Two Hearts

This is two views of the Heart Nebula (IC1805). One is a pseudo-true color image using a Hydrogen-alpha filter for the red channel combined with standard green and blue filters. The second is a false-color image using the [SII], Hydrogen-alpha, and [OIII] narrow band filters.

These images were taken using the facilities of JMSM Observatory, owned by Mike Sherick.

Click the image above for larger versions of this image. Read the rest of this blog entry for some more details.

I started taking this image in early August with the intention of just doing the pseudo-true color HaGB combination. I shot some green and blue exposures one night, followed by Hydrogen-alpha the next. My first attempt at processing showed I was severely lacking in blue and green data. Then it was a couple of weeks before I could shoot again due mainly to weather. Of course now the moon was out and bright so I decided to try some [SII] and [OIII] filtered exposures. I got one good night in, but that was no where near enough data, and then the weather turned sour again! Finally this month I was able to get enough data for all the channels (green, blue, [SII], and [OIII]) to finish off two images. I ended up with just over 24 hours of data for these two images.

Aside from the obvious shape, this is a very interesting region. There is lots of activity in this nebula from the young stars in the nebula (the oldest being only 4 million years old). The most prominent stars in the middle of the nebula are some of the most active. These stars have an average age of between 1 and 2 million years - very young by stellar standards (our sun is about 4.5 billion years old).

All of this activity from the young stars excites the different molecules in the gas in the nebula and causes them to emit light at different wavelengths. These light emissions are what we see and can capture with the camera. The false-color image consists of light emission from three different molecules: Sulfur ([SII]), Hydrogen, and Oxygen ([OIII]).

The amount of light that each of these molecules emits is actually quite different. The Hydrogen emission is actually the strongest, by far, of the three. This is why I am able to make a pseudo-true color image by mixing the Hydrogen-alpha image with a green and blue image. Hydrogen-alpha emission occurs at a wavelength in the red spectra and is the dominate form of red light. The [SII] and [OIII] emissions are so dim by comparison, they can be safely excluded from the pseudo-true color image. In fact, the Hydrogen emission is so strong, there is a second emission line at a wavelength in the blue spectra. I've added a small amount of the Hydrogen-alpha image into the blue channel to simulate this emission line. This is why the nebula pseudo-true color image has a magenta cast, rather then pure red.