How Daylight Length Changes in Nassau County, NY During January

During January, Nassau County, New York, experiences a measurable and consistent increase in the duration of daylight. This astronomical change follows the winter solstice in late December and marks the beginning of the Northern Hemisphere's gradual reorientation toward the sun. For residents of Nassau County, this results in nearly an hour of additional daylight by the end of the month, a scientifically predictable event governed by Earth’s orbit and axial tilt.

An Overview of Daylight Change in January

The increase in daylight hours during January in Nassau County is a direct consequence of Earth’s orbital position relative to the sun. After the winter solstice, which typically occurs around December 21, the Northern Hemisphere begins to tilt progressively more toward the sun. Nassau County’s geographic location at a latitude of approximately 40.7° North means that the duration of sunlight received each day starts to lengthen. This change is gradual, beginning with small increments in the first days of January and accelerating as the month progresses. The process is a standard, predictable part of the annual solar cycle for mid-latitude locations like Nassau County. (U.S. Naval Observatory, National Aeronautics and Space Administration)

Earth's Axial Tilt and Nassau County's Latitude

The primary cause of seasonal variations in daylight is Earth’s axial tilt, which is approximately 23.5 degrees relative to its orbital plane. As Earth orbits the sun, this tilt remains fixed in direction, causing each hemisphere to receive varying amounts of direct solar radiation over the course of the year. For Nassau County, located at latitude 40.7° N, this tilt means that during winter, the county is angled away from the sun. This results in the sun’s rays striking the surface at a lower, more oblique angle and for a shorter duration each day. The winter solstice marks the point of maximum tilt away from the sun for the Northern Hemisphere. Throughout January, as Earth continues its orbit, Nassau County’s position begins to angle back toward the sun, causing a steady increase in the length of the day. (National Aeronautics and Space Administration)

Changes in Sunrise and Sunset from Early to Late January

In Nassau County, the duration of daylight increases significantly from the beginning of January to the end. On January 1, the county typically experiences approximately 9 hours and 15 minutes of daylight. By January 31, this duration increases to approximately 10 hours and 5 minutes. This represents a total gain of about 50 minutes over the course of the month. This increase is a result of both earlier sunrises and later sunsets. For example, the sunrise time shifts from approximately 7:18 a.m. at the start of the month to around 7:05 a.m. by the end, while the sunset time moves from approximately 4:33 p.m. to 5:10 p.m. during the same period. These precise times are calculated based on astronomical data and vary slightly by specific location within the county. (U.S. Naval Observatory Astronomical Applications Department)

Nassau County's Daylight Pattern Within Long Island

The daylight pattern observed in Nassau County during January is nearly identical to that experienced across the entirety of Long Island. This uniformity is due to Long Island's primarily east-west geographic orientation, which places nearly all locations on the island at a similar latitude. Since the duration of daylight on any given day is determined by latitude, residents from Valley Stream to Montauk experience the same amount of total daylight. While there are minor differences in the exact timing of sunrise and sunset due to longitude—with locations farther east experiencing both events a few minutes earlier—the total length of the day remains consistent across the island. Therefore, the daylight changes that occur in Nassau County are representative of the broader Long Island region. (map of Long Island, NY, with zip codes)

Daylight Increase Versus Temperature Change

An increase in daylight hours during January does not immediately result in warmer temperatures in Nassau County due to a phenomenon known as seasonal lag. The coldest period of winter typically occurs after the winter solstice because Earth's land and oceans, particularly the Atlantic Ocean adjacent to Long Island, lose heat more slowly than they gain it. This thermal inertia means that even as the duration of sunlight increases, the region continues to radiate more heat than it absorbs from the sun. Furthermore, the sun's angle remains low in the sky throughout January, causing solar radiation to be less direct and intense. The atmosphere continues to cool, and average temperatures do not begin to rise until the net energy balance becomes positive, which generally happens weeks after the days start getting longer. (National Oceanic and Atmospheric Administration)

Summary of January Daylight Changes

In summary, Nassau County residents experience a predictable and scientifically verifiable increase in daylight throughout January. This change is driven by Earth’s 23.5-degree axial tilt and its orbital path around the sun, which, following the winter solstice, begins to increase the duration of sunlight received at the county’s mid-latitude location. Over the month, daylight lengthens by approximately 50 minutes, with sunsets occurring noticeably later by January 31. This pattern is consistent across all of Long Island due to its shared latitude. However, this increase in daylight does not correspond with an immediate rise in temperature, as the region’s land and water continue to lose heat, a phenomenon known as seasonal lag.

Sources Reviewed

The information presented in this article is based on factual data and scientific explanations from authoritative sources. Sunrise, sunset, and daylight duration data were derived from tables provided by the U.S. Naval Observatory. Explanations of Earth’s axial tilt, seasons, and orbital mechanics are based on information published by the National Aeronautics and Space Administration (NASA). The concept of seasonal lag and its effect on regional temperatures is explained using principles outlined by the National Oceanic and Atmospheric Administration (NOAA) and the National Weather Service.