For a standard candle to measure the universe
I'm thinking Lush might be a bit more reliable.
Astrophysicists have spied an extremely rare type of supernova from an exploding and possibly radioactive white dwarf that emits mysterious flashes of UV light. A white dwarf star in a binary system goes nova when it strips enough matter from its companion star to reach critical mass. The aged star will blow apart, shedding …
Four supernovae (SNe), exploding 300 pc from Earth, were recorded 44, 37, 32, and 22 kyr ago in the radiocarbon (14C) record during the past 50 kyr. Each SN left a nearly identical signature in the record, beginning with an initial sudden increase in atmospheric radiocarbon, when the SN exploded, followed by a hiatus of 1500 yr, and concluding with a sustained 2000 yr increase in global radiocarbon due to gamma-rays produced by diffusive shock in the SN remnant (SNR). For the past 18 kyr excess radiocarbon has decayed with the 14C half-life.
SN22kyrBP, is identified as the Vela SN that exploded 250 ± 30 pc from Earth. These SNe are confirmed in the 10 Be, 26 Al, 36 Cl, and NO3- geologic records. The rate of near-Earth SNe is consistent with the observed rate of historical SNe.
See however the comment https://arxiv.org/pdf/1406.5141.
Place: A galaxy 140 million lightyears away. Time: 140 million years ago.
A red-necked alien stares beneath the bonnet of his friend's UFO. He tugs experimentally at the mechanism, provoking short flashes of UV light. He hands his drink to his friend and picks up a large wrench.
"Hold my Djinn N'tonnix, I've got this."
Q. Two trains are travelling towards each other, each with a light on their engines. At what speed would they be travelling at for the light to appear blue to the other?
Or put another way - Assuming red shift to be caused by nothing other than the Doppler effect, what kind of speeds are we talking for a z value of -0.2 (blue shift)?
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