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Moonrise and moonset

Moonrise and moonset refer to the moments when the Moon becomes visible above the eastern horizon and disappears below the western horizon, respectively, as observed from Earth.^[1] These events are defined precisely as the instants when the upper limb of the Moon appears tangent to the horizon, accounting for atmospheric refraction and the Moon's apparent size and parallax.^[1] Unlike the Sun's more predictable daily cycle, moonrise and moonset times shift by approximately 50 minutes later each day on average, due to the Moon's eastward orbital motion around Earth, which requires the planet to rotate an additional angle to bring the Moon back into view.^[2] The timing of moonrise and moonset is intimately linked to the Moon's phases, which result from the changing geometry of sunlight illuminating the Moon as seen from Earth.^[3] During a new Moon, the Moon rises and sets with the Sun, remaining invisible against the daytime sky; in contrast, a full Moon rises around sunset and sets around sunrise, appearing opposite the Sun and visible throughout the night.^[3] First-quarter Moon rises near noon and sets near midnight, making it prominent in the evening, while the last-quarter Moon rises near midnight and sets near noon, favoring early morning observations.^[3] Waxing and waning phases cause progressive shifts, with the Moon's illuminated portion growing or shrinking accordingly, influencing visibility and the duration it remains above the horizon each night.^[3] Calculations for moonrise and moonset incorporate the Moon's geocentric position, its semi-diameter (angular radius of about 15-17 arcminutes), horizontal parallax (54-61 arcminutes due to its proximity to Earth), and standard atmospheric refraction (about 34 arcminutes), setting the geometric zenith distance of the Moon's center at approximately 90.57° + semi-diameter - horizontal parallax, or roughly 89.9°, placing the center 5 to 10 arcminutes above the geocentric horizon.^[1] These times can occur at any hour of the day or night, and in some locations or dates, the Moon may not rise or set at all, leading to moonless periods.^[1] Factors like local topography, weather, and the Moon's elliptical orbit introduce variability, with predictions accurate to within a minute under ideal conditions but potentially affected by refraction or elevation.^[1] Understanding these phenomena is essential for astronomical observation, tidal predictions, and cultural practices tied to lunar cycles.^[2]

Fundamentals

Definition

Moonrise is defined as the instant when the upper limb of the Moon's disk becomes visible just above the horizon, while moonset occurs when the upper limb disappears just below the horizon.^[1] This definition assumes ideal conditions, including a level, unobstructed horizon and standard atmospheric refraction.^[1] Calculations of moonrise and moonset rely on the topocentric position of the Moon from the observer's location on Earth, rather than geocentric coordinates, due to the Moon's relative proximity and resulting horizontal parallax of approximately 57 arcminutes.^[4]^[1] The Moon's apparent angular diameter, typically around 0.5 degrees (or 30 arcminutes), is accounted for in these determinations to precisely identify the upper limb's position.^[5] Times are computed for the upper limb to ensure consistency and accuracy, mitigating discrepancies from parallax variations across different terrestrial locations.^[1] Traditional concepts of moonrise and moonset originated in ancient astronomy, where Babylonian observers from around 1800 BCE systematically recorded the Moon's motions, including its risings and settings, to develop lunar calendars and predict eclipses.^[6] These early definitions were refined over centuries through Greek and medieval Islamic contributions to positional astronomy, culminating in modern ephemerides such as those produced by the U.S. Naval Observatory, which incorporate precise orbital data for global predictions.^[7] Atmospheric refraction plays a minor role by slightly advancing the apparent time of moonrise and delaying moonset, effectively making the Moon visible a few minutes earlier or later than its geometric position would suggest.^[1]

Comparison to Sunrise and Sunset

Moonrise and moonset share fundamental similarities with sunrise and sunset, primarily arising from Earth's daily rotation on its axis, which causes both the Sun and the Moon to appear to cross the horizon at specific times. In both cases, the celestial body is considered to rise when its upper limb becomes visible above the horizon and sets when it disappears below it, under ideal conditions. Atmospheric refraction plays a key role in both phenomena, bending light rays through layers of varying air density near the horizon, which elevates the apparent position of the body by about 0.57 degrees on average. This effect advances the observed time of sunrise and moonrise by approximately two minutes and delays sunset and moonset by the same amount compared to geometric calculations without refraction.^[1]^[8]^[9] Despite these parallels, moonrise and moonset differ markedly from sunrise and sunset due to the Moon's orbital motion around Earth, which introduces variability absent in the Sun's apparent path. While sunrise and sunset occur at roughly fixed clock times each day (varying only slightly with seasons and latitude due to Earth's tilt), moonrise and moonset shift later by an average of about 50 minutes daily. This delay results from the Moon's eastward orbital progression, completing a full circuit relative to the stars in 27.3 days but lagging the Sun's position by approximately 12.2 degrees per day in the synodic sense. Consequently, the Moon can rise or set at any hour, including during daylight, unlike the Sun, which is confined to the daytime sky.^[10]^[11]^[12] Another key distinction lies in visibility and predictability: the Moon's phase determines whether it is observable during its rise or set, as a full Moon rises near sunset when it is brightly illuminated and visible against the evening sky, whereas a new Moon rises near sunrise and remains faint or invisible during the day. In contrast, the Sun is always visible at horizon crossings by definition, providing consistent illumination. This orbital-induced variability in timing and direction— with moonrise azimuth shifting eastward daily—further contrasts the Moon's dynamic path against the Sun's more stable seasonal arc.^[3]

Astronomical Factors

Earth's Rotation and Moon's Orbit

The apparent motion of the Moon across the sky is primarily driven by Earth's rotation on its axis, which completes one full turn of 360 degrees every 24 hours, resulting in an eastward-to-westward progression of approximately 15 degrees per hour for celestial objects including the Moon, similar to the daily path of stars.^[13] This diurnal motion causes the Moon to rise in the east and set in the west each day, with its position shifting predictably due to the planet's spin.^[14] Superimposed on this daily rotation is the Moon's own orbital motion around Earth, which occurs in a prograde direction with a sidereal period of 27.32166 days relative to the fixed stars.^[15] This orbit produces an eastward drift of about 13 degrees per day against the stellar background, as the Moon advances roughly 360 degrees in its path over that period.^[16] Consequently, moonrise occurs approximately 50 minutes later each successive day on average, since the additional angular displacement requires extra time for Earth's rotation to bring the Moon back to the horizon.^[17] The timing of moonrise is further modulated by the synodic month, the period of 29.53059 days between successive identical lunar phases, which accounts for both the Moon's orbit and Earth's motion around the Sun.^[18] This cycle links moonrise directly to the Moon's phases; for instance, during full moon, when the Moon is opposite the Sun in the sky, it rises near sunset and sets near sunrise, maximizing its nighttime visibility.^[3] The Moon's orbital plane is inclined by about 5.145 degrees relative to the ecliptic, the plane of Earth's orbit around the Sun, leading to variations in the Moon's declination—the angular distance north or south of the celestial equator.^[19] This inclination causes the Moon's declination to fluctuate monthly, with the amplitude varying from about ±18° during minor standstills to ±28.5° during major standstills over the 18.6-year nodal precession cycle, influencing the latitude range over which the Moon rises and sets at different times throughout the year.^[20]

Geographic Influences

Latitude profoundly influences the visibility, timing, and direction of moonrise and moonset by determining the Moon's path relative to the local horizon. At high northern latitudes, particularly above approximately 61.5°N during a major lunar standstill when the Moon's declination reaches its maximum of about 28.5°N, the Moon can become circumpolar, remaining above the horizon without setting for extended periods of up to several days. This effect arises because the observer's latitude exceeds 90° minus the Moon's maximum declination, preventing the Moon from dipping below the horizon during its daily circuit. Conversely, at extreme southern latitudes below about 61.5°S during major lunar standstills when the Moon's declination reaches its northern maximum of about +28.5°, the Moon may remain below the horizon for longer durations, resulting in shorter visible periods or complete invisibility for parts of the month. At the equator, the azimuth of moonrise varies minimally, typically ranging from roughly 90° (due east) to deviations of about 30° north or south depending on the Moon's declination, while moonset occurs near 270° (due west) with similar limited deviation. In contrast, at the poles, the flat horizon allows the Moon to rise and set in virtually any azimuthal direction over the course of a year, leading to variations spanning up to 360° as the Moon's position relative to the observer shifts with its orbital and rotational dynamics. These latitudinal differences in azimuth stem from the geometry of the celestial sphere, where higher latitudes amplify the impact of the Moon's declination on its horizontal position at horizon crossing.^[21] Longitude affects moonrise and moonset primarily through its role in defining local mean solar time, which shifts the clock time of these events relative to coordinated universal time (UTC). Observers at the same latitude but separated by 15° of longitude experience moonrise approximately one hour apart in local clock time, as the Earth's rotation brings the Moon to the local meridian sequentially from east to west; this adjustment is incorporated into calculations using the observer's longitude to convert from Greenwich mean time.^[22] Observer elevation above sea level slightly advances the timing of moonrise and delays moonset by geometrically lowering the effective horizon. The horizon dip angle η is approximated as η ≈ 0.029° × √(elevation in meters), allowing the Moon to be visible a few minutes earlier or later compared to sea-level observations; for example, at 1000 m elevation, this dip is about 0.9°, translating to a time shift of roughly 3-4 minutes near the horizon. Additionally, higher elevations reduce the path length through the atmosphere, diminishing refraction effects that otherwise lower apparent positions near the horizon. These corrections are applied in precise computations to account for the observer's height.^[23]

Calculation Methods

Core Principles

Moonrise and moonset refer to the instants when the Moon's upper limb appears tangent to the horizon, as seen from a specific location on Earth. These times are computed using the Moon's topocentric position, which accounts for the observer's location relative to Earth's center, because the Moon's proximity results in a significant parallax effect of up to approximately 1 degree.^[24] This adjustment is essential for accuracy, as geocentric positions alone would introduce errors of several minutes in rise and set timings.^[25] The horizon for these calculations is defined geometrically at an altitude of 0 degrees, but practical computations adjust this to reflect the Moon's visible upper limb crossing the true horizon. This involves subtracting the Moon's semi-diameter (typically 15 to 17 arcminutes) and atmospheric refraction (standard value of about 0.57 degrees or 34 arcminutes), while adding the Moon's horizontal parallax (54 to 61 arcminutes).^[1] The net effect places the Moon's center roughly 5 to 10 arcminutes above the geocentric horizon when the upper limb is tangent, ensuring predictions align with unaided visual observations under clear conditions.^[1] To determine these times, algorithms rely on iterative interpolation between discrete ephemeris points, as the Moon's right ascension and declination change continuously due to its orbital motion. Hourly ephemeris data provide approximate positions, and the exact horizon-crossing moment is found by solving iteratively for the time when the adjusted altitude equals zero, refining the solution until convergence (typically in 2-4 steps).^[26]^[25] Geographic latitude influences the inputs to this process, as it affects the observer's orientation relative to the celestial equator. A central concept in these computations is the hour angle at rise or set, which quantifies the angular distance from the local meridian to the point where the Moon crosses the horizon. For a geometric horizon, this is given briefly by \cos(HA) = -\tan(\phi) \tan(\delta), where \phi is the observer's latitude and \delta is the Moon's declination; adjustments for semi-diameter, refraction, and parallax modify the effective altitude input.^[26] This approach bridges the Moon's equatorial coordinates to local time, enabling precise predictions without exhaustive numerical simulation.^[25]

Azimuth and Timing Formulas

The calculation of the azimuth and timing for moonrise and moonset relies on spherical trigonometry to determine the Moon's position relative to the observer's horizon. The fundamental equation derives from the spherical law of cosines applied to the astronomical triangle formed by the zenith (Z), the north celestial pole (P), and the Moon (M). The co-latitude (90° - φ, where φ is the geocentric latitude) forms side ZP, the co-declination (90° - δ, where δ is the Moon's declination) forms side PM, and the co-altitude (90° - h, where h is the altitude) forms side ZM. The angle at P is the hour angle H, and the angle at Z is the azimuth A measured from north. Using the cosine rule for sides yields the relation for altitude: \sin h = \sin\phi \sin\delta + \cos\phi \cos\delta \cos H This equation connects equatorial coordinates (δ, H) to horizontal coordinates (h, A) at the observer's location (φ).^[27]^[25] To find the timing of moonrise or moonset, solve for the hour angle H when the apparent altitude of the Moon's upper limb is 0°. Accounting for atmospheric refraction, semi-diameter, and parallax, the effective geometric altitude of the Moon's center is set to a slightly positive value, approximately 0.12 degrees (or 5 to 10 arcminutes). The equation becomes: $0 = \sin\phi \sin\delta + \cos\phi \cos\delta \cos H + \Delta h where Δh is the net correction (approximated as negative in this convention to adjust for the positive geometric position). Rearranging gives: \cos H = -\frac{\sin\phi \sin\delta + \Delta h}{\cos\phi \cos\delta} H is then found using the arccosine, selecting the appropriate value (H between 0° and 180° for rise, 360° - H for set, ensuring the Moon crosses the horizon from below to above or vice versa). The local sidereal time of the event is the Moon's right ascension α plus or minus H (rise: α + H, set: α - H, converted to mean solar time). The time from local solar noon is t = H / 15 hours (negative for morning events, positive for evening), adjusted to clock time with the equation of time and longitude. For the Moon, δ and α vary rapidly, requiring iteration over ~1-hour steps to refine the ephemeris values at the event time.^[25]^[28] The refraction correction Δh (in degrees) near the horizon is approximated by Saemundsson's formula, adapted for low altitudes: \Delta h = \frac{0.57}{\tan\left(h + \frac{7.31}{h + 4.4}\right)} where h is the geometric altitude in degrees; this empirical fit accounts for the increased bending of light rays through the denser lower atmosphere, with values around 0.57° (34 arcminutes) at the horizon. For the Moon, additional corrections for its semi-diameter (~16 arcminutes) and horizontal parallax (~57 arcminutes) are applied: the upper limb rise/set occurs when the geometric center is below the horizon by approximately the semi-diameter minus parallax plus refraction, but the basic formula above provides a starting point before iteration.^[29]^[25] The azimuth A at horizon crossing (h = 0°) is derived from the spherical law of cosines for angles or sides in the same triangle: \cos A = \frac{\sin\delta - \sin\phi \sin h}{\cos\phi \cos h} With h = 0 and sin h = 0, cos h = 1, this simplifies to: \cos A = \frac{\sin\delta}{\cos\phi} A is then arccos of this value, adjusted for quadrant: for rise, A is in the eastern half (0° < A < 180° from north toward east), and for set, in the western half (180° < A < 360°). The sign of sin A = (cos δ sin H) / cos h confirms the direction (positive for east, negative for west). Refraction slightly modifies A by ~0.5° near the horizon due to differential bending, but the basic formula suffices for most calculations.^[27]^[25] As a representative example, consider an observer at the equator (φ = 0°) when the Moon has zero declination (δ = 0°), ignoring refraction for simplicity. Then cos H = 0, so H = 90° (or 6 hours), corresponding to moonrise 6 hours before transit (local noon) at azimuth A where cos A = 0 / 1 = 0, so A = 90° (due east). Moonset follows symmetrically at 270° (due west) 6 hours after transit. This equinox-like case illustrates the symmetry absent at higher latitudes or nonzero δ, where |H| > 90° and A deviates from 90°/270°. In practice, refraction shifts the times earlier by ~2-4 minutes and azimuths slightly northward.^[27]^[25]

Direction and Timing

Azimuth Determination

The azimuth of moonrise and moonset is the compass bearing, measured clockwise from true north (0°), at which the Moon intersects the horizon, determined primarily by the observer's latitude and the Moon's declination at the moment of rising or setting. For locations at mid-northern latitudes (around 40°N), moonrise azimuths typically span 50° to 130°, encompassing directions from northeast to southeast, while moonset azimuths range from 230° to 310°, covering southwest to northwest; these ranges adjust with latitude and the Moon's position relative to the celestial equator.^[30]^[31] The primary factor driving azimuth variation is the Moon's declination, which oscillates monthly between approximately ±18.3° during minor standstills and up to ±28.6° during major standstills, producing a maximum directional shift of about 28° northward or southward from the mean position. This declination amplitude arises from the Moon's orbital inclination of 5.1° relative to the ecliptic, combined with Earth's 23.4° axial tilt, with the effective range modulated by the 18.6-year precession of the lunar nodes that tilts the orbit relative to the equator. Seasonal extremes in azimuth occur near solstices, when the Moon's nodal position aligns to maximize declination deviations in concert with the Sun's path.^[32]^[33] Every 18.6 years, a major lunar standstill amplifies these effects, pushing declination to its widest monthly swing of ±28.6° and resulting in azimuth extremes that can deviate up to 50° from due east (90°) or due west (270°), far exceeding the Sun's corresponding maximum offset of approximately 39° at mid-northern latitudes such as 51°N. A major lunar standstill is currently occurring (2024-2025), amplifying these declination extremes until approximately 2026.^[34]^[35]^[36] Azimuths for moonrise and moonset exhibit symmetry on a flat horizon, where the rise azimuth plus the set azimuth equals 360°, reflecting the antipodal geometry of the celestial sphere across the observer's local meridian. These azimuths can be computed using standard formulas that incorporate latitude, declination, and the hour angle at the horizon crossing.^[37]

Time Variations

The timing of moonrise and moonset exhibits a consistent daily shift, occurring approximately 48 to 52 minutes later each successive day on average, primarily due to the Moon's orbital motion around Earth relative to the Sun. This progression stems from the synodic month lasting about 29.5 days, during which the Moon laps the Sun in the sky, resulting in the observed delay. The shift's rate accelerates near new and full moons, where the Moon's path aligns more directly with the daily rotation, leading to smaller daily changes compared to the quadratures (first and last quarters), where delays can reach up to 60 minutes or more.^[38]^[10] Over the course of a month, moonrise and moonset times follow the lunar phases closely, creating a predictable cycle of earlier and later occurrences. At new moon, the Moon rises near sunrise and sets near sunset, making it visible primarily during daylight hours. In contrast, at full moon, it rises around sunset and sets around sunrise, providing nighttime illumination. Yearly patterns in moonrise timings arise from the Moon's declination cycle, which repeats every 27.3 days as the Moon's orbit tilts relative to the celestial equator, shifting the rise and set times northward or southward. This short-term cycle is modulated by the 18.6-year nodal precession, during which the orientation of the Moon's orbital plane rotates, alternating between minor and major lunar standstills that amplify or dampen the declination extremes and thus the temporal variations. In mid-latitudes, these combined effects allow moonrise to occur over a wide range, for example, as early as about 4 a.m. during summer new moons with high northern declination to as late as about 8 p.m. during summer full moons with high southern declination, highlighting the seasonal and long-term influences on observation windows.^[34]^[36]

Visual Characteristics

Apparent Size and Illusion

The Moon illusion refers to the perceptual phenomenon where the Moon near the horizon appears significantly larger than when it is high in the sky, despite its angular diameter remaining constant at approximately 0.5 degrees. Observers typically estimate the horizon Moon as 1.3 to 1.7 times larger in apparent size compared to the zenith Moon, creating a striking visual effect during moonrise and moonset. This illusion is not due to any physical change in the Moon's size or distance but arises from cognitive processing in the human visual system.^[40]^[41] One prominent explanation involves the Ponzo illusion, where contextual cues from the surrounding landscape, such as converging lines of perspective (e.g., roads or buildings receding toward the horizon), trick the brain into perceiving the horizon Moon as farther away than it actually is. To maintain size constancy—the brain's tendency to perceive objects as unchanging in size despite varying distances—the visual system compensates by enlarging the perceived size of the Moon. Alternative accounts emphasize misjudgment of angular size due to the flattened appearance of the sky near the horizon, leading to an overestimation of the Moon's retinal image extent relative to familiar terrestrial objects. In both cases, no actual enlargement occurs; the illusion stems purely from perceptual interpretation.^[41]^[42]^[43] Experimental studies have demonstrated that the magnitude of the Moon illusion varies with horizon features, providing further insight into its contextual dependence. For instance, when the Moon is viewed against a cluttered city skyline rich in depth cues like buildings and streets, the perceived size increase is more pronounced than over an open sea, where minimal terrestrial references reduce the illusion's intensity. These findings underscore how environmental surroundings modulate the brain's distance estimation, amplifying the effect during moonrise over urban landscapes. Atmospheric distortions can briefly enhance this perceptual bias by slightly flattening the Moon's shape, though they do not cause the primary illusion. Ultimately, the actual angular size of the Moon remains unchanged throughout its path, with the brain's compensatory mechanisms for perceived horizon distance driving the deceptive enlargement.^[44]^[45]^[46]

Colors and Distortions

During moonrise and moonset, the Moon frequently takes on a reddish or orange hue due to Rayleigh scattering in Earth's atmosphere, where shorter-wavelength blue light is preferentially scattered away, allowing longer red and orange wavelengths to dominate the view, much like during sunsets.^[47] This effect intensifies when the Moon is low on the horizon, as its light traverses a longer atmospheric path, filtering out more blue light.^[48] The "harvest moon," the full moon nearest the autumnal equinox, often appears particularly golden because of this low-angle path through the denser lower atmosphere, enhancing the warm coloration.^[49] Atmospheric refraction further alters the Moon's appearance by bending incoming light rays through layers of air with varying densities, primarily in the lower troposphere, which compresses the Moon's circular disk into an oval or egg-like shape, with the bottom portion appearing flattened or elevated relative to the top.^[50] These distortions arise because the refractive index of air, approximately 1.0003 under standard sea-level conditions, causes greater bending for light passing through thicker atmospheric columns near the horizon, increasing the optical path length and introducing chromatic dispersion that separates colors slightly.^[51] Additionally, atmospheric turbulence from irregular air movements creates a shimmering "boiling" effect, where pockets of warmer and cooler air act as transient lenses, further blurring and warping the Moon's edges.^[52] Temperature and pressure gradients in the atmosphere can produce superior mirage effects, occasionally resulting in the rare green flash—a brief burst of green light at the Moon's upper rim during moonset—caused by differential refraction that isolates shorter green wavelengths after red and orange portions are obscured or bent away.^[53] Such mirages stem from sharp vertical changes in air density near the horizon, amplifying distortions when the Moon is at very low altitudes, typically 1-2 degrees above it, where the light path encounters the most variable conditions.^[50] These physical optical phenomena contribute to the Moon's altered visual characteristics without relying on perceptual illusions.

Observation and Prediction

Viewing Techniques

Observing moonrise and moonset requires selecting locations with a clear, unobstructed horizon, such as open plains or ocean vistas, to ensure the Moon emerges without interference from terrain features.^[54] Minimal light pollution is ideal, as it enhances the contrast of the Moon against the twilight sky, allowing better appreciation of its initial colors and shapes.^[55] Observers should arrive 10-20 minutes after the calculated rise time to allow for any blocking by minor elevations and to view the Moon once it has stabilized above potential obstacles.^[54] Practical techniques include using fixed landmarks, like distant hills or structures, to track the Moon's rising direction and azimuth, providing a reference for repeated observations from the same spot.^[2] Binoculars with 7x to 10x magnification are particularly useful during the initial rise, revealing surface details such as craters while the Moon's low position accentuates atmospheric colors without excessive shake.^[56] Noting the lunar phase aids in timing; a full Moon, rising near sunset, offers the most vivid colors due to its opposition to the Sun and low horizon passage.^[57] Always avoid sites where trees, buildings, or other structures block the view, as they can delay visibility by several minutes.^[58] In the Northern Hemisphere, winter moonrises occur higher in the sky and earlier in the evening compared to summer, owing to the Moon's opposition to the low winter Sun.^[59] A key aspect of successful viewing is patience during the Moon's ascent, as atmospheric distortions—such as wavering and elongation—gradually fade once it reaches 5-10° altitude, yielding a steadier image.^[9]

Modern Tools

Contemporary tools for predicting moonrise and moonset leverage computational algorithms and user-friendly interfaces to deliver location-specific ephemerides with high precision. Websites like Timeanddate.com allow users to input latitude and longitude or select a city to instantly retrieve moonrise and moonset times, azimuth directions, altitudes, and distances for any date.^[60] Similarly, the U.S. Naval Observatory (USNO) provides data services such as the Complete Sun and Moon Data for One Day tool, which computes rise, set, and transit times based on geographic coordinates, offering tabular outputs for single days or entire years.^[22] Open-source software like Stellarium simulates real-time celestial positions in a virtual planetarium, displaying moonrise and moonset times alongside visual trajectories when configured with the observer's location.^[61] Underlying these applications are sophisticated algorithms for celestial mechanics. Sophisticated algorithms based on dedicated lunar ephemerides, such as the ELP-2000 theory or JPL's Development Ephemeris series, calculate the Moon's geocentric position with sub-arcsecond accuracy over millennia, incorporating lunar perturbation models.^[25] Rise and set times are then determined through iterative numerical methods adapted from the Solar Position Algorithm (SPA), which solve for the moment when the Moon's apparent altitude equals zero, adjusted for the observer's horizon. These computations incorporate standard atmospheric refraction (approximately 34 arcminutes at the horizon) and the Moon's horizontal parallax (about 57 arcminutes), ensuring predictions align with observed events.^[22] Mobile applications extend these capabilities for practical use, particularly in fields like photography. For instance, The Photographer's Ephemeris app overlays moonrise azimuth lines on interactive maps, enabling users to plan compositions by aligning the Moon's path with specific landscapes or structures.^[62] GPS integration in such apps automatically populates latitude, longitude, and elevation, streamlining setup and enhancing portability.^[62] Overall, these tools achieve timing accuracy within about 1 minute under standard conditions, making them reliable for astronomers, photographers, and navigators.^[22]

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Basics of Positional Astronomy: Moon Position
The first equatorial coordinate is declination delta, measured in degrees north and south of the celestial equator (N: 0° < delta < 90°, S: 0° > delta > - 90°.
[28]
Elevation and Azimuth of the Sun
The refraction R is calculated by Saemundsson's formula (Meeus, Astronomical Algorithms):. formula. h is the true (airless) elevation in degrees, R is in ...
[29]
FAQ: Moonrise, Moonset, and Moon Phase - Time and Date
The Moonrise & Moonset page offers Moon times and directions for any location. It also shows the current Moon phase and position in real-time.
[30]
Moonrise, Moonset for Troy, MI, USA for Friday, Nov 7, 2025
Moonrise. 6:43 PM. Altitude 0°Azimuth 50° NE ; Moon Culmination. 1:55 AM. Altitude 74°Azimuth 180° S ; Moonset. 10:11 AM. Altitude 0°Azimuth 309° NW.
[31]
[PDF] Understanding tides - the NOAA Institutional Repository
The Moon's declination completes a full cycle approximately every 27% days. In completing this cycle, it can reach maximum values of nearly 28.6° north and ...
[32]
[PDF] cev trajectory design considerations for lunar missions
The Moon's inclination, relative to the Earth equator, varies between 18.3º and 28.6º over an 18.6 year period (metonic cycle). The lunar orbit inclination and ...
[33]
Major Lunar Standstill -- Moon Teachings for the Masses
Moon Phases: The Moon orbits, or revolves, around Earth and completes one revolution in 29.5 days. This is the same length of time that it takes the Moon ...Missing: Synodic USNO<|separator|>
[34]
stonehenge
May 14, 2005 · Similarly the winter full moon rise nearest solstice can be 50 degrees south of north. ... lunar standstill moonrise or moonset at a latitude L ...
[35]
Altitude and Azimuth of the Sun or Moon During One Day
This service calculates the altitude and azimuth of the Sun or Moon at multiple times during any day between 1700 and 2100, for the center of the disk.
[36]
Why does the daily moonrise time vary by as much as 60 minutes ...
Sep 28, 2015 · Moonrise times can vary between 30 and 60 minutes in a month due to our satellite's tilted orbit and changing speed.
[37]
Lunar Perigee and Apogee - Time and Date
Jan 13, 2025 · The Moon's orbit around Earth is elliptical. The point of the orbit closest to Earth is called perigee, while the point farthest from Earth is known as apogee.
[38]
Extreme Moon: The Major Lunar Standstills of 2024 - 2025
The major lunar standstill results from the rotation of the Moon's inclined orbit over an 18.6-year cycle. Because the greatest monthly excursion of the Moon ...Missing: declination 27.3 nodal precession
[39]
[PDF] The Moon Illusion Explained - UW-Whitewater
The ones higher than an elevation of 45 degrees are arbitrarily on a circular arc at a perceived distance 1.6 times greater than those on the arc for the same ...
[40]
The Moon Illusion: Why Does the Moon Look So Big Sometimes?
Feb 13, 2025 · ... Moon is both closer and bigger than it is? There's an effect discovered a century ago called the Ponzo illusion that describes how this works.
[41]
Explaining the moon illusion - PMC - NIH
The moon illusion makes the horizon moon appear larger and more distant than the elevated moon, as the perceptual system treats the horizon moon as if it were ...
[42]
The Moon Illusion.
The moon illusion will undoubtedly contribute to the theory of normal size-distance perception, as "the study of the illusions of the senses is... a very ...
[43]
The horizon line, linear perspective, interposition, and background ...
compared with when it was viewed over a city skyline—a circumstance in which ... moon illusion. Emmert's law—a specific variation of the size–distance ...
[44]
(PDF) The horizon line, linear perspective, interposition, and ...
Aug 9, 2025 · ... experiments that explored the magnitude of the moon illusion in pictures. ... city skyline—a. circumstance in which a horizon line did not ...
[45]
[PDF] The Moon Illusion, I - Stacks
The horizon moon appears larger than the zenith moon because the terrain creates the impression that the horizon moon is farther away.
[46]
[PDF] Lect. Notes 13 - High Energy Physics
The scattering of EM radiation off of atoms is known as Rayleigh scattering. ... Note that this is also true for moonrise and moonset – the moon will {likewise} ...
[47]
Harvest supermoon to light up night sky: How to see October's full ...
Oct 4, 2025 · Color: Expect a golden-orange glow in the first hour after moonrise. That's because Earth's atmosphere scatters shorter wavelengths of blue ...
[48]
Super Harvest Moon: When, How to See It, and Why It's Special
Sep 26, 2025 · When it's low on the horizon, Earth's atmosphere scatters blue light and lets red and orange wavelengths pass through, giving the Moon its warm ...Missing: angle | Show results with:angle
[49]
What makes oddly shaped suns and moons on the horizon?
Apr 8, 2025 · The answer is atmospheric refraction, the effect of light traveling through different densities and temperatures of air.
[50]
Refractive index of Air - Ciddor - RefractiveIndex.INFO
Air has a refractive index very close to 1 (approximately 1.0003 at sea level under standard conditions), which varies slightly with temperature, humidity, and ...
[51]
How to Successfully Beat Atmospheric Seeing - Sky & Telescope
Sometimes, when watching an extended object like the Moon or a planet, you can focus the telescope on a horizontal layer of "shear turbulence" a few thousand ...
[52]
Rare Green Flashes Captured From the Moon - Universe Today
Apr 29, 2011 · When the conditions are just right, with an additional mirage effect due to the temperature gradient in the atmosphere, the elusive green flash ...Missing: pressure | Show results with:pressure
[53]
Moonrise Tonight: The Ultimate 2025 Guide to Viewing ... - CITIPEN -
Jun 12, 2025 · Successful moonrise observation requires unobstructed eastern horizons extending at least 5-10 degrees above landscape features to ensure clear ...
[54]
Which moon phase is best for stargazing? That depends. - EarthSky
Jun 1, 2025 · To see these deep-sky objects well, the sky must be dark, free of light pollution and moonlight. ... observe before moonrise or after moonset.Missing: clear | Show results with:clear
[55]
https://earthsky.org/tonight/what-moon-phase-is-best-for-stargazing/
[56]
Why is the Moon not redder at moonrise/moonset?
Oct 5, 2014 · The rising Moon appears to be quite red on the horizon. This quickly changes to yellow and then to white as the elevation angle increases.
[57]
Guide to Planning and Photographing the Moonrise - Skylum
Nov 13, 2023 · Consider local geography, the direction of the moonrise and possible obstacles, such as buildings or trees that could obstruct your view.
[58]
Lunistices/Lunar Standstills - Rice University
Jan 18, 2025 · Similarly, at the winter solstice the Sun is lowest in the sky, so a northern lunistice occurs when the Moon is opposite in the sky from the Sun ...
[59]
Moonrise and Moonset Calculator - Time and Date
Calculate moonrise and moonset times, Moon direction, as well as the altitude, distance and when the moon passes the meridian.Moon Light World Map · Moon Phases · New York · Los Angeles, California, USAMissing: winter summer
[60]
[PDF] Stellarium 25.2 User Guide - Georg Zotti, Alexander Wolf (editors ...
... sunrise and sunset, twilights, moonrise and moonset. Civil Twilight occurs when the zenith angle of the center of the Sun is less than 96◦ (6◦ below the ...
[61]
VSOP87 Multilang - Celestial Programming
The purpose of this project is to provide implementations of the VSOP87 theory in multiple languages at different levels of precision.
[62]
The Photographer's Ephemeris
Photo Ephemeris is a map-based app for photographers to plan outdoor shots using natural light, including sun, moon, and Milky Way, with 3D visualization.Photo Ephemeris Web · 3D · Photo Ephemeris · Support