Thanks, Art. I think I understand, at least in general terms, the concept of "peculiar velocity" (and I don't necessarily think that the solar peculiar velocity is exactly "peculiar"). I don't understand, however, what the (U_o,V_o,W_o)=(8.9,10.3,6.8)\pm(0.6,1.0,0.4) km/s means.
I understand what it means, more or less, that
the circular rotation velocity of the solar neighborhood is |V_o|=252\pm14 km/s)
That ought to mean, more or less, that the general rotational speed of things in the part of the galaxy where the Sun is located is, by and large, 252 km/second.
I don't, however, understand what it means that
the Galactic rotation parameters {\Omega}_o=-31.5\pm0.9 km/s/kpc, {\Omega}'_o=+4.49\pm0.12 km/s/kpc^2, {\Omega}"_o=-1.05\pm0.38 km/s/kpc^3, (the corresponding Oort constants are A=17.9\pm0.5 km/s/kpc, B=-13.6\pm1.0 km/s/kp
I have heard about spiral density waves. I don't know if I really understand what they are, except that I think they are a product of the rotation of the galaxy and that the spiral density waves are responsible for piling up matter in such a way that we get spiral arms. But I don't understand what it means that
the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f_R = -12.5\pm1.1 km/s and f_{\theta}=2.0\pm1.6 km/s
I understand, more or less, what the pitch angle for the spiral pattern means. It has to do with how much the spiral arms "flare out" from a bar structure, or how tightly they are "drawn towards" the bar structure. I think the pitch angle has to do with the mass of the black hole in the in the center of the galaxy, which is of course hugely interesting. Take a look at this image of NGC 5247 by Adam Block and Tom Boerner and David Young:
The arms seem to "flare out" quite a lot, which suggests to me that the black hole in the center of this galaxy isn't very massive.
But take a look at this Adam Block image of NGC 1300:
The black hole seems to exert a strong pull on the spiral arms, preventing them from "flaring out".
What about the pitch angle of the Milky Way's spiral arms? How much do they "flare out? What does it mean that
the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f_R = -12.5\pm1.1 km/s and f_{\theta}=2.0\pm1.6 km/s
And what does it mean that
the Sun's phase in the spiral wave {\chi}_o=-91\pm4 degrees.
Ann
Thanks, Art. I think I understand, at least in general terms, the concept of "peculiar velocity" (and I don't necessarily think that the solar peculiar velocity is exactly "peculiar"). I don't understand, however, what the (U_o,V_o,W_o)=(8.9,10.3,6.8)\pm(0.6,1.0,0.4) km/s means. :?:
I understand what it means, more or less, that [quote]the circular rotation velocity of the solar neighborhood is |V_o|=252\pm14 km/s)[/quote]
That ought to mean, more or less, that the general rotational speed of things in the part of the galaxy where the Sun is located is, by and large, 252 km/second. :!:
I don't, however, understand what it means that
[quote]the Galactic rotation parameters {\Omega}_o=-31.5\pm0.9 km/s/kpc, {\Omega}'_o=+4.49\pm0.12 km/s/kpc^2, {\Omega}"_o=-1.05\pm0.38 km/s/kpc^3, (the corresponding Oort constants are A=17.9\pm0.5 km/s/kpc, B=-13.6\pm1.0 km/s/kp[/quote]
:?:
I have heard about spiral density waves. I don't know if I really understand what they are, except that I think they are a product of the rotation of the galaxy and that the spiral density waves are responsible for piling up matter in such a way that we get spiral arms. But I don't understand what it means that
[quote]the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f_R = -12.5\pm1.1 km/s and f_{\theta}=2.0\pm1.6 km/s[/quote]
:?:
I understand, more or less, what the pitch angle for the spiral pattern means. It has to do with how much the spiral arms "flare out" from a bar structure, or how tightly they are "drawn towards" the bar structure. I think the pitch angle has to do with the mass of the black hole in the in the center of the galaxy, which is of course hugely interesting. Take a look at this image of NGC 5247 by Adam Block and Tom Boerner and David Young:
[img]http://www.noao.edu/outreach/aop/observers/n5247youngs.jpg[/img]
The arms seem to "flare out" quite a lot, which suggests to me that the black hole in the center of this galaxy isn't very massive.
But take a look at this Adam Block image of NGC 1300:
[img2]http://www.spiral-galaxies.com/Pictures/Eridanus/pictures-ngc-1300.jpg[/img2]
The black hole seems to exert a strong pull on the spiral arms, preventing them from "flaring out".
What about the pitch angle of the Milky Way's spiral arms? How much do they "flare out? What does it mean that [quote]the spiral density wave parameters, namely: the perturbation amplitudes for the radial and azimuthal velocity components, respectively, f_R = -12.5\pm1.1 km/s and f_{\theta}=2.0\pm1.6 km/s[/quote] :?:
And what does it mean that [quote]the Sun's phase in the spiral wave {\chi}_o=-91\pm4 degrees.[/quote] :?:
Ann