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Comment by racingmars | Hacker News Reader

The image details do have the dimensions listed in a standard measure down under the "Fast Facts" section; I assume this will be included for every image release.

The deep field image says it's about 2.4 arcmin across[1], Stephan's Quintet image is about 7.4 arcmin across[2], etc.

[1] https://webbtelescope.org/contents/media/images/2022/035/01G... [2] https://webbtelescope.org/contents/media/images/2022/034/01G...

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I know that's usually there. I'd just love to see a little map scale bar or something in EXIF.

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Super easy.

Nice idea, really, and very easy to implement.

Is there a way to rapport an arcmin to a measurement that would be more easily understandable? Not necessarily as a multiple of grains of rice.

Your thumb at arms length is ~2 degrees or ~120 arcminutes wide. The fingernail on your index finger at arm's length is ~1 degree or 60 arcminutes wide.

The moon is about half a degree or 30 arcminutes wide. This doesn't make sense but give it a try tonight if the moon is out.

FWIW many of the galaxies and nebula you see in astrophotography are actually bigger in the night sky than one might guess. Andromeda for example is about 6 times wider than the moon at ~3 degrees across - https://slate.com/technology/2014/01/moon-and-andromeda-rela...

I propose we use Moon Diameters (MD) as the official HN unit for sky distance.

A minute of arc is one sixtieth of a degree. (A "minute", get it?)

The moon is between 29.4 and 33.5 arcminutes wide, depending on where it is in its orbit. So about a tenth of the width of the moon.

> So about a tenth of the width of the moon.

this is so much more digestible than "grain of sand at arm's length", and those two metrics dont feel at all equivalent -- the moon is not ten grains of sand at arm's length wide, right?

The moon is pretty darn small. Half a degree wide. Imagine gluing ten grains of sand together, balancing it on a fingertip, then stretching your arm out. Around a degree wide? Depending on your grain of sand, of course.

hmmm, about the size of an asprin tablet or pea at arm's length, seems to agree with somewhat smaller than thumbnail [1]. maybe i should find and measure some sand now :).

in either case, 1/10 the width of the moon is so much easier to comprehend. when is the last time anyone tried holding a grain of sand at arms length? what a weird comparison to make when everyone on earth already has a stable/familiar reference in the sky.

[1] https://astronomy.com/magazine/stephen-omeara/2010/01/stephe...

I always translate it in my mind to full moons. 30 arcmin == diameter of full moon as seen from earth.

7.3 arcminutes = 16 light-years

Wait, but it’s a ~cone, right? So it must be 16ly across at some specific distance from us?

That's the distance of an object away that has a parallax of 7.3 arcminutes and a baseline of 1AU. The 7.3 arcminutes referenced here is the width of the image on the celestial sphere.

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