# Sun’s corona is so much hotter than Chromosphere [duplicate]

What makes Sun’s corona so hot? I tried to google it but can’t find satisfactory answer.

## marked as duplicate by John Rennie thermodynamics StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Jul 9 at 4:40

This has been a puzzle for many years, here is what's thought to be at work in this situation:

The Sun has a powerful magnetic field that extends a significant distance from the edge of the photosphere, which represents what we see as the "surface" of the sun.

The atmosphere of the Sun (by this I mean the gases that exist outside of the photosphere) are at least partially ionized and as such are electrically conductive.

Since the Sun revolves, its magnetic field sweeps through that atmosphere and induces eddy currents in the ionized gas out there.

This in turn causes significant amounts of I-squared-R power dissipation in that part of the sun's atmosphere, which heats it up.

I invite the experts here to weigh in with their perspectives on this.

• Also note that the corona has a low density, around $10^{-16} g/cm^3$, so a given volume of corona material contains much less heat than the same volume of material at the photosphere. – PM 2Ring Jul 9 at 3:45
• Okay..but by this concept chromosphere should be hotter than photosphere which the case is. But corona is farther than surface of sun then how can you explain that? – Avinash Tiwary Jul 9 at 9:02
• there's plenty of magnetic field out there to do the work, and only a tiny amount of mass to apply it to. – niels nielsen Jul 9 at 16:30