1. The Beginning

There is no doubt that Optical Astronomy is the oldest part of Astronomy. Nature gave us a very sophisticated instrument that is most sensitive to electromagnetic waves emitted by the Sun. The Sun does not emit just one wavelength but a whole range of wavelengths, from those that correspond to blue, to those that correspond to red color (actually the range of wavelengths is wider but our atmosphere does not let them in). The Sun is quite a typical star, and other stars emit similar ranges of wavelengths.
It turns out then, that adjusting our vision to the radiation that we are getting from the Sun, nature allowed us to see various colors of light. And by decreasing the number of clouds in the sky, nature was kind enough to show us the stars and everything else that can be seen.
This is how Astronomy was born.

For quite a long time, until Galileo and Kepler built their first telescopes about four hundred years ago, the only astronomical instrument in use was a human eye. Nicholas Copernicus, who was first to show in a convincing way that the Earth was not the center of the Universe, did not have a telescope, which was invented later. Telescopes, by magnifying the image, and collecting much more light than the eye alone, quickly allowed to discover things not seen before, like the moons of Jupiter, phases of Venus, craters on the Moon, or sunspots.
Three hundred years ago, Sir Isaac Newton invented another type of the telescope, created most of what we today know as Calculus and, using Kepler's empirical deductions about planetary orbits, created a unified scheme of dynamics and gravitation.
Since then we understand why an apple falls down to the ground and why at the same time the Earth is falling on the apple.
That was the beginning of Physics that we know today, that was also how Modern Astronomy was born.

 

 

2. Various Kinds of Astronomy

Combination of Physics and Mathematics, applied to everything we have in space around us, is what we call Astronomy today.

All information about everything that exists or happens in the Universe comes to us in the form of electromagnetic waves of many different wavelengths, extending from the shortest wavelengths of gamma rays, to the longest radio waves. With our eyes we can see and explore only part of this enormous spectrum of electromagnetic waves, and this is what many people know as Astronomy. This is however only part of the story. To be able to "see" those electromagnetic waves that cannot be seen with our eyes, we need additional, very complex and sophisticated equipment that extends our sense of vision.

Electromagnetic Spectrum

Frequency
(Hz)

wavelength
(meters)

104

Radio

3.104

106

3.102

108

3

1010

3.10-2

1012

Infrared

3.10-4

1014

3.10-6

Light

1016

Ultraviolet

3.10-8

X-Rays

1018

3.10-10

1020

3.10-12

Gamma Rays

1022

3.10-14

Depending on which part of the electromagnetic spectrum is investigated and what instruments are used for observations, Astronomy may be divided into several fields of research. That division may look like this:

  • Gamma-Ray Astronomy

  • X-Ray Astronomy

  • Ultraviolet Astronomy

  • Optical Astronomy

  • Infrared Astronomy

  • Radio and Radar Astronomy

Various instruments, sensitive to different wavelengths, provide information about quite different physical processes in galaxies, stars, nebulae, interstellar, and interplanetary matter. Obviously, the same object may be observed with many instruments, each instrument filling the gap in information not provided by other techniques. This way, putting all the pieces together, we learn how stars are born and evolve, why they shine, and what happens to them when their fuel is over. We learn about interstellar matter, galaxies, quasars, pulsars, comets, and many other objects that exist out there. We learn about planets, and the Earth. And the more we know about all this, the more we know about us.
This is Astronomy.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3. What We Investigate

We have mentioned above how we investigate astrophysical objects with various instruments. Now let us have a quick look at what we investigate.
From that point of view, Astronomy may be divided into many, sometimes overlapping, areas of interest. That division, perhaps somewhat arbitrary and incomplete, may look like this:

  • Planetary and Lunar Astronomy.
    This is obviously the Astronomy of the Solar System, investigating the Moon, planets of our Solar System and their satellites, and also asteroids, comets, and interplanetary matter.

  • Solar Astronomy.
    Our Sun is a typical star and the only star that is so close to us that we can investigate in detail phenomena that cannot be investigated in other stars (see also Astrophysics below).

  • Celestial Mechanics.
    Investigates orbits of all possible objects: planets around the stars, moons around planets, comets, asteroids, artificial satellites, interplanetary probes, motions of stars in complex systems, and so on.

  • Astrophysics.
    In general - physics applied to all kinds of objects we have in the Universe. The most important problems investigated in Astrophysics are:
    - sources of energy in the interior of a star,
    - transfer of energy from the center to the outer layers of a star,
    - internal structure of a star as a function of time (i.e. evolution of the stars),
    - analysis and interpretation of stellar spectra. Since all information about stars is carried by electromagnetic waves, spectral analysis is one of the most powerful tools in Astrophysics. Using that tool one gets information about chemical composition of stars, temperature and pressure of the outer layers, rotation, magnetic and electric fields, radial velocities, stellar pulsations, and so on. In recent years this technique has been used to discover planets outside our Solar System.

  • Galactic Astronomy.
    Investigates objects in our Galaxy - that includes motions and positions of the stars, their proper motions, radial velocities of stars and star clusters, measuring distances to stars and clusters, investigations of the structure of our Galaxy. That also includes investigations of stellar populations, and interstellar matter - its distribution, chemical and physical properties, and motions in our Galaxy. Since all but a few out of nearly a thousand radio pulsars are located in our Galaxy, investigations of these objects may be also included here. We can also include here novae and supernovae stars that sporadically appear in our Galaxy.

  • Extragalactic Astronomy.
    Investigates, generally speaking, similar problems as Galactic Astronomy but outside our Galaxy. Apart from this, Extragalactic Astronomy investigates problems like
    - formation, evolution and classification of galaxies,
    - distribution of galaxies in space,
    - spectra and radial velocities of galaxies,
    - active galaxies,
    - extragalactic radio sources,
    - quasars,
    - intergalactic matter.

  • Cosmology.
    In general, investigations of the history of the Universe, from the beginning until now, and attempts to predict the future of the Universe as a whole. Problems studied here include:
    - the Big Bang,
    - cosmic nucleosynthesis,
    - formation of galaxies,
    - noncosmological redshifts.

 

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