Sh2-308, also designated as Sharpless 308, RCW 11, or LBN 1052, and commonly known as the Dolphin-Head Nebula, is an

H II region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

located near the center of the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Canis Major Canis Major is a constellation in the Southern Celestial Hemisphere, southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin fo ...

, composed of ionised hydrogen. It is about 8 degrees south of

Sirius Sirius is the list of brightest stars, brightest star in the night sky. Its name is derived from the Ancient Greek language, Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinisation ...

, the brightest

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the night sky. The

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

is bubble-like and surrounds a

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

named

EZ Canis Majoris EZ Canis Majoris (abbreviated to EZ CMa, also designated as WR 6) is binary system in the constellation of Canis Major. The primary is a Wolf-Rayet star and it is one of the ten brightest Wolf-Rayet stars, brighter than ...

. This star is in the brief, pre-

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

phase of its

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

. The nebula is about away from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, but some sources indicate that both the star and the nebula are up to away. Yet others indicate the nebula is as close as from Earth.

Central star

Sh2-308 surrounds the Wolf–Rayet star EZ Canis Majoris, also designated EZ CMa or WR 6. Its

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

varies from 6.71 to 6.95. Its

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

indicates that the star is very hot and luminous. The

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

shows that it is devoid of hydrogen at the surface. EZ Canis Majoris is expected eventually to explode in a supernova, therefore subsuming the nebula.

Formation

The nebula was formed about 70,000 years ago by the star EZ Canis Majoris throwing off its outer

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

layers, revealing inner layers of heavier elements. Fast

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

s, blowing at from this star, create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of the star's evolution. The hydrogen composing the nebula is

ionised Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...

by intense

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

radiation. The nebula is approximately 60 light-years across at its widest point.

Observation

The most favorable period for observing the nebula in the night sky is between the months of December and April. Its southern

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...

makes it easier to observe from the Southern Hemisphere, though it is easily visible from most of the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

as well. It appears as a faint cloud in photographs taken with high-power amateur instruments, with the help of special filters.

Gallery

File:Inflating Sh2-308.jpg, A portion of Sh2-308 to the west of

File:Sh2-308.jpg, A small portion of Sh2-308 imaged by the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

(up is north-west) File:SH2-308.jpg, alt=SH2-308 astrophotograph, Dolphin Head Nebula – SH2-308. Processed by Jim DeLillo via TelescopeLive One-Click Imaging

References

External links

APOD
December 20, 2016 {{DEFAULTSORT:Sh2-308 Sharpless objects Canis Major Emission nebulae Nebulae