APOD: Tropic of Cancer (2013 Aug 02)

[APOD Robot]

Tropic of Cancer

Explanation: This intriguing monument can be found in Taiwan between the cities of Hualian and Taitong. Split into two sides, it straddles a special circle of latitude on planet Earth, near 23.5 degrees north, known as the Tropic of Cancer. Points along the Tropic of Cancer are the northernmost locations where the Sun can pass directly overhead, an event that occurs once a year during the northern hemisphere's summer solstice. The latitude that defines the Tropic of Cancer corresponds to the tilt of planet Earth's rotation axis with respect to its orbital plane. The name refers to the zodiacal constellation Cancer the Crab. Historically the Sun's position was within Cancer during the northern summer solstice, but because of the precession of Earth's axis, that solstice Sun is currently within the boundaries of Taurus. In this starry night scene the otherwise all white structure is colored by city lights, with its orange side just south of the Tropic of Cancer and the white side just north. Of course, there is a southern hemisphere counterpart of the Tropic of Cancer. It's called the Tropic of Capricorn.

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[Boomer12k]

Did not know that....thanks!


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[firstmagnitude]

This structure is called "the Monument of Tropic of Cancer, Chiayi!" I didn't see the proper name for this structure within the text (I could be wrong).

[neufer]

<<Tropic of Cancer is a novel by Henry Miller which has been described as "notorious for its candid sexuality" and as responsible for the "free speech that we now take for granted in literature". It was first published in 1934 by the Obelisk Press in Paris, France, but this edition was banned in the United States. Its publication in 1961 in the U.S. by Grove Press led to obscenity trials that tested American laws on pornography in the early 1960s. In 1964, the U.S. Supreme Court declared the book non-obscene. It is widely regarded as an important masterpiece of 20th century literature. Miller wrote the book between 1930 and 1934 during his "nomadic life" in Paris. Miller gave the following explanation of why the book's title was Tropic of Cancer: "It was because to me cancer symbolizes the disease of civilization, the endpoint of the wrong path, the necessity to change course radically, to start completely over from scratch.”>>

JERRY: This you're not goin' to believe. The NYPL says that I took out Tropic of Cancer in 1971 and never returned it.

KRAMER: Do you know how much that comes to? That's a nickel a day for 20 years. It's going to be $50,000
=============================================================
SEINFELD STAND UP

It was a weird school day, you know what I mean because it kind of like started of kind of normal. You have like English, Geometry, Social Studies and then suddenly you're like in Lord of The Flies for 40 minutes you know you're hangin' from a rope. You have hardly any clothes on. Teachers are yellin' at ya' "Where's your jock strap?" Ya' know and kids are throwin' dodge balls at you. You're tryin' to survive ... Then its History, Science, Language. There's something off in the entire flow of that day.
========================================================

[Douglas Barros]

I think there is a mistake in the phrase "The latitude that defines the Tropic of Cancer corresponds to the tilt of planet Earth's rotation axis with respect to its orbital plane". Actually, the tilt is the angle of planet Earth's rotation axis with respect to its orbital axis. Or, equivalently, the angle between the Earth's equatorial plane and its orbital plane.

[K1NS]

Are there different names for the tropics on other planets? On Mars? Or Venus? Or are they simply called the something like "Martian Tropic of Capricorn?"

And how about Uranus, tilted at such an extreme angle. Does Uranus have tropics?

[Chris Peterson]

I think there is a mistake in the phrase "The latitude that defines the Tropic of Cancer corresponds to the tilt of planet Earth's rotation axis with respect to its orbital plane". Actually, the tilt is the angle of planet Earth's rotation axis with respect to its orbital axis. Or, equivalently, the angle between the Earth's equatorial plane and its orbital plane.

That's true. The latitude of the ToC is actually 90 degrees minus the tilt of Earth's rotation axis with respect to its orbital plane.

[Case]

The monument doesn't look very smooth on the sides at about 2/3s up. I thought, maybe an image artefact, but the big click-through image has it too, even more visible.
The photographer’s page shows why it isn't so smooth, in an image from a different angle. There is lettering on the monument, that we’re seeing sideways in the APOD image.

[Chris Peterson]

Are there different names for the tropics on other planets? On Mars? Or Venus? Or are they simply called the something like "Martian Tropic of Capricorn?"

Using the same naming strategy as on Earth, I've seen the tropics on Mars called "the Tropic of Pisces" and "the Tropic of Virgo". I've not seen the term used on other planets. In general, I think something like "northern tropical boundary" and "southern tropical boundary" would make better sense when considering other planets.

BTW, on Mars, the polar circles have the same names as on Earth: Arctic Circle and Antarctic Circle.

And how about Uranus, tilted at such an extreme angle. Does Uranus have tropics?

Since its inclination isn't exactly 90°, it has tropics.

[rockythemountaineer]

I wish there weren't a goofily-posed man in the otherwise simple shot.

[bystander]

That's true. The latitude of the ToC is actually 90 degrees minus the tilt of Earth's rotation axis with respect to its orbital plane.

Earth's axial tilt 23° 26'
Tropic of Cancer 23° 26′ N
Tropic of Capricorn 23° 26' S

[Chris Peterson]

That's true. The latitude of the ToC is actually 90 degrees minus the tilt of Earth's rotation axis with respect to its orbital plane.

:?: :? :?:
Earth's axial tilt 23° 26'
Tropic of Cancer 23° 26′ N
Tropic of Capricorn 23° 26' S

Earth's axial tilt with respect to its orbital plane is 66° 34'. Its axial tilt with respect to its orbital axis (the perpendicular to the orbital plane) is 23° 26'.

[rcharlet]

This structure is called "the Monument of Tropic of Cancer, Chiayi!" I didn't see the proper name for this structure within the text (I could be wrong).

Hi-ya firstmagnitude,
I came to ask for the name of the monumnet, and there you were in the second post. Thanks.

[Beyond]

Chris, Oklahoma is very flat. They're not used to tilt's.

[BMAONE23]

Looking at the design - and something that isn't mentioned in the write-up on the day of the solstice the sun will rise framed within the monument

[geckzilla]

Chris, Oklahoma is very flat. They're not used to tilt's.

Oklahoma is actually not that flat. It has three ancient mountain ranges in it. They're very old so they're weathered down but they're still mountains. Northwestern Oklahoma is relatively flat but is dotted by mesas. Kansas, is a much better example of flat. http://en.wikipedia.org/wiki/Mount_Sunflower

[Beyond]

Ok, so Oklahomans are used to a little tilt. But nothing like you'd find in Colorado.

[retrogalax]

The vegetation is not much greener on the left. The Tropics are different from what i have imaginated.

[George Kaplan]

I hope they made the monument portable, because the obliquity is not a fixed quantity. It has changed significantly over historic time, and the current estimated rate of change is about -47 arcseconds per century. Each arcsecond is about 31 meters on the surface of the Earth. So the thing should be moved about 15 meters per year! I wonder what value of the obliquity was used to determine the monument's latitude.

I'm glad the man is there for scale, because otherwise I had no idea how big this thing is.

[Lford]

Exactly where is the monument? Google Earth cannot find the cities Hualian and Taitong. Looking along the 23.45 degree meridian did not show anything.

[Chris Peterson]

This structure is called "the Monument of Tropic of Cancer, Chiayi!" I didn't see the proper name for this structure within the text (I could be wrong).

I think that is a different monument, in a different part of Taiwan (Chiayi). The monument in the picture is in Ruisui Township, inland from the east coast of the island.

[Chris Peterson]

Exactly where is the monument? Google Earth cannot find the cities Hualian and Taitong. Looking along the 23.45 degree meridian did not show anything.

I had no problem finding Hualian- it's a major city. Taitong is better transcribed Taidong, and is south of Hualian.

Try 23.46546, 121.35789, or just enter "Tropic of Cancer Monument, Ruisui Township, Taiwan" in Google Maps.

[Dustin Science-guy]

That is exactly what I was thinking. And at noon on the solstice the sun would shine straight down the structure. Like a giant solstice "clock"

Looking at the design - and something that isn't mentioned in the write-up on the day of the solstice the sun will rise framed within the monument

[Case]

Exactly where is the monument? Google Earth cannot find the cities Hualian and Taitong. Looking along the 23.45 degree meridian did not show anything.

I had no problem finding Hualian- it's a major city. Taitong is better transcribed Taidong, and is south of Hualian.
Try 23.46546, 121.35789, or just enter "Tropic of Cancer Monument, Ruisui Township, Taiwan" in Google Maps.

That looks to be a different monument from the one in the APOD?

[Chip Huete]

You mentioned precession of the Earth's axis. Could precession have anything to do with climate change?