Starship Asterisk*

<<In Inuit legend, the narwhal's tusk was created when a woman with a harpoon rope tied around her waist was dragged into the ocean after the harpoon had struck a large narwhal. She was transformed into a narwhal herself, and her hair twisted around in the water until it became the characteristic spiral narwhal tusk.

Some medieval Europeans believed narwhal tusks to be the horns from the legendary unicorn. The tusks were used to make cups that were thought to negate any poison that may have been slipped into the drink. During the 16th century, Queen Elizabeth received a carved and bejeweled narwhal tusk for £10,000—the cost of a castle. Herman Melville wrote a section on the narwhal in Moby Dick. In it, he claims that a narwhal tusk hung for "a long period" in Windsor Castle after Sir Martin Frobisher had given it to Queen Bess.>>

<<Basically, there are two types of [comet] tails, the Type I ion, or gas, tail, and the Type II dust tail. The ion tail is typically bluish, and it is carried almost straight outward away from the Sun by the solar wind. But, the dust tail is a bit more complicated. It is pushed outward by light pressure. When the dust shed by outgassing of the nucleus of the comet, it forms a cloud around the nucleus. Most people don’t realize it, but light can actually push on things. So, the light from the Sun is able to push the tiny dust grains outward. But, these dust grains are still orbiting the Sun. So, a push outward causes them to be pushed into farther orbits. The farther an orbit is from the Sun, the slower it moves. So, these dust grains lag ever so slightly behind the nucleus of the comet. The farther they are pushed, the more they lag, so the tail gently sweeps backward, though still largely pointing away from the Sun. The result is a bifurcated tail, one bluish Type I and one yellowish Type II.



But photographs are inherently two dimensional. The tail is curved in three dimensions. So, projecting this onto a two dimensional photograph, taken from the perspective of the Earth, not the Sun or some observer external to the Solar System, can often do some strange things. For example, in 1957, Comet Arend-Roland passed near the Sun, and the dust tail curved so much that it swung around behind the head of the comet, as seen from Earth. Though the tail was most definitely curving away from the Sun, from the perspective of the Earth, you could see the back end of it appear to swing around onto the other side of the head and appear as a spike pointing towards the Sun as seen in this photograph from the Armagh Observatory. We call this sunward appearing spike an antitail. Not all comets show an antitail, only those who happen to be just the right position for the orbital geometries to give this perspective. The tail definitely is not pointing sunward. It just seems to be from our perspective.>>

BMAONE23 wrote:I find the explanation a bit misleading. It states that his is likely this comets first ppearance yet goes further to state that the "Anti Tail" is caused by dust debris in its orbital path. How could this be the comets first pass and still have a prior orbital debris path?

Earthbelow wrote:I have another question: why is this comet green? I thought they were always white.

[b] http://science.nasa.gov/headlines/y2005/05jan_machholz.htm[/b] wrote: <<A frequently-asked question: Why do some comet atmospheres glow green?

Answer: The coma contains cyanogen (CN), a poisonous gas, and diatomic carbon (C2).
Both of these substances glow green when illuminated by sunlight.
This is called "resonant fluorescence.">>

DavidLeodis wrote:I am confused as to the date when the image was taken. The second 'Comet Lulin' hyperlink in the explanation brought up a page in the Sky & Telescope website. That page had the image used as the APOD and it was said to have been taken on February 2nd (presumably 2009). How does an image get to be used as an APOD on the day it was taken, particularly as the APOD of February 1st stated that the APOD of February 2nd was about Comet Lulin? I hope that is not confusing, but I'm confused over the date! but still :)ing.

neufer wrote:

DavidLeodis wrote:I am confused as to the date when the image was taken. The second 'Comet Lulin' hyperlink in the explanation brought up a page in the Sky & Telescope website. That page had the image used as the APOD and it was said to have been taken on February 2nd (presumably 2009). How does an image get to be used as an APOD on the day it was taken, particularly as the APOD of February 1st stated that the APOD of February 2nd was about Comet Lulin? I hope that is not confusing, but I'm confused over the date! but still :)ing.

Ned: Phil? Phil Connors? Phil Connors, I thought that was you!

Phil: Hi, thanks for watching. [Starts to walk away]

Ned: Hey now, don't you tell me you don't remember me 'cause I sure as heckfire remember you.

Phil: Not a chance.

Ned: Ned... Ryerson. "Needlenose Ned"? "Ned the Head"? C'mon, buddy. Case Western High. I did the whistling belly-button trick at the high school talent show? Bing. Ned Ryerson, got the shingles real bad senior year, almost didn't graduate? Bing, again. Ned Ryerson, I dated your sister Mary Pat a couple of times until you told me not to anymore? Well?

Phil: Ned Ryerson?

Ned: BING!

Phil: Bing.

DavidLeodis wrote:Sorry but I've no idea how that answers or helps with my query. Your post just seems totally pointless and I can't help but wonder why you made it.

neufer wrote:

DavidLeodis wrote:Sorry but I've no idea how that answers or helps with my query. Your post just seems totally pointless and I can't help but wonder why you made it.

I didn't mean to offend, David.
It was simply my peculiar way of implying that your question is rather baffling one.

The February 2, 2009, APOD was most certainly not taken on February 2, 2009,
and it is not at all clear why you should think that it was.

DavidLeodis wrote:I have an apology to make concerning my query about the date when the iamge was taken. For whatever reason I semed to have missed the "this picture, taken from Italy last Friday" in the explanation to the APOD. That makes the date January 30th, which seems much more likley than the February 2nd given in the Sky & Telescope webpage.