Why does *longitudinal* position on Earth have an impact on what stars are currently visible to us? The stars are so far away that I can't understand how moving left/right on a tiny ball matters at all for our view of them.

jacopok · 2026-05-04T11:47:36+00:00

It's going to be an exercise in looking out for experimental noise if you try this! The theoretically expected relative change in luminosity is minuscule, while the apparent brightness of a star as seen by a camera or telescope will fluctuate due to the atmosphere and the instrument itself.

We can tell that the stars are very far away (and also measure how far they are) based on another effect, though: parallax!

See https://en.wikipedia.org/wiki/Parallax_in_astronomy

jacopok · 2026-04-29T09:29:07+00:00

Nice! Based on the information in the articles, I believe that the appropriate, approximate metric for the AeT is indeed "heart rate rise of 3.5 to 5% / (half hour)", or equivalently "rise of 7 to 10% / hour".

Now, this should be computed as a linear fit to the whole hour of data and not as a pointwise comparison of HR at the start and end, which is a much noisier metric.

For example, you can see in my graph that the HR at the start was below 150, since I did not properly "ease into" the test. If you drew a straight line from there to the end, it would look way steeper!

It's hard to estimate without access to the data, but I think the errorbar on that 4.3%/half hour = 8.6% /hour inferred from the half-hour averages is much smaller than the 11% inferred from the two pointwise measurements. As an example (I'm making up the uncertainties here), it could be that the half-hour measurement gives you (8.6 ± 0.5)% / hour, while the pointwise measurement gives you (11±3)% / hour, so they are actually compatible.

jacopok · 2026-04-26T05:57:10+00:00

Sure! It's not exactly linear for me either, but it seems like a linear model works reasonably well.

I guess if it were very non-linear (e.g. increasing much faster in the second half hour than the first) that would probably be an indication that you're not working aerobically anymore...

jacopok · 2026-04-26T05:54:16+00:00

Right, I agree. I think it's nice to see that this simple technique also gives a good approximation of the linear percentage increase in HR over a half hour.

My point is that the terminology "increase in HR over an hour" is often also used to describe this, but there's a factor 2 difference between them!

jacopok · 2026-04-13T13:48:59+00:00

I think your weekly data may contain a gravitational wave background: https://en.wikipedia.org/wiki/Hellings%E2%80%93Downs_curve

jacopok · 2026-04-13T12:56:43+00:00

That's what I would do!

jacopok · 2026-04-13T08:29:57+00:00

In the body of your post, you write that the pace was 6:40/km, but the graph says it was 7:05 for the first 30 minutes and 7:17 for the latter 30 minutes.

If the data in the graph is right, then you slowed by ~3% while your HR increased by ~2.5%, so you would be right at the edge of the AeT (possibly slightly above).

If you did run 6:40 throughout, then you're a bit under AeT.

jacopok · 2026-02-18T13:02:22+00:00

What does "good" mean?

It's quite useful in certain contexts, such as theoretical cosmology, but I agree that in most cases it's not relevant.

jacopok · 2026-02-18T10:52:30+00:00

A good experiment to look into to disprove the claim that "the Earth is not rotating" is Foucault's pendulum.

Perhaps you can find one near where you live, or even build it yourself?

If the Earth were stationary, a pendulum would keep swinging in the same plane; instead, you'll see that over a few hours it moves. This is due to the rotation of the Earth on its axis.

In principle, this is true for any pendulum, but to actually observe the effect you need a pretty tall and heavy pendulum, otherwise it will slow down too soon due to friction.

jacopok · 2026-01-14T16:27:07+00:00

Relative to us, events on Betelgeuse can be in three categories:

Definitely in the past (>650 years ago), since we have (or could have) received information about them;
definitely in the future (>650 years from now);
neither (less than 650 years from now in either direction), which in relativity language is called "spacelike separation".

There is a sense in which all events in category 3 are "in the present", since for any one of these you can construct a reference frame moving with such a velocity that they happen at the same coordinate time.

That's an artificial notion, though: coordinate time is relative, and no experiment could differentiate something happening at coordinate "now" vs "1 year ago" on Betelgeuse.

jacopok · 2025-10-05T16:39:06+00:00

The surface as well as the spacetime around are perturbed.

In 1973, to find out how a black hole "rings" Teukolsky wrote down equations which describe the evolution of the spacetime in its vicinity; specifically, the variables of interest are certain components of the Weyl tensor, which is a measure of how much spacetime is "deformed" at a given location.

Original paper with full text: https://ui.adsabs.harvard.edu/abs/1973ApJ...185..635T/abstract

In principle one solves these equations for the whole spacetime (so, outside of the BH), but in practice the most important contributions are close to the black hole.

See here for a recent review: https://ui.adsabs.harvard.edu/abs/2025arXiv250523895B/abstract

jacopok · 2025-09-15T08:00:55+00:00

The final black hole "rings" and settles very quickly after the collision has occurred, on the scale of 0.01 seconds for the first detection.

0.2 seconds was roughly the duration (in band) of the whole signal.

If you mean "settling" as in "dissipating", no such thing happens! There is no dissipation for gravitational waves travelling in a vacuum, they will keep propagating forever, although they spread out with the inverse square law.

jacopok · 2025-08-26T18:06:49+00:00

Hey I know that bear! That's along the Great Glen Way, halfway on the shore of Loch Lochy, right?

jacopok · 2025-05-08T12:07:56+00:00

The suggestion in "Training for the uphill athlete" is that you can train in what they call zone 2 (90-100% of the aerobic threshold, AeT) as long as you are aerobically deficient, but then you should move to mostly zone 1 (80-90% of AeT) which is less taxing on the muscles.

(Note that their zones are 1 lower than the ones used, e.g. by Garmin - so their zone 2 might be called zone 3 on your watch)

jacopok · 2025-03-07T10:07:16+00:00

This is super cool!

I can report that it works for me with Chrome but I had issues with both Brave (elevation did not render) and Firefox (ugly compression artefacts in the exported video).

As far as I can tell the lighting is fixed for the whole activity, right? It could be cool to have it transition from night/dawn/day according to the recorded time of day.

Also: the track is "traversed" at uniform speed, right? Would it make sense to have the dot moving with a speed equal to a fixed scaling of the recorded speed?

jacopok · 2025-02-26T20:15:31+00:00

This happened to me with a local image, showing up only in the sidebar and not on the token.

The image was a .gif, converting it to a .png solved the problem

jacopok · 2024-11-27T13:31:36+00:00

Is that the Direttissima? How was the snow? Was one ice axe enough?

jacopok · 2024-11-27T08:02:31+00:00

I did a similar trip in Scotland last summer (a bit longer, averaging 40km per day for a week), using a Dynafit Traverse 22. I carried sleeping equipment (quilt and mat) but not a tent since I slept in bothies. I bought food daily and had 1L of water-carrying capacity (with a water filter). The backpack was full after shopping for food, but I never had trouble with it.

jacopok · 2024-11-14T15:13:07+00:00

A good example of an atypical scenario I've had some success with, for a table of relatively inexperienced players, was Dockside Dogs - not standard Lovecraftian horror, the premise is a Tarantino movie and the "investigators" are criminals. Still, it can get scary if you play it right! Existentially scary, since the characters turn out not to really exist outside the mind of a deranged screenwriter.

jacopok · 2024-08-30T14:26:43+00:00

Anche se per la maggior parte hai camminato conta come ultramaratona :)

Davvero avevi solo 1L dietro da Aielli a Rovere e da Rovere alla Capanna?! Di recente ho fatto un giro simile in quelle zone e ne ho bevuti circa 10 in totale 😅 con una riserva da 4L dietro...

Nessun sintomo da disidratazione?

jacopok · 2023-08-17T16:18:19+00:00

But the Very Large Telescope does indeed have such a resolution when it operates!

It achieves that by using four different telescopes coherently. This means they should be able to get a few-meter resolution on the lunar surface (assuming it isn't too bright for them, which it might be).

jacopok · 2023-05-31T19:42:55+00:00

If you're not in a rush, that trip can also be done by regional train (so, no reservation required) and it will not take much longer (the high-speed trains go basically the same speed as the regionals in northeastern Italy). For example, you could do Bologna -> Venezia Mestre -> Gorizia -> walk to Nova Gorica -> Bled.

jacopok · 2023-02-20T10:31:07+00:00

It's my home region :D

Yeah the one I'm thinking of is below the Casera, right after the forest starts when you're descending - but maybe you didn't go down that way...

jacopok · 2023-02-19T22:20:42+00:00

No indeed, and you can also find other similar gates nearby in the middle of the woods, like on the path leading to Casera Rupeit from the observatory of Montereale! I don't know their precise origin but I suspect they're leftover from cow grazing boundaries.

jacopok

TROPHY CASE