Right ascension

The instrument, which is placed at the telescope focal plane, consists of optics and a detector to measure the light. As depicted in Fig. 2, the instrument attempts to measure a three-dimensional data cube - intensity as a function of wavelength (A) and two spatial dimensions on the sky (right ascension and dechnation). 

Figure 2. Three-dimensional data cube that is probed by an astronomical instmment the intensity is a function of two spatial directions on the sky (right ascension and declination - analogous to longitude and latitude) and the wavelength dimension.

On the other hand ARCHEOPS only scanned around a circle of constant elevation and then let the center of the circle move in right ascension as the Earth turned. This provides only a two way modulation. Since the sky itself is a two dimensional function, just about any time history of drifting baselines is consistent with some pattern on the sky. Thus ARCHEOPS is very vulnerable to striping. This can be seen in the last panel of Figure 2 of astro-ph/0310788 (Hamilton et al., 2003) which clearly shows correlated residuals aligned with the scan path. These stripes have a low enough amplitude to not interfere with measurements of the temperature-temperature angular power spectrum CjT, but they would ruin a measurement of the polarization power spectrum CfE. 

Figure 5. Sky map (4 year data) plotted in coordinates of right ascension and declination overlaid with observed events (+ symbols). The scale on the right reflects excess or deficit in terms of standard deviation with respect to the mean background events.

Figure 1. The sky map of the events excess. The Declination and Right Ascension axes have been reconstructed (the two axes in the map), by means of the reference stars. In the sky map it is evident a maximum, located at the NE region of the SN 1006 remnant shell (The SN1006 shell is represented with the black double ellipse).

The development of the tidal potential of the moon and sun is given, for example, by Bartels and Hom (1952). The potential is expressed in a geocentric coordinate system and depends on the location (2, tp) and on the time-dependent quantities distance r, declination <5 and right ascension a. 

The equation of time is the difference of right ascension between the average and apparent sun, and caused by the fact that the movement of the sun in a day shifts east and west since the revolution angular velocity of the earth is different by season due to the elliptical orbit and the declination of the earth s axis from the celestial equator by 23° 27. ... 

Let us discuss the latter coordinate systems first. They are of two distinct varieties the apparent places and the orbital. The apparent places (AP) and its close relative, the right ascension (RA) coordinate systems, are the ones in which (angular) coordinates of stars are published. The orbital coordinate systems (OR) are designed to be used in describing satelhte positions and velocities. The relations between these systems and with the systems introduced below will be discussed in Section ILF. Interested readers can learn about these coordinate systems in Vam dek and Krakiwsky (1986, Chap. 15). 

Fig. 1. A FT-band image of the field surrounding the quasar 3C 345. North is up and east to the left and the mosaic extends over 180 in declination and 168 in right ascension. The numbers identify the objects listed in Table 1.

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