How Well Do You Know Shade? The Quiz
Twelve questions on where the sun is, what shade really blocks and how to keep it off your house, from which wall gets the hottest afternoon to what UPF 50 means. Every answer comes with the reason and the source it comes from, and your score at the end is yours to share.
Take the quiz
Twelve questions, one at a time. Pick an answer and you see at once whether you were right, why, and where the figure comes from.
The west side. In the afternoon the sun is in the west and low enough to strike a wall or window almost square on. On 21 June in London the sun is on a west-facing wall from about 1:05 pm until it sets at about 9:20 pm (this site's garden aspect tool works it out for any place).
The US Department of Energy's figures point the same way: awnings can cut summer solar heat gain by up to 65% on south-facing windows and up to 77% on west-facing ones (DOE Energy Saver, window treatments, archived 2018), and passive solar designers list too little shading in the hot season, "especially on the West wall", among the common faults (Wikipedia, passive solar building design).
Read next: shading windows to cut cooling costs, or draw your own wall's shade.
So the cloth twists. With one pair of opposite corners high and the other pair low, the sail takes a saddle shape, and ShadeSails.com says a twisted shape is preferred "when possible" because it "imparts a 3rd dimension of tension into the membrane", while "flat 2 dimensional sails tend to concentrate forces at the corners and edges." A flat sail also holds rain: it asks for a slope of at least 1 in 4 so the water runs off, and warns that too little slope causes puddling and sag (ShadeSails.com, design parameters).
Coolaroo gives a rule for how much: the high corners should be at least 16% of the longest side above the low ones, which for a 5 m (16 ft 5 in) sail is 0.8 m (about 2 ft 8 in) (Coolaroo shade sail installation guide, 2026).
Read next: how to install a shade sail, or plan your own sail.
98%. The Skin Cancer Foundation's example is that a UPF 50 fabric blocks 98 percent of the sun's rays and lets two percent (one fiftieth) through. It rates UPF 30 to 49 as very good protection and UPF 50+ as excellent (Skin Cancer Foundation, sun-protective clothing).
The rating was built for clothing. How much UV reaches you under a shade sail also depends on the sky and the ground around it: the next questions come back to that.
Read next: the outdoor fabric comparer, and the types of awning.
14° or steeper. markilux says water droplets pick up dirt and run off its awning covers, a self-cleaning effect, as long as the awning is set at a pitch of at least 14° (markilux patio and balcony awnings brochure). The same brochure says the integral gutter of one model assures water drainage from a pitch of only 5°, so water can leave a flatter awning; it is the self-cleaning that needs the 14°.
For scale, a 14° pitch rises about 1 foot in every 4 feet of projection (tan 14° is 0.249), the same 1 in 4 that ShadeSails.com asks of a sail.
Read next: retractable or fixed awnings, or size an awning's projection and pitch.
The sum is the standard one: near solar noon the sun's angle from straight overhead is the latitude minus the sun's declination, and the declination swings between +23.44° at the June solstice and −23.44° at the December one (Wikipedia, sun path). The solstice falls on 21 June in 2026 (US Naval Observatory). The sun is only straight overhead between the tropics.
Read next: how the sun moves across your garden, or see the sun's path at your place.
About 2.5 times as heavy. Shademaker's minimum base for its 9 ft (2.7 m) Libra center-pole umbrella is 120 lb (54 kg); for its 9 ft (2.7 m) Solaris cantilever umbrella it is 300 lb (136 kg). A cantilever's canopy hangs out to one side and levers against the base, so the weight has to rise with it (Shademaker Libra, Shademaker Solaris).
These are one maker's minimums for free-standing umbrellas, so check your own umbrella's manual. Shademaker also says no umbrella, regardless of size or weight, should be left open and unattended (Shademaker support).
Read next: how to choose a patio umbrella, or work out your canopy and base.
The color goes into the fiber before it is spun into yarn. Sunbrella describes its fibers as "saturated with color and UV-stabilized pigments before they're spun into yarn", so the pigment goes all the way through the fibers and the color stays true over time (Sunbrella, the fabric difference). Olefin is made the same way, with the color added to the polymer before it is spun (American Fiber Manufacturers Association, olefin).
Cloth dyed after it is woven carries its color nearer the surface. Polyester can be made either way, and the maker's page on polyester gives no fade figure (American Fiber Manufacturers Association, polyester), so for a polyester awning ask whether it is solution-dyed and for the fade test result.
Read next: the fabric comparer, and how to clean an awning.
The awning outside. The Department of Energy says window awnings can reduce solar heat gain in summer by up to 65% on south-facing windows and 77% on west-facing windows, while a completely closed, highly reflective interior blind on a sunny window can reduce heat gain by around 45% (DOE Energy Saver, window treatments, archived 2018; the page has since left energy.gov's address, so this is the archived copy).
The reason is where the sun is stopped. Shade outside the glass keeps the sunlight from reaching the glass at all; a blind inside lets it pass the window first and can only turn some of it back out. Those are the department's "up to" and "around" figures for ideal cases, not a promise for your window.
Read next: shading windows to cut cooling costs, or estimate your window's heat gain.
North. Sydney is at 33.9° S, south of the Tropic of Capricorn (about 23.4° S), and Wikipedia's page on the sun's path states the rule: south of the Tropic of Capricorn the noon shadow always points south, which means the sun is always in the north (Wikipedia, sun path). The sun is never overhead there. Worked with NOAA's solar equations (NOAA), it stands about 80° high in the north at noon on 21 December and about 33° high in the north on 21 June.
So in Sydney, Auckland or Cape Town (all between 34° and 37° S) a north-facing wall gets the midday sun, the way a south-facing one does in the US and UK.
Read next: shade for hot climates, or find which way your garden faces.
60% to 90%, for well-designed and well-placed shade. SunSmart says shade can be an effective form of sun protection, with UV exposure cut by that much, but UV is also scattered by particles in the air and reflected off surfaces, so how much sky you can see and what the ground is made of both matter (SunSmart, shade comparison check). Cancer Council Australia agrees that shade reduces UV but it can still reach you by reflection, so use it with a hat, sunscreen and sunglasses (Cancer Council, Be SunSmart).
Read next: the UV index and time in the sun guide, and shade for hot climates.
The winter sun is low. At noon in London the sun stands about 15° above the horizon on 21 December and about 62° on 21 June (90° minus the latitude, plus or minus 23.4°, worked with NOAA's equations). A ray that just skims the front edge of an awning 8 ft (2.4 m) above the ground comes down 4.3 ft (1.3 m) beyond that edge's footprint in June, but 29.9 ft (9.1 m) beyond it in December. No normal awning is deep enough to catch that, so the winter sun walks in under it and reaches the wall and the window.
On a sun-facing wall that is often what you want. Passive solar designers rely on it: the low midday winter sun readily admits light and warmth, and a well-designed overhang may be all that is needed to shade the glass in summer (Wikipedia, passive solar building design).
Read next: retractable or fixed awnings, or size an awning for your wall.
Around solar noon. The World Health Organization says the day's maximum UV level occurs in the four-hour period around solar noon, which falls between noon and 2 p.m. depending on where you are and whether daylight saving time applies (WHO, the UV index). In London on 21 June solar noon is at about 1:02 pm British Summer Time.
The EPA's rule of thumb is that the sun's UV rays are strongest between 10 a.m. and 4 p.m. (EPA, sun safety tips), and it adds a check you can make without a forecast: if your shadow is shorter than you are, the UV is high (EPA, UV index scale).
Read next: the UV index and time in the sun guide, and how the sun moves across your garden.
What the quiz covers
The questions run from the sun itself to the things people buy to shade from it: the hottest wall, the noon sun's height where you live, a shade sail's shape, an awning's pitch and the cloth it is made of, an umbrella's base, what a window blind does against an awning, and what shade does and does not do to ultraviolet light. Each has one answer that a maker, a standards body, a health agency or the sun's own geometry supports. Where an answer is one maker's rule or an "up to" figure, the explanation says so.
The fifth question is worked out for your own place: pick a city (or use your location) and the options are the sun's height there. Nothing is sent anywhere, the quiz works offline once the page has loaded, and your best score stays in your browser.
The twelve questions and where each answer comes from
| # | Question | Answer | Source |
|---|---|---|---|
| 1 | Hottest afternoon sun | The west side | Awnings cut summer heat gain by up to 77% on west windows against 65% on south (DOE); passive solar design |
| 2 | Why a sail's corners differ in height | The cloth twists, which sheds rain and spreads the load | ShadeSails.com; Coolaroo |
| 3 | What UPF 50 blocks | 98% | Skin Cancer Foundation |
| 4 | Awning pitch and rain | 14° or steeper for the cover to rinse itself | markilux brochure |
| 5 | The noon sun's height | 90° − |latitude − declination| | Wikipedia, sun path; NOAA; USNO |
| 6 | Umbrella base weights | A 9 ft cantilever needs 300 lb (136 kg), a 9 ft center pole 120 lb (54 kg) | Shademaker Solaris and Libra |
| 7 | Solution-dyed fabric | The color goes into the fiber before it is spun | Sunbrella; AFMA |
| 8 | Window shade outside or inside | An awning outside: up to 65% to 77%, against about 45% for a closed reflective blind | DOE Energy Saver (archived) |
| 9 | Sydney's noon sun | In the north, all year | Wikipedia, sun path; this site's NOAA-based sums |
| 10 | Shade and UV | Well-designed shade cuts UV by 60% to 90%, not all of it | SunSmart; Cancer Council Australia |
| 11 | Winter sun under an awning | It is low, so its rays slip in under the front edge | This site's NOAA-based sums; passive solar design |
| 12 | When UV peaks | Around solar noon | WHO; EPA |
The sun at noon where you live
Question 5 is the one worth remembering, because it explains most of the others. At solar noon the sun is due south of you if you live north of the Tropic of Cancer and due north if you live south of the Tropic of Capricorn, and its angle from straight overhead is the difference between your latitude and the sun's declination, the latitude at which the sun is overhead that day. Wikipedia puts it as the zenith angle being the absolute value of latitude minus solar declination near solar noon, so the sun's height above the horizon is 90° minus that. The declination runs from +23.44° at the June solstice, 21 June in 2026 by the US Naval Observatory, through 0° at the equinoxes to −23.44° at the December solstice.
London is at 51.5° N, so on 21 June the sun is 90° − |51.5° − 23.4°| = 61.9° high, on the equinoxes 90° − 51.5° = 38.5° and on 21 December 90° − |51.5° + 23.4°| = 15.1°. Sydney, at 33.9° S, takes the latitude as negative: on 21 June it is 90° − |−33.9° − 23.4°| = 32.7°, and the sun stands in the north. The table gives the heights at solar noon, worked out by this site's sun maths, which uses NOAA's solar position equations and includes the small lift the atmosphere gives the sun.
| Place | 21 Dec | 20 Mar | 21 Jun |
|---|---|---|---|
| London (51.5° N) | 15° | 38° | 62° |
| New York (40.7° N) | 26° | 49° | 73° |
| Sydney (33.9° S) | 80° | 56° | 33° |
The low December sun in London is why question 11's answer is what it is. A ray that just skims the front edge of an awning 8 ft (2.4 m) above the ground comes down h ÷ tan(altitude) beyond the edge: 8 ÷ tan 62° = 4.3 ft (1.3 m) in June, but 8 ÷ tan 15° = 29.9 ft (9.1 m) in December. In summer a deep awning shades the ground; in winter the sun goes in under it. The awning size calculator works this through for your own wall.
Where the answers stop being facts
Some of the answers rest on one source and are worth treating that way. The Department of Energy's 65%, 77% and 45% are "up to" and "around" figures for good cases, and we could not find the page they come from at its old energy.gov address, so the quiz links the Internet Archive's copy of it, taken in January 2018. markilux's 14° is that maker's figure for its covers. Shademaker's base weights are its own minimums for its own umbrellas. SunSmart's 60% to 90% is a range for well-designed shade, and how much UV reaches you depends on the sky you can see and the ground around you. The explanations after each answer say which kind of figure it is.
For the same reason the quiz does not give a "how much will I save" or "how many minutes until I burn" figure: those depend on your window, your skin and your day. For those, use the window heat tool and the UV index guide, which show their working.
If you want to read more
How the sun moves across your garden explains the noon height, the sunrise and sunset points and why the shade moves. Shade sail, awning or pergola sets the three side by side, types of awnings and what they cost and retractable versus fixed awnings cover the awning questions, and how to install a shade sail the twist and the fall. For umbrellas, how to choose a patio umbrella; for cloth, how to clean an awning and how to clean outdoor fabric. For windows, shading windows to cut cooling costs; for heat, shade for hot climates, the louvered pergola guide and the best shade for a south-facing garden.
Sources: US Department of Energy, Energy Saver: energy efficient window treatments (Internet Archive copy, 17 January 2018); Skin Cancer Foundation, sun-protective clothing; ShadeSails.com, design parameters; Coolaroo shade sail installation guide; markilux, patio and balcony awnings brochure; Shademaker Libra, Solaris and support; Sunbrella, the fabric difference; American Fiber Manufacturers Association, olefin and polyester; SunSmart, shade comparison check; Cancer Council Australia, Be SunSmart; WHO, the UV index; EPA, sun safety tips and UV index scale; Wikipedia, sun path and passive solar building design; NOAA Global Monitoring Laboratory, solar calculator details; US Naval Observatory, seasons for 2026. The noon heights, the awning rays and the ratios are this site's own sums from those sources, tested in the page's test file. All pages read on 19 October 2026.