Nebula image Archives - Hidden Skies

In Shakespeare’s Romeo and Juliet, Juliet affirms that she would love Romeo just as much if he had a different name; “That which we call a rose by any other name would smell as sweet”. Surely this applies to Bode’s Nebula, a wonderful example of a spiral galaxy.

I had the rare treat of going to the library the other day and looking in a dictionary. I was looking for the etymology of the word “nebula”. The Oxford English Dictionary says the word is from Latin, meaning mist or vapor. Universe Today has a great article on Bode’s Nebula, where its discovery is discussed. In 1774, the German astronomer Johann Elert Bode described “two small nebulous patches” near Ursa Major. The French astronomer Charles Messier added these objects to his catalog as M 81 and M 82. The larger of these two objects, M 81, became known as Bode’s Nebula.

Over the next hundred years, advances in telescopes allowed thousands of deep sky objects to be discovered. These were cataloged in 1888 by the Danish astronomer Johan Ludvig Emil Dreyer. Still, most of these objects appeared as nebulous patches, and were therefore categorized as nebula. About this time, William Huggins, an English astronomer, determined that some nebulae were characterized by large amounts of gases, principally hydrogen, while other nebula were mostly large groups of stars. The objects in this latter group were called galaxies, after our own Milky Way. By the way, according to the Barnhart Dictionary of Etymology, the word galaxy has its root in ancient Latin and Greek and means milky. Chaucer, in his 1380 House of Fame, records that “galaxy” referred to the milky white band seen in the night sky. This became known as the Milky Way. It wasn’t until the mid-1800’s that it was discovered that the Milky Way was composed of billions of stars, and that ours wasn’t the only galaxy. Thus, the term “galaxy” changed from meaning the milky white object in the sky to a large organized group of stars.

We now know that Bode’s Nebula is in fact a spiral galaxy about 12 million light years distant. As the largest galaxy in the M 81 Galaxy Group, it contains over 250 billion stars and a supermassive black hole. Today, the deep sky object M 81 is often still referred to as Bode’s Nebula to honor Johann Bode and his “nebulous patches”. Whether you call it M 81, Bode’s Galaxy or Bode’s Nebula, it’s a beautiful wonder of the night sky, shining down on us from the Great Bear, Ursa Major.

Have you ever wondered about the amazing colors in pictures of nebulae? The reds and greens in the Dumbbell nebula are amazing! The best part is these are the real colors I see in the telescope – they aren’t photoshopped. Today, I’m going to explore why nebulae have such fantastic colors. There are several types of nebulae, but this blog is only about emission and planetary nebulae. Those are the nebulae that are spectacular shades of red and green.

First, you need to know what nebulae are. They’re clouds of gas and dust floating in the space between stars – the interstellar space. The gas and dust is called interstellar medium (ISM). Some nebulae form because gravity causes the gases and dust in the ISM to clump together. Others form by supernova explosions. The dust and gas thrown out by the explosion become the clouds we can see. Still other nebulae are formed from the material given off by red dwarf stars. Most of the gas in nebula is hydrogen, but there are small amounts of other gases, including oxygen, nitrogen, helium and sulfur.

So, we have these clouds of gases and dust, but why can we see them? After all, our atmosphere has a lot of oxygen, nitrogen and hydrogen, but we don’t see bright clouds of red and green in our sky. It turns out that when these gases are energized, they absorb the energy and turn into a form of the gases called ions. These ionized gases give off the energy they’ve absorbed in the form of light. Hydrogen gives off a red light, and oxygen emits a greenish-blue light. Those two gases account for most of the color we see in nebulae.

Now, we’re going to get a bit technical. When you look at a rainbow, you see all the colors of the spectrum; from red through orange, yellow, green, all the way to blue. Light can be described as a wave, and each color of light has a specific wavelength. The wavelengths of light are measured in nanometers (nm). Red light is about 400 nm, and blue light is on the other end of the spectrum at around 800 nm. But there are other colors we can’t see. For example, infrared light has a wavelength that’s too small for the human eye to see, and ultraviolet has a wavelength that’s too long for us to see. It turns out that both ionized hydrogen and oxygen give off light that the human eye can see. Hydrogen gives off light at both 486 nm and 656 nm and oxygen gives off light at 501 nm. Those are the colors of light you can see in my nebula images.

But I have a problem in making these wonderful images. I live in Sierra Vista, AZ. It’s a small town, so the light pollution isn’t too bad, but it’s nowhere near as dark as out on a mountaintop or in the middle of the desert. Also, on nights when there is a lot of moonlight, the sky can be so bright that you can’t see many stars at all. So how is it that I get images of these colorful nebulae when there’s all this light in the sky? I use a filter from Optolong, called the L-eNhance filter. This filter only lets light around 500 nm and about 660 nm through, while it blocks all the other light. That means that the red and green light from the nebula gets through to the camera, while the light from the Moon and nearby streetlamps is blocked!

The Dumbbell Nebula is a tight cloud with lots of oxygen and hydrogen gas. That’s why it’s such a spectacular display in green and red.

Alan Biel – Thanks for joining me as I ponder the hidden wonders of the deep-sky. Until next time!

Tag: Nebula image

Bode’s Nebula – a rose by any other name

Why is the Dumbbell Nebula so spectacularly colorful?