Longitude

About: Longitude is a research topic. Over the lifetime, 2260 publications have been published within this topic receiving 54988 citations. The topic is also known as: angle of longitude.

Emission characteristics and source location of the smooth Neptunian kilometric radiation

Abstract: The observations of the planetary radio astronomy (PRA) experiment aboard Voyager 2 reveal the existence of smooth and bursty radio emission. Both recur in a rather regular pattern with a 16.1-hour period (the Neptunian spin period). We describe the phenomenology of the smooth component in terms of frequency, polarization, and occurrence in magnetic longitude and latitude. The existence of both right-handed and left-handed polarized emissions is consistent with two sources (one in each hemisphere) which radiate independently in the TUX mode. Because Voyager passed Neptune at less than 5000 km from the surface at high northern magnetic latitudes, the radio sources were occulted by the planet near the encounter. We have taken advantage of this occultation to locate the northern hemisphere sources by calculating the radio horizon (based on the offset tilted dipole (OTD2) model) for two spacecraft positions close to the encounter. We find that the northern source is located at high magnetic latitudes δm > 40°. By using a geometrical beaming model which assumes emission in a hollow cone pattern we fit the observed PRA intensity profile. The best fit is obtained for a radio source at L=6, thus confirming δm > 40°. The longitudinal extent of the source is at least 180°, from −90° to +90° magnetic longitude. To locate the southern sources we use the large excursions of Voyager 2 to high southern magnetic latitudes. The source is found to be located also at high magnetic latitudes but is possibly more limited in longitude than the northern source. We estimate the uncertainty in source location due to the very limited knowledge of the magnetic field near the Neptunian surface, and we show that the current OTD2 model is satisfactory for the source locations for the lowest observed frequencies; however, an angular uncertainty of about 20° remains for sources in the northern hemisphere. The observed pattern of the smooth emission is strongly frequency dependent, which is in agreement with the azimuthal asymmetries of the magnetic field as predicted by the OTD2 model.

Preliminary analysis of the IRAS solar system dust data

Abstract: The structure of the solar system dust cloud as revealed by IRAS all-sky survey data is discussed Fourier analysis was used to separate the smooth, large-scale zodiacal background from the narrower dust lanes The geometry of the background zodiacal cloud appears to show features associated with both the forced inclinations and the forced eccentricities of the dust particle orbits The ecliptic latitude of the peak of the background zodiacal emission varies nearly sinusoidally with ecliptic longitude with an amplitude of 21 + or -02 degrees However, there are marked displacements, both in latitude and longitude, between the leading or ascending curve and the trailing or descending curve, implying that the curves exhibit significant deviations from a simple sinusoidal variation It is suggested that the plane of symmetry of the background cloud is inclined to the ecliptic by 147 + or -010 degrees with a descending node of 230 + or -4 degrees, and that the sun is not at the center of symmetry of the cloud