The Universe

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The Universe


The Universe is about 15 billion years old. How many galaxies are there? A rough estimate is 100 billion. There are approximately 200 billion star systems in each galaxy. Our sun-system, the earth and the human race are part of our "Milky Way Galaxy". Our Galaxy is about 100,000 light-years in diameter. It contains 200 billion stars like our sun, plus an assortment of nebulas and black holes. 

One of the myriad of galaxies: NGC 4314: A nuclear starburst ring. 

NGC 4314: A Nuclear Starburst Ring

Credit: G. F. Benedict (U. Texas) et al., WPFC2, HST, NASA

The barred spiral galaxy NGC 4314 is billions of years old and contains about 200 billion star systems. But, its appearance has changed markedly over just the past few millions of years. During that time, a nuclear ring of bright young stars has been evolving. The inset picture (lower right) shows the whole galaxy and boxes the small region around the core imaged by the Hubble Space Telescope. This inner region appears much like a miniature spiral galaxy itself, complete with dust lanes and spiral arms, even though it is only a few thousand light-years across.

Where Stars a born: NGC 604: A Giant Stellar Nursery

NGC 604: Giant Stellar Nursery

Credit: H. Yang (UIUC), HST, NASA

Scattered within this cavernous nebula, cataloged as NGC 604, are over 200 newly formed, hot, massive, stars.  At 1,500 light years across, this expansive cloud of interstellar dust is effectively a giant stellar nursery located some three million light years distant from our sun in the spiral galaxy, M33. The newborn stars irradiate the gas with energetic ultraviolet light, stripping electrons from atoms and producing a characteristic nebular glow.

Another Immense Galaxy: M 101

M 101: The Pinwheel Galaxy

Credit: W. Keel (U. Alabama), KPNO 4-m Mayall Telescope

Why do many galaxies appear as spirals? A striking example is M 101, whose relatively close distance to Earth of about 22 million light years allows it to be studied in some detail.  M 101 contains about 175 billion (billion, not million) stars. Recent evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to circle the galaxy. These waves compress existing gas and cause star formation. One result is that M 101, also called the Pinwheel Galaxy, has several extremely bright star forming regions (called HII regions) spread across its spiral arms. M 101 is so large that its immense gravity distorts smaller nearby galaxies.

A Matter of Perspective

The United States at Night

Credit and Copyright: NOAA/NGDC, DMSP Digital Archive

This is what the United States of America looks like at night. Can you find your City on this image? Surprisingly, city lights make this task quite possible. The above picture is actually a composite of over 200 images made by satellites orbiting the Earth. (USAF Defense Meteorological Satellite Program).

Andromeda: The Galactic twin to our Milky Way Galaxy

M31: The Andromeda Galaxy

Credit & Copyright Jason Ware 

Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about two million years for light to reach us from there. Much about M31 remains unknown, including why the center contains two nuclei.


Our Sun is to the Universe what a Grain of Sand is to all the Beaches on Earth. From the Perspective of the Universe, Man does not exist.


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Copyright Walter E. Requadt  All Rights Reserved