May 2016

Tony Martinez

                                      Tony Martinez

Each month  I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into three sections; what you can see with the naked eye, with binoculars, and with a small telescope. The best time to view the night sky is at and around the times when the Moon is not visible, what is known as a New Moon; which will occur this month on May 6th. For May, your best viewing nights will be from May 1st to the 10th, and May 24th until the end of the month. The Star chart below is set for Florence, SC on May 15th at 9 pm. Note: A table of contents for earlier columns is located in the February 2016 column.

wholeskychart 1

Where is the color?
One thing that is most obvious with Hubble telescope images is color. Everything is colorful. Then you search the skies with your new telescope, and everything is in black and white. So the question is do these deep sky objects really have these colors, or is it just computer enhancement. The answer is both.

Every element in the universe can emit light when enough energy is supplied. The energy supplied to an element can be heat, or other forms of electromagnetic energy. In addition, when you burn certain elements the can have different color flames. Examples: Sodium burns yellow, and since sodium is ubiquitous, when you spill water on a gas stove, you see a burst of yellow. Copper burns green, strontium burns red and selenium burns blue. Other examples: When high voltage is passed through gases, hydrogen emits a rose color, argon emits a red/orange color and helium emits white with a tint of orange. See hydrogen emission below.

Hydrogen discharge tube

If we observe these emissions through a diffraction grating, which can separate colors, we will see many lines of color each representing different electrons releasing energy as they move from one energy level to another. The result is every element has a light emission “fingerprint.” These light emission fingerprints are used to determine which elements are present in stars and other night time objects. Therefore, because the stars and nebulas in the sky are high energy systems, night sky objects can be very colorful.

To further understand why seldom see any color, let’s consider the biology/biochemistry of your eyes. Your eyes have two primary light receptor cells, rod and cones. The cones are designed for bright light and can readily detect colors. The rods are designed for low light, night vision, and have very little color sensitivity. Example, go outside at night in the Florence area, away from lights, and you will be able to see trees and objects in your yard, but not their color. Likewise, when you look at a deep sky object through a telescope at night, your eyes are not very responsive to any colors coming from the object.

If you venture in to the area of astrophotography and take long exposure images of objects, you will then see the colors. Yes, astrophotographers often use photo-enhancing software on their images, but it is not always necessary. The nebula image below was taken by an amateur; no filters, no enhancing, just time exposure. In addition, this person used a regular 35 mm camera and the now seldom seen photographic color film; see results below.

eta_carina

However, in addition to seeing mainly black and white images, some color can be seen with your naked eye, and through your simple telescope. Let’s discuss these by object type.

Stars: Use your star charts to check out these stars; some are not visible this month.

Using your naked eye only: Follow the curve of the Big Dipper’s handle to the bright yellow/orange star Arcturus, and continue in the same direction to the bluish/white star Spica. As Scorpius rises late in the evening, it is obvious that the “heart” of the scorpion, Antares is red/orange in color. Early in the month in the northwest, the bright yellow star Capella in Auriga is visible. In the winter months the most obvious colored stars are Betelgeuse, red/orange, and Rigel, blue/white. To the casual nighttime observer, all of the stars appear to be white. I find that only when you tell them that a particular star has color does it then become obvious.

Next turn to your telescope: I believe that the most colorful star in the sky is Albireo, the head of the constellation Cygnus the Swan or the bottom of the asterism the Northern Cross. Through a simple telescope, you can easily see that Albireo is a double star with one star yellow/gold, and the other sapphire blue; see below.

Albireo

If you would like to search for other colorful stars, the easiest method is to go on-line and find a list of double stars (binaries). Focus on which constellation the star is in, and magnitudes below 8, and of course look in the column showing the colors of the two stars; see example below.

Double Stars

Planets: To the naked eye; Mars looks yellow/orange, and Saturn looks yellow. With a telescope: Uranus and Neptune definitely are blue. Jupiter’s cloud bands are brownish.

Deep Space: The problem with deep sky objects is that only a small amount of light reaches us, and as mentioned earlier, low light means loss of color. I have only seen one colorful deep sky object, NGC 7662, the Blue Snowball Nebula. I was able to see the blue color with my 25 X 100 mm binoculars. The image below approximates the tiny blue dot I saw through my large binoculars.

NGC_7662_00

In conclusion, although most astronomy objects are seen in black and white, if you make an effort, you can find some color in the night sky.

Naked Eye Sights: Colorful Stars

Binocular Sights (7 to 10 power): Colorful stars

Telescope Sights (60-100mm): Check out colorful double star systems. If you are dedicated, try to find the Blue Snowball Nebula at 4 am near Pegasus.

NGC 7662

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