Starship Asterisk*

A visitor to the inner solar system every 70 years or so Comet 13P/Olbers ... Now on a return voyage to the distant Oort cloud ... A comet with a 70-year period isn't returning to the Oort cloud! (Wikipedia tells me that Olbers has an aphelion of 32 AU but the Oort cloud starts around 2000 AU out.)...

Can a short-period comet originate from the Oort cloud? :-| Yes, but most seem to have originated in the Kuiper belt and were perturbed into short period orbits by interactions with Jupiter and the Sun. Most short-period comets are in orbits with fairly small inclinations, consistent with a Kuiper ...

Comet 13P/Olbers This Halley-type comet with a period of 69 years just passed perihelion in June. Captured here is the typical green glow of the coma (from CN and C 2 emissions) and just a hint of reflected sunlight from a diffuse trailing dust cloud. Very prominent is the blue ion tail which shows...

I am well aware that redshift is not a reliable measure of distance. Hubble himself doubted it, even after he compiled his table of values with nearby galaxies that led to the concept of a Hubble constant. Which all Big-bang astronomers use as a distance measure. Halton Arp’s Seeing Red discusses i...

[youtube][/youtube] The narrative seems way off the mark on at least 2 points. Firstly, how can two galaxies (insofar as we can trust red shift distance estimates) 17 million light years apart be gravitationally affecting one another? (326 mly and 343 mly) Secondly, how is it that the spiral is bad...

The first thing I thought of when I saw " Uluru ", was Lurulu the troll from Lord Dunsany 's The King of Elfland's Daughter : https://en.wikipedia.org/wiki/The_King_of_Elfland%27s_Daughter#:~:text=he%20is%20young.-,Lurulu,-%E2%80%94A%20troll%20sent And it turns out that Lurulu is actually...

The narrative seems way off the mark on at least 2 points. Firstly, how can two galaxies (insofar as we can trust red shift distance estimates) 17 million light years apart be gravitationally affecting one another? (326 mly and 343 mly) Secondly, how is it that the spiral is badly broken but the el...

I think the distinct lack of evidence for advanced civilizations suggests they occur rarely in the universe. It’s an interesting but (probably) unanswerable question because there are so many variables we have yet to quantify. I’d start by asking a series of nested questions: how rare is life in th...

Do planetary occultations help in calculating planetary orbits these days, or have we already got such precise knowledge that we don't need the measurements of exactly when there are occultations any more? We have much more precise tools now. But occultations of stars by asteroids and more distant ...

Anyway. The caption said that NGC 6946 is in Cepheus. Well, I don't think so! Because unless my software is very wrong, NGC 6946 is straddling the border of Cepheus and Cygnus! While the extended galaxy does indeed straddle Cepheus and Cygnus, its photometric center, which is what defines its recog...

I don't know about Pluto. All the other moons, though, are tidally locked to their planets, so one side is heated from the planet, and other from the Sun as they rotate/orbit. Of course, the cold spots on the Moon are created by relatively shallow craters and specifics of the Moon's orientation. If...

Okay! :ssmile: But bear in mind that the extreme proximity of the Earth's own moon means that we have great opportunities to observe it. If the temperature of very small spots on the Moon is indeed -238 C, then we are indeed able to confirm it. When it comes to objects in the Kuiper Belt, we have e...

For Kuiper Belt object, though, we don't really need to measure them. We know that they are not tidally locked to the Sun, and therefore have their entire surfaces exposed to sunlight as they rotate. And even at that distance, that's a lot of heating when we're talking about objects sitting at just...

APOD Robot wrote: Central filaments of the reflection nebula glow with a faint reddish photoluminescence as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light . Infrared observations indicate that this nebula contains complex carbon molecules known ...

Okay, I asked Google. :wink: Well, there is nothing here about the temperature of the south pole of the Moon, so I asked Google specifically about that, and this is what it told me: So that suggests that the south pole of the Moon is colder than Uranus or Neptune! But I don't believe that is true. ...

Avalon wrote: ↑Wed Jul 24, 2024 2:13 am What a spectacular image! I assume there is another jet shooting out on the other side of the disc? What sets that pulsar rotating so incredibly fast?

Conservation of angular momentum. The same thing that speeds up a figure skater when they pull in their arms.

Looks like two annular rings with a jet or ejection down from the center. Anyway, we can calculate the average expansion velocity of the nebula - given a diameter of 10 ly, radius of 5 ly, 946 years from first observed to image referenced for Hubble visible light (2000 - 1054) = 1585 kilometers per...

Sublime 36 hour exposed photo of the Chamaeleon Dark Nebula. I wonder if Chang Lee would kindly share what telescope he used to get this beautiful pic? Always follow the link to the source image. It often contains much more information about the technical details than we see in the APOD caption. _ ...

Well, so much for pareidolia! Tell me though, what does it take to create a formation like this hoodoo? Could it exist on any other planet or moon in the solar system? You need some kind of system that allows for the deposition of rock layers over time, where those layers have different composition...

I wonder how sturdy that overhang is. And I'm surprised it hasn't been broken by "adventurers" standing on it while trying to take selfies. It's rather like the diving board on a pool. You could comfortably stand on the ground underneath the overhang and put your hands on its base. It ext...

Astronomical images, by convention, should be presented with east counterclockwise from north. (And ideally with north up, but this convention is often ignored in order to match the geometry of the object to that of the camera, or sometimes for purely aesthetic ends.) This is what we see when we lo...

p.s. great close-up image AVAO! (but do you mean by "mirrored" that this is not the actual state of the galaxy but an optical effect? I'm not sure I understand) Astronomical images, by convention, should be presented with east counterclockwise from north. (And ideally with north up, but t...

Obquote: [cue klaxon] "Intruder Alert! Intruder Alert!" -Star Trek. Obquote 2: "What you see is what you get!" -Geraldine, played by Flip Wilson. Are the spikes from stars within the Milky Way? Every star in the image (and even every galaxy) has diffraction spikes. But only the ...

Interesting. Now what about Cassini's cameras? 😉 Cassini's wide field camera was a refractor. Its narrow field camera was a Ritchie-Chretien design with its secondary mirror supported by a 4-vane spider. So it should show diffraction spikes on bright enough point sources. Ok, so I guess that means ...

Astronomical images, by convention, should be presented with east counterclockwise from north. (And ideally with north up, but this convention is often ignored in order to match the geometry of the object to that of the camera, or sometimes for purely aesthetic ends.) This is what we see when we lo...