Dark nebulae are a type of interstellar cloud that is dense enough to obscure the light from objects behind them, such as stars and other celestial bodies. Unlike diffuse nebulae, which are composed of gas and dust and can often emit their own light (typically due to excited hydrogen gas), dark nebulae primarily absorb light, creating visually dark patches against the backdrop of brighter stars or regions of space.
They are very well chosen for their high safety and level interest, so you can just go into them without putting much thought into it.
Sometimes they go a bit too much on the side of safety, making certain transitions annoying, but in general the selection is spot on.
The routes do sometimes go on a bit of gravel, so they are most adequate for hybrid bikes rather than road bikes, although road bikes would be able to to much of them. A more road-bike dedicated possibility is the The National Byway.
Note however that there are many many other local routes which are not in the network, but arguably equally, or more worthwhile.
Their diginal map distribution mechanisms are a bit shitty and sometimes asks you to pay for certain formats, which is hard to understand given that the maintainer of those maps, the Ordnance Survey appears to be public... github.com/cirosantilli/cirosantilli.github.io/issues/61 "How to see the Sustrans National Cycle Network on Google maps?"
Googling "National Cycle Netowrk KML" leads to: data-sustrans-uk.opendata.arcgis.com/ from which we can download the KML. gis.stackexchange.com/questions/216770/how-to-open-kml-file-in-google-maps-for-android then shows how to make that viewable on Google Maps by going through www.google.com/maps/d/u/0/?hl=en on the browser. TODO 2021-11:
GPSPrune 20.2-1 can open the KML however, so that file can't be entirely wrong.
"Ralph Hughes" www.linkedin.com/in/ralph-hughes-501474121 is listed as the creator/responsible of the exports, but can't find his email. Sent an email to gissupport@sustrans.org.uk and he did reply a few days later that they are aware of the issue, and are particularly trying to reach out to Google about it. Great news!
GPSPrune 20.2-1 can open the KML however, so that file can't be entirely wrong.
OpenStreetMaps has them on by default though if you just click "Cycle Map" layer. It is not as incredibly detailed as the Ordnance Survey one, e.g. does not show which side of the street to ride on, but still, is very good.
Or in other words: there is no Turing machine that always halts for every input with the yes/no output.
Every undecidable problem must obviously have an infinite number of "possibilities of stuff you can try": if there is only a finite number, then you can brute-force it.
Lists of undecidable problems.
Coolest ones besides the obvious boring halting problem:
A:
- decidable problem is to a decision problem
- like a computable problem is to a function problem
The prototypical example is the Busy beaver function, which is the easiest example to reach from the halting problem.
Difference between recursive language and recursively enumerable language by 
Ciro Santilli 40 Updated 2025-07-16
Ciro Santilli 40 Updated 2025-07-16The most important ones are:
- theory of everything. We are certain that our base equations are wrong, but we don't know how to fix them :-)
- full explanation of high-temperature superconductivity. Superconductivity already has a gazillion applications, and doing it in higher temperatures would add a gazillion more, and maybe this theoretical explanation would help us find new high temperature superconducting materials more effectively
- fractional quantum Hall effect 5/2
Other super important ones:
- neutrino mass measurement and explanation
HD 101584 is a star located in the constellation of Centaurus, approximately 1,140 light-years away from Earth. It is classified as a post-AGB (Asymptotic Giant Branch) star, which indicates that it is in a late stage of stellar evolution. In this phase, a star has exhausted the hydrogen in its core and has moved beyond the red giant phase, potentially leading towards becoming a white dwarf.
www.nytimes.com/2023/07/09/world/asia/north-korea-china-defectors.htmlK-drama, the ultimate symbol of resistance. Epic.
North Korea keeps itself cut off from the internet and sends these highly trained specialists to do work in China, Southeast Asia and elsewhere to avoid international sanctions imposed on the country for its nuclear weapons program. The specialists usually live together in dormitory apartments, where they are instructed to spy on each other. Their North Korean minders look for signs of disloyalty - like watching K-dramas.
Ciro Santilli believes that the Donald Trump bans were extremely unfair, and highlight the need for government to ensure greater freedom of speech in social media, more information at: cirosantilli.com/china-dictatorship/unjust-social-media-censorship-in-the-west, related: globalization reduces the power of governments.
Pinned article: Introduction to the OurBigBook Project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Intro to OurBigBook
. Source. We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivativeVideo 2. OurBigBook Web topics demo. Source. - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 3. Visual Studio Code extension installation.
Figure 4. Visual Studio Code extension tree navigation.
Figure 5. Web editor. You can also edit articles on the Web editor without installing anything locally.Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.Video 4. OurBigBook Visual Studio Code extension editing and navigation demo. Source. 
- Infinitely deep tables of contents:
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact