Facts about the Milky Way

The planet we live in belongs to a large group of planets we call as the Solar System. This planetary system in turn belongs to a much larger network of stars, planets, and cosmic bodies known as the Milky Way Galaxy. How much do we know about the galaxy we live in? Here are some fun and quick facts about the Milky Way Galaxy.

• The Milky Way is a spiral galaxy containing 200-400 billion stars and at least 50 billion planets. New data suggests that there may be up to twice as many free-floating planets in the Milky Way as there are stars.

• The name “Milky Way” is from the Latin Via Lactea, in turn translated from the Greek word Galaxias, referring to the pale band of light formed by stars as seen from Earth.

 

• The stellar disk of the Milky Way is approximately 100,000 light-years or 9x10¹⁷ km in diameter. The Solar System is very small compared to the Milky Way. If the Solar System were as big as the size of a US quarter, approximately one inch in diameter, the Milky Way would be the size of New England or France. That is how insignificant the size of the Solar System is compared to the Milky Way.

• The Milky Way could be as old as the Universe itself. In 2007, a star in its Galactic halo, called HE 1523-0901, was estimated to be about 13.2 billion years old, nearly as old as the Universe. The star is the oldest known object in the Milky Way.

• The Milky Way is actually a barred spiral galaxy, meaning that the galaxy’s central bar is larger than previously assumed. Specifically, it is consists of a bar-shaped core region surrounded by a disk of gas, dust, and stars forming four distinct arm structures spiraling outward in a logarithmic spiral shape.

• The Sun and the Solar System is found in the galactic habitable zone, close to the inner rim of the galaxy’s Orion Arm. It travels through space in the Milky Way in the direction of the Apex of the Sun’s Way or the solar apex. Its motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The Sun’s orbit around the galaxy is roughly elliptical, and in addition, the Sun oscillated up and down relative to the galactic plane.

 

• The orbital speed of the Solar System about the center of the galaxy is approximately 220 km/s or 0.073% of the speed of light. At this speed, it takes around 1,400 years for the Solar System to travel a distance of 1 light-year, or 8 days to travel 1 AU (astronomical unit).

• There are many myths about the origin of the Milky Way. In Greek myths, the Milky Way was caused by milk spilt by Hera when suckling Heracles. In Sanskrit, the Milky Way is called as Akash Ganga, or Ganges of Heaven. It is considered to be sacred in Hindu, and the Ganges and the Milky Way are believed to be terrestrial-celestial analogs of each other.

Why Do Stars Twinkle?

Kids love to sing the nursery rhyme “Twinkle, twinkle, little star…” And kids are really right, for not only they but everyone “wonder what you are”. For like diamonds in the sky, they sparkle and glow. So do stars naturally flicker? If not, what makes them twinkle?

Stars are objects in the space that are balls of gases and fire. In our view here on Earth, they appear to twinkle. Twinkling of stars, scientifically referred to as stellar scintillation or astronomical scintillation, is due to the presence of thick layers of moving air in the Earth’s atmosphere through which we see them.

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All stars, except for the Sun, appear to be tiny dots in the sky because of their relative distance to us. As the light of the stars travel through several layers of turbulent air and impurities in the atmosphere, it is bent or refracted many times and in random directions. The total different refractions for star results to “sparkling” and “gleaming” which our eyes interpret as “twinkling.”

Stars closer to the horizon appear to twinkle more than those overhead of us. This is because these stars have travelled to more layers, and consequently refracted more times, than those just above us. That is why that the Sun that is nearest to us does not twinkle at all. Further, planets do not twinkle. They are so close to us that their twinkling is not prominent, except maybe when the air is extremely turbulent. So the next time you are looking out at the sky and see a “star” that does not twinkle, chances are that you are viewing a planet.

 

Assuming we are in the outer space and are star gazing. Do you think stars will twinkle? No, it is because the space has no atmosphere. Even with moons and planet with no atmosphere, twinkling is not possible. That is why, telescopes in the outer space, just like the Hubble telescope, are successful in giving precise astronomical data because of the absence of twinkling that gives better images of objects in space.