M33 is a nearby galaxy in what astronomers call our "local group" of 60 or so neighboring galaxies. It is 2.9 million light years away, and has 40 billion stars. It is an enormous object, spread out over an area equal to four full moons! Yet, I had difficulty finding it in my big 20" telescope because it is so faint. It has what astronomers call a "low surface brightness," which occurs with large objects whose visible light is spread out over a large area. It is best seen at lower powers under dark skies. Of course, with a CCD camera, the dim light from this object can be seen in just seconds.
This image is a combination of over 3 hours of images taken through clear, red, green and blue filters and then combined to produce color. It shows detail that you could never see with any amateur telescope, no matter how big.
M33 is perhaps the most famous example of a "face-on" spiral galaxy, meaning that we are seeing it like a wheel moving past us (instead of toward or away from us, as in the case of an "edge-on" spiral).
This image was taken with my CCD camera and 5" refractor telescope. It is the first color image that I took of a galaxy.
Note the many red and pink "knots" throughout the galaxy. These are known as "HII" regions, meaning that they consist of ionized hydrogen gas (hydrogen atoms that have been stripped of their single electron by the intense ultraviolet energy emitted by newly formed stars in the spiral arms). The energetic "bachelor" electrons are quickly captured by the ionized hydrogen nuclei, and emit discrete amounts of energy as they cascade down the various energy levels to the "ground state" near the core of the nucleus. This process is known as "fluorescence," and is the same process that occurs inside a fluorescent light fixture. These knots appear red or pink since the energy emitted as the electrons give up energy and return to the ground state corresponds to the color red in the visible spectrum.
This image was selected by NASA as its "Astronomy Picture of the Day" (APOD) for December 14, 2004. Here is the link: http://antwrp.gsfc.nasa.gov/apod/ap041214.html
The Triangulum Galaxy (M33)
Date Taken:December 7, 2004
Location Taken: Conditions of Location:FWHM 2.17
Equipment Used:Takahashi TOA-130 5" apochromat refractor telescope, SBIG ST-10XME CCD camera, Optec TCF-S focuser, Astrodon RGB filters.
Processing Used:7x10 minutes luminance, 4x10 minute red, green and blue (total exposure time of 3 hours 10 minutes), combined in Maxim and processed in Photoshop.
Distance from Location:3 million light years
Constellation:Triangulum
Other Link: