Astronomy Principles and Practice Fourth Edition.pdf

Observational radio astronomy 423
Figure 24.15. Position lines obtained from a morning observation and a transit of the Sun, allowing the observer’s
position to be determined.
The intercept is to be drawn in the direction 139 ◦ 23 ′ east of north, from the DRP, and its length
is 0·45 nautical miles (see figure 24.15).
The intersection of the position line obtained earlier with the position line obtained from the
observations of the meridian passage gives the position of the observatory in terms of latitude and
departure from the DRP.
From figure 24.15, the latitude is given by 55 ◦ 53·′7 and the departure is equal to 1·′51. Now the
difference in longitude is given by
This might be checked by using GPS.
difference in longitude = departure × sec φ
= 1·′51 × 1·78
= 2·′69.
Hence, the longitude is 4 ◦ 22 ′ − 2·′69
= 4 ◦ 19·′3W.
Summarizing:
λ = 4 ◦ 19·′3 W
φ = 55 ◦ 53·′7N.
24.4 Observational radio astronomy
Although most radio celestial objects require sophisticated instrumentation for their detection, it is
possible to undertake a couple of simple exercises with a satellite dish and a power meter. The detector
system is the kind used by professional satellite dish installers for orienting the collector to the best
direction in the sky. The equipment is also capable of detecting the solar output at 10 GHz.
The receiving dish should be set in a cradle in the form of an alt-azimuth mount with scales marked
in degrees. The supports can be made of wood with a large horizontal base carrying the azimuth scale
marked out in degrees. The size of the circular scale should be sufficient to allow the azimuth setting
to be read to an accuracy ∼1/2 ◦ . The scale should be fixed with N = 0 ◦ ,E= 90 ◦ ,S= 180 ◦ and
W = 270 ◦ . When setting out the equipment, the N direction may be established using a compass,
making allowance for the local magnetic deviation. Control of the altitude setting can be arranged by