Same Clock, Different Sun: A Solar Offset Table for Eight Places
Does the western edge of a time zone cut sleep? A computed table of how far the sun trails the clock in Kashgar, Madrid, Indianapolis and five more places.
In this article12 sections
On the longest day of 2026, the sun sets over Kashgar, in the far west of China, at about 10:30 p.m. on the clock that appears on every train ticket and phone. On December 21 it rises at about 10:13 a.m. Both times are correct. They are also what happens when a city at 76 degrees east keeps the time of a meridian 44 degrees away. (Agreeing on which meridian counts was once a physical errand: for decades a Londoner named Ruth Belville carried Greenwich time to subscribers in a handbag.)
Kashgar is the extreme case of a common condition: a clock that runs ahead of the sky. Living in the western part of a time zone tends to push sleep and wake timing later relative to the clock, and in the best natural-experiment evidence it shortens sleep, by about 19 minutes for each additional hour of evening daylight (Giuntella and Mazzonna, Journal of Health Economics, 2019). That is a population average from U.S. data, and the rest of this piece is about how big the underlying gap is in different places and what the research can and cannot say about it.
The tool for this is a single number, defined below, computed for eight places and read against the published studies.
What is a solar offset, and how was it computed?
The solar offset is the clock time of local solar noon minus 12:00, in minutes, for a given place and date. Zero means the sun is highest at noon on the clock. A positive number means the sun runs late: at +120, solar noon arrives at 2:00 p.m. A negative number means the sun runs early.
Two things move the number. The first is geography and law: how far the city sits from the meridian its zone is built on, and whether the zone adds an hour for summer. Daylight saving time adds 60 minutes to the offset on the days it applies. The second is the equation of time, the slow drift of solar noon through the year caused by the tilt and ellipticity of Earth’s orbit. It swings the offset by roughly 30 minutes from its low in early November to its high in mid-February, the same drift that delays the latest sunrise of winter past the solstice. The table reports three views so neither effect hides the other: January 15, July 15, and the mean of all 365 days of 2026. Each date uses the clock actually in force in that place that day.
The computation uses the NOAA solar position equations in Python (the same formulas behind the NOAA solar calculator, built on Jean Meeus’s Astronomical Algorithms), with the standard 0.833 degree correction for refraction and the sun’s disk. As a check, the same code agreed to within a minute with the astral package for New York (December 21), Madrid and Indianapolis (June 21), and with published almanac figures: Madrid’s June 21 sunrise and sunset of 6:45 and 9:49 p.m., and Kashgar’s June sunset, which published tables put at 10:26 p.m. against 10:27 here. Elevation and local horizons are ignored, and each place is a point at a city center.
What does the table say?
| Place | Clock | Longitude | Jan 15 | Jul 15 | 2026 mean | Dec 21 sunrise | Jun 21 sunset |
|---|---|---|---|---|---|---|---|
| Kashgar, China | Beijing (UTC+8) | 76.0 E | +185 | +182 | +176 | 10:13 | 22:27 |
| Urumqi, China | Beijing (UTC+8) | 87.6 E | +139 | +136 | +130 | 09:40 | 21:55 |
| Urumqi, China | Xinjiang time (UTC+6) | 87.6 E | +19 | +16 | +10 | 07:40 | 19:55 |
| Harbin, China | Beijing (UTC+8) | 126.5 E | -17 | -20 | -26 | 07:12 | 19:27 |
| Madrid, Spain | CET / CEST | 3.7 W | +84 | +141 | +109 | 08:34 | 21:49 |
| Indianapolis, US | Eastern | 86.2 W | +54 | +111 | +84 | 08:02 | 21:16 |
| Detroit, US | Eastern | 83.0 W | +42 | +98 | +71 | 07:58 | 21:13 |
| Eastport, Maine, US | Eastern | 67.0 W | -23 | +34 | +7 | 07:03 | 20:18 |
| Kathmandu, Nepal | UTC+5:45 | 85.3 E | +13 | +10 | +4 | 06:50 | 19:02 |
Offsets are in minutes, positive meaning solar noon falls after 12:00 on the clock. Sunrise and sunset use each place’s own clock, which is why Urumqi appears twice.
Four readings follow from it.
The first is that political choice dominates. Kashgar and Urumqi sit nearly 12 degrees of longitude apart, which is about 46 minutes of sun time, and the offsets differ by 46. Put Urumqi on UTC+6 and the offset collapses from +130 to +10. Longitude did not change — the clock did. Kathmandu is the other pole of the table: Nepal’s UTC+5:45 was set in 1986 to match the 86 degrees 15 minutes east meridian through Gaurishankar, and the result is a capital whose solar noon sits within four minutes of 12:00 averaged over the year.
The second is that daylight saving time is the largest swing in the American and Spanish rows. Between January 15 and July 15 the offset in Indianapolis moves from +54 to +111, a 57-minute jump, and Madrid’s from +84 to +141. Kashgar and Urumqi barely change, because China does not observe daylight saving time. The seasonal variation in the Beijing-time rows is only the equation of time, three to four minutes in the mid-January to mid-July comparison, whereas the American rows pick up an hour on top of it.
The third is that a mid-zone label hides large offsets. Indianapolis is in the Eastern time zone, centered on 75 degrees west, and sits 11 degrees west of that line. Its longitude term alone is +45 minutes before summer time adds another hour. Detroit is at +32 on the same arithmetic. Eastport, Maine, at the eastern tip of the zone, has a negative offset in winter (-23) and is within 7 minutes of zero averaged over the year, because the summer hour offsets its eastern longitude and the yearly average lands near zero. Madrid is the sharpest comparison in the table — at 3.7 degrees west, it runs on Central European time, which is built on 15 degrees east, 18.7 degrees away. Spain adopted that clock in March 1940, and its 2026 mean of +109 is larger than any American row. Had Madrid stayed on Greenwich time, the mean would be +15.
The fourth is that the darkest winter mornings in the table are not at the highest latitudes. Kashgar’s sunrise on December 21 is 10:13 a.m. on the clock, nearly three and a half hours later than Kathmandu’s 6:50 at a latitude 12 degrees further south. Latitude shortens the day; the offset slides the whole day later.
Why is Xinjiang the test case?
China has used a single standard time, Beijing time at UTC+8, since 1949, when the central government abolished the five-zone scheme of the Republican era. One of those five zones, called Sinkiang-Tibet, ran at UTC+6. A parallel, informal clock often called Xinjiang time or Urumqi time, two hours behind Beijing, remains in use in parts of the region. Descriptions of it commonly report that its use divides along ethnic lines, with most of the Han population on Beijing time and many Uyghurs and others on Xinjiang time, that local television channels schedule by different clocks depending on language, and that rail and air tickets are issued in Beijing time.
The table gives the physical side of that arrangement without taking a view on the politics. A resident of Urumqi on Beijing time lives with solar noon at roughly 2:10 p.m. and a December sunrise at 9:40 a.m. On Xinjiang time, the offset is +10 and the sun looks like Kathmandu’s. People who keep the second clock are, in effect, correcting a +130 minute offset by hand. The cost is coordination: two sets of hours in one city, with official services, transport and much of the workplace anchored to the national clock. How many people use which clock, and for what, varies by place and setting, and the published descriptions are largely informal. The firm fact is arithmetic. The distance between the two clocks in Urumqi is 120 minutes, and the offset between sun and national clock is 130.
Does a bigger solar offset mean less sleep?
The research says yes on average, with caveats that matter. Three studies carry most of the weight.
Roenneberg, Kumar and Merrow (Current Biology, 2007) used the Munich Chronotype Questionnaire to ask whether the human clock follows social time or sun time. Within one time zone, dawn and dusk progress from east to west, so if people entrain to the sun, average chronotype should get about four minutes later for every degree of longitude westward. In Germany, where the zone spans nine degrees, chronotype did correlate with position: the further east, the earlier. This is the foundation for the idea that the body tracks the sun more than the wall clock. Its reach is limited to timing. It says when people prefer to sleep, not how long they sleep when a school bell or a shift fixes the morning.
Giuntella and Mazzonna (Journal of Health Economics, 2019) supply the duration result. They compared counties on either side of U.S. time zone borders, where the clock jumps by an hour while the sun does not, so that the western side gets an hour more evening light at the same latitude. A spatial regression discontinuity design is what allows that comparison. The western side sleeps about 19 minutes less on average and is more likely to report insufficient sleep. The channel they propose is mundane: later light delays bedtime, and an unchanged start to the school or work day eats the difference, the mismatch usually called social jetlag.
Gibson and Shrader (Review of Economics and Statistics, 2018) used sunset time within U.S. time zones as an instrument for sleep and found that later sunset reduces sleep and wages. Their estimate is that a one-hour increase in a location’s average sleep raises earnings by about 1.1 percent in the short run and about 5 percent in the long run. The study is evidence of direction and rough scale for the economy, and it cannot say that any particular worker in Indianapolis earns less than a counterpart in Eastport.
A fourth paper brings in China directly. Giuntella, Han and Mazzonna (Demography, 2017) exploited the fact that a single time zone covers the whole country, so sunset time varies across cities while the clock does not. Using sunset time to isolate the effect of sleep, they tied shorter sleep among workers over 45 to lower cognitive skills and more depression symptoms, and the effect was concentrated among employed urban residents. They found none for the self-employed or farmers. That pattern matters for the interpretation: the sun matters most where a schedule is imposed from outside.
What do the studies predict for the table?
If the 19 minutes per hour of later sunset applies across the board, the table can be translated into a rough sleep gap relative to a place with no offset. The assumption is that the offset is a stand-in for sunset delay at fixed latitude, which is the quantity the border studies vary. Kathmandu is the reference at +4.
| Place | 2026 mean offset | Gap vs Kathmandu | Implied sleep gap |
|---|---|---|---|
| Kashgar (Beijing time) | +176 | 172 min | about 54 min |
| Urumqi (Beijing time) | +130 | 126 min | about 40 min |
| Madrid | +109 | 105 min | about 33 min |
| Indianapolis | +84 | 80 min | about 25 min |
| Detroit | +71 | 67 min | about 21 min |
| Urumqi (Xinjiang time) | +10 | 6 min | about 2 min |
| Eastport | +7 | 3 min | about 1 min |
| Harbin | -26 | -30 min | about -10 min |
This table should be read as an upper-range illustration. The border studies identify an effect near a one-hour discontinuity in American counties, and Kashgar’s gap is three hours, well outside what the data cover. Linear extrapolation is a convenience and carries no evidence of its own; the true relationship could flatten, because people eventually move bedtimes and school hours, or steepen. The estimates describe average sleep in populations, not what any one person gets, and individuals differ widely in chronotype and in how much light they get indoors. The sleep measures in these studies are largely self-reported or taken from time diaries. A large offset can also be absorbed by schedule: later opening hours, later school starts, a second clock. Madrid may be a case of that, with meals and bedtimes shifted late, but whether such adjustments restore the lost sleep is a separate question the studies here do not answer.
The Chinese result may be the most useful one for reading the table. If the cost lands on employed urban workers and skips the self-employed and farmers, then the size of a place’s offset sets a ceiling on the loss, and the rigidity of its start times sets how much of the ceiling people pay.
Where does this leave a person in the west of a zone?
The research points at evening light. The border studies tie shorter sleep to later sunset delaying bedtime, so the lever with the best support is the evening, and the schedule that cannot move is the morning. A person in Indianapolis whose workday starts at 8:00 has the same wake-up constraint as one in Eastport, and a solar noon that arrives 77 minutes later on the clock, on average across the year.
The offset also swings by season. In the American rows it is smallest in winter and largest in summer, when the clock change adds an hour on top of the longitude term. Keeping summer hours all year would hold the summer-level offset all year, which is part of why the American Academy of Sleep Medicine opposes it.
Where a clock mismatches the sky by two hours for decades, people tend to build workarounds: a second clock in Urumqi, a late dinner in Madrid, an early school start somewhere that has no alternative. The solar offset shows the size of what is being worked around, and the studies show it costs some sleep on average. The same arithmetic that puts Kathmandu’s solar noon within four minutes of 12:00 across the year puts Kashgar’s 176 minutes past it, and on December 21 the sun there clears the horizon at 10:13 a.m. by the clock on the train ticket.
FAQ
Does living in the western part of a time zone have effects beyond sleep?
Giuntella and Mazzonna found that the sunset discontinuity at U.S. time zone borders also lined up with worse outcomes typically tied to circadian disruption (obesity, diabetes, cardiovascular disease) and with lower per capita income. These are county-level patterns, and the authors frame sleep loss under rigid schedules as the channel; none of it proves a cause for any one person.
What is the difference between solar noon and clock noon?
Solar noon is the moment the sun crosses your meridian and stands highest; clock noon is 12:00 on whatever time your zone uses. Two places on the same clock can sit far apart: on June 21 the sun sets at 8:18 p.m. in Eastport, Maine, and at 9:16 p.m. in Indianapolis, both on Eastern time, a gap of 58 minutes.
Why is the sun so late in Xinjiang?
Beijing time is built on the 120 degrees east meridian, and Xinjiang spans roughly 74 to 96 degrees east. That puts local solar noon between about 1.6 and 3 hours after 12:00 on the clock. Harbin, in the northeast and on the same clock, sees its December 21 sunrise at 7:12 a.m., about three hours before Kashgar’s 10:13. China does not observe daylight saving, so the gap does not change by season.
Do people in western time zones wake up later?
On free days, yes, in the direction the sun predicts: Roenneberg’s team expected average chronotype to shift about 4 minutes later per degree of longitude westward. Detroit and Eastport sit 16 degrees apart on the same Eastern clock, which at that rate predicts about 64 minutes, the same as the gap between their solar noon offsets (+71 against +7). On workdays an alarm fixes the wake time, so the difference lands in bedtime and sleep length instead.
Would permanent daylight saving time widen these offsets?
It would add 60 minutes to every winter value in the table. Indianapolis on January 15 would go from +54 to +114 minutes and Detroit from +42 to +102, close to what those cities already see in July (+111 and +98).