Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. The study of cosmology is theoretical astrophysics at the largest scales.

Observational astrophysics

Most astrophysical processes cannot be reproduced in laboratories on Earth. However, there is a huge variety of astronomical objects visible all over the electromagnetic spectrum. The study of these objects through passive collection of data is the goal of observational astrophysics.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The equipment and techniques required to study an astrophysical phenomenon can vary widely. Many astrophysical phenomena that are of current interest can only be studied by using very advanced technology and were simply not known until very recently.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The majority of astrophysical observations are made using the electromagnetic spectrum.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• Radio astronomy studies radiation with a wavelength greater than a few millimeters. Radio waves are usually emitted by cold objects, including interstellar gas and dust clouds. The cosmic microwave background radiation is the redshifted light from the Big Bang. Pulsars were first detected at microwave frequencies. The study of these waves requires very large radio telescopes.
• Infrared astronomy studies radiation with a wavelength that is too long to be visible but shorter than radio waves. Infrared observations are usually made with telescopes similar to the usual optical telescopes. Objects colder than stars (such as planets) are normally studied at infrared frequencies.
• Optical astronomy is the oldest kind of astronomy. Telescopes and spectroscopes are the most common instruments used. The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality. In this range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies and nebulae.
• Ultraviolet, X-ray and gamma ray astronomy study very energetic processes such as binary pulsars, black holes, magnetars, and many others. These kinds of radiation do not penetrate the Earth's atmosphere well, so they are studied with space-based telescopes such as RXTE, the Chandra X-ray Observatory and the Compton Gamma Ray Observatory.

Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study our Sun. Cosmic rays consisting of very high energy particles can be observed hitting the Earth's atmosphere.

Related Topics:
Gravitational wave - Neutrino - Cosmic ray

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale (millisecond pulsars) or combine years of data (pulsar deceleration studies). The information obtained from these different timescales is very different.

Related Topics:
Millisecond pulsar - Pulsar deceleration

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The study of our own Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Our understanding of our own sun serves as a guide to our understanding of other stars.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The topic of how stars change, or stellar evolution, is often modelled by placing the varieties of star types in their respective positions on the Hertzsprung-Russell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction. The material composition of the astronomical objects can often be examined using:

Related Topics:
Stellar evolution - Hertzsprung-Russell diagram

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• Spectroscopy
• Radio astronomy

~ ~ ~ ~ ~ ~ ~ ~ ~ ~