Chris Peterson wrote:neufer wrote:Boomer12k wrote:
It is interesting that the tail does not point directly away from the sun....as is sometimes depicted in drawings and things...
:---[===] *
At perihelion the comet was moving faster than the solar wind.
More or less. The perihelion speed was 370 km/s. The densest solar wind has a speed of about 400 km/s, with faster winds from coronal holes about twice that. Material from CMEs can move in excess of 1000 km/s. Of course, the comet did not need to exceed the speed of the solar wind to show a substantial apparent deflection in the direction of its ion tail. That said, I think we are seeing a dust tail in these images, and the dust tail isn't affected by the solar wind, but by radiation pressure. That doesn't provide much force, so near the Sun we see the dust trail virtually in the same orbit as the comet, and not pointing away from the Sun much at all.
There certainly was a recent CME in the vicinity
however, the super-sonic solar wind is rather difficult to define closer than 10 solar radii:
http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/node3.html wrote:
Parker's solar wind model
<<Parker (1958) suggested that the corona could not remain in static equilibrium but must be continually expanding since the interstellar pressure cannot contain a static corona. The continual expansion is called the solar wind. The existence of a solar wind had been known from comet observations but the properties predicted by Parker were confirmed by the satellites Lunik III and Venus I in 1959 and by Mariner II in the early 1960s. The main assumptions of Parker's model are that the outflow is steady, spherically symmetric and isothermal. It is straightforward to relax the isothermal assumption and consider an adiabatic or polytropic atmosphere.
where
C is a constant.
Five distinct types of solutions for different values of
C are indicated. Solution I is doubled valued and so is unphysical. It is not possible for the plasma to leave the solar surface with a velocity below the sound speed, reach a maximum radius below
rc and then turn round and return to the Sun with a super-sonic speed. Solution II is also double valued but it never even starts from the solar surface and it is also unphysical. Solution III starts with a velocity greater than the sound speed but such a fast steady outflow is not observed. Hence, this solution must also be neglected. The only two types of solution that are physically reasonable at this stage are IV and V. Solution V is the particular case where the plasma leaves the solar surface with a particular speed and passes through the critical point (also called the sonic point) at
r = rc and
v = cs. Solution IV always remains below the sound speed and is called the solar breeze solution. For solution V we choose the constant
C so that
r = rc and
v = cs and this requires
C = -3. Is it possible to decide between solutions IV and V?
Assuming a typical coronal temperature of 10
6K the sound speed is
The real solar wind does not come from the whole of the solar surface but only from the coronal hole regions where the magnetic field is open. This is only about 20 percent of the whole surface. The strong magnetic field of the other 80 percent is closed and effectively holds in the hot corona.>>
[quote="Chris Peterson"][quote="neufer"][quote="Boomer12k"]
It is interesting that the tail does not point directly away from the sun....as is sometimes depicted in drawings and things...
:---[===] *[/quote]
At perihelion the comet was moving faster than the solar wind.[/quote]
More or less. The perihelion speed was 370 km/s. The densest solar wind has a speed of about 400 km/s, with faster winds from coronal holes about twice that. Material from CMEs can move in excess of 1000 km/s. Of course, the comet did not need to exceed the speed of the solar wind to show a substantial apparent deflection in the direction of its ion tail. That said, I think we are seeing a dust tail in these images, and the dust tail isn't affected by the solar wind, but by radiation pressure. That doesn't provide much force, so near the Sun we see the dust trail virtually in the same orbit as the comet, and not pointing away from the Sun much at all.[/quote]
[c]There certainly was a recent CME in the vicinity :!:
however, the super-sonic solar wind is rather difficult to define closer than 10 solar radii:[/c]
[quote=" http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/node3.html"]
[float=right][img3="[b][color=#0000FF][size=115]Super-sonic solar wind Parker solution V as a function of radiu[/size]s[/color][/b]
[img]http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/img60.gif[/img]"]http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/img51.gif[/img3][/float]Parker's solar wind model
<<Parker (1958) suggested that the corona could not remain in static equilibrium but must be continually expanding since the interstellar pressure cannot contain a static corona. The continual expansion is called the solar wind. The existence of a solar wind had been known from comet observations but the properties predicted by Parker were confirmed by the satellites Lunik III and Venus I in 1959 and by Mariner II in the early 1960s. The main assumptions of Parker's model are that the outflow is steady, spherically symmetric and isothermal. It is straightforward to relax the isothermal assumption and consider an adiabatic or polytropic atmosphere.
[img]http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/img50.gif[/img]
where [b][i]C[/i][/b] is a constant.
Five distinct types of solutions for different values of [b][i]C[/i][/b] are indicated. Solution I is doubled valued and so is unphysical. It is not possible for the plasma to leave the solar surface with a velocity below the sound speed, reach a maximum radius below [b]r[sub]c[/sub][/b] and then turn round and return to the Sun with a super-sonic speed. Solution II is also double valued but it never even starts from the solar surface and it is also unphysical. Solution III starts with a velocity greater than the sound speed but such a fast steady outflow is not observed. Hence, this solution must also be neglected. The only two types of solution that are physically reasonable at this stage are IV and V. Solution V is the particular case where the plasma leaves the solar surface with a particular speed and passes through the critical point (also called the sonic point) at [b]r = r[sub]c[/sub][/b] and [b]v = c[sub]s[/sub][/b]. Solution IV always remains below the sound speed and is called the solar breeze solution. For solution V we choose the constant [b][i]C[/i][/b] so that [b]r = r[sub]c[/sub][/b] and [b]v = c[sub]s[/sub][/b] and this requires [b][i]C[/i][/b] = -3. Is it possible to decide between solutions IV and V?
Assuming a typical coronal temperature of 10[sup]6[/sup]K the sound speed is
[img]http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/img60.gif[/img]
[img]http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/img59.gif[/img]
The real solar wind does not come from the whole of the solar surface but only from the coronal hole regions where the magnetic field is open. This is only about 20 percent of the whole surface. The strong magnetic field of the other 80 percent is closed and effectively holds in the hot corona.>> [/quote]