The AAT and the Schmidt are on Siding Spring Mountain, also called Mount Woorut, 28km by road from Coonabarabran. Figure 1.1 shows the location of Coonabarabran within south-eastern Australia, while Figure 1.2 shows the vicinity of the Observatory. The Warrumbungle National Park has some of the most attractive scenery in Australia and contains a selection of native flora and fauna including a large population of kangaroos , some koalas, echidnas and emus. Astronomers should consider spending extra time in the area to recuperate after their observing session. Coonabarabran itself offers a range of inexpensive motels, while bushwalkers and campers are well catered for in the park.
Figure 1.1: South-Eastern New South Wales in colour of black-and-white.
(Click on one the images for larger versions)
Figure 1.2: The Coonabarabran area
Figure 1.3: Siding Spring Observatory
The Siding Spring mountain top is run by the Australian National University (ANU) through the Mount Stromlo and Siding Spring Observatories (MSSSO). A general plan of the mountain is shown in Figure 1.3. The ANU-operated Lodge, where astronomers normally stay while observing, is described in more detail in § 1.8.5.
The time difference is such that NSW is ahead of the UK by:
Eastern Standard Time - British Summer Time
Eastern Standard Time - UTC
Eastern Daylight-Saving Time - UTC
The geodetic coordinates of the AAT relative to the Australian National
Spheroid (a= 6378.160km, e2=0.00669454)
|Longitude||149:03:57.91 = 9h56m15.861 East|
The declination axis, at hour-angle zero, is 1164m (3819ft) above sea level and 29.5m (97ft) above ground floor level.
The coordinates of the Schmidt are:
|Longitude||149:04.2 = 9h56m17 East|
The weather on Siding Spring is not very seasonal, and is roughly 40% photometric and 65% usable. Figure 1.4 shows the fraction of usable time for each month, averaged over the past 15 years. Although this suggests slightly poorer weather in winter (May-August) than in summer, it is important to note that the variation from one year to the next is much greater than the difference in the month-to-month averages, as may be seen from Figure 1.5. Also, since the winter nights are longer, there may be more useable hours of observing time in June/July than in December/January.
Figure 1.4: Average fraction of clear time per month
Figure 1.5: Fraction of clear time per year for 1976-90
Figure 1.6: AAT seeing measurements over a five-year period
The temperature in the control room is always about 19°C. In the dome it varies from roughly 22°C to 0°C depending on outside conditions. Outside, the maximum daily temperature varies seasonally from about 5°C to 30°C. Apart from padded clothing for prime focus work, warm clothes are not &endash;provided.
From both the AAT and Schmidt records, the seeing is usually in the range 1"&endash;3". Figure 1.6 shows a histogram of the seeing measurements recorded by AAT night assistants at the start, middle and end of each night over the five years 1984-1988.
The median seeing recorded at the AAT over this period was 1.8±0.05" FWHM, with no significant change from year to year. There is also little or no seasonal variation - the median was 1.7±0.1" for the best month (April) and 1.9±0.1" for the worst month (February).
There is, however, a significant deterioration in seeing over the course of a typical night. The median seeing recorded at the beginning, middle and end of the night is 1.6±0.1", 1.8±0.1"and 2.1±0.1" respectively. This may be associated with a trend for the seeing to worsen when the air in the dome is colder than the mirror, which usually happens later in the night as the air temperature drops.
As yet, we do not know whether this is an outside effect (i.e. a sharp drop in temperature generally accompanies weather conditions which cause the outside seeing to deteriorate), or whether the poor seeing arises within the dome as a result of turbulence at the interface between the warm mirror and the cold dome air. Further tests are in progress.