Binary stars, also known as double stars, are systems that are composed of two stars that orbit around each other. Sixty percent of all stars in the universe are binary stars.   There are a few types of binary stars such as visual binary stars, spectroscopic binary stars, and astrometric binary stars. Before the invention of the telescope, people were unable to determine if something was a binary star. With the invention of the telescope, astronomers were able to discover binary star systems. With the discovery of binary stars astronomers proved that there was gravity outside our solar system.
Binary stars orbit around each other and will always be across from each other in their orbit. As the stars get farther apart, they start to travel slower which is referred to as apastron. When they get closer together, they will start to speed up in a process called periastron. Binary stars are spread out all over the universe, some are as close as 100 light years while others are over 16,000 light years away. With in the orbits, some stars have shorter orbital planes and therefore will orbit the other star quickly while others stars can take up to 80 years to fully orbit around them.
The first binary star was discovered not long after the invention of the first telescope. The Italian astronomer J.B. Riccioli discovered the binary star Mizar in 1650. Over the next 70 years only a few other binary stars were discovered and named. Many of the stars that were found were accidental. In 1656 three parts of the Ori were discovered and in 1719 the binary star Castor was discovered by Bradley and Pound.   In 1781 a catalogue containing 80 binary stars that had been discovered was published by C. Mayer. He guessed that these stars could be small suns that orbited around bigger suns. William Herschel, an English astronomer who owned the largest telescope of that time, discovered many binary star systems in the late 1700s.  Herschel didn't believe that there was enough evidence to support Mayer's theory.  William Herschel stated:
|“||If, on the contrary, two stars should really be situated very near each other, and at the same time so far insulated as not to be materially affected by the attractions of neighbouring stars, they will then compose a separate system, and remain united by the bond of their own mutual gravitation towards each other. This should be called a real double star; and any two stars that are thus mutually connected, form the binary sidereal system which we are now to consider. ||”|
After observing the orbits of two different stars, Herschel discovered that they were, in fact, orbiting around each other. This discovery showed that there was gravity outside of this solar system.  He published his first catalogue in 1782 which contained 269 binary stars. Two years following his first publication he published a second catalogue containing 434 more binary stars. John Herschel, William Herschel's son, continued his father's research with his friend James South. Together they were able to find and name 380 binary stars and later published a catalogue showing their findings. In 1833, John sailed to South Africa with 3 of his father's telescopes in search of a better knowledge of the solar system. For four years he explored the sky searching for nebulae, star clusters, and binary stars. During the four years he discovered 2100 new binary stars. In 1838 he returned to England and ended his research. The first eclipsing binary star, called Algol, was discovered in 1782 by Gooderike. The first spectroscopic binary star was discovered in 1889 by E.C. Pickerings. Spectroscopic binary stars are stars that are close together and have a very high velocity. In 1889 H.C. Vogel discovered that Algol was also a spectroscopic binary star. 
Visual binaries are stars that can be seen through a telescope or with the naked eye.
Spectroscopic binaries are star systems that are so close together that they appear to be one star.
Eclipsing binaries refers to when the orbital plane of the stars is lined up with the edge of the sky. This causes one star to cross in front of another creating an eclipse of the stars. 
Binary stars have a tendency to be too far away, too bright, or too close for astronomers to accurately determine if the star system is a binary star. One way that astronomers find if a system is binary was found with the discovery of astrometric binaries. 
Astrometric binaries are star systems where only one star can be seen, but because of the way the star orbits it shows that there is another star that has a gravitational pull on it. This means that their are two stars orbiting around each other. Star's mass is determined by the gravitational effects that it has on another object. This has been a major problem for determining the mass of binary stars. Astronomers have found that they can know the masses of each star in the system from the overall size of the star's orbit and by determining how long it takes for the stars to revolve around each other.
Astronomers use Kepler's Third Law of Planetary Motion to determine if it is a astrometric binary. They use the following equations to find the center mass that the stars are rotating around. 
m1r1 = m2r2 and r1 + r2 = R
If P and R are known then astronomers can solve for the total mass in the first equation. If they can determine the distance between the orbits in the second equation then they can determine the individual mass of each star. This is the most accurate way that they have found to determine the mass of these stars.  Kepler's third law is then modified with P being the orbital time period, m1 and m2 are the masses of both stars, m1r1 = m2r2 and r1 + r2 = R are the centers of mass, and R is the overall distance between the the centers of each star.
( m1 + m2 ) P2 = ( r1 + r2 )3 = R3  
This equation allows the astronomers to see if a star is revolving around a center of mass and if so that would prove that there is a binary star system. 
There are also x-ray binary stars where a star orbits with a collapsed star such as a black hole, white dwarf, and neutron star. If these stars get close enough together than the collapsed star will begin to pull particles off of the main star. This results in very high temperatures and the production of x-ray around the collapsed star. 
Binary stars follow orbits that are determined by Isaac Newton's modification to the Kepler's Third Law. Both stars orbit around each other and will always be across from each other in their orbit. When the two stars are the farthest apart then they will be traveling slower and this is referred to as apastron. When they are close together in there orbit then they speed up and this is called periastron. Some of the binary stars that have been discovered have not yet fully revolved around each other. Through the path that the stars are taking astronomers have determined that there is a gravitational pull on the star that causes it to move in that orbital. Binary stars can be close together and orbit each other rapidly or they can be farther apart and orbit at a much slower rate. For example Alpha Centauri is a binary star system that is the brightest star system in Centaurus. It is 4.22 light years away from earth and the two stars in Alpha Centauri take 79 years to orbit each other. The stars that are located in the Alpha Centauri are bigger than the sun.  In contrast astronomers have discovered a binary star system 16,000 light years away in which the stars orbit each other in 5.4 minutes. HM Cancri is the smallest binary system that has ever been discovered it is only 8 times the diameter of the earth. Astronomers used the Doppler effect to determine the cause of the change in velocity and this led to the discovery of the second star.   Astronomers have been able to discover more about the universe through the use of binary stars and their orbits. One example of this is with white dwarfs which are usually only found in binary stars. White dwarfs are usually found in the orbits of binary star system. Through the study of the orbits of binary stars astronomers were able to get a more accurate reading of the mass of other stars.
Visual binary stars are usually tilted from our perspective. The reason for this is because the orbital plane are not necessarily perpendicular with our line of sight. This means that many of the binary star systems that have been discovered have a tilt in relation to earth. Astronomers can't see the actual orbit of most of these stars instead they have a projection of binary orbits based on the data they can collect. In the case of elliptical binary stars the orbit could truly create an eclipse or it can just be the tilt that we see from earth. Astronomers have found ways to determine what the tilt is and in many cases it is successful in determining a ellipse or just a tilt that makes it appear elliptical. In the other cases they are unable to determine the tilt and the angle remains uncertain.
Evolutionists believe that binary stars form at the same time, from the same kind of gas, and should have the same mass and composition. For 15 years, Vanderbilt Scientists have been researching two stars that are near the Orion Nebula. One of the stars is two times brighter than the other and has a temperature 300 degrees higher than the other star. This recent discovery disproves evolutionist’s ideas and is forcing them to think of a new way to explain the existence of binary stars. 
When I consider your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is man that you are mindful of him, the son of man that you care for him? Psalms 8:3-4
Science and Astronomers try to explain how something so incredible could take place through scientific ideas and theories. The complexity of the stars proves that there must be a creator.
- Binary and Variable Stars By Stuart J. Robbins, Journey Through the Galaxy
- Stellar Model Applied to Close Binary Star Systems West, Jon K., Creation Research Society Quarterly Journal, Creation Research Society. Volume 18, Number 1. June, 1981
- A Short History and Other Stories of Binary Stars By Niemela, V., IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", Nov 9-13, 1998, p. 23-26.
- Visual Binaries By By Astronomy 161, Dept. Physics & Astronomy University of Tennessee
- Types of Binary Systems By Science Clarified, Advameg, Inc.
- Binary Stars HistoryBy moonpebble, Drupal. February 28, 2009
- Binary Stars By Martha Haynes Ph.D. Biophysics and Stirling Churchman, Astronomy 2201
- Astrometric Binaries By Astronomy 161, Dept. Physics & Astronomy University of Tennessee
- Measuring the Mass of Stars By Astronomy 161, Dept. Physics & Astronomy University of Tennessee
- X-ray Binaries By Dr. Alan Smale, Astrophysics Science Division. NASA's Goddard Space Flight Center.
- Binary Star Orbits By Martha Haynes and Stirling Churchman, Astronomy 2201
- Alpha Centauri By Fahad Sulehria
- HM Cancri: Binary Star With Shortest Known Orbital Period By Scientific Blogging, ION Publications LLC. March 9, 2010
- Superfast Stars Have Five-Minute Orbits By James Owen, National Geographic News. March 12, 2010
- A Review of Stellar Remnants: Physics, Evolution, and Interpretation Faulkner, Danny R., Creation Research Society Quarterly, Creation Research Society. Volume 44, June, 2007.
- Non-Identical ‘Identical Twin’ Stars Defy Evolution By Thomas, Brian. M.S., Daily Science Updates, Institute for Creation Research. June 25, 2008
- New Planet Challenges Evolutionary Models By Robert Newton, Journal of Creation 17(3) 2003.
- What is a Binary Star? By Fraser Cain, Universe Today