Light Echoes Solve Mystery of Tycho's Supernova

Ponca City, We love you writes "Powerful telescopes in Hawaii and Spain are using 'light echoes' from the original supernova explosion that have bounced off dust in the surrounding interstellar clouds to identify the precise type of supernova that Tycho Brahe saw 436 years ago. Although the echoed light from Tycho's supernova is around 20 billion times fainter than the original light observed in 1572, the team took identical images of the sky a few months apart and then digitally subtracted one from the other to find evidence for several sets of light echoes rippling across patches of dust in the northern Milky Way. 'Using light echoes in supernova remnants is time-travelling in a way, in that it allows us to go back hundreds of years to observe the first light from a supernova event. We got to relive a significant historical moment and see it as the famed astronomer Tycho Brahe did hundreds of years ago,' said Tomonori Usuda, of the Subaru Telescope in Hawaii. Tycho's original observations were particularly important as he immediately concluded that the new star, visible even by day, could not be closer than the Moon challenging the Aristotelian view of the cosmos, widely accepted since ancient times, which held that the sky beyond the Moon never changed."

Wikipedia links just for the sake of completeness

[Anonymous Coward]

Here's a link [wikipedia.org] to the supernova in question. Also, here's Brahe [wikipedia.org] himself. Remember that all his observations were naked-eye - pre telescopes.

Re:Tycho Brahe - Amazing

[Aliks]

Well he had already done a lot of work on parallax measurements for astronomical objects. So when the supernova appeared, and showed no parallax against the moon . . . he was on pretty firm ground stating that the moon was closer to earth than the supernova.

More details in Wikipedia.

Re:Reverse Ray Tracing

[glaswegian]

We would need monumentally large telescopes for this. The largest optical telescope on earth, the Keck, has a diameter of 10m. Using the Rayleigh Criterion [wikipedia.org], we can calculate the minimum resolvable detail at a given distance. For example, we can resolve details on the surface of the moon (in the visible) that are around ~20 meters across. If you want to resolve an apple falling on somebodies head you need ~10 cm resolution. So to see this happening on the moon we would need a telescope with a primary mirror ~ 2.6 km across. To see the same thing echoed back from a dust cloud near the closest star to our sun (4 ly * 2), you would need a telescope with a primary ~ 7e+10 m across or around half the distance between the earth and the sun. Not to mention that the signal would be very weak and completely lost in noise.

Re:Light echoes?

[mrsquid0]

North in the sky is defined to be the point directly above the Earth North Pole of rotation. The northern half of the sky is the part of the sky between the celestial equator and the north celestial pole. For a planet north is defined using the right hand rule of rotation. Curl the fingers of your right hand. That is the direction of the planet's rotation. Stick out your right thumb. That is the direction of the planet's north pole. The same rule applies to Galactic north. Just apply the rotation rule to the Galaxy. Once you get outside the Galaxy supergalactic coordinates are used, which are defined here: http://en.wikipedia.org/wiki/Supergalactic_plane [wikipedia.org].

Re:Doubting Thomas

[mrsquid0]

Actually, the scientific community of the time (such that it was) was mostly convinced by Tycho's observations.

Re:A galactic yardstick?

[halcyon1234]

Although... if we know when that light was emitted, then we know the distance to the supernova already. There's four pieces of information that could be known. If we know two of them, we can map out the Earth/Supernova/Cloud system:

1. The distance from Earth to the Supernova at the time of the supernova event (equal to the time it took for light from the supernova to reach Earth)
2. The distance from the supernova to the reflecting cloud (equal to the time it took for the light from the supernova to reach the cloud)
3. The distance from the reflecting cloud to Earth (equal to the time it took for the reflected light to travel from the cloud to Earth)
4. The angle between the cloud and the supernova, with earth at the origin (projected onto two dimensions of your choice, for convenience)

5. 1. We know 1 is about 7500 light years. I can only presume that the smart brains behind the telescopes can tell determine 3 from looking at the cloud. However, if they can already position the cloud, then you don't need to know 2, you can work it out even without the reflected light

      The hard part, I would assume, would be doing the math on not where everything is, but where everything was when the light hit, and adjusting accordingly.