Amateur Astronomy


#1361

There was 1 last night that lit up the sky like lightening. I was driving so didn’t see it directly unfortunately.
I saw maybe 8-9 meteors before the clouds rolled in.


#1362

Any recommendations for a documentary on Boltzmann brain?


#1363

It’s a fairly straightforward (and somewhat fanciful?) philosophical idea. Not sure you could have a whole documentary on it. I know PBS Spacetime did a video of the usual high quality, will see if I can dig it out.

EDIT: Here…

One of my objections would be to his statement at 5:25: “in the far future the universe will reach a state of maximum entropy”. The remainder of the argument is that the assemblage of a Boltzmann brain – no matter how improbable – is assured given infinite time. But I don’t think that follows.

What if the universe keeps expanding as we expect it to? Then there is no state of maximum entropy. In Boltzmann statistical terms the number of possible microstates continues to increase without end, so entropy always increases. The very low fractional probability of a BB therefore always decreases. As you know, you can sum an infinite series of decreasing fractions (or, in this case, integrate over infinite time) and get a finite sum. Therefore the probability of a BB can be finite and tiny, even in infinite time.

Another personal objection is that the BB idea entails some version of an anthropic principle, and I find that principle very unsatisfying in general for other philosophical reasons.


#1364

One of my go-to sites for digestible summaries of astrophysics papers – astrobites.org – is rapidly becoming unreadable. Woke students now report on micro-aggressions, and sign their bios with preferred pronouns. The gist of the latest summarised thesis is:

Stories and beliefs surrounding the night sky are reflections of the culture that creates them and their ideals; accordingly, the goal of this study is to look at feminine celestial bodies to understand “how the idealized role of women gets projected onto the sky and how the behavior of celestial bodies gets projected onto women” in various cultures.

I failed to spot any actual astrophysics in it. There was a helpful Google map of Africa just in case you didn’t know where it is ( – quite likely for some of these students), or that it’s a big place.


#1365

https://news.sky.com/story/signs-of-alien-life-detected-on-venus-12071625


#1366

Detective work reconstructs the final movements of the European Space Agency’s Philae probe.

https://www.nature.com/articles/d41586-020-03043-4


#1367

@ps200306 Interesting article on latitude sailing using star declinations.

https://www.yachtingmonthly.com/sailing-skills/celestial-navigation-understanding-the-night-sky-76487

Also has a linky to a site that’s developed a reference tool - if you e-mail them (tidalcompass) referencing the #YM article they give you a code to get the printable version (that you put together) for free :slight_smile:


#1369

In fairness there was usually a plate with the string but yes, difficult! Plus cumulative retinal damage was a real issue from taking sun sightings, either with that or the cross-staves.

https://www.kotsanasmuseumshop.com/en/product-categories/astronomy

Modern sextant are really accurate - taking simultaneous sightings with another person you’ll often get close readings to the minute. Harder to Mark the exact time at higher latitudes I think, where things whizz around more quickly. Even the difference putting down the sextant to turn to a watch - best to have a second person. And calculating position within a few miles is fine for the middle of the ocean.

Latitude sailing (by sun) it’s fairly easy to get the noon sight. But - absolute zenith of Polaris… I agree awkward to get and it’s never really encouraged for practical use with celestial navigation as far as I recall. It’s in the almanac, but Sun, Moon, Planets & (other) stars are what are actually used. I haven’t tried the star compass for latitude sailing yet - only came on my radar recently, but thought it interesting theoretically anyway!

Seeing the horizon - yes, impossible at night, unless you’ve got a good moon, so star sights are done at dawn or dusk.

There are a few books on lower tech techniques & history of methods & skills from the past (Emergency Navigation, David Burch; The Bareback Navigator, Jack Lagan) that I keep meaning to read in more depth.