an hii region be seen in what constellation

an hii region be seen in what constellation插图

Orion Nebula

Where did the constellation list come from?

The constellation list was produced by American astronomer Henry Norris Russell and adopted by the International Astronomical Union (IAU) at its General Assembly in Rome in May 1922. Russell also provided three-letter abbreviations for each of the 89 constellations (the 88 modern ones and the Greek constellation Argo, which was later dropped).

What is the brightest star in the constellation Orionis?

Rigel – β Orionis (Beta Orionis, 19 Orionis) Rigel is the brightest star in the constellation. With an apparent magnitude of 0.18, it is also the sixth brightest star in the sky. Even though it does not have the designation alpha, it is almost always brighter than Betelgeuse, Alpha Orionis.

When were the boundaries of the modern constellations defined?

The boundaries of the modern 88 constellations ( listed below) were defined in the early 20th century. The constellation list was produced by American astronomer Henry Norris Russell and adopted by the International Astronomical Union (IAU) at its General Assembly in Rome in May 1922.

What is the most famous nebula in the Rigel constellation?

The most famous one is IC 2118, also known as the Witch Head Nebula, a faint reflection nebula located about 2.5 degrees to the northwest of Rigel, in the constellation Eridanus. Rigel is a member of the Taurus-Orion R1 Association.

What is the name of the nebula in the constellation Sagittarius?

The foreground dark material obscures about half the ionized nebula. Lagoon Nebula (M8, NGC 6523) in the constellation Sagittarius.This bright diffuse nebula is so large that light from the stars involved does not penetrate its boundaries, and the bright nebula appears to be seen against a larger, darker one.

How many miles is the Orion Nebula?

In the Orion Nebula this is about 6 billion km (4 billion miles), or about the radius of the orbit of Pluto around the Sun. Even finer details almost surely exist, and there is evidence from spectra that much of the matter may be gathered into dense condensations, or knots, the rest of the space being comparatively empty.

How fast is the Orion nebula?

A plume of gas (lower right) in the Orion Nebula.This highly supersonic shock wave—moving at a speed of more than 238,000 km (148,000 miles) per hour— was produced by a beam of material emanating from a newly formed star.

What pressure is needed to restrain nebular gas?

The nebular gas must be restrained from expansion by the pressure of million-degree tenuous material between the filaments. Its pressure, however, is comparable to that in the visible “warm” (8,000 K) gas of the H II region.

Where does the energy for ionizing and heating hydrogen come from?

The energy that is responsible for ionizing and heating the hydrogen in an emission nebula comes from a central star that has a surface temperature in excess of 20,000 K. The density of these clouds normally ranges from 10 to 100,000 particles per cubic cm; their temperature is about 8,000 K. Like molecular clouds, H II regions typically have …

Which nebula is ionized?

The Orion Nebula, for example, is merely a conspicuous ionized region on the nearby face of a much larger dark cloud; the H II region is almost entirely produced by the ionization provided by a single hot star, one of the four bright central stars (the Trapezium) identified by Dutch astronomer Christiaan Huygens in 1656.

How does the stellar wind move in the interior of a bubble?

In the interior of the bubble, the radially flowing stellar wind passes through a transition in which its radial motion is converted into heat. The hot gas then fills most of the cavity (perhaps 90 percent or more) and serves to separate the filaments of the warm, comparatively dense H II region.

What year were the Russell constellations listed?

The constellations on Russell’s list corresponded to those listed in the Revised Harvard Photometry star catalogue (1908) , published by Harvard College Observatory.

How many constellations are there?

There are 88 constellations officially recognized by the International Astronomical Union (IAU). 36 modern constellations predominantly lie in the northern sky, while 52 are found in the southern celestial hemisphere. Most constellations (more than 40) represent animals. Many were named after humans or figures from mythology, …

Who created the constellation list?

The constellation list was produced by American astronomer Henry Norris Russell and adopted by the International Astronomical Union (IAU) at its General Assembly in Rome in May 1922.

Why is the nebula black?

The reason why the patch appears black has not yet been determined, but one theory suggests that narrow jets of gas from the neighbouring young stars may have punctured the sheet of dust and gas in the nebula and strong radiation from an older star in the region may have helped create the hole.

How far apart are the stars in the Orionis system?

Unlike most binary and multiple stars that share the same Bayer designation, the stars in the Pi Orionis system are fairly wide apart . Pi-1 Orionis and Pi-6 Orionis are separated by almost nine degrees.

How many stars are in Sigma Orionis?

Sigma Orionis is a multiple star system in Orion constellation. It consists of five stars located a little south of Alnitak. The components’ apparent magnitudes range from 4.2 to 6.7. The system is approximately 1,150 light years distant.

What is the brightest star in the constellation?

The brightest star in the constellation is Rigel, Beta Orionis, with an apparent magnitude of 0.18. Rigel is also the sixth brightest star in the sky. The second brightest star in Orion, Betelgeuse, Alpha Orionis, has an apparent magnitude of 0.43 and is the eighth brightest star in the night sky. The constellation Orion contains 10 formally named …

What is the 26th constellation?

Orion is the 26th constellation in size, occupying an area of 594 square degrees. It is located in the first quadrant of the northern hemisphere (NQ1) and can be seen at latitudes between +85° and -75°. The neighboring constellations are Eridanus, Gemini, Lepus, Monoceros and Taurus.

How many light years away is Phi Orionis?

Phi Orionis refers to two star systems in Orion, Phi-1 Orionis and Phi-2 Orionis, separated by 0.71° degrees. Phi-1 Orionis is a double star approximately 1,000 light years distant. The main component is a main sequence star belonging to the spectral type B0, with an apparent magnitude of 4.39.

What is the magnitude of Mintaka?

In the order of brightness, the apparent magnitudes of the components are 2.23 (3.2/3.3), 6.85, 14.0. Mintaka is the faintest of the three stars in Orion’s Belt and the seventh brightest star in Orion. It is the closest bright star to the celestial equator: it rises and sets almost exactly east and west.

What is the charge of an ionized hydrogen atom?

Ionization is a change in the charge of an atom by removing electrons, so an ionized Hydrogen region is composed of just protons and free electrons. In astronomy, it is usual to denote the neutral atom with a roman numeral I (HI), then an ion that lost one electron with II (HII), an ion that lost two electrons with III (OIII) etc.

What are the characteristics of HII regions?

Another interesting characteristic of HII regions is that it is relatively straightforward to measure their temperature and density. This is due to the fact that less abundant elements like Oxygen and Sulphur may also be ionized and then be recombined, however the electron will not always “cascade” down to a lower energy level from the same excited level. From the ratio of the spectral lines this causes, it is possible to infer either the temperature (usually OIII is used) or the density (usually OII or SII are used).

What is ionized hydrogen?

Ionization is a change in the charge of an atom by removing electrons, so an ionized Hydrogen region is composed of just protons and free electrons. In astronomy, it is usual to denote the neutral atom with a roman numeral I (HI), then an ion that lost one electron with II (HII), an ion that lost two electrons with III (OIII) etc. HI regions, clouds of neutral Hydrogen, do exist and observed in radio wavelengths can be used to determine properties of spiral galaxies. We are more interested in HII regions here, since they emit light in visible wavelengths, which makes them amazing targets for astrophotography.

How does recombination occur in HII?

In our HII region, at the same time as photoionization, the opposite process recombination occurs, where a nucleus “captures” a passion electron into an excited energy level, the electron then falls back to the ground state. This causes the emission of a photon with an energy (and thus a wavelength) corresponding to that transition. The hotter the region, the faster the free electrons will move and the faster they can encounter and be reabsorbed into a Hydrogen atom; but the faster the electron is the less likely it is to be “captured”. After some maths, this leads to a limit to the size of a photoionized region, where the number of recombinations equals the number of ionizing photos that the star emits, approximated as the “Strömgren sphere” of typically 1-100parsecs in radius.