Places · Observatory
Siding Spring Observatory
Australia's main optical site, and the base for southern sky surveys that catch supernovae and near-Earth objects before anyone else is looking.
- Where
- New South Wales, Australia
- Coordinates
- 31.27°S 149.06°E
- Since
- 1965
- On the map
- Show me
- More
- aao.gov.au
The sky from here
This is a zone 1 sky — pristine on the nine-grade scale, Bortle 1–2, reaching roughly magnitude 7.2–8.0 unaided. The Milky Way casts a shadow. Airglow is visible, the zodiacal light reaches across the sky, and the darkest places on Earth look like this.
That grade puts 107 of the catalogue within easy reach of 10×50 binoculars and 107 within a 130mm — 58 of them need no instrument at all. There is nowhere darker worth driving to; this is already among the better skies on the planet.
There is no season here in which the sky fails to get properly dark — the Sun clears eighteen degrees below the horizon on all 365 nights.
The centre of the galaxy climbs to 88° at its best — high enough that the summer Milky Way is genuinely three-dimensional rather than a band low in the south. Of the 110 Messier objects, none are circumpolar and 4 never rise.
Of everything in the catalogue, Butterfly Cluster, Southern Pinwheel and Ptolemy's Cluster are the best served here, climbing to within a few degrees of straight up — an object at the zenith is being seen through the least air it will ever be seen through, and the difference against the same object low in the south is not subtle.
Against that, Bode's Galaxy and Cigar Galaxy never clear the horizon here at all. No amount of aperture or patience changes that; the only remedy is to travel.
Read at 31.27°S 149.06°E. Darkness is estimated rather than measured; everything else follows from the latitude and holds along the whole parallel. How accurate this is.
Nearby
Questions
What part of the sky never rises at Siding Spring Observatory?
Everything north of declination +59°. From 31.3°S that is a cap 31° in radius centred on the north celestial pole, which is 7.3% of the whole celestial sphere. Nothing about the calendar or the aperture changes that — the cap is below the horizon at every hour of every night. Its mirror image, the same 7.3% around the south celestial pole, is circumpolar here and never goes down.
How many hours of true darkness does Siding Spring Observatory get?
11 hours on the best night, around 21 June, falling to 6 hours 31 minutes around 21 December. The measure is astronomical darkness — the Sun a full eighteen degrees under — not simply the hours between sunset and sunrise. Every night of the year gets there eventually, which is the quiet advantage of not being any further from the equator than this.
When is the Milky Way best from Siding Spring Observatory?
June and July, and the timing is the whole point. The core transits at midnight around 17 June everywhere, but at 31.3°S that is the depth of winter: the longest nights of the year, sitting underneath the galaxy at its highest. Northern sites get the same transit date during their shortest and least dark nights. It is the single biggest structural advantage a southern observatory has.
How far is Siding Spring Observatory from the other sites on this map?
Its closest neighbour on this map is Warrumbungle National Park, 5.8 km away to the west. The nearest other observatory is Murriyang — the Parkes dish, 206 km to the south. Distances are great-circle, so they are what a signal covers rather than what a road does.