APOD: The Little Dipper (2011 May 14)

[geckzilla]

Don't you guys make me plop this discussion into the Proper Post Modern Verbal Etiquette thread.

[Czerno 1]

If you want a proper name, call it Alpha Ursa Minor (α UMi or α Ursae Minoris).

Alpha UM, that's a technical or scientific designation, not a proper name !

Maybe you missed my point, did you look at today's APOD (with javascript) ? All signficant stars are labeled with their traditional "Arab" (most of the time) name, not a catalog designation. All, /except/ the polar star, which is why I think appropriate to recall her name. My God, had I imagined M. Peterson would find it worthy of his time to write a contribution /just/ to "correct" my "factual error" : calling a name : /a name/! What's in a name...

Regards

--
Czerno

[Tuk]

Look, there's Alruccabah!!! -- said the dad to his kid as they both stared at the northern star.

Many starts go by different names. It's interesting to learn other names, but IMHO it's perfectly OK to label Polaris as Polaris, whether in an outreach image like this one or in planetary software, etc. Maybe each star was labeled with the name most people use when referring to them by name??

[geckzilla]

They're stars, not people. They don't get offended if we give them many different names and neither should anyone here. Polaris is probably what most westerners know that star as so that's a good name for it. We don't have common names for the other ones but luckily another culture did that work for us a long time ago so we just go with what they came up with, right? Right. Nothin' wrong with a little mix 'n' matching.

[neufer]

Look, there's Alruccabah!!!

Look, there's Alruccabah!!! -- said the dad to his kid as they both stared at the northern star.

Many starts go by different names. It's interesting to learn other names, but IMHO it's perfectly OK to label Polaris as Polaris, whether in an outreach image like this one or in planetary software, etc. Maybe each star was labeled with the name most people use when referring to them by name??

[Ann]

Well, Polaris is a fine name, if you ask me. Better than Thuban and Kochab, and better than - what was it now? - Alruccabah? But hey, as Shakespeare said, a rose by any other name would smell as sweet, and a Pole star by any other name would still help us find our way down here on good old Earth!

And Thuban used to be the Pole star! What a fine Pole Star it must have been, if only because it is my favorite color - it's blue! Yes, and not only because it is an A star, which are all blue, as I'm arguing in a post in the Asterisk Café. No, Thuban is even unusually blue as A stars go, with a color index that suggests that it is hot enough to be a B star.

I found this pretty picture of a blue star on a page called Universal-Link-On-line, and I'm not altogether sure the picture will stay here if I post it, but I'll make a try anyway...

Click to view full size image

Go Thuban!

Ann

[Czerno 1]

And Thuban used to be the Pole star! What a fine Pole Star it must have been, if only because it is my favorite color - it's blue!
I found this pretty picture of a blue star on a page called Universal-Link-On-line...

Go Thuban!
Ann

Wow pretty ! A real diamond ! And diamonds have porper names too (oops, no, enough names from me today).

Thanks for the fine jewel and the smile

--
Czerno

[neufer]

Go Thuban!

<<Thuban (α Draconis, α Dra) is a relatively inconspicuous star in the night sky of the Northern Hemisphere, it is historically significant as having been the north pole star in ancient times. Thuban is an Arabic word for snake. Even though Johann Bayer gave Thuban the designation Alpha, it is 3.7 times fainter than Gamma Draconis (Eltanin/The great serpent), whose apparent magnitude is 2.24.

Due to the precession of Earth's rotational axis, Thuban was the naked-eye star closest to the north pole from 3942 BC, when it moved farther north than Theta Boötis, until 1793 BC, when it was superseded by Kappa Draconis. It was closest to the pole in 2787 BC, when it was less than two and a half arc-minutes away from the pole. It remained within one degree of true north for nearly 200 years afterwards [; the Great Pyramid of Giza was built c. 2560 BC], and even 900 years after its closest approach, was just five degrees off the pole. Thuban was considered the pole star until about 1900 BC, when the much brighter Kochab began to approach the pole as well.

Thuban has a spectral class of A0III, indicating its similarity to Vega in temperature and spectrum, but more powerful and more massive. Thuban is not a main sequence star; it has now ceased hydrogen fusion in its core and is fusing helium. That makes it a white giant star, being 250 times more powerful than our Sun but over 300 light-years distant.

Thuban has no real anomalies other than the relative rarity of being a giant star in the A class, which is usually reserved for main sequence stars and the occasional supergiant. This indicates that Thuban has not been a giant star for very long and may well still be in the process of expanding, probably to eventually become a K class red-orange giant of the Aldebaran sort. It may also mean that it has recently run out of helium to fuse and is contracting before starting to burn carbon, in which case it may end up a blue giant such as Beta Centauri.

Thuban is a binary star, with a companion star in a 51-day orbit. The companion has not been directly imaged, and from its mass is probably a red dwarf or a low mass white dwarf.>>

[bystander]

Maybe you missed my point,

Maybe you missed my point

Polaris has numerous traditional names: ... (Alruccabah just one of many, including Polaris)
Google searches for Alruccabah, most often take you to links for Polaris.

[kaigun]

Only Thuban comes really close to the precessional circumference.

Less than a degree off the pole is plenty close enough to be useful. In the Navy my job was navigation, including celestial navigation. With a few quick computations we could use Polaris to check for gyro compass error, if it was low enough to get a view through a bearing circle or alidade. A sextant sighting of Polaris would give you latitude, although I didn't mess with that much. At second magnitude Polaris doesn't come out well until after the horizon is already fairly dark. I rarely bothered with any stars other than first magnitude stars.

[neufer]

<<Ursa Minor (Latin: "Smaller Bear"), also known as the Little Bear or the Little Dipper. Ursa Minor is commonly visualized as a baby bear with an unusually long tail. The tail was said to have been lengthened from that usually expected for a bear, because of its being held by the tail and spun around the pole.

Ursa Minor and Ursa Major were related by the Greeks to the myth of Callisto and Arcas. However, in a variant of the story, in which it is Boötes that represents Arcas, Ursa Minor was considered to represent a dog. This is the older tradition which sensibly explains both the length of the tail and the obsolete alternate name of Cynosura (the dog's tail) for Polaris, the North Star.

Previously, Ursa Minor was considered to be just seven close stars, mythologically regarded as sisters. In early Greek mythology, the seven stars of the Little Dipper were considered to be the Hesperides, daughters of Atlas. Together with the nearby constellations of Boötes, Ursa Major, and Draco, it may have formed the origin of the myth of the apples of the Hesperides, which forms part of the Labours of Hercules.

In earliest times, Ursa Minor was named the Dragon's wing, and was considered a part of Draco. The dragon's wing as an asterism is now long forgotten.

In Hindu scriptures Dhruva, ध्रुव, was an ardent young devotee of Vishnu, a prince blessed to eternal existence and glory as the Pole Star (Dhruva Nakshatra in Sanskrit) by Lord Vishnu. The story of Dhruva's life is often told to Hindu children as an example for perseverance, devotion, steadfastness and fearlessness.

In Hungarian mythology the constellation's called 'Little Goncol cart' (Göncöl szekér) after a legendary shaman (Ursa Major is 'Big Goncol cart'). His knowledge knew no limit; he invented the cart: his nation was wandering, cart was the biggest present of the Gods to them. Legends claim he knew everything on the world. Nobody saw his death, his body disappeared among the stars.

Polaris (α UMi), the brightest star in the constellation, is a 'yellow-white' supergiant shining at 2.02 apparent magnitude . It belongs to the rare class of Cepheid variable stars. Only a bit less bright is β UMi (Kochab), a 2.08 orange giant star.>>

[NoelC]

Aww, neufer, did you make a Boo Boo?

-Noel

[Chris Peterson]

Maybe you missed my point, did you look at today's APOD (with javascript) ? All signficant stars are labeled with their traditional "Arab" (most of the time) name, not a catalog designation. All, /except/ the polar star, which is why I think appropriate to recall her name. My God, had I imagined M. Peterson would find it worthy of his time to write a contribution /just/ to "correct" my "factual error" : calling a name : /a name/! What's in a name...

Please note that I was not referring to your use of the obscure name Alruccabah as being an error. It was not. I was referring to your comment, "Polaris is a label, not a proper name." That is incorrect. Polaris is a proper name- indeed, the most proper of proper names by virtue of being the most commonly known and used. It's etymology is irrelevant.

[Beyond]

So i visit the APOD picture of the day to get the scoop on The Little Dipper, and i find that i must have a hole in my brain. The Little Dipper is in the North and not in the South, like I've always thought it was, and there is a rotating star-map of some kind that shows the Big and Little Dippers are not that far from each other. Then i can't figure out why i have only ever seen one dipper that must be The Big Dipper, because the handle is attached to the wider part of the scoop, whereas The Little Dipper's handle is attached to the narrower part of the scoop. I'd feel embarassed, but this is to stupid for that. I guess I'll just have to look a little harder for The Little Dipper.

[Chris Peterson]

So i visit the APOD picture of the day to get the scoop on The Little Dipper, and i find that i must have a hole in my brain. The Little Dipper is in the North and not in the South, like I've always thought it was, and there is a rotating star-map of some kind that shows the Big and Little Dippers are not that far from each other. Then i can't figure out why i have only ever seen one dipper that must be The Big Dipper, because the handle is attached to the wider part of the scoop, whereas The Little Dipper's handle is attached to the narrower part of the scoop. I'd feel embarassed, but this is to stupid for that. I guess I'll just have to look a little harder for The Little Dipper.

The Little Dipper is not a very easy constellation to see. It requires fairly dark skies. From most cities, you are unlikely to see enough of the stars in the asterism to actually identify it as being dipper-like at all.

[Beyond]

Thanks Chris. Yea!! I'm not that stupid after all. I'm just like everyone else and can't see very good!
Of course i still don't know where i ever got the idea that it was in the Southern Hemisphere.

[NoelC]

I guess I'll just have to look a little harder for The Little Dipper.

It's actually reasonably dim.

When talking with friends, I sometimes ask "Do you have good skies for astronomy?" and when they ask "What's your threshold" I ask "Can you see all the stars in the little dipper?"

-Noel

[owlice]

Some (don't make me name names) obviously need to read the rules before posting again on this thread.

[gpronger]

An object not mentioned in the description caught my eye in the larger image. Above and slightly to the right of Polaris, appears to be a meteor or comet.

Any thoughts on what was also inadvertently captured?

Greg

[BMAONE23]

An object not mentioned in the description caught my eye in the larger image. Above and slightly to the right of Polaris, appears to be a meteor or comet.

Any thoughts on what was also inadvertently captured?

Greg

Greg
This was mentioned part way down the first page of this thread
see http://asterisk.apod.com/viewtopic.php? ... 72#p148423

[dfs]

Out of curiosity, at which longitude (northern hemisphere) would you have to be for the position of exact north to be "straight up" from the pole star?

[Chris Peterson]

Out of curiosity, at which longitude (northern hemisphere) would you have to be for the position of exact north to be "straight up" from the pole star?

The declination of Polaris is 89.264°. That means it travels around the true pole (90°) in a tiny circle once each day. So from any longitude, a northern hemisphere observer will see the true pole directly above Polaris (with respect to the local horizon) once a day... only the time will change with location.

[neufer]

Out of curiosity, at which longitude (northern hemisphere) would you have to be
for the position of exact north to be "straight up" from the pole star?

Code: Select all

The declension of Polāris: Of or pertaining to the poles.

nominative 	  polāris 		 polārēs 
genitive 	    polāris 		 polārium
dative 	      polārī 		  polāribus
accusative 	  polārem  		polārēs
ablative 	    polārī 		  polāribus
vocative 	    polāris		  polārēs

The declination of Polaris is 89.264°. That means it travels around the true pole (90°) in a tiny circle once each day. So from any longitude, a northern hemisphere observer will see the true pole directly above Polaris (with respect to the local horizon) once a day... only the time will change with location.