What is a light year? What is diff. between a solar flare and solar prominence?

Question

Hi, I teach my boys at home and the question of a light year came up. It says in our book that it takes 8 light minutes for sunlight to reach the earth. So, do 60 light minutes equal a light hour? Are there then 365 light days in a light year?

Also, my son said he saw on the discovery channel that it takes "millions of years" for the light from the core of the sun to reach its surface. Is this true? It then takes 8 light minutes from there? I've tried to research this on the web, but haven't found any answers.

Also, what is the difference between a solar flare and solar prominence? Do solar flares just burn hotter and quicker?

Thank you so much for your answers!

Answer 1

I takes 8 minutes for light from the Sun to reach the Earth, so that's 8 light minutes. Yes, 60 light minutes is a light hour, 24 light hours is a light day, and 365.24 light days is a light year - how far light travels in one year. The star Vega is about 4 light years away from Earth, so we're seeing Vega now as it looked 4 years ago - like it sent us a postcard that took a long time to get here.

Yep. Photons produced in the core of the Sun take about a million years to reach the surface of the Sun. It's so dense in the core that they keep 'bouncing off' electrons (really, actually, being absorbed and re-emitted, but it's essentially the same photon). Photons are light particles - little packets of light.

A solar prominence is a loop of plasma on the Sun. Plasma is the fourth state of matter, and is a super-heated, conducting gas. On the Sun, since plasma is conducting, it often follows the magnetic field lines, tracing out the field of the Sun. Prominences are large loops in the magnetic field. Sometimes they can seperate from the Sun, and head out into space - and then they become solar flares. But they have to leave the Sun to become a flare.

It can take the flares a few days to reach the Earth, if they are headed that way, since they are made of plasma (matter), not light. When they do reach us, they cause the Aurora - the Northern Lights. You can see some cool pictures of it here http://www.spaceweather.com or find a 'real-time' map of the areas of the globe experience aurora here http://www.sel.noaa.gov/pmap/pmapN.html. The dark orange parts - like Northern Russia right now - are getting a great show.

Answer 2

Essentially, yes, you've got the concept right. But when dealing with light years, it's actually not a unit of time ; rather, it's a unit of distance. One light year is the distance that light will travel in a year. For reference purposes, using a multiple of 365.25 days, light will travel 5,879,000,000,000 miles in a year .
As for solar flares and prominences, they're not the same thing. A solar flare is basically an enormous electro-magnetic discharge from the sun that arcs from a starting point to a point of dissimilar charge . A prominence is similar in appearance, but the mechanism that causes it is not electo-magnetic; rather, it is caused by an eruption of gases, then held in place by the sun's magnetic field. As for the amount of time it takes for "light" to reach the earth from the core of the sun, I'll try to investigate it and edit my post if I can find anything.

Answer 3

A light year is the distance light travels in a vacuum in a year. In the core of the Sun, a quantum of light, called a photon, is emitted as the result of a nuclear reaction atom and then goes only a fraction of an inch before getting absorbed by a nearby atom. Then that atom re-emits the photon (really a different photon being emitted as a result of the first one being absorbed) which goes another fraction of an inch in a different random direction and gets absorbed by another atom again. This process goes on countless times for thousands of years until, by chance, a photon is finally emitted by an atom on the Sun's surface in a direction that misses all the atoms in the Sun, after which it travels many miles through space without hitting any atoms until it reaches Earth 8 minutes later and gets absorbed by an atom on Earth; maybe an atom in your eye. If that photon misses Earth then it might well travel through interstellar space for years without ever hitting anything, and it does that at 186,000 miles per second in a straight line the whole time.

Answer 4

A "light year" is the distance light travels in an earth-year (364 1/4 days)...in other words, it takes a flash of light from the Sun 8 minutes to reach the Earth because of the distance and as that flash of light continued travelling past the Earth, it would take another 4 years and 2 months for that same flash of light to reach the nearest star (proxima Centauri). (The speed of light is approximately 186,000 miles per second.)

Answer 5

One light year is the distance light travel in one year in a vacuum.
And yes, it takes several million years for radiation to travel from the sun's core to its surface. That is because it doesn't come straight to the surface, but via a 'random' walk'.