A very brief introduction to astronomy|
Humans have always looked up at the clear night sky. We have been fascinated by the stars and the Moon and the regular movements of bodies in the sky. |
What is it then that we are gazing at? Well, first we have to remember that what we actually can see with our eyes is a very small part of the electromagnetic spectrum, which goes from radio waves to gamma rays. That means that the information we can get through our eyes is somewhat limited.
If we look at our solar system we have of course the Sun and the nine planets and their moons. Then there are also some smaller bodies in orbit like asteroids, comets and meteors.
The Sun is basically a gaseous sphere where gravitation creates enormous temperatures in it's center. These high temperatures will start a nuclear reaction that turn hydrogen into helium, emitting a lot of energy during the process. The Sun consists mainly of hydrogen and helium and only small amounts of heavier materia. This is the recipe for a star and the way all stars generate energy under normal conditions (in a big star the nuclear process can go beyond the hydrogen > helium stage and produce heavier elements up to iron).
The inner planets Mercury, Venus, Earth and Mars are rocky bodies with none or very little gas around them and are called terrestrial planets. The much larger gas giants Jupiter, Saturn, Uranus and Neptune have a thick gaseous shell around a solid core. Pluto is a small body made of rock and ice and if it was found today, it would hardly be called a planet. (IAU has 2006.08.24 decided that Pluto is no longer a planet. It belongs to a group called dwarf planets). All planets but Mercury and Venus have at least one moon.
All planets except Pluto, Neptune and Uranus can be found without any optical aid and with a good pair of binoculars only Pluto is undetected. With a telescope it is possible to see planetary details and find some of the larger moons of other planets and also a lot of surface detail on our satellite the Moon. The smaller bodies of our solar system need some kind of optical aid to be seen, except for some comets that can be seen with the naked eye.
When we look beyond the solar system we reach the deep sky and the objects we can find there :
- Materia for making stars, principally gas clouds (mainly hydrogen).
- Stars under formation.
- Different types of stars (variable, double, spectral type, size...).
- Stars in groups (open clusters, globular clusters, galaxies...).
- Dying stars.
- Remnants and materia of former stars.
All this is ruled by a king named Gravitation.
This sounds rather monotonous but fortunately there is more visual variation than what the list suggests. Only a few of these deep sky objects can be found by the naked eye and we need a telescope to see any detail in them.
A few words about distance.
For a beginner (and even for a experienced one) it is hard to grasp the vast distances of astronomy. It is a good idea to downscale to a understandable level. If we compress the Sun to the size of an orange (diameter = 11cm, 800 billion times smaller than the real size) we do have a good starting point.
When we look at the size and the mean distance of the planets in this scale we will find:
-The diameter of the earth is 1 mm and the distance from the Sun (the orange) is 12 m.
-The Moon is found 3 cm from the earth and the diameter is only 0.35 mm.
-Jupiter, the giant among planets has a diameter of 1.14 cm (the size of pea) and orbits 64 m from the Sun.
-Pluto is found 470 m from the sun and the diameter is smaller than the one of the Moon.
-In this scale the nearest star (orange) Proxima Centauri is found 3200 km away! (Approx. the distance from New York to Salt Lake City or Stockholm to Cairo).
Let's continue the downsizing. We shall squeeze the diameter of the orbit of Pluto to 2.5 cm (940 m in the previous example to the size of a coin).
In this scale the disk of our own galaxy the Milky Way will have a diameter of 2100 km and cover about half of the USA. If we go even another step further and compress the Milky Way until its diameter is 2.5cm the nearest large galaxy M31 is about 30cm away. The nearest larger galaxy cluster the Virgo-Coma cluster is at a distance of 6m. The scale we are now using is 1 : 1.33e-23 or in other words: we have compressed the universe 755,000,000,000,000,000,000,000 times in three steps.
If you remember that when the Sun had the size of an orange, the Moon was approx. 3cm from the earth. This is the only space traveling mankind has done so far and that with a great effort. This reveals that our ability for traveling in space is very very limited; we can only dream of going to other stars and journeys to other galaxies goes right back to the science fiction where it started (sorry Han Solo).
So why all these pictures?
There are many reasons for practicing astrophotography.
The information of a picture can be seen any time and not only outside in the middle of the cold night. If the picture is in color, there is information of the kind of materia and the process that is taking place. At low light levels the human eye turns b/w and looses its capability to distinguish colors. From longtime or stacked exposures we can see much more detail than it's possible to do visually through a telescope.
And finally. Though it's a challenge to get good pictures of different kinds of celestial objects, it is also rewarding because besides from being aesthetically appealing the images also work as very small keyholes to the universe.