[Europan Ocean (OP)]

I recall that a supernova was visible from the Earth centuries ago, and Chinese astronomers made records and kept dates. And others too. We can now see the Nebula with telescopes. But the blast travels slower than light and will reach the Earth but when, and what effect will it have? Firestorms, atmosphere stripping, blackouts, mere aurora?

[evan_au]

The amount of damage depends on the distance and type of supernova - and which side of the Earth is facing the supernova at the time.

There are unstable isotopes of iron (Iron 60, half-life 2.6 million years) present in Earth sediments that suggest that a supernova has occurred relatively close to the Earth in the past 5 million years.
 
Of course, if these iron-60 nuclei were blasted out at relativistic speeds, they may have experienced time dilation, and lasted a bit longer...

See: https://en.wikipedia.org/wiki/Near-Earth_supernova

[Europan Ocean (OP)]

A bomb blast may last for one second, but a supernova like the one that made the Crab Nebula, that could be an event that lasts for days?

[evan_au]

a supernova like the one that made the Crab Nebula, that could be an event that lasts for days?

The supernova that created the Crab Nebula appeared in 1054, and was visible to the naked eye for about 2 years. It was officially ignored in Europe.

Tycho's Supernova in 1572 peaked as bright as Venus, and was visible to the naked eye for a few months.

A considerable amount of energy in a supernova is released by the radioactive decay of cobalt 56 (half-life 77 days).

Other supernovae are listed here; ones with apparent magnitude < 7 would be visible to the naked eye:
https://en.wikipedia.org/wiki/List_of_supernovae

[chris]

A considerable amount of energy in a supernova is released by the radioactive decay of cobalt 56

Evan, how is that known, and why should cobalt-56 play such a significant role? Where does it come from?

[evan_au]

how is that known?

This was originally deduced from light curves of Type 1a supernova, and the theoretical composition of various types of supernova.

More recent confirmation was provided by gamma-ray satellites observing SN 1987A, which were able to determine the gamma-ray spectrum of the nuclear decays.

See: https://en.wikipedia.org/wiki/Supernova#Light_curves

Where does (Cobalt-56) come from?

Massive stars at the end of their lives burn much of their fuel into Iron-56 (an exothermic fusion reaction). In the fury of the supernova, extreme temperatures and pressures create elements heavier than iron by fusion, including the elements copper to silver; this process absorbs energy.
A considerable amount of elements close to iron are formed, in particular Nickel-56 (half-life 6 days) which decays to Cobalt-56 (half life 77 days) which decays back to Iron-56 (stable). Stable isotopes of nickel are also formed, which is why many meteorites are formed of a nickel-iron alloy (the center of the Earth is believed to be similar).

Less massive stars don't reach the temperatures and pressures needed to produce an iron core, but the temperatures and pressures of the supernova form iron and nickel (and elements beyond).

why should cobalt-56 play such a significant role?

As the debris of the supernova expands, it emits energy from a larger surface area. But it also cools down rapidly.
It is the radioactive decay of Nickel 56 to Cobalt 56 to Iron 56 which provides energy to keep the supernova remnant glowing during the initial few weeks and months.
Other radioactive species with longer half-lives contribute energy over the succeeding years.
Hints are provided in the decay of the supernova light curve.

[Europan Ocean (OP)]

I just watched a nuclear test go off on TV and the radiation burns the house first, then the material blast follows and pushes the house off. When will the blast from one of the near supernovas reach the Earth if ever? What would it be like, what could it do?

[Bored chemist]

Well, it's tricky comparing a supernova to a nuclear blast but it's probably as close as anything on earth will ever get to mimicking one.

The light form a supernova is incredibly bright, and yet they are so far away that they are less bright than sunlight.
The flash from a nuke is much brighter than sunlight.
It's not unreasonable to say that the blast will be very roughly proportional to the brightness.
Because the supernova is very far away, it's not as bright as a nuke, and not as dangerous.

A nearby supernova would be a problem- but not one we could hope to do much about.

[Europan Ocean (OP)]

I was inspired to post this thread because of a prophecy about a three day fire storm, producing hurricanes of fire and putting out electric lights, requiring Christians to remain indoors and curtains closed and using candle light.

I am thinking the blast from a previously visible local supernova could be coming and could be elongated with time and distance and could compress against the Earth for three days.

[Europan Ocean (OP)]

My interest in this began with a media release saying that the wave the blast was coming from a supernova and that it would strip the Earth of it's atmosphere.

[evan_au]

a media release saying that the wave the blast was coming from a supernova

Did they say which supernova?

I expect that the material ejected by a supernova will travel with a wide variety of speeds.

• So if the supernova was distant, it will gradually arrive, spread out over many years
  
• Some of the material will be slowed by colliding with the layers of gas puffed off by a massive star as it goes through successive red giant phases, prior to the supernova.
  
• Some of it will be slowed by the interstellar medium.
  
• More of it will be slowed by the Sun's Solar Wind (which forms a denser "bubble" in the interstellar medium).
  
• More of it will be slowed by the Earth's atmosphere. 

I guess shockwave effects could occur, if the velocity of the propagating blast wave exceeds the (very low) speed of sound in the interstellar medium. Some of the shockwave would be reflected from the denser Solar bubble, but some would propagate into this bubble (where we reside).