Explanation: Sweeping through northern skies, Comet Catalina (C/2013 US10) made its closest approach on January 17, passing about 6 light-minutes from our fair planet. Dust and ion tails clearly separated in this Earth-based view, the comet is also posed for a Messier moment, near the line-of-sight to M101, grand spiral galaxy in Ursa Major. A cosmic pinwheel at the lower left, M101 is nearly twice the size of our own Milky Way galaxy, but some 270 thousand light-centuries away. Both galaxy and comet are relatively bright, easy targets for binocular-equipped skygazers. But Comet Catalina is now outbound from the inner Solar System and will slowly fade in coming months. This telescopic two panel mosaic spans about 5 degrees (10 Full Moons) on the sky.
Ah, a new term. I don't recall ever having heard the term "light-centuries" before.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 5:57 am
by Nitpicker
270 thousand light-centuries, hey? You may as well have said about 1/2000th of the way to the edge of the observable universe.
Lovely APOD.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 6:13 am
by Ann
Nice! But check out this image, too. Here Comet Catalina is between two galaxies!
Ann
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 6:26 am
by Nitpicker
Ann wrote:Nice! But check out this image, too. Here Comet Catalina is between two galaxies!
Ann
There are many galaxies in the (much deeper) APOD. M101 is merely the most prominent.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 6:30 am
by Ann
Nitpicker wrote:
Ann wrote:Nice! But check out this image, too. Here Comet Catalina is between two galaxies!
Ann
There are many galaxies in the (much deeper) APOD. M101 is merely the most prominent.
Right, but M51 and M101 are not just any galaxies!
Ann
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 7:08 am
by Nitpicker
Ann wrote:Right, but M51 and M101 are not just any galaxies!
[sacrilege] Meh, not being much of a galaxy person, they're mainly just numbers to me. [/sacrilege]
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 10:15 am
by inertnet
Shouldn't that have been 210 thousand light-centuries?
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 12:02 pm
by hamilton1
Nope, the consensus seems to be 27 million LY and not 21 million.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 1:22 pm
by inertnet
That's funny, NASA and Wikipedia say 21 million, the Messier catalog says 27 and many others say in between. So who's right?
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 1:39 pm
by trench
I think the real question here is, why wasn't the distance given in light-millenia?
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 1:47 pm
by bls0326
The APOD shows the comet to the right and above M101. The "telescopic two panel mosaic" link shows the same (?) picture but the comet is to the left and above M101. Which version would I see looking into the night sky with a telescope?
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 2:36 pm
by Ann
Nitpicker wrote:
Ann wrote:Right, but M51 and M101 are not just any galaxies!
[sacrilege] Meh, not being much of a galaxy person, they're mainly just numbers to me. [/sacrilege]
<<SN 2011fe, initially designated PTF 11kly, was a Type Ia supernova discovered by the Palomar Transient Factory (PTF) survey on 24 August 2011 during an automated review of images of the Messier 101 from the nights of 22 and 23 August 2011. It was located in Messier 101, the Pinwheel Galaxy, 21 million light years (six megaparsecs) from Earth. It was observed by the PTF survey very near the beginning of its supernova event, when it was approximately 1 million times too dim to be visible to the naked eye. It is the youngest type Ia ever discovered. About 13 September 2011, it reached its maximum brightness of apparent magnitude +9.9 which equals an absolute magnitude of about -19 at six megaparsecs [-19 = +9.9 - 5log(6,000,000/10)]. This was the fourth supernova recorded in M101. The first, SN 1909A, was discovered by Max Wolf in January 1909 and reached magnitude 12.1. SN 1951H reached magnitude 17.5 in September 1951 and SN 1970G reached magnitude 11.5 in January 1970.>>
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 3:46 pm
by Chris Peterson
neufer wrote:
inertnet wrote:
That's funny, NASA and Wikipedia say 21 million, the Messier catalog says 27
and many others say in between. So who's right?
First thought was that the weather network had co-opted my homepage.
Then it became clear, Neil Degrasse Tyson is contributing to APOD. He is championing the switch from light-year to light-century and all the clarity it will bring.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 4:39 pm
by neufer
Chris Peterson wrote:
neufer wrote:
inertnet wrote:
That's funny, NASA and Wikipedia say 21 million [light years], the Messier catalog
says 27 [million light years] and many others say in between. So who's right?
https://en.wikipedia.org/wiki/Cepheid_variable#Uncertainties_in_Cepheid_determined_distances wrote:
<<Chief among the uncertainties tied to the classical and type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination (blending) and a changing (typically unknown) extinction law on Cepheid distances. All these topics are actively debated in the literature.
Click to play embedded YouTube video.
These unresolved matters have resulted in cited values for the Hubble constant (established from Classical Cepheids) ranging between 60 km/s/Mpc and 80 km/s/Mpc. Resolving this discrepancy is one of the foremost problems in astronomy since the cosmological parameters of the Universe may be constrained by supplying a precise value of the Hubble constant. Uncertainties have diminished over the years, due in part to discoveries such as RS Puppis.
RS Puppis (or RS Pup) is a Cepheid variable star in the constellation of Puppis. It is one of the brightest known Cepheids in the Milky Way galaxy and has one of the longest periods of 41.4 days. Because it is located in a large nebula, astronomers using the ESO's New Technology Telescope at La Silla Observatory, Chile have been able to measure its distance in 2013 by strictly geometric analysis of light echoes from particles in the nebula, determining it to be 6500 ± 90 light years from Earth, the most accurate measurement achieved for any Cepheid as of early 2008. The accuracy of the new measurement is important because Cepheids serve as a marker for distances within our galaxy and for nearby galaxies.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 7:29 pm
by Ron-Astro Pharmacist
Between Cepheid variables and dark matter models it makes you wonder how many astronomers just want to go back to good old-fashioned telescopes.
Speaking of Cepheid variables did you know they are being used to study dark matter?
(That dead dark horse is going to haunt my subconscious) I could probably disprove my own hypothesis by learning about the sun's plasma. If dark matter was in atoms it would have to go somewhere. Maybe I'll grab a Corona and go out and bask in the sun and wonder "why" is dark matter?
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Thu Jan 21, 2016 9:30 pm
by ta152h0
Light century must be a Star Wars thing. Tis the season ..........
Light century
Posted: Thu Jan 21, 2016 10:00 pm
by neufer
ta152h0 wrote:
Light century must be a Star Wars thing. Tis the season ..........
It's been suggested that the 99 years from 1AD thru 99 AD
be called the first "century" but that never quite caught on.
(Kramer and Newman move to the door to leave. Newman stops as Jerry speaks to him, and Kramer exits to his apartment.)
JERRY: By the way Newman, I'm just curious.
When you booked the hotel, did you book it for the millennium New Year?
NEWMAN: (smug) As a matter of fact, I did.
JERRY: Oh, that's interesting, because as everyone knows, since there was no year zero, the millennium doesn't begin until the year two-thousand and one. Which would make your party, one year late, and thus, quite lame.
(Newman absorbs the logic of Jerry's argument. His face twitches as he realises his error.)
JERRY: Aww!
(Newman makes a noise redolent of his frustration - a sort of half-strangulated nasal squeak. He then waddles away after Kramer.)
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Fri Jan 22, 2016 12:06 am
by Nitpicker
Ann wrote:
Nitpicker wrote:
[sacrilege] Meh, not being much of a galaxy person, they're mainly just numbers to me. [/sacrilege]
The worldwide Mars bar differs from what is sold in the US. The American version was discontinued in 2002 and was replaced with the slightly different Snickers Almond. The US version of the Mars bar was relaunched in January 2010 and is initially being sold on an exclusive basis through Walmart stores. The European version of the Mars bar is also sold in some United States grocery stores. It was once again discontinued at the end of 2011.
The British and Canadian Mars bars are very similar to the United States Milky Way bar, which Mars, Inc. produced (not to be confused with the European version of Milky Way, which is similar to the United States' 3 Musketeers).
It all seems pretty universal to me. Though I am somehow left with the mental image of a chocolate bar being launched into space.
Re: APOD: The View Toward M101 (2016 Jan 21)
Posted: Fri Jan 22, 2016 12:27 am
by Ann
neufer wrote:
<<Chief among the uncertainties tied to the classical and type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination (blending) and a changing (typically unknown) extinction law on Cepheid distances. All these topics are actively debated in the literature.
Metallicity could be a problem when it comes to estimating the distance to a galaxy like M101. Although I haven't made an effort to learn anything about the average metallicity of the stars in M101, my impression is that the galaxy is metal-poor. Its yellow population is small, while its blue population is large, bright and widespread. This suggests that M101 has had long periods of relative quiescence in its history, when few stars formed and only low levels of metals were synthesized in stars and mixed with the interstellar medium of M101.
M101 might therefore have a large population of rather metal-poor Cepheids. If metal-poor Cepheids behave differently than metal-rich ones, then the Cepheid-induced distance to M101 might be off. It is even possible that metal-poor SN type Ia might be different than metal-rich ones.
Even so, the combination of large numbers of Cepheids in M101 (there must be!) and a very well-observed SN Ia suggests that the distance to M101 should be relatively well understood.
The View Toward M101
[/snicker(s)]
[/galaxy]
Going back in history we found even 
I could probably disprove my own hypothesis by learning about the sun's 
Maybe I'll grab a 