Binary Stars & Clusters

What are binary stars?

More than four fifths of the bright objects we see in the night sky actually represent multiple stars orbiting together, sometimes in star clusters although much more commonly as binary stars. Binary stars is the term used to describe a celestial object that appears to be a singular point-light to the naked eye, however is in reality a system of two stars orbiting a common center of mass. These are different from double stars, which appear near one another to terrestrial observers, however are not near each other, and have no relationship in space.

While it is possible for a binary star system to be created when a star captures another into its gravitation field, the more common creation of these systems is when two stars develop together, from one envelope of gas. Wide binary stars, which are further apart than close binaries, have little effect on each other's development, and either star instead develops as if it were a singular star. In close binaries, material can be shed from one star to another, meaning if one of the stars in the system were to explode into a supernova, or shed its outer layer and form a pulsar, it would likely result in the destruction of its binary star. Even if the second star does survive, it will usually continue to orbit the newly formed object, contributing material to it.

Albireo

With a larger distance between them as well as a significant difference in color, Albireo is one of the most easily observed binary stars. The brighter of the two stars comprising Albireo is itself another binary star as well.

Castor

The system comprising Castor is actually significantly greater than just a binary star. Instead, it is made up of three pairs of binary stars. While the three star pairs are distinguishable through the Celestron 130GT telescopes, the pairs are all spectroscopic binaries, which means they are indistinguishable to an amateur observer.

Mizar and Alcor

One of the most famous binary star systems in the night sky, Mizar and Alcor, are distinguishable to the naked eye. Under dark skies, it should not be too difficult to spot the pair, and with a telescope it will become any easy task.

Star Clusters

A star cluster is a region of stars bound together by gravitational pull, and observable as a field of distinct objects to an observer with a telescope (although a few, such as the Pleiades, can be seen with the naked eye). Star clusters can be categorized as either open or globular.

Open clusters contain dozens to hundreds of young stars in non-symmetrical arrangements. An example of this would be the Pleiades.

Globular clusters contain thousands to hundreds of thousands of stars, packed into symmetric, roughly spherical forms. These were not identified or studied in depth until after the invention of the telescope.

The Pleiades star cluster is one of the brightest and largest in the night sky, and provides both historical significance and astronomical.

The seven sisters, as they are known, actually number significantly greater than seven, however due to varying levels of light pollution, the amount you can count may be different from one location to another.

The cluster is known as Subaru to the Japanese, and is the inspiration for the car brand's name (they're logo is actually a stylized representation of the seven brightest stars in the cluster).

While this image was captured with a larger aperture telescope, the Pleiades are easy to see with the Academy's 130mm Newtonian, and are even visible to the naked eye if you have dark enough skies and know where to look. For naked-eye observing, the marsh on campus provides dark enough skies for most people to be able to find it, and a more experienced observer utilizing averted-vision techniques can even find them from the middle of a small city.

Beehive Cluster (Praesepe, M44)

One of the earliest known star clusters, the Beehive Cluster is visible in the constellation Cancer as a small, bright patch of haze in the night sky, and was first distinguished as a star cluster by Galileo. The Beehive Cluster, like the Pleiades, is also an open cluster.

Wild Duck Cluster, M10

The Wild Duck Cluster is a summer object located in the constellation Ophiuchus. This globular cluster should be easy to observe through a small telescope, and is most notable for the large number of blue stars within it, which would signal a difference in ages that does not align with how astronomers expected the cluster to have formed. (NASA, ESA, Hubble, 2017)

Messier 3

Messier 3 is a globular cluster located in the constellation Canes Ventetici, most easily visible during the spring. M3's brightness fluctuates with time due to its containing more variable stars than any other known star cluster. (NASA, ESA, STScl, Sarajedini, 2017)

References and Further Reading

Binary Stars via Space.com: https://www.space.com/22509-binary-stars.html

Castor Sextuple via Sol Station: http://www.solstation.com/stars2/castor6.htm

Large list of binary stars: https://pastebin.com/LAk0jdR5

Mizar and Alcor: https://earthsky.org/brightest-stars/mizar-and-alcor-the-horse-and-ride

Beehive Cluster, via Britannica: https://www.britannica.com/place/Praesepe

Star Clusters, via Britannica: https://www.britannica.com/science/star-cluster

NASA Hubble's Messier Catalogue: https://www.nasa.gov/content/goddard/hubble-s-messier-catalog

Astropixels Messier Chart: http://astropixels.com/messier/messiercat.html

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