Starship Asterisk*

APOD wrote:< | Archive | Index | Search | Calendar | RSS | Education | About APOD | Discuss | >

http://en.wikipedia.org/wiki/Canopus wrote:
<<Canopus (α Car / α Carinae / Alpha Carinae) is the brightest star in the southern constellation of Carina and Argo Navis, and the second brightest star in the night-time sky, after Sirius. Canopus's visual magnitude is −0.72, and it has an absolute magnitude of −5.53. Canopus is a rare example of a supergiant of spectral type F. Canopus is essentially white when seen with the naked eye (although F-type stars are sometimes listed as "yellowish-white"). In the southern hemisphere, Canopus and Sirius are both visible high in the sky simultaneously, and reach the meridian just 21 minutes apart. It is a circumpolar star when seen from points that have latitude south of 37°18' south. Since Canopus is so far south in the sky, it never rises in mid- or far-northern latitudes; however, it should just be visible under ideal conditions from Gibraltar or Los Angeles. Canopus is part of the Scorpius-Centaurus Association, a group of stars which share similar origins.

To anyone living in the northern hemisphere, but far enough south to see the star, it served as a southern pole star. To the Bedouin people of the Negev and Sinai, Canopus is known as Suhayl. It and Polaris are the two principal stars used for navigation at night. Due to the fact that it disappears below the horizon, it became associated with a cowardly or changeable nature, as opposed to always-visible Polaris, which was circumpolar and hence 'steadfast'. In modern times, Canopus serves another navigational use. Canopus' brightness and location well off the ecliptic makes it popular for space navigation. Many spacecraft carry a special camera known as a "Canopus Star Tracker" plus a sun sensor for altitude determination.

Before the launching of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most powerful stars in our galaxy. Hipparcos established Canopus as lying 310 light years (96 parsecs) from our solar system; this is based on a parallax measurement of 10.43 ± 0.53 mas. The difficulty in measuring Canopus' distance stemmed from its unusual nature. The spectral classification for Canopus is F0 Ia (Ia referring to "bright supergiant"), and such stars are rare and poorly understood; they are stars that can be either in the process of evolving to or away from red giant status. Canopus is too far away for Earth-based parallax observations to be made, so the star's distance was not known with certainty until the early 1990s.

Canopus is 15,000 times more luminous than the Sun and the most intrinsically bright star within approximately 700 light years. For most stars in the local stellar neighborhood, Canopus would appear to be one of the brightest stars in the sky. Canopus appears less bright than Sirius in our sky only because Sirius is much closer to the Earth (8.6 light years).

Its diameter has been measured at 0.6 astronomical units (the measured angular diameter being 0.006 arcseconds), 65 times that of the sun. If it were placed at the centre of the solar system, it would extend three-quarters of the way to Mercury. An Earth-like planet would have to lie three times the distance of Pluto for its star to appear the same size in the sky as our own sun.

Canopus is a strong source of X-rays, which are likely produced by its corona, magnetically heated to around 15 million K.

___ Etymology and cultural significance

The name "Canopus" is a Latinisation of the Greek name "Kanôbos", recorded in Claudius Ptolemy's Almagest (c150 AD). The name has two common derivations, both listed in Richard Hinckley Allen's seminal Star Names: Their Lore and Meaning; and one less so. All are matters of conjecture:

* One from the legend of the Trojan War, where the constellation Carina was once part of the now-obsolete constellation of Argo Navis, which represented the ship used by Jason and the Argonauts. The brightest star in the constellation was given the name of a ship's pilot from another Greek legend: Canopus, pilot of Menelaus' ship on his quest to retrieve Helen of Troy after she was taken by Paris.

* A second from the Egyptian Coptic Kahi Nub ("Golden Earth"), which refers how Canopus would have appeared near the horizon in ancient Egypt, reddened by atmospheric extinction from that position. A ruined ancient Egyptian port named Canopus lies near the mouth of the Nile, site of the Battle of the Nile.

* A third is its possible origin from the Semitic root G(C)-N-B (Gimmel-Nun-Beth), from which the Arabic word for south, janūb ( جنوب ), is derived. The southeastern wall of the Muslim Ka'bah points to Canopus, and is named Janūb ("south") as well.>>

http://en.wikipedia.org/wiki/Iguazu_Falls wrote:
<<Iguazu Falls, Iguassu Falls, or Iguaçu Falls are waterfalls of the Iguazu River located on the border of the Brazilian state of Paraná and the Argentine province of Misiones. Their name comes from the Guarani or Tupi words y (water) and ûasú (big). Legend has it that a god planned to marry a beautiful aborigine named Naipí, who fled with her mortal lover Tarobá in a canoe. In rage, the god sliced the river creating the waterfalls, condemning the lovers to an eternal fall. The first European to find the falls was the Spanish Conquistador Álvar Núñez Cabeza de Vaca in 1541, after whom one of the falls in the Argentine side is named. The falls were rediscovered by Boselli at the end of the 19th century, and one of the Argentine falls is named after him.


Walkways allow close views of the falls from both Brazil and Argentina.

The waterfall system consists of 275 falls along 2.7 kilometers of the Iguazu River. Some of the individual falls are up to 82 meters in height. The Devil's Throat (Garganta del Diablo in Spanish or Garganta do Diabo in Portuguese), a U-shaped, 82-meter-high, 150-meter-wide and 700-meter-long (490 by 2300 feet) cataract, is the most impressive of all, and marks the border between Argentina and Brazil. The edge of the basalt cap recedes only 3 mm (0.1 in) per year. With the flooding of the Guaíra Falls in 1982, Iguazu currently has the second greatest average annual flow of any waterfall in the world, after Niagara, with an average rate of 1746 m³/s. Niagara's average flow is about 2,400 m³/s.

The falls have been featured in several movies including The Mission, Happy Together, Miami Vice, Mr. Magoo, Moonraker, and Indiana Jones and the Kingdom of the Crystal Skull.>>

http://earthobservatory.nasa.gov/IOTD/view.php?id=4060 wrote:
<<Iguaçu Falls is one of the wonders of the world. After flowing westward through southern Brazil, the Iguaçu River crashes over the rim of the Paraná Plateau in a broad crescent interlaced with tree-covered islets. Some of the falls plunge hundreds of feet straight down to the valley below, while others cascade down in a series of smaller steps. The river then joins the south-flowing Paraná.

The immediate surrounding area of Brazil, Argentina, and Paraguay was once native forest and grasslands, and both Argentina and Brazil have set aside land near the Falls as National Parks. The effect of differing land use policies can be clearly seen by comparing the 1973 Landsat MSS scene with the August 2001 scene from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on the Terra satellite. Both scenes use a combination of infrared and visible wavelength data to contrast vegetation (red), water (blue), and bare ground (greens and whites).

Paraguay has permitted complete development of the land. In 1973, nearly the entire area west of the Paraná River, which runs vertically through the center of the scene, was vegetated; in 2001, nearly all the land appears to be under human development, with a patchwork of cleared and vegetated areas.

In Brazil, a sharp line between solid vegetation and developed lands to the north marks the boundary of the National Park. It's interesting to note that in 1973, there were some cleared areas near the Iguaçu River northeast of the falls that have since regrown. Meanwhile to the north, a huge lake has been created from a dam on the Paraná, and development has grown up all around it.

In the Misiones Province of northeast Argentina, development is considerably more modest than Paraguay, though it too shows a new reservoir. To the northeast of the reservoir, patches of terraced-looking bare ground appear green in this color combination because they are rich with iron, which would appear reddish in a natural-color image. This region of Argentina is home to some of the last remaining tracts of a tropical ecosystem called the Atlantic Forest, a tropical rainforest that is distinct from the Amazon and that once stretched along most of Brazil’s Atlantic Coast and inland several hundred kilometers.>>

This specific shot is a panorama of four stitched shots all made by a 28mm lens and by one-minute exposure. I have also used a star tracking drive on my tripod to make a bit longer exposure without having startrails [streaks of starlight created by Earth's rotation]. Near the center along the horizon are lights from Argentina's Iguazú Falls International Airport.

I started the session before sunset with setting up everything, and it took a few hours until I got a good result. I was in the area for four nights, finding locations and waiting for clear skies. I was hoping to get much closer to the falls (something like this) but it was too wet with raining mist and the clear sky didn't last long, so maybe next time!

Boergass@AOL.com wrote:Oh, My. If this image is correct then I must do over my Lizard room. Long story abreciated. I am an artist who likes to make environments for Winter guests from the frozen North. I created a powder room with a night sky that, when the lights are turned off, shows the stars of Southern sky viewed at just about the latitude of this photo between February-March, which is when most visitors come down. I used the Southern Hemisphere star chart in the front of my large National Geographic World Atlas. My husband has sailed the Equatorial Pacific and helped me with relative distances and directions, difficult when you are doing this inside a cube. I used the magnitude indications to determine the size of the "stars". If this image is not reversed, then my whole sky IS reversed. Please let me know if the image could have been reversed.
Debbie Boerger