Astronomy is a natural science
Natural science
The natural sciences are branches of science that seek to elucidate the rules that govern the natural world by using empirical and scientific methods...

 that deals with the study of celestial objects
Astronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...

 (such as star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s, planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

s, comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

s, nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...

e, star cluster
Star cluster
Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...

s and galaxies
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

) and phenomena
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

 that originate outside the atmosphere of Earth (such as the cosmic background radiation
Cosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....

). It is concerned with the evolution, physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

, chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, meteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

, and motion
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...

 of celestial objects, as well as the formation and development of the universe
Physical cosmology
Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...


Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the Egyptian monuments
Egyptian astronomy
Egyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments...

, Nubian monuments
Nubian pyramids
Nubian pyramids are pyramids that were built by the rulers of the Kushite and Egyptian kingdoms. Prior to the Kushites building these pyramids , there had been no pyramid construction in Egypt and the Nile Valley for more than 500 years.The area of the Nile valley known as Nubia, which lies within...

 and Stonehenge
Stonehenge is a prehistoric monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury. One of the most famous sites in the world, Stonehenge is composed of a circular setting of large standing stones set within earthworks...

, and early civilizations such as the Babylonians, Greeks
Greek astronomy
Greek astronomy is astronomy written in the Greek language in classical antiquity. Greek astronomy is understood to include the ancient Greek, Hellenistic, Greco-Roman, and Late Antiquity eras. It is not limited geographically to Greece or to ethnic Greeks, as the Greek language had become the...

, Chinese
Chinese astronomy
Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...

, Indians, Iranians
Iranians may refer to:* Persian people, who are synonymous with the people of Iran/Persia...

 and Maya
Maya civilization
The Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period The Maya is a Mesoamerican...

 performed methodical observations of the night sky
Night sky
The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight,...


Although Uranus|Uranus and Neptune|Neptune are superficially twin planets, they are different enough to remind us - as do Venus|Venus and Earth|Earth - that we still have a lot to learn about the mix of natural laws and historical accidents that formed the planets and fashioned their destinies.

Timothy Ferris|Timothy Ferris - Seeing in the Dark, 2002

The wonder is, not that the field of stars is so vast, but that man has measured it.

Anatole France - The Garden of Epicurus, 1894

Over the rim of waiting earth the moon lifted with majesty till it swung clear of the horizon and rode off, free of moorings...

Kenneth Grahame - The Wind in the Willows, 1908

A strange weasel-built creature with a curly tail.

W:Johannes Hevelius|Johannes Hevelius on his newly described constellation Lacerta|Lacerta the lizard in 1687 - reported in SkyNews The Canadian Magazine of Astronomy and Stargazing September/October 2002.

I open the scuttle at night and see the far sprinkled systems,And all I see multiplied as high as I can cyper edge but rim of the farthest systems. Wider and wider they spread, expanding, always expanding,Outward and outward, forever outward.

Walt Whitman - Leaves of Grass, 1855