Category: Nebula Images

Nebula images = astrophotography images of nebulae taken either with telescopes or DSLR cameras.

This category features images of nebula taken in my observatory with an 8″ SCT. Nebulae are interstellar clouds of dust and gas with amazing colors and shapes. The main types of nebulae pictured in these blogs are emission, reflection and planetary.

Emission nebulae are clouds of gasses such as hydrogen and oxygen. Energy from nearby stars ionizes these gasses. The ionized gasses emit colored light, resulting in the spectacular colors seen in the nebula images.  Ionized hydrogen emits red light, as do ionized sulfur and nitrogen.  Ionized oxygen produces a blue-green light. I often use a special narrowband filter to block the light from the moon and enhance the light from the emission nebula.

We can image reflection nebula because the gas and dust of the nebula reflects the light from bright stars.  Usually, these stars are blue and cause the nebula to take on a blue color. Light from the moon will wash out these images, so we can only get good images of reflection nebula on moonless nights.

Planetary nebulae are a type of emission nebula. The difference between planetary nebulae and other emission nebulae is that planetary nebulae usually contain much more oxygen and nitrogen.  This often results in images with large areas of blue-green.

Along with amazing nebula images, posts in this category will feature interesting facts from the arts, entertainment, history and science related to the nebula.

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This Pac-Man is ready for Halloween

In 1883, American astronomer E. E. Barnard discovered a large faint nebula in the constellation Cassiopeia.  While it’s officially designated NGC 281, it’s most commonly known as the Pacman Nebula.  While the nebula normally appears in shades of red, a mistaken setting during processing yielded this eerie green version, which seems perfect for Halloween.

While the video game Pac-Man is almost 40 years old, the nebula is several million years old.  The nebula is 9200 light years from Earth, so the light used to make this image is 9200 years old!  The Pacman Nebula is so large that it takes light 48 years to travel from one side to the other.

The red glow (green in this image) is caused by ionized hydrogen gas.  The stars within the nebula energize the gas, which causes it to glow.  The small dark “eye” in the middle of the nebula is a Bok globule.  Bok globules are small areas of dust and gas.  They are very dense, often having a mass of up to 50 suns.  The dust and gasses are collapsing under the force of gravity and may eventually form new stars.  The “mouth” is caused by relatively cool, dark gas and dust obscuring the glowing gasses behind it.

The Pacman Nebula is located near the brightest star in the constellation Cassiopeia. The constellation itself looks like a W high in the northern sky near Polaris.  It is part of the Perseus Family of constellations, which includes the constellations Cepheus, Andromeda and Perseus.  In Greek mythology, Cassiopeia is the wife of Cepheus and the mother of Andromeda.  Perseus is the hero who saved Andromeda and later married her.

Pac-Man is the most successful video game in history.  Introduced in 1980, it’s been estimated that more than 10 billion quarters were fed into arcade games over the next 20 years in pursuit of higher scores.  The Pac-Man character became so famous it’s been featured in several movies, including Pixels (2015) and Guardians of the Galaxy 2 (2017).

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Capturing the miracle of the Western Veil Nebula

The Western Veil Nebula is aptly named. It’s a wondrous lace of magenta and green spread among the stars of the constellation Cygnus. It’s a large emission nebula about 2600 light years from Earth.  The nebula was formed by the explosion of a star between 5000 and 8000 years ago.  The Western Veil Nebula is what remains from that supernova.  As I described in a previous blog, the magenta color is due to ionized hydrogen gas, while the bright green light is given off by ionized oxygen.

In the rest of this blog, I’ll walk you through how I captured this image.  While the night skies in southeast Arizona are usually extraordinarily clear, summer is monsoon season, and on most nights the night sky is too cloudy for astrophotography.  But in early July I caught a break and had a cloudless night sky. 

My observatory is equipped with an 8” Schmidt-Cassegrain Advanced VX 8 from Celestron.  Because the Western Veil Nebula is so large, I was able to use the Hyperstar 8 lens system, developed and produced by Starizona.  The Hyperstar makes the telescope much faster, so I can get an image of the nebula within a minute.  I captured 40 one-minute exposures with a ZWO ASI 294 MC Pro ccd camera, and combined them to make the final image. Because the Moon was out that night, it was too bright to take pictures without a special filter.  I used the Optolong eNhance filter which blocks moonlight, and only lets red and green light through. 

Have you ever just sat out at night and watched as the stars wheel across the sky?  Nebulae move across the sky in the same way.  To get a sharp image, the telescope must move with the nebula.  The telescope I use has a German equitorial mount that allows it to track deep-space objects. First, however, there’s an involved alignment process.  After aligning and focusing the telescope, I start capturing images using the SharpCap software program. 

At this point, I have 40 images of the nebula, each about 24 Mb – that’s almost a gigabyte of data!  If you look at these images, they’re in shades of gray.  I use a second program, PixInsight, to process the images and extract the color information.  The software combines these 40 images into a single full-color image.  At this point, the image is just about done.  All that remains is to adjust the brightness, crop the image and set the file type.  I use Photoshop and Lightroom for these final steps and either publish it to the web or print it.

While it only took 40 minutes to get the data, it took hours of preparation and processing to turn that data into amazing wisps of magenta and green floating across a starry sky.  When that image appeared, I realized I was looking at the remnants of a supernova explosion that happened more than 5000 years ago.  I was seeing the universe in all its wonder and beauty!

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

©2019 Hidden Skies

https://hiddenskies.com

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Why is the Dumbbell Nebula so spectacularly colorful?

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!

©2019 Hidden Skies
https://hiddenskies.com