Astrobiology

studies the advent and evolution of biological systems in the universe.

Astrophysics

branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior.

The sub disciplines of theoretical astrophysics are:

Planetary Science

study of the planets of the Solar System.

The sub disciplines of Planetary science are:

Observational astronomy

It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.

The sub disciplines of observational astronomy are generally made by the specifications of the detectors:

1. Radio astronomy(studies celestial objects at radio frequencies) – Above 300 µm
   1. The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy.

2. Submillimetre astronomy(conducted at Submillimetre wavelengths (i.e., terahertz radiation) of the electromagnetic spectrum) – 200 µm to 1 mm
   1. Submillimetre observations are used to determine the mechanisms for the formation and evolution of galaxies and also the process of star formation from earliest collapse to stellar birth.

3. Infrared astronomy(study of the infrared radiation(heat energy) emitted from objects in the Universe) – 0.7–350 µm
   1. Many objects in the universe which are much too cool and faint to be detected in visible light, can be detected in the infrared.
   2. It helps to Study the early evolution of galaxies. As a result of the Big Bang (the tremendous explosion which marked the beginning of our Universe), the universe is expanding and most of the galaxies within it are moving away from each other.
   3. Astronomers have discovered that all distant galaxies are moving away from us and that the farther away they are, the faster they are moving. This recession of galaxies away from us has an interesting effect on the light emitted from these galaxies. When an object is moving away from us, the light that it emits is "redshifted". This means that the wavelengths get longer and thereby shifted towards the red part of the spectrum. This effect, called the Doppler effect, is similar to what happens to sound waves emitted from a moving object. For example, if you are standing next to a railroad track and a train passes you while blowing its horn, you will hear the sound change from a higher to a lower frequency as the train passes you by. As a result of this Doppler effect, at large redshifts, all of the ultraviolet and much of the visible light from distant sources is shifted into the infrared part of the spectrum by the time it reaches our telescopes. This means that the only way to study this light is in the infrared. Infrared astronomy will provide a great deal of information on how and when the universe was formed and on what the early universe was like.

4. Optical astronomy(Visible-light astronomy) – 380–750 nm
   1. encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light (optical telescopes).

5. Ultraviolet astronomy(observation of electromagnetic radiation at ultraviolet wavelengths) – 10–320 nm
   1. Light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space.
   2. used to discern the chemical composition, densities, and temperatures of the interstellar medium, and the temperature and composition of hot young stars.
   3. UV observations can also provide essential information about the evolution of galaxies.

6. X-ray astronomy(deals with the study of X-ray observation and detection from astronomical objects.) – 0.01–10 nm
   1. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites.

7. Gamma-ray astronomy( astronomical observation of gamma rays) – Below 0.01 nm
   1. Gamma ray telescopes collect and measure individual, high energy gamma rays from astrophysical sources. These are absorbed by the atmosphere, requiring that observations are done by high-altitude balloons or space missions. Gamma rays can be generated by supernovae, neutron stars, pulsars and black holes. Gamma ray bursts, with extremely high energies, have also been detected but have yet to be identified.
   2. Gamma rays in the MeV range are generated in solar flares (and even in the Earth's atmosphere), but gamma rays in the GeV range do not originate in our solar system and are important in the study of extrasolar, and especially extra-galactic astronomy.

8. Cosmic ray astronomy – Cosmic rays, including plasma
   1. Cosmic rays are immensely high-energy radiation, mainly originating outside the Solar System.
   2.  They may produce showers of secondary particles that penetrate and impact the Earth's atmosphere and sometimes even reach the surface.
   3. Composed primarily of high-energy protons and atomic nuclei, they are of mysterious origin.
   4. Cosmic rays attract great interest practically, due to the damage they inflict on microelectronics and life outside the protection of an atmosphere and magnetic field, and scientifically, because the energies of the most energetic ultra-high-energy cosmic rays (UHECRs) have been observed to approach 3 × 1020 eV, about 40 million times the energy of particles accelerated by the Large Hadron Collider.
   5. Microwave space telescopes have primarily been used to measure cosmological parameters from the Cosmic Microwave Background.

9. Neutrino astronomy(observes astronomical objects with neutrino detectors in special observatories) – Neutrinos
   1. Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions such as those that take place in the Sun, in nuclear reactors, or when cosmic rays hit atoms.
   2. Due to their weak interactions with matter, neutrinos offer a unique opportunity to observe processes that are inaccessible to optical telescopes.
   3. The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources so far are the Sun and supernova SN1987A.
   4. The Moon has also been detected by its absorption of background neutrinos.

10. Gravitational wave astronomy – Gravitons
    1. aims to use gravitational waves (minute distortions of space-time predicted by Einstein's theory of general relativity) to collect observational data about objects such as neutron stars and black holes, events such as supernovae, and processes including those of the early universe shortly after the Big Bang.
    2. LISA Pathfinder - A new type of telescope to detect gravitational waves; ripples in space-time generated by colliding neutron stars and black holes.

Divisions based on astronomical research