The Basics of Astronomy

The Basics of Astronomy

Astronomy has been studied since ancient times, though it may have always gone by that name. When you think about it all things that exist on Earth have at least some dependence on Celestial Objects most notably the Sun. Our calendars and measurements of Time are based on Celestial Movements, all of the Weather we see is given strength by the Sun’s Rays, the Seasons and harvest Times are all due the orientation of the Sun. It is no wonder that almost all Ancient people revered the Sun and the Night sky, and we continue to do so today.

Still throughout most of History Astronomy was not studied as the science we know it today. People still used mathematics and geometry to determine many facets of how the heavens moved, but for a slightly different purpose than we do today. I speak of course of Astrology, the study of how the movements and orientations of the planets and stars both affect and predict everyday life. In today’s scientific terms Astrology has little merit as its claims cannot be tested and are often very vague, it along with many forms of Divination have been deemed unscientific and unfounded. Still before the Scientific Revolution Astronomy and Astrology were considered one and the Same, and many of the great minds that developed Astronomy as we know it cast Horoscopes and made predictions with Astrology.

I wish I could discuss all of the Great minds and ideas that founded Astronomy, as well as some of the early pitfalls, but there is just so much to speak of. Perhaps if enough people show interest in the Subject I will do my best to write a detailed History, or you could always go research the subject yourself.

Size and Scale of the Universe

To Quote the Hitchhikers Guide to the Galaxy, “’Space,’ [The Guide] says, ‘is big. Really big. You just won't believe how vastly hugely mind-boggling big it is. I mean you may think it's a long way down the road to the chemist, but that's just peanuts to space.’”

Indeed, space is so large and vast, that the human mind cannot even comprehend the distance from the Earth to the Sun, much less to another Star.

Still, scale models help, and so do some helpful analogies.

Let us begin with the Speed of light. To our eyes light travels so fast that it appears to be instantaneous, but of course it just travels amazing fast (in fact faster than anything else can travel). Light moves at roughly 3,000 Million meters per Second, which is fast enough to Travel around the Earth about 7500 times in one second! And yet it takes light a full 8 minuets to travel from the Sun to Earth.

Let us also look at a scale model to give us a feel for the size of the Sun compared to the Earth, as well as distance. In our model we will say the Sun is the size of a Grapefruit (you can hold it in your hand). In this model the Earth is the size of a ball point in a pen and is 15 meters from the Sun, while Jupiter (the largest planet) is still just the size of a Marble. Pluto (the furthest “Planet”) is 600 meters from the Sun, and that would still not even be the edge of the Solar system! If we were to place the next nearest star in this model, it would be 4,000,000 meters away from the Sun!

Just in case your mind still needs more boggling, let us look at the amount of time we believe has passed since the Universe first came into existence. For this model we will compress all this time into the Span on one Year, and examine the dates things happened. So if we say the Universe Began promptly at Midnight of January 1st, the Earth then formed in September! The Dinosaurs Evolved just after Christmas, and quickly passes away about 4 days later! Humans didn’t evolve until 9pm on December 31st, and the Pyramids were built just 11 seconds ago!

The Study of Light

Thanks to Science Fiction, movies, and the recent Mars expeditions many people have the Idea that Astronomy is all about sending robots into space, collecting rocks, and exploring other planets. In truth Astronomy is largely a study of Light.

The furthest our technology can send Humans, at least currently, is to the Moon. In terms of the Model where the Sun was a grapefruit and the Earth 15 meters from the Sun, we’ve managed to travel a Staggering 4cm. Mars is over 200 times that distance, sending rovers is about the best we can expect for the next century or so. So clearly most of what we know about the Universe is not from actually going to places, but it is from studying the light that comes from these places.

Light, also known as Electromagnetic Radiation, comes in a variety of forums. We are familiar with Visible Light, which is just a small fraction of what is known as the Spectrum of Light. Light is most easily conceived of as a wave, which means we can Describe Light in terms of Wavelength and Frequency. Research these terms on your own, the Important thing to know is that Light is usually described by its Wavelength (which tells you about its Frequency as well). Light in the Visible spectrum has Wavelengths from about 400 nm to 700 nm (a nm, or nanometer is one million times smaller than a meter), but Light can exist at any wavelength. The wavelength of Light also tells you about the Energy in the Light, generally the shorter the Wavelength, the more Energy.

The entire Spectrum of light (or the Electromagnetic Spectrum as it is often called) relates Light of all wavelengths. You’ve likely heard of the varying types of light, and are pretty familiar with many of them. Infrared light is the Light that has wavelengths just larger than 700 nm, and is the light given off by Warm objects such as Humans. In order of short wavelength to longer the spectrum is like this; Gamma Rays, X-rays, Ultraviolet, Visible light, Infrared, and Radio waves (microwaves are technically low wavelength Radio waves).

How is all this Important to Astronomy? Well Since light is all we have to Observe most of the Universe by, it is important we use every bit of Light available. Astronomers have Telescopes that can capture “Images” in a variety of Wavelengths as many things just aren’t visible in the Wavelengths our eyes can see. For example it is easiest to see Stars forming in the Infrared because that is the Wavelength of Light they produce the Most.

Our Eyes in the Sky

So astronomers study light, but how do they observe this light? I’m sure you know the answer is Telescopes, the tool of any Astronomer. Telescopes are built off of similar principles that are at work in your eyes all the time. That is, using Lenses (or Mirrors) to bring light to a focus.

Your eyes consists on only one lenses (unlike in telescopes) and functions similarly to a camera. Light from an object enters your eye, and then encounters a Lens. This lens changes the directions of the varying rays of light, and causes an Image to be formed at the focal point of the Lenses. In your eye you want that focal point to be at your retina, otherwise you will soon be needing glasses.

Glasses actually work much like a Refracting Telescope (the other most basic design of telescope is the Reflecting Telescope) would. One lens brings light to a focus near the focal point of the second lens which allows the final image to be at the position desired. In a Telescope you want that Image to be at a point where you will then be able to form the Image in you eye, or at a camera.

A Reflecting Telescope works on much the same principles of bringing light to different focuses, but uses Mirrors rather than lenses to achieve this effect. Reflecting telescopes also have the advantage that they can be more compact due to the fact that they can bounce light back towards a different mirror, and don’t need a long tube like Refracting telescopes.

We need large telescopes in Astronomy due to a need for good Angular resolution. Angular Resolution is just the ability to see the separation between objects. Think of seeing a car’s headlights from far away, you will only be able to see one big light. As the car gets closer you can tell there are actually two lights on the car. Having large mirrors in Reflection telescopes allows us to resolve these kinds on discrepancies. Also having a large “light-collection area” allows Astronomers to capture as much incoming light as possible.

The wavelength of the Light that you are observing also makes a difference here as well, that’s why Radio Telescopes (you may know them better as Satellite Dishes) are typically so large.

The Edge of the Universe

In Astronomy we learn from what we can observe, just as in any other science, and just like any other science we are limited in our Observations. We cannot travel to other stars with our current technology, we have a hard time finding planets, especially Earth like planets, outside our Solar System, and we are limited by Light itself.

Since we cannot travel very far, and even our most advanced Satellites and Spacecraft have never left the Solar System, we are limited in our sample of things to Observe. We simple cannot say what Planets outside our Solar System are like, though we have begun detecting many. Since objects like Planets do not emit Light like stars do we cannot detect them so easily. Even those Planets we have discovered are limited by our methods of detection (noticing the “wobble” they cause in their parent star, which tends to favor Massive planets), and so does not give us a realistic sampling.

Since our Telescopes can only be built so big with our current technology, we can only “resolve” objects so far away with the accuracy we want. Also due to effects in the Earths atmosphere we have learned that ground based telescopes cannot provide us with as accurate of an Image as Space based observations. However, it is very costly and difficult to send telescopes into space, and there the size issue is of even greater concern.

Perhaps the most interesting of Astronomers limitations is in Light itself. Remember light travels at a certain speed (3,000 million meters per second) which is still overwhelmingly slow in Astronomical terms. It takes light over 4 years to reach us from the Sun’s nearest neighbor. In reality the Light that we see at Night is many, many years old. For all we know the stars that we see are no longer there, we wouldn’t know for Years if something happened to them. This has created the Idea that Astronomers “look back in Time”, what we see is things that have long since been. This also means that we can only “see back” so far, to the beginning of the Universe in fact. Which is another one of those Mind Boggling ideas.

So keep in mind how little it is that we know about the Universe, especially as technology grows and some of these limitations become Obsolete.