Alpha Centauri, Star System Closest To Our Sun

Star Alpha Centauri very bright against a backdrop of extremely dense field of fainter stars and dust clouds. — Alpha Centauri is the third-brightest star in our night sky – a famous southern star – and the nearest star system to our sun. Through a small telescope, the single star we see as Alpha Centauri resolves into a double star. This pair is just 4.37 light-years away from us. In orbit around them is Proxima Centauri, too faint to be visible to the unaided eye. At a distance of 4.25 light years, Proxima is the closest-known star to our solar system.
**Science of the Alpha Centauri system.** The two stars that make up Alpha Centauri, Rigil Kentaurus and Toliman, are quite similar to our sun. Rigil Kentaurus, also known as Alpha Centauri A, is a yellowish star, slightly more massive than the sun and about 1.5 times brighter. Toliman, or Alpha Centauri B, has an orangish hue; it’s a bit less massive and half as bright as the sun. Studies of their mass and spectroscopic features indicate that both these stars are about 5 to 6 billion years old, slightly older than our sun.

Alpha Centauri A and B are gravitationally bound together, orbiting about a common center of mass every 79.9 years at a relatively close proximity, between 40 to 47 astronomical units (that is, 40 to 47 times the distance between the Earth and our sun).Must Watch Sky Events in 2021

In comparison, Proxima Centauri is a bit of an outlier. This dim reddish star, weighing in at just 12 percent of the sun’s mass, is currently about 13,000 astronomical units from Alpha Centauri A and B. Recent analysis of ground- and space-based data, published in 2017, has shown that Proxima is gravitationally bound to its bright companions, with a 550,000-year-long orbital period.

Proxima Centauri belongs to a class of low mass stars with cooler surface temperatures, known as red dwarfs. It’s also what’s know as a flare star, where it randomly displays sudden bursts of brightness due to strong magnetic activity.

In the past decade, astronomers have been searching for planets around the Alpha Centauri stars; they are, after all, the closest stars to us so the odds of detecting planets, if any existed, would be higher. So far, two planets have been found orbiting Proxima Centauri, one in 2016 and another in 2019. A paper published in February 2021 reported tantalizing evidence of a Neptune-sized planet around Alpha Centauri A, but so far, it has not been definitively confirmed.

Large-appearing bright star with 4 lens-effect bright spikes coming out from it.

Extremely dense star field with 2 brights stars and a small red circle around a much smaller one.

How to see Alpha Centauri. Unluckily for many of us in the Northern Hemisphere, Alpha Centauri is located too far to the south on the sky’s dome. Most North Americans never see it; the cut-off latitude is about 29° north, and anyone north of that is out of luck. In the U.S. that latitudinal line passes near Houston and Orlando, but even from the Florida Keys, the star never rises more than a few degrees above the southern horizon. Things are a little better in Hawaii and Puerto Rico, where it can get 10° or 11° high.

But for observers located far enough south in the Northern Hemisphere, Alpha Centauri may be visible at roughly 1 a.m. (local daylight saving time) in early May. That is when the star is highest above the southern horizon. By early July, it reaches its highest point to the south at nightfall. Even so, from these vantage points, there are no good pointer stars to Alpha Centauri. For those south of 29° N. latitude, when the bright star Arcturus is high overhead, look to the extreme south for a glimpse of Alpha Centauri.

Star chart with stars in black on white, of Centaurus with Southern Cross constellation. — The southern constellation Centaurus. Image via Wikimedia/ International Astronomical Union/ SkyandTelescope.com.

Observers in the tropical and subtropical regions of the Northern Hemisphere can find Alpha Centauri by first identifying the distinctive Southern Cross. A short line drawn through the crossbar (Delta and Beta Crucis) eastward first comes to Hadar (Beta Centauri), then Alpha Centauri. Meanwhile, in Australia and much of the Southern Hemisphere, Alpha Centauri is circumpolar, meaning that it never sets.

A telescope dome at in the foreground with Milky Way and bright stars in the sky. — In this image taken at the European Southern Observatory’s La Silla Observatory in Chile, the Southern Cross is clearly visible, with the yellowish star, closest to the dome, marking the top of the cross. Drawing a line downward through the crossbar stars takes you to the bluish star, Beta Centauri, and then to the yellowish Alpha Centauri. Image via ESO / Wikimedia Commons.

Alpha Centauri in mythology. Alpha Centauri has played a prominent role in the mythology of cultures across the Southern Hemisphere. For the Ngarrindjeri indigenous people of South Australia, Alpha and Beta Centauri were two sharks pursuing a sting ray represented by stars of the Southern Cross. Some Australian aboriginal cultures also associated stars with family relationships and marriage traditions; for instance, two stars of the Southern Cross were through to be the parents of Alpha Centauri.

Astronomy and navigation were deeply intertwined in the lives of ancient seafaring Polynesians as they sailed between islands in the vast expanse of the South Pacific. These ancient mariners navigated using the stars, with cues from nature such as bird movements, waves, and wind direction. Alpha Centauri and nearby Beta Centauri, known as Kamailehope and Kamailemua, respectively, were important signposts used for orientation in the open ocean.

For ancient Incas, a llama graced the sky, traced out by stars and dark dust lanes in the Milky Way from Scorpius to the Southern Cross, with Alpha Centauri and Beta Centauri representing its eyes.

Dark-on-light shepherd, mother llama with baby, partridge, toad, and snake. — A plaque at the Coricancha museum showing Inca constellations. Coricancha, located in Cusco, Peru, was perhaps the most important temple of the Inca empire. Image via Pi3.124 / Wikimedia Commons.

Ancient Egyptians revered Alpha Centauri, and may have built temples aligned to its rising point. In southern China, it was part of a star group known as the South Gate.

Alpha Centauri is the brightest star in the constellation Centaurus, named after the mythical half human, half horse creature. It was thought to represent an uncharacteristically wise centaur that figured in the mythology of Heracles and Jason. The centaur was accidentally wounded by Heracles, and placed into the sky after death by Zeus. Alpha Centauri marked the right front hoof of the centaur, although little is known of its mythological significance, if any.

Antique etching of half-man-half-horse in field of stars in black on white. — A depiction of the Centaur by Polish astronomer Johannes Hevelius in his atlas of constellations, Firmamentum Sobiescianum, sive Uranographia. Image via Wikimedia Commons.

Alpha Centauri’s position is RA: 14h 39m 36s, Dec: -60° 50′ 02″

Bottom line: Alpha Centauri is actually two binary stars that are quite similar to our sun. A third star that’s gravitationally bound to them is Proxima Centauri, the closest star to our sun.

NASA’s Kepler Mission Discovers Bigger, Older Cousin to Earth

NASA’s Kepler mission has confirmed the first near-Earth-size planet in the “habitable zone” around a sun-like star. This discovery and the introduction of 11 other new small habitable zone candidate planets mark another milestone in the journey to finding another “Earth.”

The newly discovered Kepler-452b is the smallest planet to date discovered orbiting in the habitable zone — the area around a star where liquid water could pool on the surface of an orbiting planet — of a G2-type star, like our sun. The confirmation of Kepler-452b brings the total number of confirmed planets to 1,030.

“On the 20th anniversary year of the discovery that proved other suns host planets, the Kepler exoplanet explorer has discovered a planet and star which most closely resemble the Earth and our Sun,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “This exciting result brings us one step closer to finding an Earth 2.0.”

Kepler-452b is 60 percent larger in diameter than Earth and is considered a super-Earth-size planet. While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.

Highlighted are 12 new planet candidates from the seventh Kepler planet candidate catalog that are less than twice the size of Earth and orbit in the stars’ habitable zoneCredits: NASA Ames/W. StenzelTwelve New Small Kepler Habitable Zone Candidates

There are 4,696 planet candidates now known with the release of the seventh Kepler planet candidate catalog – an increase of 521 since the release of the previous catalog in January 2015.Credits: NASA/W. StenzelRead more…

While Kepler-452b is larger than Earth, its 385-day orbit is only 5 percent longer. The planet is 5 percent farther from its parent star Kepler-452 than Earth is from the Sun. Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 percent brighter and has a diameter 10 percent larger.

“We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth’s evolving environment,” said Jon Jenkins, Kepler data analysis lead at NASA’s Ames Research Center in Moffett Field, California, who led the team that discovered Kepler-452b. “It’s awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth. That’s substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet.”

To help confirm the finding and better determine the properties of the Kepler-452 system, the team conducted ground-based observations at the University of Texas at Austin’s McDonald Observatory, the Fred Lawrence Whipple Observatory on Mt. Hopkins, Arizona, and the W. M. Keck Observatory atop Mauna Kea in Hawaii. These measurements were key for the researchers to confirm the planetary nature of Kepler-452b, to refine the size and brightness of its host star and to better pin down the size of the planet and its orbit.

The Kepler-452 system is located 1,400 light-years away in the constellation Cygnus. The research paper reporting this finding has been accepted for publication in The Astronomical Journal.

In addition to confirming Kepler-452b, the Kepler team has increased the number of new exoplanet candidates by 521 from their analysis of observations conducted from May 2009 to May 2013, raising the number of planet candidates detected by the Kepler mission to 4,696. Candidates require follow-up observations and analysis to verify they are actual planets.

Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star’s habitable zone. Of these, nine orbit stars that are similar to our sun in size and temperature.

“We’ve been able to fully automate our process of identifying planet candidates, which means we can finally assess every transit signal in the entire Kepler dataset quickly and uniformly,” said Jeff Coughlin, Kepler scientist at the SETI Institute in Mountain View, California, who led the analysis of a new candidate catalog. “This gives astronomers a statistically sound population of planet candidates to accurately determine the number of small, possibly rocky planets like Earth in our Milky Way galaxy.”

These findings, presented in the seventh Kepler Candidate Catalog, will be submitted for publication in the Astrophysical Journal. These findings are derived from data publicly available on the NASA Exoplanet Archive.

Scientists now are producing the last catalog based on the original Kepler mission’s four-year data set. The final analysis will be conducted using sophisticated software that is increasingly sensitive to the tiny telltale signatures of Earth-size planets.

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA’s Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

For more information about the Kepler mission, visit:

http://www.nasa.gov/kepler

Antikythera-The Modern Invention in the Past.

After 2,000 years under thesea, three flat, misshapen pieces of bronze at the National Archaeological Museum in Athens are all shades of green, from emerald to forest. From a distance, they look like rocks with patches of mold. Get closer, though, and the sight is stunning. Crammed inside, obscured by corrosion, are traces of technology that appear utterly modern: gears with neat triangular teeth (just like the inside of a clock) and a ring divided into degrees (like the protractor you used in school). Nothing else like this has ever been discovered from antiquity. Nothing as sophisticated, or even close, appears again for more than a thousand years.

For decades after divers retrieved these scraps from the Antikythera wreck from 1900 to 1901, scholars were unable to make sense of them. X-ray imaging in the 1970s and 1990s revealed that the device must have replicated the motions of the heavens. Holding it in your hands, you could track the paths of the Sun, Moon and planets with impressive accuracy. One investigator dubbed it “an ancient Greek computer.” But the X-ray images were difficult to interpret, so mainstream historians ignored the artifact even as it was championed by fringe writers such as Erich von Däniken, who claimed it came from an alien spaceship. It wasn’t until 2006 that the Antikythera mechanism captured broader attention. That year, Mike Edmunds of Cardiff University in Wales and his team published CT scans of the fragments, revealing more details of the inner workings, as well as hidden inscriptions—and triggering a burst of scholarly research.

The Antikythera mechanism was similar in size to a mantel clock, and bits of wood found on the fragments suggest it was housed in a wooden case. Like a clock, the case would’ve had a large circular face with rotating hands. There was a knob or handle on the side, for winding the mechanism forward or backward. And as the knob turned, trains of interlocking gearwheels drove at least seven hands at various speeds. Instead of hours and minutes, the hands displayed celestial time: one hand for the Sun, one for the Moon and one for each of the five planets visible to the naked eye—Mercury, Venus, Mars, Jupiter and Saturn. A rotating black and silver ball showed the phase of the Moon. Inscriptions explained which stars rose and set on any particular date. There were also two dial systems on the back of the case, each with a pin that followed its own spiral groove, like the needle on a record player. One of these dials was a calendar. The other showed the timing of lunar and solar eclipses.

Experts have been working to decipher inscriptions hidden inside the mechanism, in particular to understand the mechanism’s missing pieces, some destroyed, some probably still at the bottom of the sea. Though the pointers on the front face don’t survive, Alexander Jones, a historian at the Institute for the Study of the Ancient World in New York, says an inscription reveals that they carried colored balls: fiery red for Mars, gold for the Sun.

Also missing are the parts that drove the planetary pointers, leading to debate about exactly how they moved. Because planets orbit the Sun, when viewed from Earth they appear to wander back and forth in the sky. The Greeks explained this motion with “epicycles”: small circles superimposed on a larger orbit. According to Michael Wright, a former curator at London’s Science Museum who has studied the mechanism longer than anyone, it modeled epicycles with trains of small gears riding around larger ones. Though some experts have dismissed this as beyond the Greeks’ abilities, Jones says he will publish evidence supporting the idea later this year.

Other inscriptions hint at where the mechanism was made. Paul Iversen, a classicist at Case Western Reserve University in Cleveland, reports that the calendar includes month names used in Corinth and its colonies in northwest Greece. A dial that displayed the timing of major athletic festivals, including the Olympics, lists Naa, a festival held in northwest Greece, and Halieia, held to the south on the island of Rhodes. Perhaps the mechanism hailed from Rhodes and was being shipped north. The ancient philosopher Posidonius had a workshop in Rhodes that could have been the source; according to Cicero, Posidonius made a similar model of the heavens in the first century B.C.

The tradition of making such mechanisms could be much older. Cicero wrote of a bronze device made by Archimedes in the third century B.C. And James Evans, a historian of astronomy at the University of Puget Sound in Tacoma, Washington, thinks that the eclipse cycle represented is Babylonian in origin and begins in 205 B.C. Maybe it was Hipparchus, an astronomer in Rhodes around that time, who worked out the math behind the device. He is known for having blended the arithmetic-based predictions of Babylonians with geometric theories favored by the Greeks.

Regardless, the Antikythera mechanism proves that the ancient Greeks used complex arrangements of precisely cut wheels to represent the latest in scientific understanding. It’s also a window into how the Greeks saw their universe. They came to believe that nature worked according to predefined rules, like a machine—an approach that forms the basis of our modern scientific views. Edmunds argues that this “mechanical philosophy” must have developed as a two-way process. The ancient mechanics who captured the cosmos in bronze weren’t just modeling astronomical theories but were also inspiring them.

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