galaxy stars and constellations study with facts

Galaxies, Stars & Constellations brief Study with Facts

A brief study of Galaxy, Stars and Constellations


What is a galaxy?

A galaxy is a massive space that contains hundreds of billions of stars, planets, glowing nebulae, gas, dust, and space. They take many forms, the three most common being spiral, elliptical, and Seyfert.

Andromeda and Milky Way are the two galaxies that even the most casual skyward-looking, earth-bound stargazers would have heard of. However, even the keenest enthusiasts couldn’t name the other forty-eight billion galaxies.

That’s right; there are an estimated fifty billion or so galaxies in the known universe.

Read more: Galileo Galilei- Biography, Facts, Discoveries & Telescopes

And why is there consternation over constellations?

For a start, constellations do not represent scientific groupings but are woven in with ancient mythology.

Over six thousand years ago, poets, farmers, and astronomers originally developed the concept of constellations, along with their associated myths, as memory aids.

Galaxy Forms

The shape of galaxies may be spiral, elliptical, or irregular. Both the Milky Way and the surrounding Andromeda Galaxies are spiral-shaped.


It is so-called because they have a group of objects at the center (stars and possibly a black hole), surrounded by a halo and an invisible cloud of dark matter, with arms spiraling out like a pinwheel. The spiral shape is formed because the whole galaxy is rotating.

Read more: Amazing facts about all 8 Planets


It Contains mostly older stars, with very little dust or gas. It may be round or oval, flattened or spherical, and resembles a spiral galaxy’s nucleus, but without the pinwheel arms.

Read more: Einsteins theory of relativity made simple


It is a bright elliptical galaxies with violent, fast-moving spirals that swallow other galaxies often.

Discovery of other galaxies

It wasn’t until 1924 that the existence of other galaxies was proven. American astronomer Edwin Powell Hubble (1889 -1953) made this discovery using a powerful 100-inch (254-centimeter) telescope at Mount Wilson Observatory. Long ago a cluster of stars was thought to be part of the Milky Way, but later found to be a separate galaxy, now known as the Andromeda galaxy.

Facts of Milky Way

The Milky Way is Earth’s home galaxy.

It consists of a sun and billions of other stars.

It is a spiral-shaped galaxy, approximately one hundred light-years in diameter and two thousand light-years thick from top to bottom.

In one of the four spiralling arms of the Milky Way Galaxy, called Orion, our solar system is located.

The Milky Way was given its name because astronomers believed the glowing band of light resembled a river of milk in ancient times.

Galileo Galilei was the first to examine the Milky Way by means of a telescope in the early 1600s.

Andromeda Fast Facts

The closest galaxy to the Milky Way is Andromeda at just 2.2 million light-years away.

Read more: Astronauts Health Effects of Space Travel

Andromeda is the only distant object beyond our galaxy that can be seen in the night sky with a telescope.

Hundreds of billions of stars are part of the Andromeda galaxy.

Andromeda measures one hundred light-years across.

Andromeda is easier to study than the Milky Way, despite being further away. This is because, from Earth’s position, many parts of our galaxy are blocked from view by dust.

Also known as M31, Andromeda refers to its position as the thirty-first non-star object to be cataloged in 1774 by the French astronomer Charles Messier.


So what are stars really? 

In purely scientific terms, each star is a mass of contained nuclear fusion. Deep within the star’s core, where the temperature is in the millions of degrees, nuclear fusion takes place.

Just as life evolved on Earth, so have the stars in our night skies. Yet these changes haven’t been apparent because stars last for billions of years.

How is a star born?

Put simply; a star is born when a hot cloud of gas and dust in space condenses. Depending on the cloud’s size, it may become a single star or a binary star (a system of two stars that orbit around a common cluster of gravity). Inside the star, a fusion of hydrogen into helium takes place, producing starlight. The fusion process is evidence a new star has been born.

How does a star keep shining?

As long as a star has a hydrogen to fuel fusion, the star will continue to shine. When a star’s hydrogen supply begins to run low, the star begins to die. What happens at the end depends on the size of the star.

How does a star end its life?

An average star will spend the final ten percent of its life as a red giant. In this phase, the star’s surface temperature drops, and its diameter expands from ten to one thousand times that of our sun. This phase causes the star to take on a reddish color. At the core, the remaining helium left burning finally casts off the atmosphere, which floats off like a planetary nebula. For an infinite time, the glowing core, called the white dwarf, is left to cool.

For massive stars (at least ten or twenty times the mass of the sun), the collapse results in a black hole. (A black hole is a single point in space where pressure and density are infinite. Anything that gets close to a black hole gets pulled in, stretched to infinity, and remains trapped forever.)

What is a black hole?

The term “black hole” describes a location in space with extremely high gravity. There is no hole per se, just a lot of gravity. NASA describes black holes as gravitational wells. The gravitational pull is so strong inside that well that nothing can escape its pull, not even light. With little light escaping, this makes black holes almost invisible and a challenge to study.

On Earth, a rocket needs to travel at 25,000 miles an hour to escape gravity. If the same rocket entered a black hole, it could travel at 671 million miles an hour (the speed of light) and still not escape from a black hole. Up till now we know that nothing can move faster than light, nothing can escape the black hole once it is in its clutches.

Many science fiction movies have had us sitting on the edge of our seats in suspense as a starship tries to escape being sucked into a black hole. Just how true would this be?

Black holes contain what is called an event horizon. It is actually the limit at which there is no point of return when reached. The item is forever and ever lost.

Outside the event horizon, the object still has a fighting chance to escape the phenomenal pull of a black hole’s gravity, just as some light does. Inside the black hole, all matter is infinitely stretched and, at the very centre of the black hole, is crushed to what physicists call a singularity in order to characterize matter infinitely compressed to a single point. A singularity is a mathematical term.


What is a constellation?

One of the eighty-eight clusters of stars in the sky is a constellation. The constellations, the imaginary sphere that surrounds the Earth, encompass the entire celestial sphere. The celestial sphere provides a visual surface on which scientists can plot the stars and chart their apparent movement caused by the Earth’s rotation.

The Major Constellations names

The major constellations stargazers look for today are:

Andromeda, Aquarius, Aries, Cancer, Capricornus, Cassiopeia, Cepheus, Cetus, Coron Borealis, Cygnus, Draco, Eridanus, Gemini, Hercules, Hydra, Leo, Libra, Lyra, Orion, Perseus, Pisces, Sagittarius, Scorpius, Taurus, Ursa Major, Ursa Minor Virgo.

Of course, mythology has influenced a great many aspects of astronomy other than the naming of the constellations. All planets bear mythological names that reflect their features.

The mythology of the Constellations

In Homer’s works, which may date to the 7th century B.C., the earliest references to the mythological significance of the Greek constellations can be found. For instance, Homer explains the creation of the shield of Achilleus by the artisan god Hephaistos in the Iliad.

It should be noted that at the time of Homer, most of the constellations were widely acknowledged as objects or animals; for example, the Lyre and the Ram.

However, by the 5th century B.C., many of the constellations had come to be known by myths. Eratosthenes’ Catasterismi completed the mythologization of the stars.

Despite the several mentions in Greek and early Roman texts of the stars, the most extensive ‘cataloguing’ of the stars belongs to the Roman Ptolemy of Alexandria, who grouped 1022 stars into 48 constellations during the 2nd century A.D. Although the constellations which can only be seen from the southern hemisphere are not included in Ptolemy’s Almagest, they form the basis of the modern list of 88 constellations officially designated by the International Astronomical Union.

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