Daylight Hours by Season: Plan a Hanoi Day Ride So You Are Back Before Dark

Hanoi sunset time changes by season, and that matters when planning how late a motorbike day trip can run. The U.S. Naval Observatory’s 2026 table for Hanoi lists sunset between 17:14 and 18:42 across the year, a spread of 1 hour 28 minutes (calculated). Vietnam’s road traffic law runs its own clock for headlights, 18:00 to 06:00. This article sets out sunrise, sunset and civil-twilight times month by month, lines them up with the Hanoi city portal’s four seasons and shows how to count back from a return time. The section “What the pages leave out” lists what the pages do not say, including anything about rental bikes.

Where the times come from

The Observatory’s Astronomical Applications Department, which describes its site as an official U.S. Navy website, publishes a full-year table of sun rise and set times for Hanoi (E105 51, N21 02, zone 7 hours east of Greenwich) and a second table of civil twilight, both for 2026.

The Observatory’s definitions page says sunrise and sunset are the moments when the upper edge of the Sun’s disk is on the horizon, assuming average atmospheric conditions and a level region. Civil twilight begins in the morning, and ends in the evening, when the centre of the Sun is 6 degrees below the horizon. The page states that before it begins and after it ends, artificial illumination is normally required to carry on ordinary outdoor activities. It adds that the real amount of light depends on atmospheric conditions, cloud cover and the visibility of the horizon.

Sunrise, sunset and civil twilight month by month

The rows below take the 15th of each month from the two tables (local time, 24-hour clock). The last column is calculated here by subtracting sunrise from sunset; the pages do not publish day length.

Across the year the tables list the earliest sunset, 17:14, from 19 November to 4 December and the latest, 18:42, from 26 June to 13 July. Sunrise is earliest, 05:14, from 4 to 10 June and latest, 06:36, from 9 to 24 January. Civil twilight ends as early as 17:38 (16 November to 4 December) and as late as 19:07 (27 June to 9 July). The calculated sunrise-to-sunset window is 10 h 51 min on several days from 17 to 27 December and 13 h 25 min on several days from 17 to 27 June.

The Hanoi portal’s four seasons against the table

The Hanoi city government portal’s geography overview (page dated 25 December 2014) divides the year into spring from February to April, summer from May to August, autumn from August to October and winter from November to January. It adds that the boundaries are only relative, because some years the cold arrives early or late and some years the heat lasts. The table gives the range of listed times across every day of those months in 2026; August appears twice because the portal puts it in both summer and autumn.

By this grouping the earliest sunsets fall in the portal’s winter and the latest in its summer, while autumn holds the steepest change: sunset is listed at 18:35 on 1 August and 17:22 on 31 October, 1 hour 13 minutes earlier (calculated).

The 18:00 headlight rule

Article 20 of Law 36/2024/QH15 on road traffic order and safety, as shown in the National legal database (vbpl.vn, run by the Ministry of Justice; page updated 29 March 2026 and marked in force), requires drivers of motor vehicles and operators of special-purpose machinery to switch on the front lights from 18:00 to 06:00 the next day, or whenever fog, smoke, dust, rain or bad weather limits visibility. Article 2 defines “người lái xe” as the person controlling a motor vehicle (xe cơ giới), and Article 34 lists motorcycles (xe mô tô) and mopeds (xe gắn máy) among motor vehicles. Reading the two definitions together, the rule covers motorbike riders; that is a reading of the text, not a statement the page makes about visitors.

The rule follows the clock, not the Sun. In the 2026 tables sunset is at 18:00 or later from 26 February to 15 September, so the headlight hour arrives at or before sunset on those dates. On every other date, from 1 January to 25 February and from 16 September to 31 December, sunset comes before 18:00. Civil twilight has already ended before 18:00 from 10 October to 14 January.

Working back from a return time

The pages set no return time for riders, so the choice of anchor is a planning decision. Three anchors can be read from them:

On 15 December the headlight start comes 18 minutes after civil twilight ends; on 15 June it comes 39 minutes before sunset (both calculated). Counting back works the same way for any anchor: subtract the time planned away, stops included, from the anchor time. As an illustration only, with 8 hours as an arbitrary length and not a recommendation, an outing meant to end at sunset would begin by 09:18 on 15 December and by 10:39 on 15 June. For a plan built around a weather backup, see Soc Son from Hanoi by Motorbike: A Day Plan With a Weather Backup.

When weather changes the light

Both the law and the Observatory point to weather. Article 20 adds fog, smoke, dust, rain and bad weather to its clock-based hours. The Observatory says its twilight descriptions match the computed times for an observer near sea level with good weather and a level horizon, and that finding the actual lighting level would take a forensic study or eyewitness testimony. The tables therefore give astronomical times; they are not a forecast of how bright a given evening will be. For the rain side of the decision, see Hanoi Rainy-Season Riding: A Go-or-Postpone Decision Checklist. For visors and daylight, see Clear or Tinted Helmet Visor in Hanoi: Match Visibility to Daylight.

What the pages leave out

• The Observatory tables cover 2026 only; no page gives other years or says how far they differ.
• The times are for one point in Hanoi under level-horizon conventions; no page gives times for hills, mountain roads or other towns.
• The tables say to add one hour for daylight time if and when in use; no page says whether Vietnam uses it.
• No page recommends a return time, a ride length or a margin after sunset.
• Article 20 gives the headlight hours and weather triggers, but the law page names no fine for breaking that rule and says nothing about rented bikes.
• The Hanoi portal page is dated 2014, calls its season boundaries relative and gives no sunrise or sunset times.
• Window lengths, spreads and count-back examples are calculated from listed times, not published by the pages.
• This article does not cover street lighting, traffic or road conditions after dark, or rental hours and conditions.

Sources checked

• U.S. Naval Observatory: Hanoi sun rise and set, 2026
• U.S. Naval Observatory: Hanoi civil twilight, 2026
• U.S. Naval Observatory: rise, set and twilight definitions
• vbpl.vn: Law 36/2024/QH15 on road traffic order and safety
• Hanoi city portal: geography overview

Thuê xe máy Nguyễn Hà is open 09:00–21:00 daily at Ngõ 5 Nguyễn Văn Cừ, Bồ Đề, Long Biên, Hà Nội (near Gia Lâm bus station). Phone: 0334 699 969.