Science Porn

[vorlon13]

Even a very bright supernova in the Andromeda galaxy over 100 years ago was invisible to the naked human eye. Unfortunately.

So no individual star that far away, no matter what, can be seen without paraphernalia of some kind.

There are even stars, red dwarfs etal, that even when very close are also invisible to your eye. Proxima Centauri for starters.

[Anomalocaris]

The supernova SN1987A exploded in 1987 in the greater megellanic cloud about 160,000 LY away, or approximately 1.5 times the diameter of a large spiral galaxy from earth. It was easily visible to the naked eye.

If a large supernova were to explode in the andromeda Galaxy 2.5 million LY away, at a location in andromeda where line of sight to earth is not blocked by dust or nebulas, it too would be visible to naked eye on earth. The theoretical maximum distance at which an unobscured supernova can be seen by naked eye is around 8 million LYs.

Unobscured individual hypernova explosions up to 100 million LY from earth, or 1000 times the diameter of typical large spiral, if favorably oriented with axial jet pointing to earth, would be theoretically visible to the naked eye.

[vorlon13]

(I was referring to SN 1885A)

[Anomalocaris]

I know. SN1885A occurred very close to the core of andromeda, so it would have been set against a relatively bright and dense background of stars. So it was not positioned to be the most conspicuous to the naked eye. It was also probably partially obscured by dust lanes of andromeda. Even so it reach visual magnitude 5.5, which means it was brighter than naked eye threshold for some days, even if no one recorded seeing it by naked eye at the time. If it had happened today, I am sure some naked eye observers in high altitude locations would have seen it.

Also, SN1885A was a type IA Supernova, This means while its intrinsic optical brightness was high compared to the average over all types of Supernove, it was still 4-5 magnitudes dimmer than, or only as little as 1% as bright intrinsically as, the brightest hypernovea on record. This means if all other conditions are identical, a really bright supernova like type IIN would appear as bright as SN1885A From up to 10 times further away.

I think modern theory say these hypernovea are order of magnitude brighter along their spin axis than their average all aspect brightness. So if one of them is correctly aligned, it could be seen 3-4 times even further than that. Hence the maximum theoretical distance at which a hypernovea can be seen by naked eye would be around 100 million light years.

[Alex K]

Very interesting!

[Jackalope]

More fun with scales:

That's far from accurate. The furthest stars easily visible to the naked eye even in relatively light polluted areas like Los angeles are those of the andromeda Galaxy 2.5 million light years away, or a distance equal to about 20 times the diameter of a typical large spiral galaxy implied here. Admittedly I am talking about seeing a collection of stars, not resolving a single star.

The furthest single star that can be resolved by the naked eye would be blue supergiants. These can be seen out to about 5000 light years. So a circle encompassing the further individual stars visible to the naked eye would still be 1/10 the diameter of a typical large spiral galaxy - ie far larger relative to the Galaxy than the yellow circle in the picture.

You make a good point, that the distance at which stars are visible is dependent on their intrisic brightness and intervening dust, in addition to distance.

Visibility of M31 from urban skies is pretty iffy. Its pretty reliably visible (if you know where to look and what you're looking for) from my country property 30 miles north of Portland, but from the city itself, I've never been able to spot it unaided. Typical magnitude limit is 3ish. Yeah, M31 is bright, but that brightness is spread out over a very large area - and good luck resolving individual stars. ;-). Can't even do that with my 200mm Schmidt-Cassegrain (couldn't do it with my 300mm reflector either, before I sold it).

The brightest stars you can see? Most of them are really close, relatively speaking. I've seen sources that claim 4000 ly for the brightest supergiants under mag 6.5 skies (average eyes, very dark skies). 5000 ly for exceptionally dark skies and eyesight seems within the realm of possibility.

[Jenny A]

Evolution simulator thanks to Heywood (even if he was using it to make a misguided argument):





An explaination of the process and if some ways more interesting:



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[pocaracas]

[Alex K]

I wonder how my Wacom digitizer works... It seems to directly talk to/register a field from the pen.

[pocaracas]

I wonder how my Wacom digitizer works... It seems to directly talk to/register a field from the pen.

ah, the wiki coming to the rescue!

Passive tablets
Passive tablets,[9] most notably those by Wacom, make use of electromagnetic induction technology, where the horizontal and vertical wires of the tablet operate as both transmitting and receiving coils (as opposed to the wires of the RAND Tablet which only transmit). The tablet generates an electromagnetic signal, which is received by the LC circuit in the stylus. The wires in the tablet then change to a receiving mode and read the signal generated by the stylus. Modern arrangements also provide pressure sensitivity and one or more buttons, with the electronics for this information present in the stylus. On older tablets, changing the pressure on the stylus nib or pressing a button changed the properties of the LC circuit, affecting the signal generated by the pen, which modern ones often encode into the signal as a digital data stream. By using electromagnetic signals, the tablet is able to sense the stylus position without the stylus having to even touch the surface, and powering the pen with this signal means that devices used with the tablet never need batteries. Activslate 50, the model used with Promethean Ltd white boards, also uses a hybrid of this technology.[10]