

BARRED SPIRAL GALAXY

Barred spiral galaxies share the same features and functions as regular spiral galaxies, but they also have a bar of bright stars that lie along the center of the bulge, and extend into the disk. The bright bulge has very little activity here and contains mostly older, red stars. The bar and arms have lots of activity.including star formation.

While the classification for barred spirals is the same as it is for regular spiral galaxies, the bar must be considered as well. Short bars correlate to tighter galaxies and will be included in the designation SBa. SBb have longer bars and SBc are the longest. Most astronomers now agree that the Milky Way is a barred spiral galaxy.

ELLIPTICAL GALAXY

Elliptical galaxies can be recognized by their elongated spherical shape and their lack of nucleus or bulge at the center. Although there is no nucleus, the galaxy is still brighter in the center and becomes less bright toward the outer edges of the galaxy. Stars, gases and other materials are spread throughout the elliptical galaxy. An elliptical galaxy can be nearly round or long and cigar shaped.

It is believed that a great deal of the mass in an elliptical galaxy is due to the presence of a central black hole. These galaxies have very little activity and contain mostly old stars of low mass, because there aren’t the gasses and dust needed to form new stars.

IRREGULAR GALAXY

Irregular galaxies are composed of gasses, dust, stars, nebulous formations, neutron stars, black holes and other elements common to all galaxies. Irregular galaxies are named so because they have no definite shape, but like all galaxies, they are in constant motion, moving outward and away from the center of our universe. Irregular galaxies are divided into two classifications: Im and IO.

Im galaxies occur most often among irregular galaxies and may show a trace of the spiral galaxy arms. IO galaxies are completely random and can be called chaotic in nature. The Magellanic clouds that border our own Milky Way Galaxy are examples of Im galaxies. Approximately 20% of our galaxies are classified as irregular.

https://theplanets.org/types-of-galaxies/

Rate of Change

A rate of change is a rate that describes how one quantity changes in relation to another quantity. If x$x$ is the independent variable and y$y$is the dependent variable, then

rate of change=change in ychange in x$\text{rate}\text{of}\text{change}=\frac{\text{change}\text{in}y}{\text{change}\text{in}x}$

Rates of change can be positive or negative. This corresponds to an increase or decrease in the y$y$ -value between the two data points. When a quantity does not change over time, it is called zero rate of change.

Positive rate of change

When the value of x$x$ increases, the value of y$y$ increases and the graph slants upward.

Negative rate of change

When the value of x$x$ increases, the value of y$y$ decreases and the graph slants downward.

Zero rate of change

When the value of x$x$ increases, the value of y$y$ remains constant. That is, there is no change in y$y$ value and the graph is a horizontal line .

Example:

Use the table to find the rate of change. Then graph it.

Time Driving (h) x246Distance Travelled (mi) y80160240$\begin{array}{|cc|}\hline \text{Time}\text{Driving}(\text{h})x& \text{Distance}\text{Travelled}(\text{mi})y\\ 2& 80\\ 4& 160\\ 6& 240\\ \hline\end{array}$

A rate of change is a rate that describes how one quantity changes in relation to another quantity.

rate of change=change in ychange in x=change in distancechange in time=160−804−2=802=401$\begin{array}{l}\text{rate}\text{of}\text{change}=\frac{\text{change}\text{in}y}{\text{change}\text{in}x}\\ =\frac{\text{change}\text{in}\text{distance}}{\text{change}\text{in}\text{time}}\\ =\frac{160-80}{4-2}\\ =\frac{80}{2}\\ =\frac{40}{1}\end{array}$

The rate of change is 401$\frac{40}{1}$ or 40$40$ . This means a vehicle is traveling at a rate of 40$40$ miles per hour.

 https://www.varsitytutors.com/hotmath/hotmath_help/topics/rate-of-change