Ryan ICT

GALAXY

What Is Galaxy?

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.The word galaxy is derived from the Greek galaxias literally "milky", a reference to the Milky Way

Types of galaxies

EllipticalGalaxies

Spiral Galaxies

Irregular Galaxies

ELLIPTICAL GALAXIES

Elliptical galaxies are shaped like a spheriod, or elongated sphere. In the sky, where we can only see two of their three dimensions, these galaxies look like elliptical, or oval, shaped disks. The light is smooth, with the surface brightness decreasing as you go farther out from the center. Elliptical galaxies are given a classification that corresponds to their elongation from a perfect circle, otherwise known as their ellipticity. The larger the number, the more elliptical the galaxy is. So, for example a galaxy of classification of E0 appears to be perfectly circular, while a classification of E7 is very flattened. The elliptical scale varies from E0 to E7. Elliptical galaxies have no particular axis of rotation.

M89 - an E0 galaxy

M32 - An E2 galaxy

NGC 4621 - an E5 galaxy

Examples:

Irregular GalaxiesIrregular galaxies have no regular or symmetrical structure. They are divided into two groups, Irr I and IrrII. Irr I type galaxies have HII regions, which are regions of elemental hydrogen gas, and many Population I stars, which are young hot stars. Irr II galaxies simply seem to have large amounts of dust that block most of the light from the stars. All this dust makes is almost impossible to see distinct stars in the galaxy.

NGC 6822: NGC 1427A PGC 36867

Examples:

SPIRAL GALAXIES

Spiral galaxies have three main components: a bulge, disk, and halo (see right). The bulge is a spherical structure found in the center of the galaxy. This feature mostly contains older stars. The disk is made up of dust, gas, and younger stars. The disk forms arm structures. Our Sun is located in an arm of our galaxy, the Milky Way. The halo of a galaxy is a loose, spherical structure located around the bulge and some of the disk. The halo contains old clusters of stars, known as globular clusters.

NGC 5457 NGC 628 NGC 1187

Examples:

The Milky Way

WHAT IS MILKY WAY?

What is Milky Way?The Milky Way is shaped like a huge whirlpool that rotates once every 200 million years. It is made up of at least 100 billion stars, as well as dust and gas. It is so big that light takes 100 000 years to cross from one side to the other.The centre of the Galaxy is very hard to see because clouds of gas and dust block our view. Scientists think that it contains a supermassive black hole that swallows anything passing too close.Outside the main spiral are about 200 ball-shaped clusters of stars. Each 'globular cluster' is very old and contains up to one million stars. The Milky Way belongs to a cluster of at least 40 galaxies. The so-called Local Group has two large spiral galaxies – the Milky Way and Andromeda.

ORIGIN OF MILKY WAYThe Greek name for the Milky Way (Galaxias) is derived from the word for milk (, gala). One legend explains how the Milky Way was created by Heracles when he was a baby.[2] His father, Zeus, was fond of his son, who was born of the mortal woman Alcmene. He decided to let the infant Heracles suckle on his divine wife Hera's milk when she was asleep, an act which would endow the baby with godlike qualities. When Hera woke up and realized that she was breastfeeding an unknown infant, she pushed him away and the spurting milk became the Milky Way

Pictures of Milky Way

STARS

Meaning of StarA star is a luminous ball of gas, mostly hydrogen and helium, held together by its own gravity. Nuclear fusion reactions in its core support the star against gravity and produce photons and heat, as well as small amounts of heavier elements. The Sun is the closest star to Earth.

Why Do the Stars Twinkle?

The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation). Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere.

Stars (except for the Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air). This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).

Summary of Colors and Temperature of a Star

Sirius Betelgeuse

Arcturus

Example Of Stars (1):

Rigel Deneb Vega

Example Of Stars (2):

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Watching!!