4. Earth's Setting in Space

The Universe

In that big totality called the university is a Local Supercluster, and in that Local Supercluster is a Local Galaxy Group. Somewhere in that is our Milky Way galaxy. Tugged into a corner of that Galaxy is our Solar system and within that, a Planet named Earth, our home. The known universe is about 28 trillion light-years in diameter, simply because that’s how far we can look into space right now.

A light-year is the distance light travels in a year, which is 9.46 trillion kilometers. This is enormous and very hard to grasp. Photo 8 below shows an image I took with my own digital Camera. It has a maximum shutter speed opening of 15 seconds and and ISO maximum of 1600, yet it was very hard to get a good image on this night where the sky was very clear. It does show the multitude of stars in the sky.

Photo 8: Stargazing with my Canon PowerShot SX10 IS. 2010-09-11

The Solar system

The Milky Way Galaxy formed about 12 billion years ago, our solar system 4.6 billion years ago. Our solar system has one sun, as opposed to a binary system, which has two suns. Earth is part of four terrestrial planets; the other ones are Mars, Venus, and Mercury. The four outer planets are the gas giants Jupiter, Saturn, Uranus, and Neptune. The Sun accounts for 99.8% of the total mass of our solar system. Of that 0.2% planetary matter, 99% is in the outer four gas giants, also called major or Jovian planets. Therefore, 0.002% of our solar systems matter is contained in the four inner planets. This means that the Sun is gargantuan compared to earth, located 149.6 million kilometers away from the Sun.

Planet Earth

The planets rotate around the Sun, not in a circle, but in an elliptical shape, being sometimes father away (aphelion) and other times closer to the Sun (perihelion). There are many things that can be said about the Earth’s rotation around the Sun.  One thing I would like to highlight is the Earth’s yearly Axis Tilt, which makes the sun seem higher in the sky in summer (photo 9) and lower in the winter. This creates our four seasons and the phenomena we know as Summer solstice (longest day) on 22 June, Winter solstice (shortest day) on 22 December, Vernal equinox on 21 March, and the Autumnal equinox on 23 September.

Photo 9: Sun angle a little after the noon hour, a week after summer Solstice, Lacombe, Alberta. 2011-06-28