Explore the Depths of Orion

The constellation Orion rises to prominence beginning in December and is visible through mid-April each year. The bright orangeish star at the lower left is called Betelgeuse. Three stars form the belt of the mighty hunter, and the upper right bright star is called Rigel. Mouser/Wikimedia CC BY-SA 3.0

From late November to early April, stargazers around the world are treated to the evening appearance of the constellation Orion, the Hunter. It's an easy pattern to spot and tops every list of observing targets, from both stargazing beginners to experienced pros. Nearly every culture on Earth has a story about this box-shaped pattern with an angled line of three stars across its center. Most stories tell of it as a strong hero in the sky, sometimes chasing monsters, other times frolicking among the stars with his faithful dog, denoted by the bright star Sirius (part of the constellation Canis Major).  

Look Beyond Orion's Stars

Look at Orion with telescopes sensitive to many wavelengths of light and you find a giant cloud called a nebula surrounding the bright stars of the constellation. Wikimedia, Rogelio Bernal Andreo, CC BY-SA 3.0

Tales and legends only tell part of the story of Orion, however. To astronomers, this area of the sky portrays one of the greatest stories in astronomy: the births of stars. If you look at the constellation with the naked eye, you see a simple box of stars. But with a powerful enough telescope and could see into other wavelengths of light (such as infrared), you'd see a huge roughly circular cloud of gases (hydrogen, oxygen, and others) and dust grains glowing in soft hues of reds and oranges, laced with darker blues and blacks.This is called the Orion Molecular Cloud Complex, and it stretches across hundreds of light-years of space. "Molecular" refers to the molecules of mostly hydrogen gas that make up the cloud.

Zeroing in on the Orion Nebula

The Orion Nebula lies near the three belt stars. Skatebiker/Wikimedia Commons

The most famous (and more easily spotted) part of the Orion Molecular Complex cloud is the Orion Nebula, which lies just below the belt of Orion. It stretches across about 25 light-years of space. The Orion Nebula and the larger Molecular Cloud Complex lie about 1,500 light-years from Earth, making them the closest areas of star formation to the Sun. It also makes them fairly easy for astronomers to study

The Beauty of Star Formation in Orion

The Orion Nebula as seen by the collection of instruments aboard Hubble Space Telescope. NASA/ESA/STScI

This is one of the most famous and beautiful images of the Orion Nebula, taken with the Hubble Space Telescope, and using instruments sensitive to different wavelengths of light. The visible light portion of the data shows what we'd see with the naked eye, and with all the gases color-coded. If you could fly out to Orion, it probably would look more gray-green to your eyes. 

The center of the nebula is lit up by four fairly young, massive stars that create a pattern called the Trapezium. They formed about 3 million years ago and could be part of a larger group of stars called the Orion Nebula cluster. You can make out these stars with a backyard-type telescope or even a pair of high-powered binoculars. 

What Hubble Sees in Starbirth Clouds: Planetary Disks

Images of some of the many proplyds found in the Orion Nebula. NASA/ESA/STScI

As astronomers explored the Orion Nebula with infrared-sensitive instruments (both from Earth and from orbit around Earth), they were able to "see into" the clouds where they thought stars might be forming. One of the great discoveries in the early years of the Hubble Space Telescope was the unveiling of protoplanetary disks (often referred to as "proplyds") around newly forming stars. This image shows disks of material around such newborns in the Orion Nebula. The largest of these is about the size of our entire solar system. Collisions of large particles in these disks play a role in the creation and evolution of worlds around other stars. 

Starbirth Beyond Orion: It's Everywhere

This planetary disk around another newborn star in nearby Taurus (the next constellation over from Orion), shows evidence of world-building activity. European Southern Observatory/Atacama Large Millimeter Array (ALMA)

The clouds around these newborn stars are very thick, which makes it tough to pierce through the veil to see inside. Infrared studies (such as observations done with the Spitzer Space Telescope and the ground-based Gemini Observatory (among many others)) do show that many of these proplyds have stars in their cores. Planets are likely still forming in those shrouded regions. In millions of years, when the clouds of gas and dust have drifted away or been dissipated by the heat and ultraviolet radiation from the newborn star, the scene could look like this image done by the Atacama Large Millimeter Array (ALMA) in Chile. This series of antennas looks at naturally occurring radio emissions from distant objects. Its data allow images to be constructed so that astronomers can understand more about their targets.

ALMA looked at the newborn star HL Tauri. The bright central core is where the star has formed. The disk appears as a series of rings around the star, and the dark areas are where planets could be forming. 

Take a few minutes to go out and gaze at Orion. From December through mid-April, it gives you a chance to see what it looks like when stars and planets form. And, its available to you and your telescope or binoculars by simply finding Orion and checking out the dim glow beneath its glittering belt stars.