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<!DOCTYPE html>
<html lang="en-us">
<head>
<!-- Google tag (gtag.js) -->
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<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1" />
<meta name="description" content="On this web page you can look at images of astronomical objects.">
<title>Astronomy Safari - Explore the wonders of the Universe</title>
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<div class="container">
<header>
<h1>Astronomy Safari</h1>
<nav>
<a class="menu-button" href="./index.html">About</a>
<a class="menu-button" href="./explanation-of-astronomical-terms.html">Explanation</a>
<!-- <a class="menu-button" href="./d3-celestial.html">Skymap</a> -->
<label for="astro-type" class="astro-type">
<select id="astro-type">
<option value="">Type of object</option>
<option value="All objects">All objects</option>
<optgroup label="Galaxies">
<option value="Galaxy" class="optionGroup">Galaxies</option>
<option value="Blazar galaxy">Blazar</option>
<option value="Elliptical galaxy">Elliptical galaxies</option>
<option value="Distant galaxy">Distant galaxy</option>
<option value="Dwarf galaxy">Dwarf galaxy</option>
<option value="Interacting galaxy">Interacting galaxies</option>
<option value="Irregular galaxy">Irregular galaxies</option>
<option value="Lenticular galaxy">Lenticular galaxy</option>
<option value="Quasar galaxy">Quasar</option>
<option value="Peculiar galaxy">Peculiar galaxy</option>
<option value="Radio galaxy">Radio galaxy</option>
<option value="Ring galaxy">Ring galaxy</option>
<option value="Seyfert galaxy">Seyfert galaxy</option>
<option value="Spiral galaxy">Spiral galaxies</option>
</optgroup>
<optgroup label="Multiple Galaxies">
<option value="Cluster galaxy">Galaxy Cluster</option>
<option value="Group galaxy">Galaxy group</option>
<option value="Super-cluster galaxy">Supercluster</option>
</optgroup>
<optgroup label="Clusters">
<option value="Cluster" class="optionGroup">Clusters</option>
<option value="Globular cluster">Globular clusters</option>
<option value="Open cluster">Open clusters</option>
<option value="Star cluster">Star clouds</option>
<option value="Super-star cluster">Super star cluster
</option>
</optgroup>
<optgroup label="Nebulae">
<option value="Nebula" class="optionGroup">Nebulae</option>
<option value="Dark nebula">Dark nebula</option>
<option value="Herbig–Haro nebula">Herbig–Haro nebula</option>
<option value="Emission nebula">Emission nebulae</option>
<option value="Planetary nebula">Planetary nebulae</option>
<option value="Reflection nebula">Reflection nebulae</option>
<option value="Star-forming nebula">Star-forming regions</option>
<option value="Supernova-remnant nebula">Supernova remnant</option>
<option value="Variable nebula">Variable nebula</option>
</optgroup>
</select>
</label>
<label for="astro-const" class="astro-const">
<select id="astro-const">
<option value="">Constellations</option>
<optgroup label="A">
<option value="Andromeda">Andromeda</option>
<option value="Antilia">Antilia</option>
<option value="Apus">Apus</option>
<option value="Ara">Ara</option>
<option value="Aries">Aries</option>
<option value="Aquarius">Aquarius</option>
<option value="Aquila">Aquila</option>
<option value="Auriga">Auriga</option>
</optgroup>
<optgroup label="B">
<option value="Boötes">Boötes</option>
</optgroup>
<optgroup label="C">
<option value="Caelum">Caelum</option>
<option value="Camelopardalis">Camelopardalis</option>
<option value="Cancer">Cancer</option>
<option value="Canes Venatici">Canes Venatici</option>
<option value="Canis Major">Canis Major</option>
<option value="Canis Minor">Canis Minor</option>
<option value="Capricornus">Capricornus</option>
<option value="Carina">Carina</option>
<option value="Cassiopeia">Cassiopeia</option>
<option value="Centaurus">Centaurus</option>
<option value="Cepheus">Cepheus</option>
<option value="Cetus">Cetus</option>
<option value="Chamaeleon">Chamaeleon</option>
<option value="Circinus">Circinus</option>
<option value="Columba">Columba</option>
<option value="Coma Berenices">Coma Berenices</option>
<option value="Corona Australis">Corona Australis</option>
<option value="Corvus">Corvus</option>
<option value="Crater">Crater</option>
<option value="Crux">Crux</option>
<option value="Cygnus">Cygnus</option>
</optgroup>
<optgroup label="D">
<option value="Delphinus">Delphinus</option>
<option value="Dorado">Dorado</option>
<option value="Draco">Draco</option>
</optgroup>
<optgroup label="E">
<option value="Equuleus">Equuleus</option>
<option value="Eridanus">Eridanus</option>
</optgroup>
<optgroup label="F">
<option value="Fornax">Fornax</option>
</optgroup>
<optgroup label="G">
<option value="Gemini">Gemini</option>
<option value="Grus">Grus</option>
</optgroup>
<optgroup label="H">
<option value="Hercules">Hercules</option>
<option value="Horologium">Horologium</option>
<option value="Hydra">Hydra</option>
<option value="Hydrus">Hydrus</option>
</optgroup>
<optgroup label="I">
<option value="Indus">Indus</option>
</optgroup>
<optgroup label="L">
<option value="Lacerta">Lacerta</option>
<option value="Leo">Leo</option>
<option value="Leo Minor">Leo Minor</option>
<option value="Lepus">Lepus</option>
<option value="Libra">Libra</option>
<option value="Lupus">Lupus</option>
<option value="Lynx">Lynx</option>
<option value="Lyra">Lyra</option>
</optgroup>
<optgroup label="M">
<option value="Mensa">Mensa</option>
<option value="Microscopium">Microscopium</option>
<option value="Monoceros">Monoceros</option>
<option value="Musca">Musca</option>
</optgroup>
<optgroup label="N">
<option value="Norma">Norma</option>
</optgroup>
<optgroup label="O">
<option value="Octans">Octans</option>
<option value="Ophiuchus">Ophiuchus</option>
<option value="Orion">Orion</option>
</optgroup>
<optgroup label="P">
<option value="Pavo">Pavo</option>
<option value="Pegasus">Pegasus</option>
<option value="Perseus">Perseus</option>
<option value="Phoenix">Phoenix</option>
<option value="Pictor">Pictor</option>
<option value="Pisces">Pisces</option>
<option value="Piscis Austrinus">Piscis Austrinus</option>
<option value="Puppis">Puppis</option>
<option value="Pyxis">Pyxis</option>
</optgroup>
<optgroup label="R">
<option value="Reticulum">Reticulum</option>
</optgroup>
<optgroup label="S">
<option value="Sagitta">Sagitta</option>
<option value="Sagittarius">Sagittarius</option>
<option value="Scorpius">Scorpius</option>
<option value="Sculptor">Sculptor</option>
<option value="Scutum">Scutum</option>
<option value="Serpens Caput">Serpens Caput</option>
<option value="Serpens Cauda">Serpens Cauda</option>
<option value="Sextans">Sextans</option>
</optgroup>
<optgroup label="T">
<option value="Taurus">Taurus</option>
<option value="Telescopium">Telescopium</option>
<option value="Triangulum">Triangulum</option>
<option value="Triangulum Australe">Triangulum Australe</option>
<option value="Tucana">Tucana</option>
</optgroup>
<optgroup label="U">
<option value="Ursa Major">Ursa Major</option>
<option value="Ursa Minor">Ursa Minor</option>
</optgroup>
<optgroup label="V">
<option value="Vela">Vela</option>
<option value="Virgo">Virgo</option>
<option value="Volans">Volans</option>
<option value="Vulpecula">Vulpecula</option>
</optgroup>
</select>
</label>
<label for="astro-dist" class="astro-dist">
<select id="astro-dist">
<option value="">Distance</option>
<optgroup label="A">
<option value="100">100 ly - 1 kly</option>
<option value="1000">1 kly - 10 kly</option>
<option value="10000">10 kly - 100 kly</option>
<option value="100000">100 kly - 1 Mly</option>
<option value="1000000">1 Mly - 10 Mly</option>
<option value="10000000">10 Mly - 100 Mly</option>
<option value="100000000">100 Mly - 1 Gly</option>
<option value="1000000000">1 Gly - 10 Gly</option>
</optgroup>
</select>
</label>
</nav>
</header>
<main>
<div class="start-page">
<article class="explanation">
<!-- <div id="num-obj"> </div> -->
<h2>Galaxies</h2>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/NGC_4414_%28NASA-med%29.jpg/291px-NGC_4414_%28NASA-med%29.jpg"
alt="Spiral galaxy NGC 4414">
<figcaption>Spiral galaxy NGC 4414</figcaption>
</figure>
<p class="start-text">A galaxy is a collection of stars, stellar remains, interstellar gas, dust,
and dark matter that are gravitationally bonded together. A galaxy range in size from dwarf
galaxies with
fewer than 100 million stars to supergiants, which have 100 trillion stars around their galaxy's
center of mass. It's believed that the centers of several of them contain supermassive black
holes. The majority of galaxies are between 3,000 and 300,000 light years apart and are spaced
at intervals of millions of light years. </p>
<p>Galaxies can be classed as spiral, elliptical, or irregular based on certain characteristics.
They can also be further split based on the predominant morphology of their visible stars. These
various geometries are believed to be the result of various rates and types of star formation,
as well as later dynamical influences from dark matter distributions.</p>
<p>Galaxies are made up of many different elements, such as stars, gas, and dust, as well as an
opacity that is typically attributed to dark matter. Particular importance is attached to a
galaxy's star component.</p>
<h3>Blazar</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Blazar-illustration.jpg/320px-Blazar-illustration.jpg"
alt="Artist's impression of a blazar">
<figcaption>Artist's impression of a blazar</figcaption>
</figure>
<p class="start-text">A relativistic jet, which is a jet made up of ionized matter moving at almost
the speed of light, is directed very nearly at an observer and is characteristic of an active
galactic nucleus (AGN) called a blazar. Blazars appear significantly brighter than they would if
the jet were pointing away from Earth because of relativistic beaming of electromagnetic
radiation from the jet. It has been established that blazars are generators of high-energy gamma
ray photons and are potent sources of emission across the electromagnetic spectrum. Blazars are
extremely variable sources that frequently experience abrupt and dramatic changes in brightness
over short periods of time (hours to days). Another result of material in the jet moving toward
the observer at almost the speed of light is the apparent superluminal motion that some blazar
jets appear to be experiencing.</p>
<h3>Elliptical galaxies</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/d/d3/Abell_S740%2C_cropped_to_ESO_325-G004.jpg/224px-Abell_S740%2C_cropped_to_ESO_325-G004.jpg"
alt="Elliptical galaxy ESO 325-G004">
<figcaption>Elliptical galaxy ESO 325-G004</figcaption>
</figure>
<p class="start-text">A form of galaxy known as an elliptical galaxy has a smooth, nearly
featureless appearance and an approximate ellipsoidal shape. The majority of elliptical galaxies
are made up of older, low-mass stars, have a scant interstellar medium, little star formation,
and are frequently ringed by numerous globular clusters. Elliptical galaxies range in size from
dwarf ellipticals with tens of millions of stars to supergiants with more than one hundred
trillion stars that are the dominant members of their galaxy clusters..</p>
<h3>Distant galaxies</h3>
<figure> <img src="https://upload.wikimedia.org/wikipedia/commons/9/98/MACS0647-JD.JPG"
alt="Distant galaxy MACS0647-JD">
<figcaption>Distant galaxy MACS0647-JD</figcaption>
</figure>
<p class="start-text">It is challenging to determine the sort of galaxy distant galaxies are due to
their tremendous distance. It has also taken time for the light to reach us so the observed
galaxy was
probably very early in its development. Another aspect is that we have so little data to go
on
with that other than say it is some kind of early galaxy we can’t be sure what type it is.
</p>
<h3>Dwarf galaxies</h3>
<figure> <img
src=" https://upload.wikimedia.org/wikipedia/commons/thumb/b/b3/NGC_5264_HST.jpg/233px-NGC_5264_HST.jpg"
alt="Hubble Space Telescope image of MACS0647-JD">
<figcaption>Dwarf galaxy NGC 5264 </figcaption>
</figure>
<p class="start-text">A dwarf galaxy is a relatively tiny galaxy with between 1000 and several
billion stars. Some people believe the Large Magellanic Cloud, which closely orbits the Milky
Way and has about 30 billion stars, to be a dwarf galaxy, while others see it as a full-fledged
galaxy. It is believed that interactions with larger galaxies have a significant impact on the
development and activity of dwarf galaxies. Based on their structure and makeup, astronomers
classify dwarf galaxies into a variety of categories.</p>
<h3>Interacting galaxies</h3>
<figure>
<video width="320" height="240" controls>
<source
src="https://upload.wikimedia.org/wikipedia/commons/c/c3/Galaxy_Collision_Animation-_James_Webb_Space_Telescope_Science.webm"
type="video/webm">
Your browser does not support the video tag.
</video>
<figcaption>Animation of galaxies colliding</figcaption>
</figure>
<p class="start-text">Galaxies that perturb one another because to their gravitational fields are
known as colliding or interacting galaxies. A satellite galaxy disrupting the spiral arms of the
main galaxy is an illustration of a minor interaction. A galactic collision, which could result
in a galaxy merger, is an example of a massive collision. During galactic evolution, galaxies
frequently collide. These are gravitational interactions rather than collisions in the
conventional sense due to the exceedingly tenuous distribution of matter in galaxies.
</p>
<h3>Irregular galaxies</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Irregular_galaxy_NGC_1427A_%28captured_by_the_Hubble_Space_Telescope%29.jpg/213px-Irregular_galaxy_NGC_1427A_%28captured_by_the_Hubble_Space_Telescope%29.jpg"
alt="Irregular galaxy NGC 1427A">
<figcaption>Irregular galaxy NGC 1427A</figcaption>
</figure>
<p class="start-text">In contrast to spiral or elliptical galaxies, irregular galaxies lack a
recognizable regular shape. In addition to not fitting into any of the normal classes, irregular
galaxies frequently have a chaotic appearance and lack either a nuclear bulge or any indication
of spiral arm structure. They are estimated to make up around 25% of all galaxies in total. Some
asymmetric galaxies that are now irregular were formerly spiral or elliptical galaxies that were
distorted by an unequal external gravitational influence.
Typically, irregular galaxies are tiny, with a mass of only a tenth that of the Milky Way
galaxy. They are vulnerable to environmental influences like colliding with massive galaxies and
cosmic radiation because of their small sizes.</p>
<h3>Lenticular galaxies</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Ngc5866_hst_big.png/204px-Ngc5866_hst_big.png"
alt="Lenticular galaxy NGC 5866">
<figcaption>Lenticular galaxy NGC 5866</figcaption>
</figure>
<p class="start-text">A form of galaxy that lies somewhere between an elliptical and a spiral galaxy
is called a lenticular galaxy. It lacks large-scale spiral arms but has a large-scale disc.
Lenticular galaxies are disc galaxies with very little continuing star formation because they
have mostly used up or lost all of their interstellar materials. However, they might keep a lot
of dust in their disks. They are primarily made up of elderly stars as a result (like elliptical
galaxies). Lenticular and elliptical galaxies share characteristics including spectral features
and scale relations despite their physical variances. Both types of galaxies, at least in the
region where they are located, can be regarded as early-type galaxies that are passively
evolving.</p>
<h3>Quasar</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/38/Artist%27s_rendering_ULAS_J1120%2B0641.jpg/320px-Artist%27s_rendering_ULAS_J1120%2B0641.jpg"
alt="Quasar in ULAS J1120+0641 (Artist's rendering of the accretion disc)">
<figcaption>Quasar in ULAS J1120+0641 (Artist's rendering of the accretion disc) </figcaption>
</figure>
<p class="start-text">A supermassive black hole with a mass between millions and tens of billions of
solar masses that is fueled by a superluminous active galactic nucleus (AGN) and encircled by a
gaseous accretion disc is known as a quasar, also known as a quasi-stellar object. Due to
friction, the gas in the disc that is falling towards the black hole heats up and emits
electromagnetic radiation as a result. The most potent quasars have luminosities hundreds of
times larger than that of a galaxy like the Milky Way, demonstrating the immense radiant energy
of quasars. Typically, quasars are classified as a subclass of the AGN category, which is more
broadly defined. </p>
<h3>Peculiar galaxy</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/0e/Extragalactic_peculiarity.jpg/320px-Extragalactic_peculiarity.jpg"
alt="Quasar in ULAS J1120+0641 (Artist's rendering of the accretion disc)">
<figcaption>Peculiar galaxy ESO 162-17</figcaption>
</figure>
<p class="start-text">A strange galaxy is one that has distinctive dimensions, features, or
composition. Five to ten percent of known galaxies fall into the unusual category. Interacting
galaxies and active galactic nuclei are the two categories of strange galaxies that astronomers
have discovered.
When two galaxies are relatively close to one another, their gravitational pulls can cause them
to take on wildly erratic shapes. Since the bulk of peculiar galaxies credit their formation to
such gravitational forces, the terms "interacting galaxy" and "peculiar galaxy" have come to be
synonymous. </p>
<h3>Radio galaxies</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/a0/GRGAlcyoneusIRBlueRadioOrange.png/240px-GRGAlcyoneusIRBlueRadioOrange.png"
alt="Ring galaxy Hoag's Object">
<figcaption>Radio galaxy Alcyoneus, the largest radio galaxy yet found</figcaption>
</figure>
<p class="start-text">A radio galaxy is a galaxy having enormous radio emission areas that extend
well beyond the visible structure of the galaxy. Its active galactic nucleus's jets fuel these
powerful radio lobes. The synchrotron process is responsible for the radio emission. The
interaction of twin jets with the external medium, which is then altered by the effects of
relativistic beaming, produces the observable structure in radio emission. Large elliptical
galaxies make up the majority of the host galaxies. The ability to identify radio-loud active
galaxies at great distances makes them useful tools for observational cosmology. The impacts of
these objects on the intergalactic medium have recently received a lot of attention, especially
in galaxy groups and clusters.</p>
<h3>Ring galaxies</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Hoag%27s_object.jpg/245px-Hoag%27s_object.jpg"
alt="Ring galaxy Hoag's Object">
<figcaption>Ring galaxy Hoag's Object</figcaption>
</figure>
<p class="start-text">A galaxy that resembles a circle is known as a ring galaxy. Numerous big,
relatively young blue stars that are exceptionally brilliant can be found in the ring. There
isn't a lot of bright substance in the center. Some astronomers think that smaller galaxies pass
through the center of larger galaxies to create ring galaxies. This "collision" hardly ever
causes any actual star collisions because the majority of a galaxy is empty space. However, due
to the gravitational perturbations brought on by such an occurrence, the larger galaxy can
experience a wave of star creation. Other astronomers believe that when external accretion
occurs, rings are created around some galaxies. The shocks and compressions of the accreted
material would then induce star formation.</p>
<h3>Seyfert galaxy</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Circinus.galaxy.750pix.jpg/240px-Circinus.galaxy.750pix.jpg"
alt="Seyfert galaxy The Circinus Galaxy">
<figcaption>Seyfert galaxy The Circinus Galaxy</figcaption>
</figure>
<p class="start-text">Along with quasars, Seyfert galaxies make up one of the two major groupings of
active galaxies. They contain quasar-like nuclei (very bright, far-off sources of
electromagnetic radiation) with very high surface brightnesses, and their spectra show strong,
high-ionization emission lines. However, unlike quasars, their host galaxies are easily
discernible.</p>
<p>
Seyfert galaxies, which make up 10% of all galaxies but are closer and less brilliant than
quasars, are among the most closely researched objects in astronomy because they are assumed to
be driven by the same processes as quasars. These galaxies include supermassive black holes at
their centers that are encircled by accretion discs of material falling into the galaxy. The UV
radiation seen is thought to have originated from the accretion discs. The greatest indicators
for the makeup of the surrounding material are ultraviolet emission and absorption lines.</p>
<p>
Most Seyfert galaxies appear to be regular spiral galaxies when viewed in visible light, but
when examined at other wavelengths, it is evident that their core luminosities are on par with
that of entire galaxies the size of the Milky Way.
Carl Seyfert, who initially identified this class in 1943, is honored by the term Seyfert
galaxies.</p>
<h2>Multiple Galaxies</h2>
<h3>Galaxy cluster</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Color_image_of_galaxy_cluster_MCS_J0416.1%E2%80%932403.jpg/250px-Color_image_of_galaxy_cluster_MCS_J0416.1%E2%80%932403.jpg"
alt="Galaxy cluster MCS J0416.1–2403">
<figcaption>Galaxy cluster MCS J0416.1–2403</figcaption>
</figure>
<p class="start-text">A galaxy cluster, also known as a cluster of galaxies, is a structure made up
of several hundred to thousands of galaxies that are gravitationally connected together. These
galaxies typically have masses between 10<sup>14</sup> and 10<sup>15</sup> solar masses. The
intracluster
medium is a crucial component of clusters (ICM). The ICM is made up of hot gas between the
galaxies that is influenced by the cluster's overall mass. Galaxy clusters should not be
confused with globular clusters, which commonly circle galaxies, or with galactic clusters, also
known as open clusters, which are star clusters within galaxies. Galaxy groups, as opposed to
galaxy clusters, are used to describe small collections of galaxies. Superclusters can form when
galaxy groupings and clusters combine together.
The Virgo Cluster, Fornax Cluster, Hercules Cluster, and Coma Cluster are notable galaxy
clusters in the very nearby Universe. Gigantic enough to have an impact on the local expansion
of the Universe is the Great Attractor, a massive collection of galaxies dominated by the Norma
Cluster.</p>
<h3>Galaxy group</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/0b/Hubble_views_bizarre_cosmic_quartet_HCG_16.jpg/320px-Hubble_views_bizarre_cosmic_quartet_HCG_16.jpg"
alt="Galaxy group HCG 16">
<figcaption>Galaxy group HCG 16</figcaption>
</figure>
<p class="start-text">A galaxy group, also known as a group of galaxies, is a collection of galaxies
with at least 50 gravitationally bound members that are each at least as bright as the Milky
Way. Galaxy clusters are collections of galaxies that are larger than groupings. Superclusters
of galaxies can be formed by grouping together groups and clusters of galaxies.
The Milky Way galaxy is a member of the Local Group of galaxies.</p>
<h3>Supercluster</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/An_Intergalactic_Heavyweight.jpg/241px-An_Intergalactic_Heavyweight.jpg"
alt="Supercluster Abell 901/902">
<figcaption>Supercluster Abell 901/902</figcaption>
</figure>
<p class="start-text">Superclusters are among the biggest known structures in the cosmos; they are a
vast collection of smaller galaxy clusters or galaxy groups. The Milky Way is a member of the
Local Group galaxy group, which is made up of over 54 other galaxies. The Local Group galaxy
group is a member of the Virgo Supercluster, which is a member of the Laniakea Supercluster.
Superclusters, in contrast to clusters, grow with the Hubble expansion due to their huge size
and low density. There are thought to be 10 million superclusters in the observable universe.
</p>
</article>
<article class="explanation">
<h2>Nebulae</h2>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Trifid_Nebula_by_Deddy_Dayag.jpg/320px-Trifid_Nebula_by_Deddy_Dayag.jpg"
alt="text">
<figcaption>Nebula: Trifid Nebula</figcaption>
</figure>
<p class="start-text">A nebula (Latin for "cloud" or "fog"; plural: nebulae)
a distinctively luminous component of the interstellar medium that can be made up of cosmic
dust, neutral, ionized, or molecular hydrogen. Nebulae are frequently areas where stars are
being formed, as seen in the Eagle Nebula's "Pillars of Creation." The gas, dust, and other
material formations in these areas "clump" together to form denser regions, which draw in more
matter and finally reach a density where stars can form. Planets and other planetary system
objects are then believed to be formed from the material that is left over.</p>
<p class="start-text">Most nebulae are enormous in size; some have diameters of hundreds of
light-years.
Most nebulae are much less dense than any vacuum formed on Earth, despite the fact that they are
denser than the space around them; an Earth-sized nebular cloud would have a total mass of only
a few kilograms. Earth's air has a density of approximately 10<sup>10</sup> molecules per cubic
centimeter; The densest nebulae, in contrast, can contain 10,000 molecules per cubic centimeter.
While some nebulae are so diffused that they may only be seen with long exposures and
specialized filters, others are visible owing to fluorescence created by embedded blazing stars.
</p>
<h3>Herbig–Haro object</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/1/19/Hubble_Sees_the_Force_Awakening_in_a_Newborn_Star_%2823807356641%29.jpg/202px-Hubble_Sees_the_Force_Awakening_in_a_Newborn_Star_%2823807356641%29.jpg"
alt="Herbig–Haro object HH 24">
<figcaption>Herbig–Haro object HH 2</figcaption>
</figure>
<p class="start-text">Herbig–Haro (HH) entities manifest as luminous nebulous patches linked to
recently formed stars. These formations arise from the convergence of slender jets of partially
ionized gas, expelled by stars, with adjacent clouds of gas and dust, colliding at velocities of
several hundred kilometers per second. Typically located in regions where stars are actively
forming, multiple Herbig–Haro entities are frequently observed in proximity to a single star,
aligning with its rotational axis. While the majority are situated within approximately one
parsec (3.26 light-years) of the source, instances of some being observed several parsecs away
have been documented.</p>
<h3>Dark nebulae</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/1/19/All_Quiet_in_the_Nursery%3F.jpg/252px-All_Quiet_in_the_Nursery%3F.jpg"
alt="Dark nebula LDN 1768">
<figcaption>Dark nebula LDN 1768</figcaption>
</figure>
<p class="start-text">A dark nebula, also known as an absorption nebula, is a form of interstellar
cloud, particularly a molecular cloud, that is so dense that it absorbs all of the light from
objects behind it, including emission or reflection nebulae and background stars, at visible
wavelengths. Interstellar dust grains found in the coldest, densest areas of molecular clouds
are what are responsible for the light's extinction. Large complexes and clusters of dark
nebulae are connected to giant molecular clouds. Bok globules are tiny, isolated dark nebulae.
It obscures objects that are only visible in radio astronomy or infrared astronomy using radio
waves or other interstellar dust or debris.</p>
<h3>Emission nebulae</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/62/New_Hubble_image_of_NGC_2174.jpg/240px-New_Hubble_image_of_NGC_2174.jpg"
alt="Emission nebula NGC 2174">
<figcaption>
Emission nebula NGC 2174
</figcaption>
</figure>
<p class="start-text">A nebula made of ionized gases that produce light at different wavelengths is
known as an emission nebula. High-energy ultraviolet photons emitted from a nearby bright star
are the primary cause of ionization. There are many different kinds of emission nebulae,
including H II regions, where star formation is occurring and young, massive stars are the
source of the ionizing photons, and planetary nebulae, where a dying star has shed its outer
layers, exposing the hot core, which then ionizes the surrounding gas. </p>
<h3>Planetary nebulae</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/NGC7293_%282004%29.jpg/223px-NGC7293_%282004%29.jpg"
alt="text">
<figcaption>
Emission nebula NGC 7293, the Helix Nebula.
</figcaption>
</figure>
<p class="start-text">A planetary nebula is a particular kind of emission nebula made up of an
expanding, blazing disk of ionized gas that red giant stars late in their lives expel.
They have nothing to do with planets, therefore calling them "planetary nebula" is a misnomer.
</p>
<p class="start-text">
All planetary nebulae are created upon the death of intermediate-mass stars, which range in mass
from 1 to 8 solar masses. At the conclusion of its life cycle, it is anticipated that the Sun
will create a planetary nebula. Comparatively speaking to the somewhat longer phases of star
evolution, these occurrences are quite brief, lasting perhaps a few tens of millennia. After the
red giant's entire atmosphere has gone, the ejected material is ionized by strong ultraviolet
radiation from the exposed hot luminous core, also known as a planetary nebula nucleus. The
central star's nebulous gas shell is then energized by absorbed ultraviolet light, giving rise
to a vividly colored planetary nebula.</p>
<h3>Reflection nebulae</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Reflection.nebula.arp.750pix.jpg/182px-Reflection.nebula.arp.750pix.jpg"
alt="Reflection nebula IC2118. The Witch Head">
<figcaption>Reflection nebula IC2118. The Witch Head</figcaption>
</figure>
<p class="start-text">Reflexion nebula are interstellar dust clouds in astronomy that may reflect
the light of one or more nearby stars. Although the energy from the neighboring stars is
insufficient to ionize the nebula's gas and produce an emission nebula, it is sufficient to
scatter light in such a way that the dust becomes visible. As a result, the frequency spectrum
displayed by reflection nebulae resembles that of the stars that illuminate the universe.
Diamond dust, for example, and compounds of other metals like iron and nickel are two examples
of the minuscule particles that cause the scattering. The latter two frequently line up with the
galactic magnetic field, which results in a little polarization of the scattered light.</p>
<h3>Star-forming regions</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Orion_Nebula_-_Hubble_2006_mosaic_18000.jpg/240px-Orion_Nebula_-_Hubble_2006_mosaic_18000.jpg"
alt="text">
<figcaption>Star-forming region M42, Orion Nebula</figcaption>
</figure>
<p class="start-text">Stars, stellar remnants, and a diffuse interstellar medium of gas and dust are
all present in spiral galaxies like our own Milky Way. The interstellar medium normally contains
around 70% hydrogen by mass, with helium making up the majority of the remaining gas. Trace
amounts of heavier elements created and ejected from stars through the fusion of helium as they
proceeded beyond the end of their main sequence lifetime have chemically enriched this medium.
Star creation occurs in clouds, or diffuse nebulae, which are formed in the interstellar
medium's higher density areas. Unlike spiral galaxies, elliptical galaxies lose their
interstellar medium's cold component in about a billion years, making it difficult for them to
generate diffuse nebulae unless they merge with other galaxies.</p>
<p class="start-text">
Since a large portion of the hydrogen in dense nebulae where stars are formed is in the
molecular (H2) form, these nebulae are known as molecular clouds. The Orion Nebula, around 1,300
light-years from the Sun, is the closest nebula where huge stars are forming.
However, in the Ophiuchi cloud complex, 400–450 light years away, lower mass star formation is
taking place. </p>
<h3>Supernova-remnant</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Crab_Nebula.jpg/240px-Crab_Nebula.jpg"
alt="Supernova remnant M1, Crab Nebula">
<figcaption>Supernova remnant M1, Crab Nebula</figcaption>
</figure>
<p class="start-text">The structure left over from a supernova explosion is known as a supernova
remnant (SNR). The supernova remnant, which is surrounded by an expanding shock wave, is made up
of the ejected material from the explosion that is expanding as well as the interstellar debris
it sweeps up and shocks along the way.
There are two common ways for a star to go supernova: either it runs out of fuel and stops
producing fusion energy in its core, collapsing inward under the weight of its own gravity to
form a neutron star or a black hole; or it may accrete material from a companion star until it
reaches a critical mass and erupts in a thermonuclear explosion.
</p>
<h3>Variable nebulae</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/Ngc2261.jpg/235px-Ngc2261.jpg"
alt="Variable nebula NGC 2261">
<figcaption>Variable nebula NGC 2261</figcaption>
</figure>
<p class="start-text">They are reflection nebulae connected to Young Stellar Objects that are
not yet Main Sequence objects (of the Hertzsprung-Russell Diagram). On observable timescales,
the nebulae themselves exhibit real changes in brightness, shape, or location. There are
probably many of them in our Milky Way Galaxy's Dark Molecular Clouds, but very few of them are
visible at optical wavelengths, with the majority most likely visible in the infrared. They are
always found there.</p>
<h2>Clusters</h2>
<h3>Globular clusters</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/A_Swarm_of_Ancient_Stars_-_GPN-2000-000930.jpg/229px-A_Swarm_of_Ancient_Stars_-_GPN-2000-000930.jpg"
alt="-">
<figcaption>Globular cluster M 80</figcaption>
</figure>
<p class="start-text">A spherical collection of stars is known as a globular cluster. Gravity holds
globular clusters together, with their centers having a concentration of stars that is greater.
There may be tens of thousands or millions of member stars in them. Their name comes from the
Latin word globulus (small sphere). Occasionally, the term "globulars" is used to refer to
globular clusters.</p>
<h3>Open clusters</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/4/4e/Pleiades_large.jpg/320px-Pleiades_large.jpg"
alt="Open cluster The Pleiades">
<figcaption>Open cluster The Pleiades</figcaption>
</figure>
<p class="start-text">An open cluster is a particular kind of star cluster made up of up to a few
thousand stars that are around the same age and were created from the same massive molecular
cloud. Within the Milky Way galaxy, more than 1,100 open clusters have been found, and many more
are believed to exist. As they orbit the Galactic Center, their tenuous gravitational bonds are
strained by near interactions with other gas clouds and clusters. As a result, cluster members
may migrate to the galaxy's main body or perish in internal close encounters. The majority of
open clusters last for a few hundred million years, with the largest ones lasting for a few
billion.</p>
<h3>Star clouds</h3>
<figure> <img
src="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Scutum_Star_Cloud.jpg/320px-Scutum_Star_Cloud.jpg"
alt="Scutum Star Cloud">
<figcaption>Scutum Star Cloud</figcaption>
</figure>
<p class="start-text">Star clouds are enormous groups of numerous stars dispersed over a very big
distance in a galaxy; they are technically not star clusters. They frequently have star clusters
embedded inside them. The stars appear closely clustered, yet they typically do not form any
kind of structure. Star clouds within the Milky Way can be seen through openings in the Great
Rift's dust clouds, providing deeper vistas along our specific line of sight. Other neighboring
galaxies have also been found to have star clouds. The Small Sagittarius Star Cloud, Large
Sagittarius Star Cloud, Scutum Star Cloud, Cygnus Star Cloud, Norma Star Cloud, and NGC 206 in
the Andromeda Galaxy are a few examples of star clouds.</p>
<h3>Super-star cluster</h3>
<figure> <img src="https://upload.wikimedia.org/wikipedia/commons/9/94/Westerlund_1.jpg"
alt="Super-star cluster Westerlund 1">
<figcaption>Super-star cluster Westerlund 1</figcaption>
</figure>
<p class="start-text">A young, extremely enormous open cluster called a super star cluster (SSC) is
hypothesized to be the forerunner of a globular cluster. These clusters are known as "super"
clusters because they are more massive and relatively more bright than other early star
clusters. However, the SSC should not physically outweigh other clusters with lower mass and
luminosity. A nearby HII zone is often ionized by the vast number of young, massive stars that
are typically present in them.</p>
</article>
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