April 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 April 7th. For April, your best viewing nights will be from April 1st to the 10th, and the last five days of the month.  The Star chart below is set for Florence, SC on April 15th at 9 pm. Note: A table of contents for earlier columns is located in the February 2016 column.


Iridium Satellites:
There is a large group of satellites that were placed in orbit for use by satellite phones. A satellite phone is similar to a cell phone, except that there are no cell phone towers needed. The satellite phones send and receive their signals directly from satellites passing overhead. You would not be able to use your cell phone in the middle of the Amazon rainforest or in the middle of the ocean, but a satellite phone would work at any location on the Earth.

In the 1990’s a corporation decided that there was a market for portable phones that could be used anywhere on Earth. The engineers then went about working out the details of this venture. One important piece of data was how many satellites would be required to have worldwide coverage. Their calculations determined that 77 satellites would be needed. Soon after, marketing people at the corporation wanted to pick a clever name for this satellite system. Someone in the company noted that these 77 satellites circling the Earth reminded him of electrons circling the nucleus of an atom.

Bohr Atom Satellites

Then someone asked which element contains 77 electrons, and the answer was Iridium. Thus was the reason for the name Iridium satellites. Later in the development of the Iridium satellites system the engineers determined that only 66 satellites were necessary to have total coverage of the Earth. One might wonder why they didn’t change the name to element 66; Dysprosium. Beside the difficulty pronouncing the name, I assume that the word Iridium was already well accepted throughout the organization. So as of today, there are 66 Iridium satellites circling the Earth, with an additional six Iridium satellites in orbit as backups whenever one of the 66 fails. A great marketing idea isn’t always successful, and addition to the high price of such a phone, most people really don’t have a need for a phone that works in remote places on the Earth. However, the Iridium satellite concept has been successful because of its use by the military.

Iridium Flares:
As Iridium satellites pass overhead they, like many artificial satellites, have a magnitude of about 6.0; that of a dim star. In the Florence area it is difficult to see magnitude 6.0 due to light pollution. It would require a distance of 10-20 miles from Florence to see objects at magnitude 6.0. However, Iridium satellites are easily visible anywhere in the Florence area when they flare.

In addition to solar panels, the Iridium satellites have three polished antennas, each about the size of a door; see image below.

Ir Sat

As the satellite moves over the Earth, at certain times, sunlight will reflect off one of the polished antennas and direct the bright beam to Earth. So for a few seconds, the observer sees a bright light moving across the sky. Remember, the lower the magnitude number, the brighter the object. In addition, the magnitude scale goes below zero to negative numbers; the higher the negative number the brighter the object. The brightest nighttime star is Sirius; mag. -1.4, the International Space Station; mag. ranges from 0 to -3, the brightest planet is Venus, with a mag. as high as -4.4. An Iridium flare can easily be as bright as -8.0! Note the image below is a time lapse, you will see the flare as a moving point of light.


If you want to see an Iridium flare, you can search the website “heavens-above.com”; be sure you login with your present location. The easiest way to see a flare is to download an Iridium Flare app on your Smartphone. If I am at home, I like to combine data from my Smartphone and from Heavens Above to give me maximum information. The beam of light that strikes the Earth is about 6 miles in diameter. The Iridium apps will tell you the magnitude of the flare where you are standing, and the magnitude if it was directly overhead. Example: A flare might be mag. -2.5 in Florence but mag. -8.0 in Lamar, SC. If you so desire, you might want to drive over to Lamar that night to experience a mag. -8.0 flare.

Some flares are so bright that they may be visible during daylight. I have not seen a daylight flare, but I will try for my first one on April 11th. This flare will be almost directly overhead before sunset at 7:25 and 30 seconds pm; you might also try to see this daylight flare. The magnitude will approach -8.0; see info below.



I think the reason I most enjoy seeing Iridium flares is that they are a testimony to the science of mathematics. These satellites are traveling about 400 miles above the Earth at about 17, 000 miles/hour, with their shiny antennas slowly turning, and we can calculate exactly when they will reflect the sunlight on your head.

Naked Eye Sights: Try to see some Iridium flares this month; much easier viewing at night.

Binocular Sights (7 to 10 power): Check out Jupiter’s moons, and the last glimpse of the Orion Nebula.

Telescope Sights (60-100mm): For the serious amateurs, search out the Virgo cluster of galaxies above Virgo and to the left of Leo the Lion.

See you next month!

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