When you study astronomy, it helps you to learn about yourself as a human. Science gives you a way to know how nature works. We are “planet walkers.” The planet you live on whirls around a star, drifting through a universe filled with other stars and galaxies, the result of billions of years of events and evolution. I will give you an introduction to some key terms and introduce the topic of astronomy.
I will now help you answer the following questions:
- Where are you in the universe?
- How does your lifespan and human history fit into the age of the universe?
The scale of the universe
Our cosmic address
Our cosmic address begins from the smallest spot in the universe where you live, to the more general and wide areas, as follows:
- Earth
- Solar System
- Milky Way Galaxy
- Cluster of Galaxies (a.k.a local galaxies)
- Super Clusters
- The filaments and walls (These go around the voids in the universe)
What is a star?
A large, glowing ball of gas that generates heat and light through nuclear fusion.
Some distances:
To avoid large numbers that exceed our imagination, we use different units that may be unfamiliar. This would be the unit AU (Astronomical unit). This unit is the distance between the Earth and the Sun. In Kilometers, this distance is 150,000,000 km.
The distance between the Earth and the Moon is around 384,000 km.
What is a planet?
A moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition.
What is a Moon (or satellite)?
It is an object that orbits a planet.
- The terms "moon" and "satellite" are often used interchangeably, but artificial objects are usually referred to as satellites, not moons.
What is an asteroid?
They are relatively small and rocky objects that orbit a star.
Note that it has a non-spherical shape; small objects are often non-spherical because their gravity is not strong enough to compress the material into a sphere.
Asteroids are sometimes referred to as “minor planets” because they orbit much like planets, but are smaller than anything we consider to be a true planet.
What is a comet?
They are relatively small and icy objects that orbit a star.
- The basic difference between an asteroid and a comet is composition – comets have tails only when they come close to the Sun, not when they are much further away.
What is a Solar (Star) System?
A star and all of the material that orbits it, including its planets and their moons.
The Solar Neighborhood
The Solar Neighborhood is a body of stars or celestial bodies that are near our Sun within the Milky Way Galaxy.
- It is 17 light-years away
- 1 light year (ly) = The distance traveled by light in 1 year (Also equal to 63,000 AU or 10 trillion km)
- The speed of light is 3 x 108 m/s (186,000 miles per second)
- The nearest star to the Sun is Proxima Centauri, at a distance of 4.2 light-years away.
What is a Galaxy?
It is a great island of stars in space – held together by gravity; orbiting around a common center.
- The diameter of our galaxy, the Milky Way galaxy, is 80,000-1000,000 light-years. (Light-years are both a distance and a time; it can be complicated)
- The distance to the nearest large galaxy is several million light-years.
What is a Universe?
The total of all matter and energy, i.e., everything within and between all galaxies.
Looking back in time
- Light travels at a finite speed. (300,000 km/s)
- Here are some of the known times of how long light takes to reach its destination:
- Here are some recorded times for light to reach its destination:
- Earth to the Moon: 1 second
- The Sun to the Earth: 8 minutes
- Sirius (The brightest star in the night sky) to Earth: 8 years
- Andromeda Galaxy (The nearest galaxy to our own) to Earth: 2.5 million years.
- Thus, we see objects as they were in the past: the farther we look into the distance, the farther we go back in time.
Thank you to Geetha S. for editing this article!
