What Are The Orion’s Belt Stars?

Thursday, January 29, 2015

What Are The Orion’s Belt Stars?

The constellation Orion. Credit: Matthew Spinelli NASA/APOD

Orion dominates the winter sky in the northern hemisphere. Its large size and collection of bright stars — such as Betelgeuse at the shoulder, Rigel below the belt, and the three stars in the belt — make it easy to spot, even for beginning stargazers.

So how about those stars in the belt? They’re one of the most famous asterisms in Western culture, but beyond what we see with our eyes, what are their astronomical properties?

Introduction to Orion

First, a brief word about the constellation itself. In many mythologies, the shape is seen as a human figure — and in Greek mythology, it was named after a hunter, according to a web page from the Chandra X-Ray Observatory.

There are several “reasons” in mythology for why Orion ended up in the sky. One was because he was too boastful about how many animals he could kill — so he was put there to teach humility, since he and his dogs (Canis Major and Canis Minor) chase after animals in the sky but can’t catch them. Some say he died from a scorpion bite, and other legends say he was killed by his lover Artemis accidentally, when her brother Apollo tricked her to shooting an arrow at him.

Wide angle shot of Comet Lovejoy with the constellation Orion, showing rich fields of red nebula, star clouds and dark nebula with the bright green naked eye comet. Credit and copyright: Chris Schur.

Because Orion is on the celestial equator, Chandra adds, it is easy to see all over the world: “Ancient Indians saw the figure as a king who had been shot by an arrow (represented by the stars in Orion’s belt). Ancient Egyptians thought the stars in the belt represented the resting place of the soul of the god Osiris. The Arabs saw the constellation as the figure of a giant.”

The Orion’s belt stars

The three stars in the belt are Mintaka, Alnilam and Alnitak. According to an astronomer with the National Radio Astronomy Observatory, Ronald Maddlaena, these are the meanings of the three stars: Mintaka (on the west) means “belt”, Alnilam (in center) means “belt of pearls” and Altnitak (right) means “girdle.” The three range between 800 and 1,000 light-years from Earth.

The stars “probably formed at about the same time some ten million years ago from the molecular clouds astronomers have found in Orion,” wrote Maddalena.

In this image, the submillimetre-wavelength glow of the dust clouds is overlaid on a view of the region in the more familiar visible light, from the Digitized Sky Survey 2. The large bright cloud in the upper right of the image is the well-known Orion Nebula, also called Messier 42. Credit: ESO/Digitized Sky Survey 2

Here are their properties compared to the Sun:

Mintaka: 20 times more massive and 7,000 times brighter. (Surface temperature 60,000 Fahrenheit.)

Alnilam: 20 times more massive and 18,000 times brigher. (Surface temperature 50,000 Fahrenheit.)

Alnitak: 20 times more massive and 10,000 times brighter. (Surface temperature 60,000 Fahrenheit).

To further blow your mind — these stars also have companion stars orbiting with them, so what you see from Earth with the naked eye isn’t necessarily what you always get.

We have written many articles about Orion for Universe Today. Here’s an article about the Orion Nebula, and another about the dust grains in the Orion Nebula. We’ve also done many episodes of Astronomy Cast about stars, such as this: Episode 12: Where Do Baby Stars Come From?

About Elizabeth Howell

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter @howellspace or contact her at her website.

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The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

UFO SIGHTINGS PHOTO PHOTOGRAPHY

The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'." The first published book to use the word was authored by Donald E. Keyhoe. The acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced Yoo-foe) for short." Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object", and "flying saucer". The phrase "flying saucer" had gained widespread attention after the summer of 1947. On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold timed the sighting and estimated the speed of discs to be over 1,200 mph (1,931 km/h). At the time, he described the objects' shape as being somewhat disc-like or saucer-like, leading to newspaper accounts of "flying saucers" and "flying discs". In popular usage the term UFO came to be used to refer to claims of alien spacecraft. and because of the public and media ridicule associated with the topic, some investigators prefer to use such terms as unidentified aerial phenomenon (or UAP) or anomalous phenomena, as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).

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UFO - Unidentified Flying Object An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not identifiable as a known object or phenomenon. Culturally, UFOs are associated with claims of visitation by extraterrestrial life or government-related conspiracy theories, and have become popular subjects in fiction. While UFOs are often later identified, sometimes identification may not be possible owing to the usually low quality of evidence related to UFO sightings (generally anecdotal evidence and eyewitness accounts). Stories of fantastical celestial apparitions have been told since antiquity, but the term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." Accordingly, the term was initially restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and/or "technical aspects" (see Air Force Regulation 200-2). During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs". The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security. Various studies have concluded that the phenomenon does not represent a threat to national security nor does it contain anything worthy of scientific pursuit (e.g., 1951 Flying Saucer Working Party, 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee).

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Photos of Nature | Nature Photography What is The Universe

Thursday, January 29, 2015