Constellations

Dear Observer,

Orion is an amazing winter constellation, and I just couldn’t resist showing you a little more of it. On a clear dark night it can be seen about half-way up in the sky to the south at about 8:30 PM. In my last report, on December 10, the second picture was of the central part of Orion showing the Hunter’s 3 belt stars and sword. I have reproduced it here as my first picture except last time we zoomed in on an area just below the lower left belt star, Alnitak. That area contained the wonderful Horsehead Nebula. This time we are going to zoom in on the belt – the area inside the current yellow rectangle – which contains the famous Orion Nebula.

The second picture is at a scale 6 and ½ times that of the first. The first picture was taken at Lookout Observatory with very dark skies. The second picture was taken in Albany, CA, with terrible S.F. Bay Area light pollution. A special filter had to be used to screen out this scattered extraneous light. Because of this difference in sky quality, even though the second image was exposed 5 times as long as the first, and a lens 5 times larger in diameter was used, both images show about the same amount of nebulosity, and both show about equally faint stars. (You can see this for yourself if you enlarge the first image until the yellow rectangle is the same size as the second image.) However, the second picture shows much more detail because at the larger scale it has about 6 times the resolution of the first, and also because special processing techniques were used to bring out the details in the swirling nebulosity and to compensate for the 50-fold variation in brightness that makes it difficult to show the faintest nebulosity without completely burning out the brightest parts.

Much of the constellation of Orion is covered in a huge cloud of nebulosity, and the Orion Nebula (also known as M42) is just the brightest part. The hot blue-white stars embedded in it reflect light off some of the gas and dust, causing it to look blue, and energize other parts of the hydrogen gas to cause it to glow red. Above the Orion Nebula is another blue nebula with darker reddish parts that give it its popular name of the Running Man Nebula. (He’s running to the left.) The Orion Nebula is about 1300 to 1400 light years distant, and it is about 24 light years across. A dark triangular patch near the top points to the brightest (whitest) part of the nebula. In the middle of this is a lumpy looking star, which is actually 4 stars – called the Trapezium – all blurred together in this image. These are just the brightest of several thousand young stars in a cluster spread throughout the Nebula. This is an area of new star and planet formation. Stars are actively condensing out of the gases, and the Hubble telescope has detected hundreds of proto-planetary disks around stars here. It is expected that in about 100,000 years most of the nebula will be gone, having either condensed into stars and planets or else been driven away by outward radiation pressure from the young, very hot stars – a process called photo evaporation. The Universe is far from static! Hang around for a few hundred thousand years – or get reincarnated then – and you’ll see lots of changes.

Keep looking up,

Carter

Dear Friends of Lookout Observatory,

Orion, The Hunter, is one of the most recognized and beautiful of the 88 officially-recognized constellations in the sky. This time of year it rises in the evening, having cleared the eastern horizon by 8 PM. By midnight it is near its highest, about half-way up in the sky to the south. Its brightest stars can be seen even from the light-polluted skies of major urban areas, but it becomes spectacular from rural, dark skies.

Image #1: This is a photo from rural Lookout Observatory, showing the tops of pine trees at the bottom and Orion just left of center. ( Ignore the yellow rectangle for now.) The main body of Orion consists of four bright stars forming an upright, somewhat crooked rectangle. The upper left star is reddish-yellow Betelguese, and the lower right one is bluish-white Rigel. In the middle are three bright stars at a 45-degree angle, representing Orion’s belt. These stars point down and to the left to the brightest star in the picture (and the brightest star in the night sky), Sirius. Just below Orion’s belt are 3 or 4 bright points in a vertical line, considered to be Orion’s sword. Because this photo is a 6½-minute time exposure, everything looks much brighter than what you can actually see with the naked eye. Now pay attention to the yellow rectangle. If you enlarged that section of sky about 5 times, you would be looking at the area in the next picture.

Image #2: This image is not actually an enlargement of the first photo, but rather a photo taken with a longer focal length (telephoto) lens. It is a 34-minute time exposure. Here the three bluish “belt” stars and the bright “sword” below are prominent. You can also see that the “sword” consists not only of stars but of some bright bluish and pinkish nebulosity. The brightest (pink) part is the famous Orion Nebula. I deliberately enhanced the red in the photo to bring out the great amount of nebulosity that engulfs much of the area of sky within Orion. This is the Orion Molecular Cloud Complex, huge clouds of dust and hydrogen gas caused to glow (“emission nebulae”) by the energy from embedded stars and star clusters. Every nebula I name in this report is part of this vast complex. This is a major area where new stars and planets are forming by gravitational condensation. These gaseous clouds are several hundreds of light years across, and centered about 1400 light years away. The large red arc to the left is part of this nebulosity known as Barnard’s Loop, named after the man who first discovered it using long-exposure photography. The yellow rectangle focuses on the lower left “belt” star – named Alnitak – and the nebulosity below it. If you enlarged it 5 times, you would be looking at the area in the next picture.

Image #3: This is a 95-minute exposure. Just to the left of the “belt” star (Alnitak) is the orange Flame Nebula, an emission nebula energized by the cluster of young bluish stars embedded (and completely hidden) it in, and by Alnitak. The red nebulosity below Alnitak, known as IC 434, is caused to glow by the energy from the bright star to its right, halfway toward the right edge. Silhouetted against this gas is the dark gas and dust cloud known as the Horsehead Nebula. If you magnify the area of the yellow rectangle about 5 times, you get the final picture,

Image #4: This is an 88-minute exposure. If you turn sideways (or download the image and rotate it counter-clockwise), you can see the Horsehead standing upright. To get a sense of how immense this formation is, imagine a series of orbits of the Earth around the Sun laid across the neck of this “horse” like a necklace. It would take more than 30,000 Earth orbits to cross the neck! It is a bit over one light-year across. The bluish nebula near the upper right corner, NGC 2023, about 4 light-years across, is mostly a reflection nebula, meaning the light we see is mostly reflected light from a hot blue star within the gaseous nebula. With this image you have zoomed in about 125 times compared to the first image. I hope you have enjoyed the trip.

Keep looking up,

Carter Mehl, (sometime) Resident Astronomer, Lookout Observatory