NASA, Earth rise  Earth rising above the Moon's horizon (NASA: Apollo 11; July 1969)
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Window on the World

Our Milky Way Galaxy and Beyond

Our Latest Post: __ May 2019

An Overview with a Touch of Philosophy

Stairway to the stars (Mayan Temple of Kukulcan): a view of our Milky Way Galaxy from Yucat√°n, Mexico (Photo at https://pixabay.com/photos/Chichen-Itza-mexico-pyramid-1025099/ ) A galaxy is a group of many individual stars. Each galaxy is composed of many millions or billions of stars. Obser­vations of the Andromeda Galaxy made in 2006 (by the NASA Spitzer Space Telescope) revealed that Andromeda contains one-trillion or more stars. In contrast, our Milky Way Galaxy  Another view of our Milky Way Galaxy, Fairyland Canyon, Utah Credit - https://pixabay.com/photos/fairyland-canyon-utah-park-1632749/ The Milky Way Galaxy contains on the order of 300 billion stars. The Milky Way and Andromeda galaxies are expected to collide about 4-billion years from now, which is also about the same time that our Sun will grow larger and cooler, marking the demise of Mother Earth. Everything in the Universe is continually changing.

Andromeda Nebula (photo taken in January 1898; Wikipedia)  The Andromeda Nebula was observed by Persian astronomers in the year 905 CE. In 1764 CE, the Andromeda Nebula was cataloged as M31 by Charles Messier. Photo­graphs of Andromeda were taken in 1899 by Isaac Roberts that began to establish M31 as a galaxy. M31 is also cataloged as NGC 224.

Despite the immense size of even the smallest galaxies, most galaxies in the heavens are not visible to the naked eye. As telescopes became more and more powerful, more and more galaxies and stars became visible. In the present era, high-definition images are created at wavelengths that are far shorter and far longer than wavelength bands of human vision. Explore electromagnetic wavelengths at "What Our Eyes Cannot See"

Andromeda: Herschel Observatory, Europe Andromeda (M31): note the fine detail in this photo. Andromeda is unquestionably a galaxy (Herschel Observatory, Europe)

As time marches on, formation of colonies on the Moon and Mars will be routine events. On a negative note, however, visiting other solar systems in our own galaxy represents a major challenge, the limiting factor being the maximum speed of light 190,000 miles per second (300,000 kilometers per second). Visiting planets in other galaxies is, thus, a bit whimsical.

Note: The symbol " ~ " (tilde), as used here, is shorthand for " approximately" or "about"

Our nearest neighboring star (Proxima Centauri), is ~4.2 light years from our place in the Universe; earthly humans will need many years to travel to other planets outside of our Solar System. At half the speed of light, a one-way journey to Proxima Centauri would require more than eight years, and at one-tenth the speed of light, the same journey would take more than 40 years.

Just a Speculation: Our future journeys into space will necessarily be via self-contained, closed-loop habitat vehicles that self-produce food, textiles, building materials, and electricity. Solar energy would not be available for most of the trip, because of the great distances between the spaceship and neighboring stars; brightness diminishes by the distance squared (y = 1/x2; i.e. brightness is inversely proportional to the distance squared).

Because of the immense distance traveled from Earth, a journey of this nature must also include plans for the next generation that must proceed from the first generation of travelers. A one-way trip to our nearest star would require the implementation of social and legal structures and rules for procreation.

Pandor's Cluster (NASA, Hubble) Pandora's Cluster is a composite image constructed by blending radiation wavelengths from many telescopes and sensors into one image. Each color represents a specific wavelength. Whether (Image by NASA)

Before the late 20th century, the heavens were viewed only in visible-light wavelengths. In the 21st century, silver-halide (stan­dard photography) surrendered to solid-state semi-­conductor sensors and other masterpieces of exotic engineering that dramatically extended our view to wavelengths well-beyond our human vision. Nowadays, astronomers can view distant objects in a very wide range of electromagnetic wavelengths, which leads to new discoveries and better understanding of Nature. View in different wavelengths A bit of Shakespeare: What is a rose? "A rose by any other name would smell as sweet."  (Image reformed by RBKOR from several NASA images)

Seeing the world in dif­ferent wave­lengths changes our perceptions of ob­jects in the sky, as well as objects in our earth-bound environment. Although these images are different, they are all the same object. "A rose is a rose is a rose is a rose. (Gertrude Stein) with a little inspiration from Shakespeare.

 Zooming in: A very small area of the original Andromeda image (NASA, Hubble) reveals much detail. One might say that this image is a "microscopic" view of the "trillion-star" Andromeda Galaxy. (Edited by RBKOR from NASA image)

NASA's space-based Hubble telescope revealed an immense amount of image detail shown in this zoomed-in view of one tiny area of the original Andromeda image. Extreme (4k imagery) magnification uncovers innumerable stars.

At a distance from Earth of ~2.5-million light years (ly), Andromeda is among the closest galaxies in our galactic neighborhood, but closeness is relative:  Compare Andromeda's ~2.5 million ly with a mere ~4.2 ly from Earth to Proxima Centauri, our Solar System's nearest star. Proxima Centauri is gravitationally bound to the alpha- and beta-Centauri stars, but is not visible in this NASA image of the Centauri gravitationally bound three-star system.

Note:
The symbol " ~ " (tilde), as used here, is shorthand for "approximately" or "about"

A and B Centauri Ironically, our nearest neighboring star is not visible in this image, because Proxima Centauri appears as a faint, very cool, reddish point of light that is overshadowed by the two very bright hot stars, alpha- and beta-Centauri.

To carry this idea of relative distance a bit further, our Sun is only ~8-light minutes from Earth and our Moon is ~1.3 light seconds from Earth.

One may have wondered why there is a noticeable gap of silence when two people are talking to each other via satellite. The speed of light explains the phenomenon. Because all electromagnetic radiation travels at or near the speed of light, a synchronous (always in the same place in the sky) Earth-orbiting satellite is about a quarter of a light second from Earth's surface; a two-way conversation, therefore, is usually delayed by at least a quarter of a second each way; normally, however, more delay is added by terrestrial- and ocean-based cables and Internet routers (machines that direct Internet traffic).

Notes:  Light travels down a fiber-optic cable at nearly the speed of light; electricity travels down a wire also at or nearly the speed of light. The word "electricity" should more precisely read, "electrons".

Communicating here on Earth, however, does not have a noticeable delay, because the maximum, straight-line distance between any two points anywhere on the surface of the Earth is about 20,000 km (~11,000 miles); at a speed of 300,000 kilometers per second (186,000 miles per second), the minimum travel time between two points anywhere on the surface of the Earth is less than the blink of an eye, i.e. ~6/100 of a second' therefore, no one notices a delay.

Edge of Universe (NASA, Hubble)Nearly every smudge of light in this Hubble photo is a galaxy, not a star. The light from many of these immensely distant galaxies has been traveling through space for the past 12 or so billion years.

Many of the stars that appear to us on Earth at this time in history will no longer be alive in the far future, and conversely, many new stars will have replaced old stars that we see now. Millions of years from now, the sky will be different; our own Milky Way galaxy will be different. Ancient Asian and Latin philosophers observed that "everything changes".

To put these ideas into some semblance of comprehension, realize that our Earth is 4.5 billion years old. About 4-million years from now, the Andromeda Galaxy and our Milky Way galaxy will collide with each other, dramatically changing the geography of this part of the Universe.

When will our Universe die, the end of "Creation", or will it die? Is our Universe forever, perhaps? How might new discoveries and the magic of "quantum physics" shape space, time, and reality? No one nows, yet. Return to top of this page


Categorizing Galaxies

Milky Way Galaxy NGC 7331 is a spiral galaxy about twice the size of our Milky Way galaxy.  (Image Credit and Copyright: Dietmar Hager, Torsten Grossmann/NASA) A galaxy is a group of stars. Some galaxies are composed of many millions (x,000,000) of stars while other galaxies contain a trillion (x,000,000,000) or more stars. Our Milky Way Galaxy is home to billions of stars, while our Universe contains billions, and perhaps trillions, of galaxies. Our Universe is indeed quite immense.

Galactic structures appear in several forms, but nearly all galaxies are categorized by their distinctive shapes:
  1. Dwarf Galaxies   Large Magellanic Clouds (contain the youngest stars)
  2. Spiral:   Milky Way Galaxy
  3. Elliptical:  Sombrero Galaxy
  4. Globular Clusters:  Messier 2
  5. Irregular: 
  6. Super Giant: (contains the oldest stars)

Galaxies are classified by their shape. The more common galactic shapes are described below. The galaxy in which our Earth resides is called the Milky Way Galaxy, which is classified as a "Spiral" galaxy. Spiral galaxies resemble earthly hurricanes, having spiral arms that appear to rotate around a central bulge.

Hurricane Katrina (2005)Hurricane: Notice the "spirals" of the cloud cover. The shape of the spirals appears similar to spiral galaxies. (Photo by NASA)
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1. Dwarf Galaxies

Dwarf galaxies are the nurseries of the Universe. Dwarf galaxies, or nebulae (foggy clouds), contain young stars and tend to not have a well-formed structure, which is why many dwarf galaxies are referred to as "nebulae". As these dwarfs create new stars, these galaxies typically increase in size and they eventually form spiral galaxies, which in turn, evolve into elliptical galaxies.

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2. Spiral Galaxies

Our Sun and Solar System are whirling around in one arm of our "Milky Way Galaxy". The spiral arms contain dust and gas clouds, as well as stars, which appear as a "milky" haze that stretches across the evening sky.

The spacing of the spirals in a spiral galaxy follows an intriguing phenomenon in Nature, the Fibonacci Series, named after the Italian mathe­matician Leonardo Fibonacci (~1170–1240 CE). The first few numbers in the Fibonacci Series are: 1 1 2 3 5 8 13 21…. The spacing of planetary distances from the Sun closely correlates with the same ratio of 1.6:1 as the ratio represented in each pair of Fibonacci numbers.

The ratio between each pair of Fibonacci numbers are not only observed in the cosmos, but also observed in geology, biology, and zoology here on Earth. For example, snail shells, hurricane swirls, and the layout of seeds in a plant pod are all arranged according to the Fibonacci Series. This phenomenon is also referred to as the Golden Ratio.

===================================== Whirlpool Galaxy  Two galaxies on a collision course: The Whirlpool Galaxy (M51) was discovered in 1773 by Charles Messier, who cataloged objects in the sky, thus the "Messier Catalog".

  The Whirlpool Galaxy is in reality two galaxies inter­acting with each other. The streaks of red in the image indicate hydrogen, which indicates regions where stars are born.

Pinwheel Galaxy M101:, also known as the Pinwheel Galaxy, is 21-million light years from Earth and 170,000 light-years across, making M101 nearly twice the size of our Milky Way Galaxy.  (NASA Hubble)
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1. Spiral Galaxies

Spiral galaxies resemble the shape of hurricane clouds. Most stars in the spherical center, or bulge, of a spiral galaxy are older stars, while younger stars inhabit the outer areas of a spiral galaxy. Our Sun and Solar System are whirling around in one arm of our "Milky Way Galaxy". The spiral arms contain dust, as well as stars, which appears as a "milky" haze that stretches across the evening sky.

2. Elliptical Galaxies

Elliptical Galaxies are usually shaped like an ellipse. In visible light, they appear smooth, revealing no features, such as individual stars or dust-laden gaseous clouds. Structural detail, however, is uncovered when these galaxies are viewed in ultraviolet and infrared light or in other wavelengths of electromagnetic radiation, such as x-rays or gamma-rays. Stars found inside elliptical galaxies are very much older than stars found in spiral galaxies.

Stars found inside elliptical galaxies are very much older than stars found in spiral galaxies. Elliptical galaxies usually display minimal star-formation. One could suggest that galaxies, as do human populations, age as the birth rate declines. M60 Galaxy M60:  is an elliptical galaxy about 60-million light years from Earth and about 120,000 light-years across. Notice NGC 4647, a spiral galaxy that is visible in the upper right corner of the figure (Australian Astro­nomical Observatory).

An international collaboration discovered a super-massive black hole inside M60, the smallest known galaxy, which is paradoxically the location of one of the largest black holes ever discovered. An apparent close neighbor of M60 is a spiral galaxy that is much smaller than M60, NGC 4647 (upper right).

Andromeda, Nebula or Galaxy? Until the 19th century, observations of the heavens revealed only a small amount of blurry detail about heavenly objects. Compare the two images of the same galaxy.

The Andromeda Nebula was first observed as a smudge of light (insetco5>, upper right) and consequently was called a "nebula". As telescopes improved, more and more detail was discovered. The former Andromeda Nebula is now known as the Andromeda Galaxy. Reality is what our eyes often do not see.

M5 is a globular cluster  Somewhat confusing is that globular clusters and galaxies are very similar in appearance and both can be described as groups of stars.


3. Globular Clusters

Globular Clusters are spherically shaped concentra­tions of stars that typically reside within the central core of galaxies and typically contain the oldest stars in their respective galaxies. We might say, "a globular cluster is a galaxy within a galaxy." In 1665, the first globular cluster was discovered and was labeled M22.

Large Magellanic Cloud The Large Magel­lanic Cloud is an irregular galaxy, having some resem­blance to a spiral galaxy. The Large Magellanic Cloud is in our galactic neighborhood, only 180,000 light years away from us.  (Photo by NASA/Ames Research Center in Public Domain)

4. Irregular Galaxies

Oddly shaped galaxies that do not resemble any of the more common forms listed above. Many of these irregular galaxies are among the oldest galaxies in our Universe. Younger galaxies seem to have more describable shapes. In visible light, irregular galaxies appear smooth, revealing no features, such as individual stars or dust-laden gaseous clouds. Structural detail, however, is uncovered when these galaxies are viewed in ultraviolet and infrared light or other wavelengths of electromagnetic radiation, such as x-rays or gamma-rays. A dense region of the larger of the two Magellanic Clouds shown here reveals many structural details.

5. Super Giant Galaxies

Among the billions upon billions of galaxies and clusters of stars flying around the Universe, the largest and brightest, thus far found, is the dying elliptical galaxy, IC-1101 in the constellation Virgo. Containing 100,000,000,000,000 stars and about 1,000,000,000 light years (1 ly = 6 trillion miles ~9-trillion kilometers) distant from Earth, telescopes at the time of IC-1101's discovery in 1789, could reveal very little of the structure of heavenly objects; at the time, objects in the sky appeared as smudges of light when viewed through early telescopes.

Another limiting factor at the time was the inability to observe objects beyond visible light. As measurement instruments opened the weay to observer objects wavelengths beyond visible light. Observing objects in infrared, ultraviolet, and x-ray wavelengths revealed much more information about individual stars, as well as galaxies.

Modern telescopes have drastically increased our ability to see very fine structural detail and to see in many different wavelengths of electromagnetic radiation, which includes visible light that our human eyes can see. We could say that our Milky Way Galaxy, as well as the Universe itself, has revealed much information about how celestial objects shine for billions of years, how they are born, mature, and die when these objects are viewed in wavelengths that are longer or shorter than visible light. In the last several decades, we can see much that was formerly invisible to humans.


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