Gegenschein

Figure 4. A CCD image of the Gegenschein, taken on 1st November 1997 at Hale Pohaku (2800 m, Hawaii) with a 10 min exposure time and a field of view of 101° x68°. The image was taken at the highest altitude of the Gegenschein (near the center of the frame). Our Galaxy is located on the left side, and airglow and atmospheric light at lower altitudes can be seen near the edge of the frame.

Figure 4. A CCD image of the Gegenschein, taken on 1st November 1997 at Hale Pohaku (2800 m, Hawaii) with a 10 min exposure time and a field of view of 101° x68°. The image was taken at the highest altitude of the Gegenschein (near the center of the frame). Our Galaxy is located on the left side, and airglow and atmospheric light at lower altitudes can be seen near the edge of the frame.

The Gegenschein is a faint patch of the ZL seen near the anti-solar direction. A comprehensive review of the observational history of the Gegenschein in the pre-CCD photometry era was given in [16]. The advantages of the CCD instrument are apparent when taking images of a faint and diffuse object, such as the Gegenschein. That is, CCD photometry of the Gegenschein can be obtained using shorter exposures than are required for conventional photography: compare the 50 s exposure of [4] or the 20 min one of [17] using CCD instruments, to the 1 hour exposure of [18] which required a photographic plate. In photoelectric observations of the Gegenschein, as reported by [19], the 2D-brightness distribution of the Gegenschein was deduced from a combination of data measured at different points, e.g. 5° intervals in ecliptic longitude and 3° intervals in ecliptic latitude, whereas CCD photometry can image a larger region of the sky in one exposure, i.e. 46°x31° [4], 98°x66° [17] (see 101°x68° in Figure 4).

The position of maximum brightness of the Gegenschein provides useful information on the spatial distribution of the zodiacal cloud beyond 1 AU. It is generally believed that the latitude of the Gegenschein shows a seasonal variation. Figure 5, cited from [17], shows considerable scatter, suggesting that the symmetry plane of the zodiacal cloud cannot be defined by one simple plane, such as the invariant plane of the Solar System. Furthermore, the existence of dust bands found in [5] in the region of the Gegenschein, described later, may cause such scattering of the observation results. Searches for seasonal variation in the position, size, shape and brightness distribution of the Gegenschein will be important scientific objectives for the new CCD instrumental].

Gegenschein Longitude (deg.)

Figure 5. The position of the maximum brightness of the Gegenschein cited from [17].

Gegenschein Longitude (deg.)

Figure 5. The position of the maximum brightness of the Gegenschein cited from [17].

Was this article helpful?

0 0

Post a comment