Universe

In this diagram, time passes from left to right, so at any given time, the universe is represented by a disk-shaped "slice" of the diagram
Television signals broadcast from Earth will never reach the edges of this image.
Astronomers have discovered stars in the Milky Way galaxy that are almost 13.6 billion years old.
The three possible options for the shape of the universe
The formation of clusters and large-scale filaments in the cold dark matter model with dark energy. The frames show the evolution of structures in a 43 million parsecs (or 140 million light-years) box from redshift of 30 to the present epoch (upper left z=30 to lower right z=0).
A map of the superclusters and voids nearest to Earth
Comparison of the contents of the universe today to 380,000 years after the Big Bang as measured with 5 year WMAP data (from 2008). (Due to rounding errors, the sum of these numbers is not 100%). This reflects the 2008 limits of WMAP's ability to define dark matter and dark energy.
Standard model of elementary particles: the 12 fundamental fermions and 4 fundamental bosons. Brown loops indicate which bosons (red) couple to which fermions (purple and green). Columns are three generations of matter (fermions) and one of forces (bosons). In the first three columns, two rows contain quarks and two leptons. The top two rows' columns contain up (u) and down (d) quarks, charm (c) and strange (s) quarks, top (t) and bottom (b) quarks, and photon (γ) and gluon (g), respectively. The bottom two rows' columns contain electron neutrino (νe) and electron (e), muon neutrino (νμ) and muon (μ), tau neutrino (ντ) and tau (τ), and the Z0 and W± carriers of the weak force. Mass, charge, and spin are listed for each particle.
3rd century BCE calculations by Aristarchus on the relative sizes of, from left to right, the Sun, Earth, and Moon, from a 10th-century AD Greek copy.
Flammarion engraving, Paris 1888
Model of the Copernican Universe by Thomas Digges in 1576, with the amendment that the stars are no longer confined to a sphere, but spread uniformly throughout the space surrounding the planets.

All of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.

- Universe
In this diagram, time passes from left to right, so at any given time, the universe is represented by a disk-shaped "slice" of the diagram

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Relevance

Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica

Heliocentrism

Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica
A hypothetical geocentric model of the Solar System (upper panel) in comparison to the heliocentric model (lower panel).
Aristarchus' 3rd century BC calculations on the relative sizes of the Earth, Sun and Moon, from a 10th-century AD Greek copy
An illustration from al-Biruni's astronomical works explains the different phases of the Moon with respect to the position of the Sun.
Nicholas of Cusa, 15th century, asked whether there was any reason to assert that any point was the center of the universe.
Portrait of Nicolaus Copernicus (1578)
In this depiction of the Tychonic system, the objects on blue orbits (the Moon and the Sun) revolve around the Earth. The objects on orange orbits (Mercury, Venus, Mars, Jupiter, and Saturn) revolve around the Sun. Around all is a sphere of fixed stars, located just beyond Saturn.
In the 17th century AD, Galileo Galilei opposed the Roman Catholic Church by his strong support for heliocentrism.
A Philosopher Lecturing on the Orrery (1766) by Joseph Wright, in which a lamp represents the Sun
William Herschel's model of the Milky Way, 1785

Heliocentrism is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe.

Timeline of the metric expansion of space, where space, including hypothetical non-observable portions of the universe, is represented at each time by the circular sections. On the left, the dramatic expansion occurs in the inflationary epoch; and at the center, the expansion accelerates (artist's concept; not to scale).

Big Bang

Prevailing cosmological model explaining the existence of the observable universe from the earliest known periods through its subsequent large-scale evolution.

Prevailing cosmological model explaining the existence of the observable universe from the earliest known periods through its subsequent large-scale evolution.

Timeline of the metric expansion of space, where space, including hypothetical non-observable portions of the universe, is represented at each time by the circular sections. On the left, the dramatic expansion occurs in the inflationary epoch; and at the center, the expansion accelerates (artist's concept; not to scale).
Panoramic view of the entire near-infrared sky reveals the distribution of galaxies beyond the Milky Way. Galaxies are color-coded by redshift.
Artist's depiction of the WMAP satellite gathering data to help scientists understand the Big Bang
Abell 2744 galaxy cluster – Hubble Frontier Fields view.
The cosmic microwave background spectrum measured by the FIRAS instrument on the COBE satellite is the most-precisely measured blackbody spectrum in nature. The data points and error bars on this graph are obscured by the theoretical curve.
9 year WMAP image of the cosmic microwave background radiation (2012). The radiation is isotropic to roughly one part in 100,000.
Focal plane of BICEP2 telescope under a microscope - used to search for polarization in the CMB.
Chart shows the proportion of different components of the universe – about 95% is dark matter and dark energy.
The overall geometry of the universe is determined by whether the Omega cosmological parameter is less than, equal to or greater than 1. Shown from top to bottom are a closed universe with positive curvature, a hyperbolic universe with negative curvature and a flat universe with zero curvature.

Detailed measurements of the expansion rate of the universe place the Big Bang singularity at around 13.8 billion years ago, which is thus considered the age of the universe.

Composite image of five galaxies clustered together just 600 million years after the Universe's birth

Galaxy cluster

Structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity with typical masses ranging from 1014–1015 solar masses.

Structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity with typical masses ranging from 1014–1015 solar masses.

Composite image of five galaxies clustered together just 600 million years after the Universe's birth
Galaxy cluster IDCS J1426 is located 10 billion light-years from Earth and has the mass of almost 500 trillion suns (multi-wavelength image: X-rays in blue, visible light in green, and infrared light in red).
The Laniakea supercluster with many galaxy clusters
Galaxy cluster SPT-CL J0615-5746.<ref>{{cite web |title=Distant and ancient |url=https://www.spacetelescope.org/images/potw1918a/ |website=www.spacetelescope.org |access-date=6 May 2019 |language=en}}</ref>
Galaxy cluster RXC J0232.2-4420.<ref>{{cite web |title=Strings of homeless stars |url=http://www.spacetelescope.org/images/potw1824a/ |website=www.spacetelescope.org |access-date=11 June 2018}}</ref>
Galaxy cluster RXC J0032.1+1808 as part of the RELICS program.<ref>{{cite web|title=From toddlers to babies|url=https://www.spacetelescope.org/images/potw1819a/|website=www.spacetelescope.org|access-date=7 May 2018}}</ref>
Massive galaxy cluster PSZ2 G138.61-10.84 is about six billion light-years away.<ref>{{cite web|title=Approaching the Universe's origins|url=http://www.spacetelescope.org/images/potw1816a/|website=www.spacetelescope.org|access-date=16 April 2018}}</ref>
HAWK-I and Hubble explore RCS2 J2327 cluster with the mass of two quadrillion Suns.<ref>{{cite web|title=HAWK-I and Hubble Explore a Cluster with the Mass of two Quadrillion Suns|url=https://www.eso.org/public/images/potw1752a/|website=www.eso.org|access-date=25 December 2017}}</ref>
Abell 2537 is useful in probing cosmic phenomena like dark matter and dark energy.<ref>{{cite web|title=Streaks and stripes|url=http://www.spacetelescope.org/images/potw1748a/|website=www.spacetelescope.org|access-date=27 November 2017}}</ref>
Abell 1300 acts like a lens, bending the very fabric of space around it.<ref>{{cite web|title=Cosmic RELICS|url=http://www.spacetelescope.org/images/potw1745a/|website=www.spacetelescope.org|access-date=6 November 2017}}</ref>
Galaxy cluster WHL J24.3324-8.477.<ref>{{cite web|title=Cosmic archaeology|url=https://www.spacetelescope.org/images/potw1743a/|website=www.spacetelescope.org|access-date=24 October 2017}}</ref>
Background galaxy has been gravitationally lensed by the intervening galaxy cluster.<ref>{{cite web|title=Hubble pushed beyond limits to spot clumps of new stars in distant galaxy|url=https://www.spacetelescope.org/images/opo1727a/|website=www.spacetelescope.org|access-date=12 July 2017}}</ref>
"Smiley" image – galaxy cluster (SDSS J1038+4849) & gravitational lensing (an Einstein ring) (HST).<ref name="NASA-20150210">{{cite web|last1=Loff|first1=Sarah|last2=Dunbar|first2=Brian|title=Hubble Sees A Smiling Lens|url=http://www.nasa.gov/content/hubble-sees-a-smiling-lens/|date=10 February 2015|work=NASA|access-date=10 February 2015 }}</ref>
Galaxy cluster SpARCS1049 taken by Spitzer and the Hubble Space Telescope.<ref>{{cite web|title=Image of the galaxy cluster SpARCS1049|url=http://www.spacetelescope.org/images/heic1519a/|access-date=11 September 2015}}</ref>
Galaxy cluster MOO J1142+1527 discovered by the MaDCoWS survey
Abell 2744 galaxy cluster (HST).<ref name="NASA-20140107" />
Magnifying the distant universe through MACS J0454.1-0300.<ref>{{cite news|title=Magnifying the distant Universe|url=http://www.spacetelescope.org/images/potw1412a/|access-date=10 April 2014|newspaper=ESA/Hubble Picture of the Week }}</ref>
Turbulence may prevent galaxy clusters from cooling ; illustrated: Perseus Cluster and Virgo Cluster (Chandra X-ray).
MACS0416.1-2403 imaged by the HST
The galaxy cluster Abell 2813 (also known as ACO 2813) image from the NASA/ESA Hubble Space Telescope
A Menagerie of Galaxies — The galaxy cluster ACO S 295
Cosmic Lens Flare
Hubble spots three images of a distant supernova

They are the second largest known gravitationally bound structures in the universe after galaxy filaments and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered.

Milky Way

Galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.

Galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.

The Origin of the Milky Way (c. undefined 1575–1580) by Tintoretto
A view of the Milky Way toward the constellation Sagittarius (including the Galactic Center), as seen from a dark site with little light pollution (the Black Rock Desert, Nevada), the bright object on the lower right is Jupiter, just above Antares
The shape of the Milky Way as deduced from star counts by William Herschel in 1785; the Solar System was assumed near center
Photograph of the "Great Andromeda Nebula" from 1899, later identified as the Andromeda Galaxy
Map of the Milky Way Galaxy with the constellations that cross the galactic plane in each direction and the known prominent components annotated including main arms, spurs, bar, nucleus/bulge, notable nebulae and globular clusters.
An all-sky view of stars in the Milky Way and neighbouring galaxies, based on the first year of observations from Gaia satellite, from July 2014 to September 2015.
The map shows the density of stars in each portion of the sky. Brighter regions indicate denser concentrations of stars. Darker regions across the Galactic Plane correspond to dense clouds of interstellar gas and dust that absorb starlight.
Artistic close-up of the Orion Arm with the main features of the Radcliffe Wave and Split linear structures, and with the Solar System surrounded by the closest large scale celestial features at the surface of the Local Bubble at a distance of 400-500 light years.
Diagram of the Sun's location in the Milky Way, the angles represent longitudes in the galactic coordinate system.
The structure of the Milky Way is thought to be similar to this galaxy (UGC 12158 imaged by Hubble)
A schematic profile of the Milky Way.
Abbreviations: GNP/GSP: Galactic North and South Poles
360-degree panorama view of the Milky Way (an assembled mosaic of photographs) by ESO, the galactic centre is in the middle of the view, with galactic north up
360-degree rendering of the Milky Way using Gaia EDR3 data showing interstellar gas, dust backlit by stars (main patches labeled in black; white labels are main bright patches of stars). Left hemisphere is facing the galactic center, right hemisphere is facing the galactic anticenter.
Overview of different elements of the overall structure of the Milky Way.
Illustration of the two gigantic X-ray/gamma-ray bubbles (blue-violet) of the Milky Way (center)
Observed (normal lines) and extrapolated (dotted lines) structure of the spiral arms of the Milky Way, viewed from north of the galaxy – the galaxy rotates clockwise in this view. The gray lines radiating from the Sun's position (upper center) list the three-letter abbreviations of the corresponding constellations
Clusters detected by WISE used to trace the Milky Way's spiral arms.
The long filamentary molecular cloud dubbed "Nessie" probably forms a dense "spine" of the Scutum–Centarus Arm
Galaxy rotation curve for the Milky Way – vertical axis is speed of rotation about the galactic center; horizontal axis is distance from the galactic center in kpcs; the sun is marked with a yellow ball; the observed curve of speed of rotation is blue; the predicted curve based upon stellar mass and gas in the Milky Way is red; scatter in observations roughly indicated by gray bars, the difference is due to dark matter
Comparison of the night sky with the night sky of a hypothetical planet within the Milky Way 10 billion years ago, at an age of about 3.6 billion years and 5 billion years before the Sun formed.
The Milky Way arching at a high inclination across the night sky, (this composited panorama was taken at Paranal Observatory in northern Chile), the bright object is Jupiter in the constellation Sagittarius, and the Magellanic Clouds can be seen on the left; galactic north is downward
The Milky Way viewed at different wavelengths

Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe.

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the 'flat' appearance of the velocity curve out to a large radius.

Dark matter

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the 'flat' appearance of the velocity curve out to a large radius.
Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter – enlarge the image to see the lensing arcs.
Dark matter map for a patch of sky based on gravitational lensing analysis of a Kilo-Degree survey.
3-D map of the large-scale distribution of dark matter, reconstructed from measurements of weak gravitational lensing with the Hubble Space Telescope.
Collage of six cluster collisions with dark matter maps. The clusters were observed in a study of how dark matter in clusters of galaxies behaves when the clusters collide.

Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.

Diagram representing the accelerated expansion of the universe due to dark energy.

Dark energy

Diagram representing the accelerated expansion of the universe due to dark energy.
A Type Ia supernova (bright spot on the bottom-left) near a galaxy
Estimated division of total energy in the universe into matter, dark matter and dark energy based on five years of WMAP data.
Estimated distribution of matter and energy in the universe

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales.

A map of the superclusters and voids nearest to Earth

Supercluster

A map of the superclusters and voids nearest to Earth
The Abell 901/902 supercluster is located a little over two billion light-years from Earth.

A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe.

Spectral lines of helium

Helium

Chemical element with the symbol He and atomic number 2.

Chemical element with the symbol He and atomic number 2.

Spectral lines of helium
Sir William Ramsay, the discoverer of terrestrial helium
The cleveite sample from which Ramsay first purified helium
Historical marker, denoting a massive helium find near Dexter, Kansas
The helium atom. Depicted are the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case.
Binding energy per nucleon of common isotopes. The binding energy per particle of helium-4 is significantly larger than all nearby nuclides.
Helium discharge tube shaped like the element's atomic symbol
Liquefied helium. This helium is not only liquid, but has been cooled to the point of superfluidity. The drop of liquid at the bottom of the glass represents helium spontaneously escaping from the container over the side, to empty out of the container. The energy to drive this process is supplied by the potential energy of the falling helium.
Unlike ordinary liquids, helium II will creep along surfaces in order to reach an equal level; after a short while, the levels in the two containers will equalize. The Rollin film also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.
Structure of the helium hydride ion, HHe+
Structure of the suspected fluoroheliate anion, OHeF−
The largest single use of liquid helium is to cool the superconducting magnets in modern MRI scanners.
A dual chamber helium leak detection machine
Because of its low density and incombustibility, helium is the gas of choice to fill airships such as the Goodyear blimp.

It is the second lightest and second most abundant element in the observable universe (hydrogen is the lightest and most abundant).

The Space Shuttle Main Engine burnt hydrogen with oxygen, producing a nearly invisible flame at full thrust.

Hydrogen

Chemical element with the symbol H and atomic number 1.

Chemical element with the symbol H and atomic number 1.

The Space Shuttle Main Engine burnt hydrogen with oxygen, producing a nearly invisible flame at full thrust.
Depiction of a hydrogen atom with size of central proton shown, and the atomic diameter shown as about twice the Bohr model radius (image not to scale)
Hydrogen gas is colorless and transparent, here contained in a glass ampoule.
Phase diagram of hydrogen. The temperature and pressure scales are logarithmic, so one unit corresponds to a 10x change. The left edge corresponds to 105 Pa, which is about atmospheric pressure.
A sample of sodium hydride
Hydrogen discharge (spectrum) tube
Deuterium discharge (spectrum) tube
Antoine-Laurent de Lavoisier
Hydrogen emission spectrum lines in the visible range. These are the four visible lines of the Balmer series
NGC 604, a giant region of ionized hydrogen in the Triangulum Galaxy
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Hydrogen is the most abundant chemical substance in the universe, constituting roughly 75% of all normal matter.

The hypothesis of Andreas Cellarius, showing the planetary motions in eccentric and epicyclical orbits.

Multiverse

The hypothesis of Andreas Cellarius, showing the planetary motions in eccentric and epicyclical orbits.

The multiverse is a hypothetical group of multiple universes.