February 2018

                               Tony Martinez

Each month I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into four sections: what you can see with the naked eye, with binoculars, with a small refracting telescope and with a Dobsonian reflector. 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 February 15th. For February, your best viewing nights will be from February 7th to the 20th. The Star chart below is set for Florence, SC on January 15th at 9 pm.  Note: A new table of contents for earlier columns is located in this January 2018 column.

The Demon Star:
There are many double (binary) stars visible in the night sky; indeed the majority of stars you see in the night sky are true binary stars. Some amateur astronomers enjoy locating as many binary stars as they can just using simple binoculars. There are really two types of binary stars. The first is a misnomer, and is just a chance alignment, in which one star is relatively close by and the other a long distance away, but because of their alignment, it appears that they are next to each other. However, a true binary star is one in which both stars are gravitationally linked to one another, and therefore rotate around a common center of gravity.

My favorite star is a binary star called Albireo in Cygnus. (The head of the swan or the bottom of the Northern Cross asterism). What makes this binary star so special are the colors, one is golden and the other sapphire blue; you will need a telescope to see them clearly. It takes thousands of years for the Albireo stars to rotate around each other.  Probably the most famous binary star is the one in the middle of the handle of the Big Dipper. The star we easily see is called Mizar, but if you have good vision, there is a smaller star right above it called Alcor. In fact is was said this binary was once used as a test of good eyesight. In reality, Mizar and Alcor have four other tiny stars linked to them resulting in a six star system. For telescope users only, there is another famous binary system called epsilon lyrae in the constellation Lyra. This is a nice double star with each star being another perfect double; known as the Double Double; see below.

So, binary stars rotate around a common center of gravity, many with long rotational times. In addition, as they rotate, they are located in many different orbital planes as viewed from Earth. It is only when the orbital plane is lined up just right, that one star

can eclipse another. Astronomers have recorded thousands of these eclipsing binaries, but most are too distant or dim for amateurs to observe, and/or have too long of an orbital time(period).  When binary stars eclipse each other they become dimmer, because you cannot see the light from the eclipsed star.  Of course other features come to play, such the brightness and sizes of each star.

This month I would like you to go out and view an eclipsing star system. The eclipsing binary star system is 92 light years away, but the first thing you do is leave your telescopes and binoculars inside, and view the eclipse with your naked eyes. Some readers might assume that this amazing naked eye eclipse of two stars 92 light years away must be a rare event that will be reported in all the news media; wrong. The stars will eclipse each other 10 times this month, 6 of these times at night.  The star is called Algol, which is translated as the demon star.  The two main stars in this binary system eclipse each other every 2 days, 20 hours and 49 minutes throughout the year. It is also known as the winking star. The ancient people thought that this strange effect was caused by a demon, and was therefore a bad luck star. However, it wasn’t until the mid-1600’s that the variability was officially reported, but it was 100 years later until an astronomer John Goodricke studied Algol, an theorized correctly that it was an eclipsing star system.

Now, let’s find Algol.  Algol is in the constellation Perseus which is in the west this month.  Check out the star chart below.

You will notice that it is about halfway between the Pleiades and the “W” in Cassiopeia. The brightest star in the constellation Perseus is Mirfak.  First find Mirfak, then move your gaze two stars below. You will find that Algol is quite easy to locate because after Mirfak, it is the brightest star in Perseus.

Almost every 69 hours, Algol is eclipsed, and the eclipse lasts about 20 minutes. The diagram below describes the event. The secondary eclipse is not noticeable.

Below is a list of the best viewing times for the eclipses this month. Go outside about an hour or so before the eclipse and notice the brightness of Algol compared to the nearby stars above and below Algol (small arrows). Then go back out later as the eclipse occurs and notice how much it has dimmed.  You can also return after to see it brighten again.

The three evening eclipses are shown below. The time represents the center of the 20 minute eclipse.

February 4:  11:38 pm
February 7:  8:27 pm
February 27:  10:12 pm

Naked Eye Sights: Find Algol in Perseus and watch it eclipse and dim.

Binocular Sights (7 to 10 power): The Pleiades Cluster and the Orion Nebula.

Big Binocular Sights (18 to 25 power):  The Double Cluster in Perseus.  The Pleiades.  The Orion Nebula.

Telescope Sights (60-100mm):  Orion Nebula

Dobsonian telescope (6 -8 inch):  Try to locate the four young stars near the center of the Orion Nebula, called the Trapezium.

Comments are closed.