Starship Asterisk*

Ann wrote: ↑Sat Mar 28, 2020 5:04 amWhat is the cluster of stars at left? I might be tempted to guess the Pleiades. But surely they are not so northerly placed in the Earth's sky?

Ann

Case wrote: ↑Sat Mar 28, 2020 10:42 am
When zoomed in, the individual exposures seem to be resolved. Fascinating!
Not sure why they’re stripes instead of dots.

• Camera detector pixelation

Ann wrote: ↑Sat Mar 28, 2020 5:04 am Star trail images are educational, since they demonstrate the fact that the Earth rotates around its axis, so that the sky appears to rotate around us.

What is the cluster of stars at left? I might be tempted to guess the Pleiades. But surely they are not so northerly placed in the Earth's sky?

Ann

Joe Stieber wrote: ↑Sat Mar 28, 2020 5:39 am

Ann wrote: ↑Sat Mar 28, 2020 5:04 amWhat is the cluster of stars at left? I might be tempted to guess the Pleiades. But surely they are not so northerly placed in the Earth's sky?

Ann

I'm not that good at picking things out of star-trail images, but I suspect it's the Alpha Persei Cluster, roughly 40° from the north celestial pole. From a darker site, it's a fine view in binoculars, and even with unaided eyes, a clump of stars pops out with averted vision.

orin stepanek wrote: ↑Sat Mar 28, 2020 2:35 pm

Ann wrote: ↑Sat Mar 28, 2020 5:04 am Star trail images are educational, since they demonstrate the fact that the Earth rotates around its axis, so that the sky appears to rotate around us.

What is the cluster of stars at left? I might be tempted to guess the Pleiades. But surely they are not so northerly placed in the Earth's sky?

Ann

Hi, Ann; I guess I am not smart enough to determine star clusters from circular star trails! I do love the Pleiades though! I guess that is one reason I got into APOD; The views are of endless beautiful astronomy photographs!

ta152h0 wrote: ↑Sat Mar 28, 2020 5:08 pm
By the way, is laser light a sign wave with very high amplitude?

• No

https://www.etymonline.com/search?q=sine wrote:
sine (n.) trigonometric function, 1590s (in Thomas Fale's "Horologiographia, the Art of Dialling"), from Latin sinus "fold in a garment, bend, curve, bosom" (see sinus). Used mid-12c. by Gherardo of Cremona in Medieval Latin translation of Arabic geometrical text to render Arabic jiba "chord of an arc, sine" (from Sanskrit jya "bowstring"), which he confused with jaib "bundle, bosom, fold in a garment."

https://www.etymonline.com/search?q=sign wrote:

Click to play embedded YouTube video.

sign (n.) early 13c., "gesture or motion of the hand," especially one meant to communicate something, from Old French signe "sign, mark," from Latin signum "identifying mark, token, indication, symbol; proof; military standard, ensign; a signal, an omen; sign in the heavens, constellation." Watkins compares Hebrew sakkin, Aramaic sakkin "slaughtering-knife," and mentions a theory that "both words are probably borrowed from an unknown third source."

It has ousted native token. Meaning "a mark or device having some special importance" is recorded from late 13c.; that of "a miracle" is from c. 1300. Zodiacal sense in English is from mid-14c. Sense of "characteristic device attached to the front of an inn, shop, etc., to distinguish it from others" is first recorded mid-15c. Meaning "token or signal of some condition" (late 13c.) is behind sign of the times (1520s). In some uses, the word probably is a shortening of ensign.>>

https://www.etymonline.com/word/ensign wrote:
ensign (n.) early 15c., "a token, sign, symbol; badge of office, mark or insignia of authority or rank;" also "battle flag, flag or banner of a ship or troop of soldiers," via Scottish, from Old French enseigne (12c.) "mark, symbol, signal; flag, standard, pennant," from Latin insignia (plural); see insignia, which is a doublet of this word. As the word for the soldier who carries the flag, 1510s.

https://science.sciencemag.org/content/312/5772/374 wrote:
Laser-Driven Particle Accelerators
Science 21 Apr 2006: by Mike Dunne*

<<Laser acceleration of protons occurs as a result of the extremely high electric field gradients created on either the front or rear surface of thin foils illuminated by subpicosecond laser pulses, whose focused intensities exceed 10¹⁸ W cm⁻². The laser ionizes and subsequently accelerates electrons to relativistic velocities. These are confined to form a beam by the azimuthal magnetic field created in the interaction. The ensuing charge separation sets up the electric field to accelerate the proton or ion species in the foil, with an overall energy efficiency between 1 and 10%. Although such laser intensities are incredibly high, they are now routinely produced at high repetition rate on table-top-sized systems. This reflects the dramatic progress seen in laser technology, where an order-of-magnitude increase in peak laser power has been achieved roughly every 3 years.>>

Dzames wrote: ↑Sat Mar 28, 2020 12:31 pm Beautiful 24 hour trails. Since Italy is south of the Arctic circle, amazing how the daytime stars came out! Or was March 14 a looong sun eclipse day?

neufer wrote: ↑Sat Mar 28, 2020 9:04 pm

ta152h0 wrote: ↑Sat Mar 28, 2020 5:08 pm
By the way, is laser light a sign wave with very high amplitude?

• No

ta152h0 wrote: ↑Sat Mar 28, 2020 5:08 pm [...] By the way, is laser light a sign wave with very high amplitude? [...]

As neufer answered correctly, "NO!"

LASER light is "coherent", all the photons are at the same [i.e. very close to the same] _frequency_.
Each fundamental colour of light has its own frequency, or often described in its wavelength (1/frequency) in nanometres.
The photons of a laser beam can be likened to a soldiers marching in formation, whereas incoherent light photons would more resemble
the runners in the Boston Marathon (except in all running toward the Finish Line, they are running in all directions (unless reflected or focused) away from the Starting Line (point source).

TheZuke! wrote: ↑Mon Mar 30, 2020 2:52 pm

ta152h0 wrote: ↑Sat Mar 28, 2020 5:08 pm [...] By the way, is laser light a sign wave with very high amplitude? [...]

As neufer answered correctly, "NO!"

LASER light is "coherent", all the photons are at the same [i.e. very close to the same] _frequency_.
Each fundamental colour of light has its own frequency, or often described in its wavelength (1/frequency) in nanometres.
The photons of a laser beam can be likened to a soldiers marching in formation, whereas incoherent light photons would more resemble
the runners in the Boston Marathon (except in all running toward the Finish Line, they are running in all directions (unless reflected or focused) away from the Starting Line (point source).

Chris Peterson wrote: ↑Mon Mar 30, 2020 3:00 pm
The spatial and temporal coherence of laser light goes beyond simply having the same wavelength. You can easily create light of a single wavelength with a filter, but that light won't be coherent. That also requires that the photons be in phase with each other. That's only possible if they have the same wavelength, but it is the phase relationship that gives laser light most of its interesting properties.

TheZuke! wrote: ↑Mon Mar 30, 2020 3:42 pm

Chris Peterson wrote: ↑Mon Mar 30, 2020 3:00 pm
The spatial and temporal coherence of laser light goes beyond simply having the same wavelength. You can easily create light of a single wavelength with a filter, but that light won't be coherent. That also requires that the photons be in phase with each other. That's only possible if they have the same wavelength, but it is the phase relationship that gives laser light most of its interesting properties.

Agreed!

neufer wrote: ↑Sat Mar 28, 2020 9:04 pm

https://science.sciencemag.org/content/312/5772/374 wrote:
Laser-Driven Particle Accelerators
Science 21 Apr 2006: by Mike Dunne*

<<Laser acceleration of protons occurs as a result of the extremely high electric field gradients created on either the front or rear surface of thin foils illuminated by subpicosecond laser pulses, whose focused intensities exceed 10¹⁸ W cm⁻². The laser ionizes and subsequently accelerates electrons to relativistic velocities. These are confined to form a beam by the azimuthal magnetic field created in the interaction. The ensuing charge separation sets up the electric field to accelerate the proton or ion species in the foil, with an overall energy efficiency between 1 and 10%. Although such laser intensities are incredibly high, they are now routinely produced at high repetition rate on table-top-sized systems. This reflects the dramatic progress seen in laser technology, where an order-of-magnitude increase in peak laser power has been achieved roughly every 3 years.>>

Gotthard wrote: ↑Thu Apr 02, 2020 11:42 pm Hi all you friends of star trails,

that is a nice image of a startrail, indeed. And it's worth to become an APOD, indeed too!

But ... how long will it still last that it's possibel that such images can be taken???

I fear ... the time already is over!

Two days before this star trail over ragusa became APOD I asked Mr. Nemiroff, if he could consider to choose an absolute impressive photography of star trails ... taken by Debra Ceravolo from Canada:



that she had postet on astrobin.

https://www.astrobin.com/khfb6v/0/

It's a pity, that this star trails had not been chosen ... maybee ... Mr. Musk and his economic interests should not have been criticised ...

Take your star trails now ... it could be the last chance ....

Be safe and ... clear skies ... ooops ... clearup skies! :))