Earth's Shadow (APOD 20 Aug 2008)

[BMAONE23]

Gotta agree with you there. I always thought it would be better if the power fluctuation (outage) rotated with the time zones starting at GMT and spreading hour by hour as the noon hour progressed around the world.

[starnut]

The series of photos of the partial lunar eclipse was taken in Athens, Greece, This made me wonder if the ancient Athenians and observers in other ancient civilizations also noticed the curvature of the shadow on the moon as it passed through the shadow. Would they have deduced that the shadow was casted by a round object and that round object might be the Earth? Would the more insightful ones have an Eureka! moment and realized that the Earth was not flat?

Gary

[John Newstead]

I am unhappy about the sequencing of the overlaps. How come the fourth image from left in in front of all others if this be a time sequence. Or am I just dumb and the whole composite is Photoshopped? That style of sequencing troubles me.

[emc]

Gotta agree with you there. I always thought it would be better if the power fluctuation (outage) rotated with the time zones starting at GMT and spreading hour by hour as the noon hour progressed around the world.

The DTESS movie and other SciFi stimuli led me to thinking that we should all be on the same time reference instead of time zones and adjust to the light as time dictates. i.e. 2008.08.21.12.00 GMT is normal morning work start for me today here in Georgia, USA... After all, we are all flying through space on the same ship

[emc]

The series of photos of the partial lunar eclipse was taken in Athens, Greece, This made me wonder if the ancient Athenians and observers in other ancient civilizations also noticed the curvature of the shadow on the moon as it passed through the shadow. Would they have deduced that the shadow was casted by a round object and that round object might be the Earth? Would the more insightful ones have an Eureka! moment and realized that the Earth was not flat?

Gary

Hi Gary,

I expect your right... I bet some insightful folks did recognize and associate but were afraid to speak out.

Perhaps some stubborn folks saw the earth as a flat disc.

[neufer]

The series of photos of the partial lunar eclipse was taken in Athens, Greece, This made me wonder if the ancient Athenians and observers in other ancient civilizations also noticed the curvature of the shadow on the moon as it passed through the shadow. Would they have deduced that the shadow was casted by a round object and that round object might be the Earth? Would the more insightful ones have an Eureka! moment and realized that the Earth was not flat? - Gary

http://en.wikipedia.org/wiki/Spherical_Earth
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Plato

<<Plato (427 BCE - 347 BCE) travelled to southern Italy to study Pythagorean mathematics. When he returned to Athens and established his school, Plato also taught his students that Earth was a sphere. If man could soar high above the clouds, Earth would resemble "a ball made of twelve pieces of leather, variegated, a patchwork of colours.">>
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Aristotle

<<Aristotle (384 BCE - 322 BCE) was Plato's prize student and "the mind of the school." Aristotle observed "there are stars seen in Egypt and [...] Cyprus which are not seen in the northerly regions." Since this could only happen on a curved surface, he too believed Earth was a sphere "of no great size, for otherwise the effect of so slight a change of place would not be quickly apparent." (De caelo, 298a2-10)

Aristotle provided physical and observational arguments supporting the idea of a spherical Earth:

* Every portion of the earth tends toward the center until by compression and convergence they form a sphere. (De caelo, 297a9-21)

* Travelers going south see southern constellations rise higher above the horizon; and

* The shadow of Earth on the Moon during a lunar eclipse is round. (De caelo, 297b31-298a10)

The concepts of symmetry, equilibrium and cyclic repetition permeated Aristotle's work. In his Meteorology he divided the world into five climatic zones: two temperate areas separated by a torrid zone near the equator, and two cold inhospitable regions, "one near our upper or northern pole and the other near the ... southern pole," both impenetrable and girdled with ice (Meteorologica, 362a31-35). Although no humans could survive in the frigid zones, inhabitants in the southern temperate regions could exist.>>

[emc]

It is interesting just how stubborn people can be...

http://en.wikipedia.org/wiki/Flat_Earth_Society

<<In 1971, Shenton died and Charles K. Johnson became the new president of the Flat Earth Society. Under his leadership, over the next three decades, the group grew in size from a few members to about 3,000. Johnson distributed newsletters, flyers, maps, and other promotional materials to anyone who asked for them, and he managed all membership applications together with his wife, Marjory, who was also a flat-earther.


United Nations flagThe most recent world model propagated by the Flat Earth Society holds that humans live on a disc, with the North Pole at its center and a 150-foot (45 m) high wall of ice at the outer edge. The resulting map resembles the symbol of the United Nations, something Johnson used as evidence for his position. In this model, the sun and moon are each a mere 32 miles (52 km) in diameter.>>

[orin stepanek]

It is interesting just how stubborn people can be...

http://en.wikipedia.org/wiki/Flat_Earth_Society

<<In 1971, Shenton died and Charles K. Johnson became the new president of the Flat Earth Society. Under his leadership, over the next three decades, the group grew in size from a few members to about 3,000. Johnson distributed newsletters, flyers, maps, and other promotional materials to anyone who asked for them, and he managed all membership applications together with his wife, Marjory, who was also a flat-earther.


United Nations flagThe most recent world model propagated by the Flat Earth Society holds that humans live on a disc, with the North Pole at its center and a 150-foot (45 m) high wall of ice at the outer edge. The resulting map resembles the symbol of the United Nations, something Johnson used as evidence for his position. In this model, the sun and moon are each a mere 32 miles (52 km) in diameter.>>

Spose Johnson's belief would be changed if he got a ride in the space shuttle?

Orin

[emc]

The series of photos of the partial lunar eclipse was taken in Athens, Greece, This made me wonder if the ancient Athenians and observers in other ancient civilizations also noticed the curvature of the shadow on the moon as it passed through the shadow. Would they have deduced that the shadow was casted by a round object and that round object might be the Earth? Would the more insightful ones have an Eureka! moment and realized that the Earth was not flat?

Gary

Hi Gary,

I expect your right... I bet some insightful folks did recognize and associate but were afraid to speak out.

Perhaps some stubborn folks saw the earth as a flat disc.

I wanted mention the probability of some 'astronomically aware' evil doers that would take advantage of simple minded villagers by claiming responsibility for the moon eclipse in order to gain power... "Worship me and give me all your goodies or I will block out the sun as well and you will all die in darkness!"

[emc]

It is interesting just how stubborn people can be...

http://en.wikipedia.org/wiki/Flat_Earth_Society

<<In 1971, Shenton died and Charles K. Johnson became the new president of the Flat Earth Society. Under his leadership, over the next three decades, the group grew in size from a few members to about 3,000. Johnson distributed newsletters, flyers, maps, and other promotional materials to anyone who asked for them, and he managed all membership applications together with his wife, Marjory, who was also a flat-earther.


United Nations flagThe most recent world model propagated by the Flat Earth Society holds that humans live on a disc, with the North Pole at its center and a 150-foot (45 m) high wall of ice at the outer edge. The resulting map resembles the symbol of the United Nations, something Johnson used as evidence for his position. In this model, the sun and moon are each a mere 32 miles (52 km) in diameter.>>

Spose Johnson's belief would be changed if he got a ride in the space shuttle?

Orin

Too late for ride... he died in March 2001.

I was curious after neufer's post as to how long people believed the earth was flat and was amazed there is a Flat Earth Society in these times.

[Chris Peterson]

I was curious after neufer's post as to how long people believed the earth was flat and was amazed there is a Flat Earth Society in these times.

In fact, it's doubtful that many people (at least, people with any hint of education) in the West believed that the Earth was flat after the Greeks demonstrated its spherical shape. Throughout medieval times Europeans, the Catholic Church, and Near East societies all understood the Earth to be a sphere.

It's also doubtful that the Flat Earth Society ever had more than a few dozen members who were "true believers" (if that). When I was in college, I was a member, as were a number of friends. We obviously didn't believe the Earth was flat - we were astronomy students! But the mailings we received from the organization were hilarious (this was before the Internet, of course). I believe most members joined for similar reasons.

[orin stepanek]

Bizarro Superman lives on a cube world. The sides would be flat there.

Orin

[emc]

I was curious after neufer's post as to how long people believed the earth was flat and was amazed there is a Flat Earth Society in these times.

In fact, it's doubtful that many people (at least, people with any hint of education) in the West believed that the Earth was flat after the Greeks demonstrated its spherical shape. Throughout medieval times Europeans, the Catholic Church, and Near East societies all understood the Earth to be a sphere.

It's also doubtful that the Flat Earth Society ever had more than a few dozen members who were "true believers" (if that). When I was in college, I was a member, as were a number of friends. We obviously didn't believe the Earth was flat - we were astronomy students! But the mailings we received from the organization were hilarious (this was before the Internet, of course). I believe most members joined for similar reasons.

Hi Chris,

That's funny... now that you bring it to light (a little astronomical pun) I imagine there were a lot of fellow astronomy students in the society across the planet just as a joke.

You know... I was a Junior Smokey the Bear Forest Ranger once and I didn't really believe that Smokey wore pants and a hat... and could talk. Kinda the same thing... sort of... but not as ironically funny.

I take it the FES never got wind of your facade or you might have been a candidate for a good roasting. But if you were also a Junior Smokey the Bear Forest Ranger, you would have known how to deal with the fire.

According the the WIKI info it appears the FES is religion based.

[emc]

Bizarro Superman lives on a cube world. The sides would be flat there.

Orin

Funny Orin... and this Asterisk page needed a picture

[emc]

Getting back to this APOD... I have a question... How large and how high would a construction need to be from earth to create a shadow on the moon? According to the earth shadow angle displayed on the moon and the horizon angle displayed in the ISS photos... the structure would need to be many times higher and larger than the ISS to make an impression. Just curious.

http://en.wikipedia.org/wiki/Space_elevator

[neufer]

Getting back to this APOD... I have a question... How large and how high would a construction need to be from earth to create a shadow on the moon? According to the earth shadow angle displayed on the moon and the horizon angle displayed in the ISS photos... the structure would need to be many times higher and larger than the ISS to make an impression. Just curious.

http://en.wikipedia.org/wiki/Space_elevator

The problem is that the sun is not a point source of light.

An opaque moon sized object will produce a penumbra
twice the size of the moon at the distance of the moon
but only a small umbral shadow.

On the other hand, the earth's thin (~10km. thick) atmosphere
already produces the dark red "shadow" of a total solar eclipse.

http://antwrp.gsfc.nasa.gov/apod/ap070308.html
http://antwrp.gsfc.nasa.gov/apod/ap070302.html
http://antwrp.gsfc.nasa.gov/apod/ap041030.html
http://antwrp.gsfc.nasa.gov/apod/ap010104.html

[emc]

Getting back to this APOD... I have a question... How large and how high would a construction need to be from earth to create a shadow on the moon? According to the earth shadow angle displayed on the moon and the horizon angle displayed in the ISS photos... the structure would need to be many times higher and larger than the ISS to make an impression. Just curious.

http://en.wikipedia.org/wiki/Space_elevator

The problem is that the sun is not a point source of light.

An opaque moon sized object will produce a penumbra
twice the size of the moon at the distance of the moon
but only a small umbral shadow.

On the other hand, the earth's thin (~10km. thick) atmosphere
already produces the dark red "shadow" of a total solar eclipse.

http://antwrp.gsfc.nasa.gov/apod/ap070308.html
http://antwrp.gsfc.nasa.gov/apod/ap070302.html
http://antwrp.gsfc.nasa.gov/apod/ap041030.html
http://antwrp.gsfc.nasa.gov/apod/ap010104.html

Hi Art,

So are you telling me there's no hope of making bunny ears appear in our moon shadow? Not even with two gigantic space elevator docking/transfer stations?

[Chris Peterson]

So are you telling me there's no hope of making bunny ears appear in our moon shadow? Not even with two gigantic space elevator docking/transfer stations?

Even a real bunny standing on the Earth's terminator casts its shadow on the Moon. In the case of a space elevator, the cables would cast shadows, as would the docking station. But the docking station would be too far out for both its and Earth's shadow to be on the Moon at the same time unless greatly foreshortened (that is, with the Earth, Moon, and docking station approaching being in line).

The problem is that the shadows in all these cases are penumbral, so the contrast is low. Imagine you were on the Moon, looking towards the shadow casting structures (possibly with a telescope). You would see them silhouetted against the Sun, but not blocking the Sun completely. In order to get an umbral shadow on the Moon, the occluding object needs to have the same angular size as the Sun- 1/2°. In other words, from the Moon, an object at Earth's distance would have to be Moon-sized: about 3500 km across. While a space elevator is longer than this radially, it is very much narrower in the other direction.

[emc]

So are you telling me there's no hope of making bunny ears appear in our moon shadow? Not even with two gigantic space elevator docking/transfer stations?

Even a real bunny standing on the Earth's terminator casts its shadow on the Moon. In the case of a space elevator, the cables would cast shadows, as would the docking station. But the docking station would be too far out for both its and Earth's shadow to be on the Moon at the same time unless greatly foreshortened (that is, with the Earth, Moon, and docking station approaching being in line).

The problem is that the shadows in all these cases are penumbral, so the contrast is low. Imagine you were on the Moon, looking towards the shadow casting structures (possibly with a telescope). You would see them silhouetted against the Sun, but not blocking the Sun completely. In order to get an umbral shadow on the Moon, the occluding object needs to have the same angular size as the Sun- 1/2°. In other words, from the Moon, an object at Earth's distance would have to be Moon-sized: about 3500 km across. While a space elevator is longer than this radially, it is very much narrower in the other direction.

The terminator in this eclipse sense is the edge peak right? So everything along this edge peak casts a penumbral (low contrast) silhouette? And this can be resolved with a telescope? I think I am following you but the real bunny ears casting a shadow on the moon has me stunned.

Could this be an expanded art form taking shadow play to the moon?!

[Chris Peterson]

The terminator in this eclipse sense is the edge peak right?

I think so. It's the line between night and day on the Earth. If you were standing there, with the setting (or rising) Sun at your back and the partially eclipsed Moon in front of you, your shadow would be cast on the Moon.

So everything along this edge peak casts a penumbral (low contrast) silhouette? And this can be resolved with a telescope? I think I am following you but the real bunny ears casting a shadow on the moon has me stunned.

Yes, everything along the edge must cast a shadow out into space. Realistically, it would have to be very large- probably mountain range sized- to be detectable at all as a shadow on the Moon. And while it's theoretically true that you could see even small objects silhouetted against the Sun using a telescope from the Moon, in actual practice you have to worry about practical resolution. You won't see a rabbit's silhouette without a telescope with an aperture of hundreds of meters.

[emc]

The terminator in this eclipse sense is the edge peak right?

I think so. It's the line between night and day on the Earth. If you were standing there, with the setting (or rising) Sun at your back and the partially eclipsed Moon in front of you, your shadow would be cast on the Moon.

So everything along this edge peak casts a penumbral (low contrast) silhouette? And this can be resolved with a telescope? I think I am following you but the real bunny ears casting a shadow on the moon has me stunned.

Yes, everything along the edge must cast a shadow out into space. Realistically, it would have to be very large- probably mountain range sized- to be detectable at all as a shadow on the Moon. And while it's theoretically true that you could see even small objects silhouetted against the Sun using a telescope from the Moon, in actual practice you have to worry about practical resolution. You won't see a rabbit's silhouette without a telescope with an aperture of hundreds of meters.

Ok - So we won't be making any shadow puppets for the moon... Thanks for helping me understand. It was fun to contemplate.

[neufer]

So are you telling me there's no hope of making bunny ears appear in our moon shadow?

Maybe if you can get Gort to help out...
----------------------------------------------
Artist Wants to Paint Moon, But Physics May Foil Plan
By Robert Roy Britt Senior Science Writer
posted: 07:00 am ET 10 August 2001
http://www.space.com/scienceastronomy/g ... 810-1.html

<<An artist hoping to recruit millions of laser-pointer owners to "paint the Moon" may instead be disappointed by physics.

James T. Downey, the artist behind the project, is intent on creating a "collaborative work of celestial art" by illuminating a fleeting red spot on our only natural satellite.

The event, an effort to help people "find the excitement of space," is scheduled for two nights, one in October and another in November. Downey has chosen a target location for the beams on the dark portion of the Moon while it's in its first-quarter. Each attempt would last five minutes. A web site, called "Paint the Moon," has been set up with instructions for where and how to point your laser and why you should participate.

"Inexpensive yet surprisingly powerful laser-pointing devices have become ubiquitous in America," said Downey. "Millions of people own such a device. Laser light stays coherent over vast distances, the beams spreading very little."

Lasers are powerful devices, concentrated bursts of energy that can damage the eye, cut through metal or, theoretically, shoot down enemy missiles. And all at the speed of light. Astronomers use lasers to measure distances between telescopes and even to enhance observations in order to improve resolution of light coming from distant stars. Experiments planted by Apollo astronauts allow scientists to use lasers to more accurately gauge the distance from Earth to the Moon, and even detect moonquakes.

But all technology has its limits. It seems there are not enough people in North America to make Downey's idea work.

"As I suspected, the number required is not millions of people, but more than millions of millions of millions of people," said Donald Umstadter, a laser expert at the Center for Ultrafast Optical Science at the University of Michigan, Ann Arbor.

Umstadter became curious about the project when SPACE.com asked him if it was feasible to illuminate the Moon in this way. He asked one of his graduate students, Chad Vandenbosch, to look into the possibility as a mathematical exercise.

To calculate how many people it would take to successfully make a temporary red spot on the Moon visible from Earth, Vandenbosch estimated several factors. He considered a typical handheld laser pointer's power and how much of the light would be absorbed by Earth's atmosphere, as well as how much of the laser light would be reflected by the Moon vs. how much would be absorbed.

As a premise, he based the calculations on what would be needed to make the spot visible to people in cities, where bright lights would obscure a faint spot that might otherwise be visible in rural locations.

A reader says there's another reason why this won't work.

Vandenbosch said there is a little wiggle room in his calculations due to the estimate of background light.

"The main thing to glean from the calculation is that the divergence of these pointers, due to their small aperture and a basic law of optics governing the diffraction of light, results in a huge diameter beam, and thus very dim beam, by the time it arrives at the Moon," Umstadter said.

Downey, the artist, was intrigued and a bit dismayed when he learned of Vandenbosch's science, but plans to proceed with the artistic attempt nonetheless.

"I knew that it would be a long shot from the start," Downey said. "But success is something that can be measured in a lot of ways. We may not be able to accomplish actually painting the Moon, but still the act of participating in something such as this has value."

In what way?

"If I can get people thinking about the Moon as something they might be able to touch, if I can get science teachers to talk about the physics involved, Moon phases, etc., if I can just help people find the excitement of space as part of the human drama again, then the project will have been a grand success."

Downey also doesn't want to spoil a good party.

"In emails, I hear from people who are planning parties around the event, who become enraptured with the whole notion and tell all their friends," he said. "Of course, I also hear from people who think the entire idea is just plain lunacy, and tell me I should be locked up for spreading such tripe. But hey, art is like that."

Downey came up with the idea as part of a novel he's writing, set 50 years into the future. "A couple of characters are discussing oddball things back at the beginning of the millenium, and this comes up. I thought that it would be fun if someone read my book (assuming I can get it published, of course) and actually tried to organize such an event, thereby having life imitate art.">>

[emc]

So are you telling me there's no hope of making bunny ears appear in our moon shadow?

Maybe if you can get Gort to help out...
----------------------------------------------
Artist Wants to Paint Moon, But Physics May Foil Plan
By Robert Roy Britt Senior Science Writer
posted: 07:00 am ET 10 August 2001
http://www.space.com/scienceastronomy/g ... 810-1.html

<<An artist hoping to recruit millions of laser-pointer owners to "paint the Moon" may instead be disappointed by physics.

...[snipped]">>

Well there we go again... reality dashing the dream of another space artist. "Man's got to know his limitations."

[henk21cm]

I am unhappy about the sequencing of the overlaps. How come the fourth image from left in in front of all others if this be a time sequence. Or am I just dumb and the whole composite is Photoshopped?

Yes John, it is photoshopped. In a real multi exposed image parts of the moon would have been overlapping, creating a chaotic image. Another way to see that it is photoshopped: place a ruler over the north poles of the moon. They are not in straight line, neither a curved line.

[neufer]

[Well there we go again... reality dashing the dream of another space artist. "Man's got to know his limitations."

More interesting & successful is a project I was a part of once:
-----------------------------------------------------------
http://en.wikipedia.org/wiki/Lunar_Lase ... Experiment
Lunar Laser Ranging Experiment

<<The ongoing Lunar Laser Ranging Experiment measures the distance between the Earth and the Moon using laser ranging. Lasers on Earth are aimed at retroreflectors previously planted on the Moon and the time delay for the reflected light to return is determined. Since the speed of light is known with very great accuracy, the distance to the moon can be calculated. This distance has been measured with increasing accuracy for more than 35 years.

The distance continually changes for a number of reasons, but averages about 384,467 kilometers (238,897 miles).

The experiment was first made possible by a retroreflector array installed on July 21, 1969, by the crew of the Apollo 11. Two more retroreflector arrays left by the Apollo 14 and Apollo 15 missions have contributed to the experiment.

The unmanned Soviet Lunokhod 1 and Lunokhod 2 rovers carried smaller arrays. Reflected signals were initially received from Lunokhod 1, but no return signals have been detected since 1971, at least in part due to some uncertainty in its location on the Moon. Lunokhod 2's array continues to return signals to Earth.

The Apollo 15 array is three times the size of the arrays left by the two earlier Apollo missions. Its size made it the target of three-quarters of the sample measurements taken in the first 25 years of the experiment. Improvements in technology since then have resulted in greater use of the smaller arrays, by sites such as the McDonald Observatory and the OCA Laser-Lune telemetry station affiliated with the Côte d'Azur Observatory.

At the Moon's surface, the beam is only about 6.5 kilometers (four miles) wide and scientists liken the task of aiming the beam to using a rifle to hit a moving dime 3 kilometers (two miles) away. The reflected light is too weak to be seen with the human eye, but under good conditions, one photon will be received every few seconds (they can be identified as originating from the laser because the laser is highly monochromatic). This is one of the most precise distance measurements ever made, and is equivalent to determining the distance between Los Angeles and New York to one hundredth of an inch. As of 2002 work is progressing on increasing the accuracy of the Earth-Moon measurements to near millimeter accuracy.

Some of the findings of this long-term experiment are:

* The moon is spiralling away from Earth at a rate of 38 mm per year.

* The moon probably has a liquid core of about 20% of the Moon's radius.

* The universal force of gravity is very stable. The experiments have put an upper limit on the change in Newton's gravitational constant G of less than 1 part in 1011 since 1969.

* Einstein's theory of gravity (the general theory of relativity) predicts the moon's orbit to within the accuracy of the laser ranging measurements.

Additionally, the accuracy of these experiments has improved historic knowledge of the Moon's orbit enough to permit timing of solar eclipses up to 3,400 years ago.

The presence of reflectors on the Moon has been used to refute claims that the Apollo landings were faked. For example, the figure on the left shows evidence of something very small, located within a few kilometers of where a landing occurred, and which reflects laser light directly back to the source as well as a mirror array.>>
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