APOD: Geminids of the South (2015 Dec 17)

[APOD Robot]

Geminids of the South

Explanation: Earth's annual Geminid meteor shower did not disappoint, peaking before dawn on December 14 as our fair planet plowed through dust from active asteroid 3200 Phaethon. Captured in this southern hemisphere nightscape the meteors stream away from the shower's radiant in Gemini. To create the image, many individual frames recording meteor streaks were taken over period of 5 hours. In the final composite they were selected and registered against the starry sky above the twin 6.5 meter Magellan telescopes of Carnegie Las Campanas Observatory in Chile. Rigel in Orion, and Sirius shine brightly as the Milky Way stretches toward the zenith. Near Castor and Pollux the twin stars of Gemini, the meteor shower's radiant is low, close to the horizon. The radiant effect is due to perspective as the parallel meteor tracks appear to converge in the distance. Gemini's meteors enter Earth's atmosphere traveling at about 22 kilometers per second.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[Guest]

who put the railroad track picture in there?

Also, is the radiant just a by product of how the picture is taken, or is it a physical phenomenon?

[Chris Peterson]

Also, is the radiant just a by product of how the picture is taken, or is it a physical phenomenon?

The paths of the meteors are all parallel. The radiant is the vanishing point of those paths.

[Guest]

After reading the description, I am left wondering... What is the difference between an 'asteroid', an 'active asteroid' and a comet? And what is the difference with respect to the debris trail left by each? The recent orbiting and landing on the comet(s) seems to indicate that they appear to be mostly rock. Is it reasonable to assume that asteroids and comets are pretty much the same thing and leaving a similar debris trail, except for the level of moisture content of the parent body of course?

[bjosch]

It´s a little confusing to watch the nightsky "upside down", but surely the bright star in this picture is Procyon not Sirius. Sirius is to high north to be inside the frame. Sirius would also shine clearly stronger then Rigel.

[Ann]

It´s a little confusing to watch the nightsky "upside down", but surely the bright star in this picture is Procyon not Sirius. Sirius is to high north to be inside the frame. Sirius would also shine clearly stronger then Rigel.

No, the very bright star is indeed Sirius, not Procyon.

Sirius, Betelgeuse and Procyon form the Winter Triangle. In today's APOD, the Winter Triangle is "upside down".

Ann

[heehaw]

Upside down? I don't think so! http://odtmaps.com/detail.asp?product_id=McA-23x35

[Chris Peterson]

After reading the description, I am left wondering... What is the difference between an 'asteroid', an 'active asteroid' and a comet? And what is the difference with respect to the debris trail left by each? The recent orbiting and landing on the comet(s) seems to indicate that they appear to be mostly rock. Is it reasonable to assume that asteroids and comets are pretty much the same thing and leaving a similar debris trail, except for the level of moisture content of the parent body of course?

There are different ways of looking at the definitions. I usually distinguish an asteroid from a comet by its formation history rather than its behavior. So as a rule, I consider an asteroid to be a rocky body left over from the material that seeded the formation of the planets (and which makes up much of the terrestrial planets), which is low in volatiles (having formed fairly near the Sun), and has spent most of its existence in the asteroid belt. I consider a comet to be a body that formed far from the Sun in a region where many ices were present, resulting in a mixed rock-ice body that has spent most of its existence well beyond Neptune. In terms of history and environment, these are very different kinds of bodies.

A active asteroid is either an asteroid with enough volatiles to produce some sort of gas or debris tail, or it's an actual comet (from the outer system) that has lost most of its volatiles and has been perturbed into an asteroid-like orbit. Other than subtleties of mineral composition, there's not much difference between the debris trails. Dynamically, an active asteroid may have lower ejection velocities for debris (because there's less gas to drive the process), but that would mainly show up in modeling the tail evolution, not the tail structure itself.

[Alohascope]

After reading the description, I am left wondering... What is the difference between an 'asteroid', an 'active asteroid' and a comet? And what is the difference with respect to the debris trail left by each? The recent orbiting and landing on the comet(s) seems to indicate that they appear to be mostly rock. Is it reasonable to assume that asteroids and comets are pretty much the same thing and leaving a similar debris trail, except for the level of moisture content of the parent body of course?

"On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt.[5] The detection was made by using the far-infrared abilities of the Herschel Space Observatory.[6] The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."[6]" From https://en.wikipedia.org/wiki/Asteroid

[Chris Peterson]

According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."

Which is why there is a growing trend to look at developmental history and not the presence of outgasing, as that defines a more natural boundary between objects which probably have no blurred boundary at all.

[bjosch]

It´s a little confusing to watch the nightsky "upside down", but surely the bright star in this picture is Procyon not Sirius. Sirius is to high north to be inside the frame. Sirius would also shine clearly stronger then Rigel.

No, the very bright star is indeed Sirius, not Procyon.

Sirius, Betelgeuse and Procyon form the Winter Triangle. In today's APOD, the Winter Triangle is "upside down".

Ann

You are absolutely right and i must have had a brainlapsus or something because for some reason i didn´t see Sirius. I was really looking at Procyon when i wrote my comment. As you can see i wrote that Sirius would shine clearly more powerful than Rigel and i looked at Procyon/Rigel in the picture. How i was able to NOT see Sirius i don´t now, but i see it clearly now....

[neufer]

<<Although meteors have been known since ancient times, they were not known to be an astronomical phenomenon until early in the 19th century. Prior to that, they were seen in the West as an atmospheric phenomenon, like lightning, ["meteor" : (Greek) "atmospheric"] and were not connected with strange stories of rocks falling from the sky. Thomas Jefferson wrote "I would more easily believe that (a) Yankee professor would lie than that stones would fall from heaven." He was referring to Yale chemistry professor Benjamin Silliman's investigation of an 1807 meteorite that fell in Weston, Connecticut. Silliman believed the meteor had a cosmic origin, but meteors did not attract much attention from astronomers until the spectacular meteor storm of November 1833. People all across the eastern United States saw thousands of meteors, radiating from a single point in the sky. Astute observers noticed that the radiant, as the point is now called, moved with the stars, staying in the constellation Leo. The astronomer Denison Olmsted made an extensive study of this storm, and concluded it had a cosmic origin. After reviewing historical records, Heinrich Wilhelm Matthias Olbers predicted the storm's return in 1867, which drew the attention of other astronomers to the phenomenon. Hubert A. Newton's more thorough historical work led to a refined prediction of 1866, which proved to be correct. With Giovanni Schiaparelli's success in connecting the Leonids (as they are now called) with comet Tempel-Tuttle, the cosmic origin of meteors was now firmly established. Still, they remain an atmospheric phenomenon, and retain their name "meteor" from the Greek word for "atmospheric".>>

[b][color=#0000FF]December 14, 1807 - Weston meteorite[/color][/b]

---

<<At 6:30 in the morning of December 14, 1807, a blazing fireball about two-thirds the size of the moon, was seen traveling southwards by early risers in Vermont and Massachusetts. Three loud explosions were heard over the town of Weston in Fairfield County, Connecticut. Stone fragments fell in at least 6 places. The largest and only unbroken stone of the Weston fall, which weighed 36.5 pounds, was found some days after Yale University professors Benjamin Silliman and James Kingsley had spent several fruitless hours hunting for it. The owner, a Trumbull farmer named Elijah Seeley, was urged to present it to Yale by local people who had met the professors during their investigation, but he insisted on putting it up for sale. It was purchased by Colonel George Gibbs for his large and famous collection of minerals; when the collection became the property of Yale in 1825, Silliman finally acquired this stone; the only specimen of the Weston meteorite that remains in the Yale Peabody Museum collection today.>>

[Chris Peterson]

Thomas Jefferson wrote "I would more easily believe that (a) Yankee professor would lie than that stones would fall from heaven."

In fact, there's no evidence that this anecdote was ever uttered by Jefferson. What he is known to have said about the Weston fall, however, is this:

We certainly are not to deny whatever we cannot account for. A thousand phenomena present themselves daily which we cannot explain, but where facts are suggested, bearing no analogy with the laws of nature as yet known to us, their verity needs proofs proportioned to their difficulty. A cautious mind will weigh well the opposition of the phenomenon to everything hitherto observed, the strength of the testimony by which it is supported, and the errors and misconceptions to which even our senses are liable. It may be very difficult to explain how the stone you possess came into the position in which it was found. But is it easier to explain how it got into the clouds from whence it is supposed to have fallen? The actual fact however is the thing to be established, and this I hope will be done by those whose situations and qualifications enable them to do it. I salute you with respect.

Click to view full size image

(And to be clear about a possible point of confusion, the Weston meteorite is not associated with the Geminid meteor shower, despite the fall occurring while the Geminids were active.)

[neufer]

(And to be clear about a possible point of confusion, the Weston meteorite is not associated with the Geminid meteor shower, despite the fall occurring while the Geminids were active.)

So how did the Weston meteor get into the clouds from whence it is supposed to have fallen

[Chris Peterson]

(And to be clear about a possible point of confusion, the Weston meteorite is not associated with the Geminid meteor shower, despite the fall occurring while the Geminids were active.)

So how did the Weston meteor get into the clouds from whence it is supposed to have fallen :?:

Zeus.

[neufer]

(And to be clear about a possible point of confusion, the Weston meteorite is not associated with the Geminid meteor shower, despite the fall occurring while the Geminids were active.)

So how did the Weston meteor get into the clouds from whence it is supposed to have fallen

Zeus.

<<Zeus, in his attempt to locate the center of the earth, launched two eagles from the two ends of the world, and the eagles, starting simultaneously and flying at equal speed, crossed their paths above the area of Delphi. From this point, Zeus threw a stone from the sky to see where it will fall. The stone fell at Delphi, which since then was considered to be the center of the world, the omphalos - "navel of the earth". Omphalos is also the name of the stone given to Cronus. In the ancient world of the Mediterranean, it was a powerful religious symbol. Omphalos Syndrome refers to the misguided belief that a place of geopolitical power and currency is the most important place in the world.>>

[b][color=#0000FF]The omphalos in museum of Delphi.[/color][/b]

---

<<Cronus sired several children by Rhea: Hestia, Demeter, Hera, Hades, and Poseidon, but swallowed them all as soon as they were born, since he had learned from Gaia and Uranus that he was destined to be overthrown by his son as he had previously overthrown Uranus, his own father, an oracle that Rhea heard and wished to avert. When Zeus was about to be born, Rhea sought Gaia to devise a plan to save him, so that Cronus would get his retribution for his acts against Uranus and his own children. Rhea gave birth to Zeus in Crete, handing Cronus a rock wrapped in swaddling clothes, which he promptly swallowed.

After reaching manhood, Zeus forced Cronus to disgorge first the stone (which was set down at Pytho under the glens of Parnassus to be a sign to mortal men, the Omphalos) then his siblings in reverse order of swallowing. Then Zeus released the brothers of Cronus, the Gigantes, the Hecatonchires and the Cyclopes, from their dungeon in Tartarus, killing their guard, Campe. As a token of their appreciation, the Cyclopes gave him thunder and the thunderbolt, or lightning, which had previously been hidden by Gaia. Together, Zeus and his brothers and sisters, along with the Gigantes, Hecatonchires and Cyclopes overthrew Cronus and the other Titans, in the combat called the Titanomachy. The defeated Titans were then cast into a shadowy underworld region known as Tartarus. Atlas, one of the titans that fought against Zeus, was punished by having to hold up the sky.>>