Galactic Tick Day – A celebration of our progress around the milky way | Hacker News Reader

Galactic Tick Day – A celebration of our progress around the milky way

galactictick.com

79 pointsglitch00335 comments

Interesting idea to use a unit that is universal to our galaxy. However, using deci-arcseconds (1/360/360/1000) seems arbitrary - it depends on the 360 degrees of a full circle and the decimal system.

Perhaps dividing the time period of 225million years by a power of two would be more universal.

For our life span, 2^27 looks good:

225.000.000 years / 2^27 = 1.67638 years, 611 days

Or perhaps 2^28? That'd be 305.94 days

I agree that divisions of 2^27 or 2^28 are in a sense less arbitrary than deci-arcseconds – but while the base (2) seems non-arbitrary, the same can't be said for the exponent (27 or 28). Wouldn't 2^32 be even better? A bit over 19 days.

Or I would argue 2^16 is even less arbitrary than 2^32. 2^(2^(2^2)) feels less arbitrary to me than 2^(2^5). A bit over 3,433 years.

This gives me an idea – write dates/times in hexadecimal. The first four hexits refer to units of 2^16 (roughly 3,433 years). The next four hexits refer to units of 2^32 (roughly 19 days). Then come units of 2^48 (roughly 25 seconds). Then units of 2^64 (about 385 microseconds), etc. However, you need to pick an epoch (zero point), and any choice of epoch is going to feel much more arbitrary than the system as a whole.

"However, you need to pick an epoch (zero point), and any choice of epoch is going to feel much more arbitrary than the system as a whole."

How about the best estimation for the 13.8 billion years old Big Bang event? Expressed through the number of galactic revolutions, of course.

Sure, we will not pick the epoch as someone else, but at least we celebrate it in the same interval.

You must be a very optimistic person to think beyond our own galaxy! Taking this path, should we think how shall we deal with the stability of our galactic movement reference if the Andromeda collision will affect it?

Sure, it's arbitrary. That's why I wrote "for our life span".

It's not universal anyway. Different stars orbit at different periods. The difference might not be large, but I am not sure you can really define a "galactic year" with much precision.

Wikipedia has this to say about the rotational speed of the milky way:

"Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been given the name "dark matter".[34] The rotational period is about 240 million years at the position of the Sun."

Yes.

If they all go at the same speed (linear, in km/s) that means they all have different angular velocities, i.e. stars near the centre will have shorter period. That's why the article specified the period as about 240Myr at the position of the Sun.

Nobody is talking about a "standard" galactic year apart from you as far as I can gather ... it's just about the specific orbital period of our sun. The parent of your reply is talking about using more universal units, not trying to define a universal galactic year.

Agreed this is arbitrary. Why not divide into 2*pi units and divide from there. Been a long time since I touched orbital stuff, but maybe add a "normalization" that factors in the Kepler area carved out by an object in orbit around the galactic center (tho... I'm not sure how well Kepler works in the galactic rotation sense... but something similar perhap?) In any case, if the orbit isn't circular, something would need to adjust for the change in relative angular rotation.

Also... may want to standardize on reporting this in terms of "seconds" and dropping "days" and other locally referenced time measures :-)

An arcsecond is 1/360/60/60 of a circle (1/360/3600), a deci-arcsecond is one tenth of that.

Yup, I meant centi-arcsecond, not deci-arcsecond. That's not the point. The point is that both "360" and the decimal system are abitrary whereas powers of two are universal.

Why are powers of ten arbitrary but not powers of two?

Two is the first positive-integer power that makes sense and is actually useful; "powers" (really the singular would do) of 1 are much less useful. Non-positive-integer powers are also wildly less useful than integer powers. (Yes, I know about the exceptions, I'm quite a fan of funny bases myself. But that's still a true statement. Don't let the tiny exceptions buried in an overwhelmingly large pile of common cases bedazzle you too much.)

We, humans, like powers of ten because of our ten fingers - when counting with the fingers, every time we reach a multiple of ten, we need to shift and start over.

So maybe others don't have ten fingers, and they prefer a different base for counting.

On the other side, powers of two are related to doubling/halving things - which should be a much more universal concept than shifting after ten.

From a physics standpoint it's easier to make transistors using powers of two. Unless your dealing with things vastly outside of our temperature range that seems fairly universal.

That's not really any more or less arbitrary.

The definition is very arbitrary: a centi-arcsecond. Why not celebrate a galactic quarter second every 704 days? Just as arbitrary, but much more relatable. As starting point, just take the year 0, so we're living at 4 galactic minutes and 21.25 seconds now.

The year 0?

this year minus 2016

Maybe thaumasiotes was pointing out that there was no year zero. Before the year 1 was the year 1 BC...

The traditional AD/BC system (aka the CE/BCE system) doesn't have a year zero. But astronomical year numbering does. (0 = 1 BC, -1 = 2 BC, etc.) Given the astronomical flavour of this discussion, the assumption that BetaCygni was using astronomical year numbering is reasonable.

https://en.wikipedia.org/wiki/Astronomical_year_numbering

I'm just a developer who by habit starts counting from 0. I meant to start at January 1st AD 1 0:00 AM.

What if our sun is not an exception?

Pluto turns around the Sun, but from Pluto the Sun is very small. Idem, the Sun could turn around a very big and very far star looking very small from the Earth.

We could be in a wide binary where currently the stars are at a maximum opposites, then the binary companion would be a very bright star at night, and not visible during the day.

This could explain the nemesis star theory for mass extinctions https://en.wikipedia.org/wiki/Nemesis_(hypothetical_star) and also the recently discovered anomaly in the planets orbit https://www.caltech.edu/news/caltech-researchers-find-eviden... or why the Kuiper Belt ends suddenly or the Pioneer anomaly or maybe even the Oort Cloud.

There are some still unproved theories that state this star could be Sirius binary and we are in fact in a triple star system.

It would be interesting to relate the galactic revolution subdivisions with other neutral units like multiples of Planck time. Like others mentioned here, the "tick" is very cultural and therefore not assured to be accepted in the long term by future generations (of our more rational off-springs).

Interesting thought. Tough to get to anything useful from Planck time though. 2^^8 (as in 2^2^2^2^2^2^2^2) Planck times would be a bit over 30 microseconds, but then I'm not sure how you'd go from there to a useful time scale.

Well you can check your Galactic Tick birthdays http://jankor.github.io/galacticbday/

If you feel too Sun-centric.

Just in time to play Galactic Escape - escape black hole :)

https://itunes.apple.com/app/apple-store/id1076368667?pt=132...

Sorry for the plug :)

Already? Seems like the time between them keeps getting shorter every year! I haven't even started my shopping yet.

Oh no, galactic ticks are going to drink all of our blood!!!!

SCNR

Um, as the Earth to the Sun, what's the length of the Sun's day with respect to the galactic center.

If my knowledge of mechanics is correct, given enough time, all days tend to infinity? (Like the moon's day with respect to Earth?)

Not sure what you mean, but according to https://en.wikipedia.org/wiki/Solar_rotation "at the equator the solar rotation period is 24.47 days and almost 38 days at the poles".

Ahh, thanks for that. Should have realized that the sun doesn't have a "fixed" surface. It seems that the center, however, has a rotational frequency of about 432nHz which results in a rotation period of 26.8 days.

All of these numbers are way faster than I imagined, which means that the length of the "solar year" is still incredibly long in "solar days".

Star core rotation is actually very interesting physics (it affects oscillations in the star in some very fun ways).

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