What Is Dark Matter?

The Moon is Earth's only natural satellite and is the fifth largest satellite in the Solar System. It is the largest natural satellite in the Solar System relative to the size of its planet, a quarter the diameter of Earth and 1/81 its mass, and is the second densest satellite after Io. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal. Its prominence in the sky and its regular cycle of phases have since ancient times made the Moon an important cultural influence on language, the calendar, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to be the same size in the sky as the Sun – allowing the Moon to cover the Sun precisely in total solar eclipses.
The Moon is the only celestial body on which humans have made a manned landing. While the Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft, the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972 – the first being Apollo 11 in 1969. These missions returned over 380 kg of lunar rocks, which have been used to develop a detailed geological understanding of the Moon's origins (it is thought to have formed some 4.5 billion years ago in a giant impact), the formation of its internal structure, and its subsequent history.
Since the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft, notably by Soviet Lunokhod rovers. Since 2004, Japan, China, India, the United States, and the European Space Agency have each sent lunar orbiters. These spacecraft have contributed to confirming the discovery of lunar water ice in permanently shadowed craters at the poles and bound into the lunar regolith. Future manned missions to the Moon are planned but not yet underway; the Moon remains, under the Outer Space Treaty, free to all nations to explore for peaceful purposes.

Moon

The Moon is Earth's only natural satellite and is the fifth largest satellite in the Solar System. It is the largest natural satellite in the Solar System relative to the size of its planet, a quarter the diameter of Earth and 1/81 its mass, and is the second densest satellite after Io. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal. Its prominence in the sky and its regular cycle of phases have since ancient times made the Moon an important cultural influence on language, the calendar, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to be the same size in the sky as the Sun – allowing the Moon to cover the Sun precisely in total solar eclipses.
The Moon is the only celestial body on which humans have made a manned landing. While the Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft, the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972 – the first being Apollo 11 in 1969. These missions returned over 380 kg of lunar rocks, which have been used to develop a detailed geological understanding of the Moon's origins (it is thought to have formed some 4.5 billion years ago in a giant impact), the formation of its internal structure, and its subsequent history.
Since the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft, notably by Soviet Lunokhod rovers. Since 2004, Japan, China, India, the United States, and the European Space Agency have each sent lunar orbiters. These spacecraft have contributed to confirming the discovery of lunar water ice in permanently shadowed craters at the poles and bound into the lunar regolith. Future manned missions to the Moon are planned but not yet underway; the Moon remains, under the Outer Space Treaty, free to all nations to explore for peaceful purposes.

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance.^[11] Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. Mars’ rotational period and seasonal cycles are likewise similar to those of Earth. Mars is the site of Olympus Mons, the highest known mountain in the Solar System, and of Valles Marineris, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.^[12][13] Unlike Earth, Mars is now geologically and tectonically inactive.^{[citation needed]}
Until the first flyby of Mars occurred in 1965, by Mariner 4, many speculated about the presence of liquid water on the planet's surface. This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents; long, dark striations were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusions, yet of all the planets in the Solar System other than Earth, Mars is the most likely to harbor liquid water, and thus to harbor life.^[14] Geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface, while small geyser-like water flows may have occurred during the past decade.^[15] In 2005, radar data revealed the presence of large quantities of water ice at the poles,^[16] and at mid-latitudes.^[17][18] The Phoenix Lander directly sampled water ice in shallow martian soil on July 31, 2008.^[19]
Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Martian Trojan asteroid. Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. On the surface are the two Mars Exploration Rovers (Spirit and Opportunity) and several inert landers and rovers, both successful and unsuccessful. The Phoenix Lander completed its mission on the surface in 2008. Observations by NASA's now-defunct Mars Global Surveyor show evidence that parts of the southern polar ice cap have been receding.^[20]
Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches −2.91,^[5] a brightness surpassed only by Jupiter, Venus, the Moon, and the Sun. Mars has an average opposition distance of 78 million km but can come as close as 55.7 million km during a close approach, such as occurred in 2003.^[5]

Rocket Science

Rocket science is the study of rockets, most frequently studied in the discipline of aerospace engineering and related fields.
Rocket science may also refer to:

• a complex or difficult mental exercise or field or study, used frequently in an ironic sense to suggest that a task should be easy or simple because it is not rocket science
• Rocket Science Games, a video game development company
• Rocket Science VFX, a Canadian visual effects production company
• Rocket Science (miniseries), a 2002 documentary series
• Rocket Science (film), a 2007 comedy film
• Rocket Science (TV series), a 2009 BBC television series

In music:

• Rocket Science (band), an Australian alternative rock band
• Rocket Science (Apoptygma Berzerk album)
• Rocket Science (Hugh Blumenfeld album), by folk artist Hugh Blumenfeld
• Rocket Science (Tribal Tech album), by the jazz fusion band Tribal Tech

About space

Thousands of years ago, on a small rocky planet orbiting a modest star in an ordinary spiral galaxy, our remote ancestors looked up and wondered about their place between Earth and sky. Today, we ask the same profound questions:

• How did the universe begin and evolve?
• How did we get here?
• Where are we going?
• Are we alone?

Today, after only the blink of an eye in cosmic time, we are beginning to answer these questions. Space probes and space observatories have played a central role in this process of discovery.
Our missions and research generate most of the coolest news coming out of NASA. We are responsible for all of NASA's programs relating to astronomy, the solar system, and the sun and its interaction with Earth. Our science stretches from the middle levels of Earth's atmosphere to the beginning of the universe, billions of light years away.
Our web site serves our science community, educators, government decision-makers, and the public. We hope your visit is enjoyable. Thanks for stopping by!

String Theory (11 dimension)

String theory is a developing theory in particle physics which attempts to reconcile quantum mechanics and general relativity.^[1] String theory posits that the electrons and quarks within an atom are not 0-dimensional objects, but rather 1-dimensional oscillating lines ("strings"), possessing only the dimension of length, but not height or width. The theory poses that these strings can vibrate, thus giving the observed particles their flavor, charge, mass and spin. The earliest string model, the bosonic string, incorporated only bosons, although this view evolved to the superstring theory, which posits that a connection (a "supersymmetry") exists between bosons and fermions, two fundamentally different types of particles. String theories also require the existence of several extra, unobservable, dimensions to the universe, in addition to the usual three spatial dimensions (height, width, and length) and the fourth dimension of time. M theory, for example, requires that spacetime have eleven dimensions.^[2]
The theory has its origins in the dual resonance model - first proposed in 1969 by Gabriele Veneziano - which described the strongly interacting hadrons as strings. Since that time, the term string theory has evolved to incorporate any of a group of related superstring theories - indeed, the "strings" are no longer considered fundamental to the theory, which can also be formulated in terms of points or surfaces. As such, five major string theories were developed, each with a different mathematical structure, and each best describing different physical circumstances. The main differences between each theory were principally the number of dimensions in which the strings developed, and their characteristics (some were open loops, some were closed loops, etc.), however all these theories appeared to be correct. In the mid 1990s, string theorist Edward Witten of the Institute for Advanced Study considered that the five major versions of string theory might be describing the same phenomenon from different perspectives. Witten's resulting M-theory, a proposed unification of all previous superstring theories, asserted that strings are really 1-dimensional slices of a 2-dimensional membrane vibrating in 11-dimensional space.
As a result of the many properties and principles shared by these approaches (such as the holographic principle), their mutual logical consistency, and the fact that some easily include the standard model of particle physics, many of the world's greatest living physicists (such as Edward Witten, Juan Maldacena and Leonard Susskind) believe that string theory is a step towards the correct fundamental description of nature.^{[3][4][5][6][unreliable source?]} In particular, string theory is the first candidate for the theory of everything (TOE), a manner of describing the known fundamental forces (gravitational, electromagnetic, weak and strong interactions) and matter (quarks and leptons) in a mathematically complete system. However, prominent physicists such as Richard Feynman and Sheldon Lee Glashow have criticized string theory for not providing any quantitative experimental predictions.^[7][8] Like any other quantum theory of gravity, it is widely believed that testing the theory directly would require prohibitively expensive feats of engineering. Although direct experimental testing of String Theory involves grand explorations and development in engineering, there are several indirect experiments that may prove partial truth to String Theory. Supersymmetry (an idea developed in the early 1970s through String Theory research) is theoretically established through String Theory and it does appear to weave into current experimentally understood High Energy Physics (Particle Physics) (Supersymmetry could possibly be discovered at CERN where energies are being probed that could motivate the emergence of Supersymmetric Particles. Also the existence of Extra Compactified Dimensions (Calabi-Yau manifold) could possibly be discovered at CERN by the permeation of a Graviton into a higher dimensional space (Membrane (M-Theory)).

Red Giant

A red giant is a luminous giant star of low or intermediate mass (roughly 0.5–10 solar masses) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower. The appearance of the red giant is from yellow orange to red, including the spectral types K and M, but also class S stars and most carbon stars.
The most common red giants are the so-called red giant branch stars (RGB stars) whose shells are still fusing hydrogen into helium, while the core is inactive helium. Another case of red giants are the asymptotic giant branch stars (AGB) that produces carbon from helium by the triple-alpha process.^[1] To the AGB stars belong the carbon stars of type C-N and late C-R.
Prominent bright red giants in the night sky include Aldebaran (Alpha Tauri), Arcturus (Alpha Bootis), and Gamma Crucis (Gacrux), while the even larger Antares (Alpha Scorpii) and Betelgeuse (Alpha Orionis) are red supergiants.

About the galaxy in space.

This article is about the astronomical structure. For other uses, see Galaxy (disambiguation).

NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant.

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.^[1][2] The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million^[3] (10⁷) stars up to giants with hundred trillion^[4] (10¹⁴) stars, all orbiting the galaxy's center of mass. Galaxies may contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.
Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy,^[5] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as irregular galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.^[6]
There are probably more than 170 billion (1.7 × 10¹¹) galaxies in the observable universe.^[7][8] Most galaxies are 1,000 to 100,000^[9] parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs).^[10] Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.^[11]
Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.^[12]

Milkyway Galaxy

The Milky Way is the galaxy which is the home of our Solar System together with at least 200 billion other stars (more recent estimates have given numbers around 400 billion) and their planets, and thousands of clusters and nebulae, including at least almost all objects of Messier's catalog which are not galaxies on their own (one might consider two globular clusters as possible exceptions, as probably they are just being, or have recently been, incorporated or imported into our Galaxy from dwarf galaxies which are currently in close encounters with the Milky Way: M54 from SagDEG, and possibly M79 from the Canis Major Dwarf). See our Messier Objects in the Milky Way page, where details are given for each object to which part of our Galaxy it is related. All the objects in the Milky Way Galaxy orbit their common center of mass, called the Galactic Center (see below).
As a galaxy, the Milky Way is actually a giant, as its mass is probably between 750 billion and one trillion solar masses, and its diameter is about 100,000 light years. Radio astronomial investigations of the distribution of hydrogen clouds have revealed that the Milky Way is a spiral galaxy of Hubble type Sb or Sc. Therefore, our galaxy has both a pronounced disk component exhibiting a spiral structure, and a prominent nuclear reagion which is part of a notable bulge/halo component. Decade-long observations have brought up more and more evidence that the Milky Way may also have a bar structure (so that it would be type SB), so that it may look like M61 or M83, and is perhaps best classified as SABbc. Recent investigations have brought up support for the assumption that the Milky Way may even have a pronounced central bar like barred spiral galaxies M58, M91, M95, or M109, and thus be of Hubble type SBb or SBc.