By Julia · weather-au.com editorial team · Published · 4 min read
Australians talk about sun protection constantly, and with reason, but the usual advice is pitched at hot days. The thermometer is the wrong instrument. Ultraviolet radiation follows the height of the sun, not the heat of the air, and a bright 15 °C day in Hobart in October carries more ultraviolet than the temperature suggests. This article lays out the numbers behind that: the midday sun height in ten cities, the hours of sunshine each receives, and one count that explains why spring catches people out.
We did not compute a UV index. The ERA5 archive we use carries no UV, and a modelled index would be a guess. What we computed is the part that is plain geometry (the height of the midday sun) and what the reanalysis records about sunshine duration. Our guide to UV and sun safety covers the scale itself and the official advice.
One: the sun's height is set by latitude
On a given day the midday sun stands at 90° minus the distance in latitude between you and the point where the sun is overhead. On 21 December that point is on the Tropic of Capricorn, 23.4° south; on 21 June it is 23.4° north; at the equinoxes it is on the equator.
| City | Latitude (°S) | Midday sun, 21 December (°) | Midday sun, equinoxes (°) | Midday sun, 21 June (°) |
|---|---|---|---|---|
| Darwin | 12.5 | 79 | 78 | 54 |
| Cairns | 16.9 | 83 | 73 | 50 |
| Alice Springs | 23.7 | 90 | 66 | 43 |
| Brisbane | 27.5 | 86 | 63 | 39 |
| Perth | 31.9 | 81 | 58 | 35 |
| Sydney | 33.9 | 80 | 56 | 33 |
| Adelaide | 34.9 | 79 | 55 | 32 |
| Canberra | 35.3 | 78 | 55 | 31 |
| Melbourne | 37.8 | 76 | 52 | 29 |
| Hobart | 42.9 | 71 | 47 | 24 |
Calculated from latitude and the solar declination at the solstices (±23.44°) and equinox (0°); the editors' calculation, no measurement.
The range is wide. On 21 December the midday sun is at 90° at Alice Springs (89.7°, to be exact, since the town lies just south of the Tropic of Capricorn), 86° in Brisbane, 83° in Cairns, 80° in Sydney and 71° in Hobart. On 21 June it drops to 54° in Darwin, 39° in Brisbane, 33° in Sydney, 29° in Melbourne and 24° in Hobart. The difference between Hobart's June and Darwin's June is 30°.
Two: a year of midday sun
DarwinBrisbaneSydneyMelbourneHobart
Calculated from the latitude and the solar declination (standard formula); the editors' calculation, no measurement.
Darwin never gets below 54°, and it reaches 87° on 15 October and 89° on 15 February. Further south, the winter dip is steep. Hobart's midday sun is below 30° in May, June and July (28°, 24° and 26° on the 15th). Melbourne's is below 30° in June alone (29°). The climb is fast: Hobart's midday sun is at 33° on 15 August, 45° on 15 September and 66° on 15 November.
Three: hours of sun
The reanalysis gives a duration of sunshine for each day. Averaged over 2016 to 2025, the annual total is 3,946 hours in Perth, 3,776 in Darwin, 3,754 in Brisbane, 3,594 in Sydney, 3,355 in Melbourne and 3,238 in Hobart. These are model values, higher than the totals recorded by sunshine instruments at weather stations, so use them to rank cities and months and not as official figures.
| Month | Darwin | Brisbane | Sydney | Perth | Melbourne | Hobart |
|---|---|---|---|---|---|---|
| January | 8.3 | 11.6 | 10.8 | 12.7 | 11.1 | 11.4 |
| February | 8.5 | 10.4 | 10.4 | 12.3 | 11.1 | 10.3 |
| March | 9.5 | 9.6 | 9.5 | 10.9 | 9.7 | 9.0 |
| April | 10.4 | 10.2 | 9.5 | 10.1 | 8.5 | 7.9 |
| May | 10.8 | 9.1 | 8.7 | 9.0 | 7.4 | 6.8 |
| June | 10.8 | 9.0 | 8.3 | 8.4 | 6.9 | 6.2 |
| July | 10.9 | 8.9 | 8.7 | 8.4 | 6.9 | 6.9 |
| August | 11.1 | 10.0 | 9.0 | 9.5 | 8.0 | 7.7 |
| September | 11.5 | 10.7 | 10.3 | 10.7 | 9.0 | 8.8 |
| October | 11.6 | 10.7 | 10.3 | 11.3 | 9.7 | 9.6 |
| November | 10.9 | 11.4 | 11.1 | 13.0 | 10.6 | 10.6 |
| December | 9.6 | 11.8 | 11.5 | 13.4 | 11.4 | 11.3 |
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editors.
DarwinSydneyMelbourneHobart
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editors.
The calendar differs from city to city. Perth is extreme in summer, with 13.4 hours a day in December against 8.4 in June. Darwin runs the other way: it is cloudier in the wet season (8.3 hours a day in January, 8.5 in February) than in the dry (11.1 in August, 11.6 in October). Hobart has the biggest seasonal gap of the cities in the table, 11.3 hours in December against 6.2 in June, about the same as Perth's 5 hours; Melbourne goes from 11.4 to 6.9 hours.
Four: why spring catches people out
By 15 October the midday sun stands at 62° in Melbourne and 57° in Hobart. That is higher than Sydney's midday sun in mid-April (47°). But the air in a southern spring is still cool. We counted the days in October and November on which the maximum stayed under 20 °C and the reanalysis gave at least 9 hours of sunshine.
| City | Cool, bright days a year (of 61) | Midday sun, 15 October (°) | Midday sun, 15 November (°) |
|---|---|---|---|
| Hobart | 30.8 | 57 | 66 |
| Adelaide | 23.2 | 65 | 74 |
| Melbourne | 22.4 | 62 | 71 |
| Canberra | 18.1 | 64 | 74 |
| Perth | 14.5 | 68 | 77 |
| Sydney | 6.2 | 66 | 75 |
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editors.
In Hobart that describes 30.8 of the 61 days in the two months on average, in Adelaide 23.2, in Melbourne 22.4, in Canberra 18.1, in Perth 14.5 and in Sydney 6.2. In other words, about half of the October and November days in Hobart are cool and bright, with the midday sun more than half-way to the zenith. They feel like a day for a jumper, not for sunscreen, and that is exactly the problem. The guide linked above explains why: the UV index measures radiation, not warmth.
The threshold (20 °C, 9 hours) is ours. It is a way of describing a type of day, not a safety limit.
Five: what to do with the numbers
- Look at the UV index, not the thermometer. The Bureau of Meteorology and the Cancer Council advise sun protection when it reaches 3. The geometry tells you when to expect that: in Hobart the midday sun is at 45° or higher on the 15th of every month from September to March. Check the index itself on the UV map.
- In Darwin, the habit is year-round. The midday sun never drops under 54°.
- In Hobart the midday sun is below 30° only from May to July, in Melbourne only in June. It does not stay that way: from August it climbs 9 to 12° a month in Hobart.
- Plan the day by the clock. The hours around solar noon carry most of the risk; see the guide.
For a place-by-place plan across the year, see when to visit Australia.
Period of the data cited: 2016–2025.