Monthly Archives June 2013

Why Can’t We See Color from Deep Space Objects?

One of my coworkers asked me a really good question today: Why can’t you see colors in space with your eyes? I actually did not know the answer so I went in search of it.  I experienced this phenomena first hand when I visited the Chabot Space and Science Center in Oakland for the first time.  The object they had in focus in their huge telescope was the Dumbell Nebula, which looked like a white fuzzy blob through the eyepiece of the telescope.  Does color really exist in space?  I found a really good explanation below but you just want the Cliffs Notes, the light in space is too dim to activate the color sensing portions of our eyes but CCD cameras are sensitive to the colors in space and are able to record the colors we can’t detect:

Why Can't Eyes See Color in Space

“The brilliant colors you see in astrophotos of nebulae are too faint to be seen live, even through a telescope. Most nebulae are just too faint to trigger the color sensors (cones) in your eye, so you see them with your monochrome night vision (rods). In particular, you can’t see the red color that’s in a lot of photos; not only is it faint, but it’s also in a part of the spectrum your eyes aren’t very sensitive to.

You can certainly see colors in planets – Mars, for example, is distinctively reddish. I’m sure the blue of Earth would be quite striking if you were seeing it from Mars.

If you look carefully, you will see that stars vary in color – some are bluish, while others are yellowish or reddish...

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M13: What a Difference 10 Months Makes

About 10 months ago, I started getting into Astrophotography, which has been an amazing and positive experience for me so far.  I started taking photos of Deep Sky Objects (DSO’s) with my Nikon D7000 DSLR and I was quickly enthralled with the beauty of what existed out in deep space.  One of the first DSO I imaged with my DSLR was M13, the Great Globlar Cluster in Hercules.  I remember being in awe that the pitch black patch of sky I pointed my telescopic contained so much beauty.  After learning how to do some rudimentary unguided imaging with my DSLR, I wanted to see if I could get more detailed photos so I looked into purchasing a CCD camera, which is a specialized imaging system for Astrophotography.  I received a ton of helpful advice from Michael Caligiuri who has been a tremendous source of inspiration and knowledge.  I also did some research and subsequently purchased a monochrome SBIG ST-2000XM and a filter wheel from Astromart so I could now image DSO’s across the Luminance, Red, Green, and Blue channels.  Flash forward to present day and here is a comparison of M13 taken 10 months and one I recently took back on June 4th:

M13 2012 and 2013 Comparison

M13 2012 and 2013 Comparison

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Flat Frame Calibration Astrophotography Example with M13

Flat Frame Calibration

Flat Frame Calibration

A couple weeks ago I built a flat frame light box for my telescope so I can take these really important images so that imperfection (dust, etc.) in my telescope and CCD camera are subtracted from the frame.  At the most basic level, flat frames are used to correct the vignetting and uneven field illumination created by dust and imperfections in the optical train.  In the example above, the photo on the left is not flat frame calibrated and you can see dark circles in many places on the image.  These imperfections are dust motes.  The photo on the right has been calibrated with flat frames, serving two very important purposes:

1.  Removing dust motes

2.  Evening out the field around the corners of the image

Here is the final LRGB image of M13 that is both dark and flat frame calibrated:

M13 Globular Cluster in Hercules

M13 Globular Cluster in Hercules

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Astrophotography Flat Frame Light Box using Electroluminescent Panel

Flat Frame Light Box Made from Electroluminescent Panel

Flat Frame Light Box Made from Electroluminescent Panel

Before I start, I wanted to say that almost 100 flat frames were sacrificed in the making of this light box.  Last weekend, I built myself a Flat Frame Light Box using 5mm Foam Core and an A5 Electroluminescent (EL) Panel.  I image with a Takahashi Sky 90II and an SBIG ST-2000XM and there are dust particles on the telescope as well as the CCD.  I am not going to describe the need for flat frames or how to take them as it is covered in many other articles around the web.  This blog aptly called DasFlatFrame does a good job at describing the need for flats.  I am going to describe how I constructed the light box

Materials Used:

  • A5 Electroluminescent Panel
  • 12 volt inverter (if you want a dimmer panel you can use a 9 volt inverter)
  • 5mm White Foam Core
  • White Printer Paper
  • Vellum Paper
  • White Duct Tape
  • Scotch Tape
  • Cardboard (used to hold the box on the telescope)

Tools

  • Protractor
  • Ruler
  • Exacto Knife

Light Box Construction

Figure out your measurements based on the size of your telescope.  This light box was made for a Takahashi Sky 90 so I figured a 10 in. x 10 in. x 10 in. box would suffice.  For the outside of the light box, I cut 6, 10 in. x 10 in. x 10 in. Foam Core panels.  I cut an additional 10 in. x 10 in. x 10 in. panel for the Diffuser Panel.  The Diffuser Panel and the Rear Panel of the box have rectangular cut outs so that paper and the EL Panel can be affixed on to them...

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