Achernar is the End of the River of Eridanus constellation

Search for Achernar from southerly latitudes

The Ninth-brightest star in all of the heavens, Achernar, is well-known to observers within the Southern Hemisphere. However many northern stargazers know this star by its identify solely. That’s as a result of – though it shines at magnitude +0.45, making it certainly one of our sky’s brightest stars – it’s extraordinarily far south on the dome of stars surrounding Earth. For those who’re north of about 33 degrees north latitude, Achernar by no means rises above your horizon in any respect. And but this star stays one of many sky’s most well-known stars because the star at the tip of the River.

The River is – in fact – the constellation Eridanus, which is massive and straightforward to see in a dark-enough sky, even if you happen to’re pretty far north on Earth’s globe. The northern a part of this constellation is situated close to the extraordinarily outstanding constellation Orion the Hunter. Eridanus seems to swell up in an amazing loop close to Orion, then meander southward. Lastly – for many within the Northern Hemisphere – it drops out of sight beneath the southern horizon earlier than it reaches its finish.

However if you’re far sufficient south – beneath 33 levels north latitude – you’ll simply spot the River’s finish as the brilliant star Achernar.

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The way to see Achernar

For all sensible functions, you have to be even additional south – round 25 degrees north latitude – to see Achernar properly. That could be a line drawn across the total globe passing by way of Miami within the U.S. and Taipei in Taiwan.

Nowhere in North America has it straightforward, seeing this star. For instance, from Key West, Florida, Achernar rises solely about 8 degrees above the southern horizon. Even farther south, from the southern tip of Hawaii’s Massive Island, Achernar by no means fairly makes it to 14 levels.

And but, if you’re far-enough south, you possibly can see Achernar simply. In any case, this star could be very brilliant!

Simply as Achernar marks the tip of the River, the River additionally has a starting. The star Beta Eridani or Cursa, which itself is well seen from the Northern Hemisphere, shines close to Orion’s brightest star, Rigel.

It’s seen from North America?

On most nights of the yr, Achernar isn’t seen from anyplace in North America. Nevertheless, round October 20 it skirts the southern horizon round midnight, by no means getting very excessive. Then because the months cross, it’s seen earlier at evening, round 10 p.m. in November, 8 p.m. in December and simply after sundown in January. Being far to the south with no brilliant stars round it, Achernar stands out in its isolation. In case you have a darkish sky, and are far sufficient south, you’ll simply see Achernar’s constellation Eridanus making its loop below the constellation Orion.

Earthly rivers are typically recognized for meandering. Within the sky, the celebrities representing Eridanus the River – Achernar’s constellation – have an analogous high quality.

Achernar’s historical past and mythology

In actual fact, the identify Achernar derives from an Arabic phrase that means Finish of the River.

Curiously, in early classical occasions the identify Achernar was given to the star we now know as Theta Eridani, or Acamar. At the moment Acamar was the brightest star of the constellation seen from Greece, and thus was thought-about the River’s finish.

When voyagers found the brighter star farther to the south, it grew to become Achernar, and the previous Achernar grew to become Acamar.

Apparently each names derive from the identical phrase, “Al Ahir al Nahr,” in keeping with Richard Hinckley Allen, whose 1899 e book Star Names: Their Lore and Meaning remains to be the very best round.

Science of Achernar

Knowledge from the Hipparcos mission positioned Achernar at about 144 light-years away. It’s a B3V star, that means that it belongs to the main sequence of stars. And, the B means the star is blue and it’s the bluest star among the many top 10 brightest stars.

Achernar is way hotter and brighter than our sun. In actual fact, it’s estimated to be over 3,100 occasions the luminosity, of our sun. It’s about six occasions the mass of the sun.

Brighter, hotter (and bluer) than the sun, Achernar produces extra power within the non-visible ultraviolet (UV) wavelengths. Once you take this into consideration, it pumps out some 3,000 to five,000 occasions the solar power degree. The discrepancy is because of an uncertainty within the quantity of UV radiation it produces.

Achernar can be a binary star system. The companion star – referred to as Alpha Eridani B – is a white foremost sequence star with about two solar plenty. It orbits the first star at a distance of 12 astronomical units each 14 to fifteen years.

Its fast rotation leads to a flattened star

As talked about above, Achernar’s mass is about six occasions that of our sun, and its common diameter is almost eight to 10 occasions that of the sun. However, whereas our sun spins on its axis as soon as about each 25 days, Achernar completes one rotation in barely greater than two days, or practically 15 occasions sooner than our sun. This quick rotation produces an odd, flattened form, first found by the European Southern Observatory’s Very Massive Telescope (VLT) in 2003. Up shut, Achernar would look extra like a blue M&M, whereas our sun would look extra like an orange. Read more about Achernar’s flattened shape from ESO.

This flattening of Achernar makes an actual floor temperature for this star laborious to find out. The flattening causes the star’s poles to be hotter than the equator. Estimates vary from about 14,500 to 19,300 kelvin (about 14,200 to 19,026 C or round 26,000 to 34,200 F).

Achernar’s place is RA: 01h 37m 42.8s, dec: -57° 14′ 12″.

Backside line: Achernar is the Ninth brightest star and flattest star recognized. It marks the tip of Eridanus the River. Right here’s why a lot of Earth by no means sees it … and how one can.

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