The same Moon that Artemis II will fly behind rises over Possession Sound every night. The same Sun that powers the SLS solar arrays sets behind the Olympics from this latitude. SOL tracks the celestial mechanics that connect the sky above Mukilteo to the missions beyond it.
Moon Phase
Day Cycle
Sun Today — March 31, 2026
Moon Today
Space Weather
Artemis II — Lunar Connection
The Sun G2V main-sequence star, 4.6 billion years
Solar Basics
| Parameter | Value |
|---|---|
| Distance from Earth | 149,597,870.7 km (1 AU) |
| Light travel time | 8 minutes 19 seconds |
| Radius | 696,340 km (109 Earths) |
| Mass | 1.989 × 10³&sup0; kg (333,000 Earths) |
| Surface temperature | 5,778 K (5,505°C) |
| Core temperature | ~15,700,000 K |
| Luminosity | 3.828 × 10²&sup6; W |
| Spectral class | G2V (yellow dwarf) |
| Rotation period | ~25.4 days (equator), ~34.4 days (poles) |
| Age | 4.603 billion years |
| Expected lifetime | ~10 billion years total |
Solar Structure
| Layer | Depth | Temperature | Notes |
|---|---|---|---|
| Core | 0 – 0.25 R | ~15.7 MK | pp-chain fusion, 99% of energy output |
| Radiative Zone | 0.25 – 0.7 R | 7 – 2 MK | Photon random walk: ~170,000 years to cross |
| Tachocline | ~0.7 R | ~2 MK | Shear layer, origin of magnetic dynamo |
| Convective Zone | 0.7 – 1.0 R | 2 MK – 5,778 K | Convection cells visible as granulation |
| Photosphere | Surface | 5,778 K | Visible "surface," sunspots form here |
| Chromosphere | +2,000 km | ~20,000 K | Visible during eclipses as pink rim |
| Corona | +millions km | 1 – 3 MK | Coronal heating problem: hotter than surface |
Solar Cycle 25
We are in Solar Cycle 25, which began December 2019. Solar maximum is expected 2025–2026, making this an active period for sunspots, solar flares, and coronal mass ejections. The Kp index measures geomagnetic disturbance driven by solar wind interaction with Earth's magnetosphere.
Kp 0–3: quiet. Kp 4: unsettled. Kp 5+ triggers aurora visible from Washington state. During Solar Cycle 25's peak, aurora has been visible from Mukilteo multiple times.
For Artemis II: Space weather affects crew radiation exposure and communications. The O2O optical system is less affected by solar radio interference than S-band. Current Kp 2.0 is benign.
Solar Cycle 25 Activity
Sunspot number tracks the 11-year solar magnetic cycle. Cycle 25 has exceeded initial predictions, with observed sunspot numbers consistently above the forecast curve since late 2023. The current ascending phase means increased flare probability and more frequent geomagnetic storms.
Data source: NOAA SWPC · WDC-SILSO (Royal Observatory of Belgium)
Latitude 47.9°N — What the Sun Does Here
At Mukilteo's latitude, the day length swings from 8h 21m (winter solstice) to 16h 02m (summer solstice) — a 7h 41m range. Today (March 31) is just past the equinox, gaining ~3 minutes of daylight per day. The Sun reaches a maximum altitude of ~65° at summer solstice, never directly overhead.
The marine layer, Olympic rain shadow, and Cascade convergence zone all interact with solar heating to create Mukilteo's microclimate — fog burns off later here than 10 miles inland.
Solar Altitude Through the Year at 47.9°N
The Sun's maximum altitude at solar noon varies with the seasons due to Earth's 23.44° axial tilt:
| Date | Event | Noon Altitude | Day Length |
|---|---|---|---|
| June 20 | Summer Solstice | 65.5° | 16h 02m |
| Mar 20 / Sep 22 | Equinoxes | 42.1° | 12h 10m |
| Dec 21 | Winter Solstice | 18.7° | 8h 21m |
The low winter sun angle means solar panels at this latitude are most efficient tilted 40-50° from horizontal. The long summer days compensate for lower per-hour insolation, giving Mukilteo surprisingly good annual solar potential (~4.2 kWh/m²/day average).
The Moon 384,400 km mean distance
Lunar Basics
| Parameter | Value |
|---|---|
| Mean distance from Earth | 384,400 km (center-to-center) |
| Perigee (closest) | ~363,300 km |
| Apogee (farthest) | ~405,500 km |
| Light travel time | 1.282 seconds (one-way) |
| Radius | 1,737.4 km (0.273 Earths) |
| Mass | 7.342 × 10²² kg (1.2% Earth) |
| Surface gravity | 1.62 m/s² (16.5% Earth) |
| Orbital period (sidereal) | 27.322 days |
| Synodic month (phase cycle) | 29.531 days |
| Orbital eccentricity | 0.0549 |
| Orbital inclination | 5.145° to ecliptic |
| Recession rate | 3.8 cm/year (moving away from Earth) |
Lunar Surface Composition
| Feature | Coverage | Composition | Age |
|---|---|---|---|
| Highlands (terrae) | ~83% of surface | Anorthosite (Ca-feldspar) | 4.4 – 4.0 Ga |
| Maria (dark plains) | ~17% of surface | Basalt (Fe, Ti-rich) | 3.9 – 3.1 Ga |
| Regolith | Entire surface | Pulverized rock, 2–20 m deep | Ongoing |
| South Pole (Artemis III target) | Craters | Water ice in permanently shadowed regions | Ancient |
The far side that Artemis II will overfly has almost no maria — its crust is thicker, preventing magma from reaching the surface. The crew will see a dramatically different landscape from what is visible from Earth.
Tidal Locking & the Far Side
The Moon is tidally locked — it rotates exactly once per orbit, so the same face always points toward Earth. The far side (not "dark side" — it gets equal sunlight) was unseen by humans until Luna 3 photographed it in 1959, and unseen by human eyes until Apollo 8 in 1968.
Artemis II will fly 6,513 km above the far side surface, the first humans to see it directly since Apollo 17 in 1972. During the flyby, there will be a communication blackout — the Moon blocks line-of-sight to Earth. The crew will be on their own for approximately 30 minutes.
Moon & Tides at Mukilteo
Puget Sound experiences mixed semidiurnal tides — two highs and two lows per day, with unequal heights. The Moon's gravitational pull is the primary driver, with the Sun contributing ~46% as much tidal force. Spring tides (highest range) occur at full and new moon; neap tides at quarter phases.
Today's tides at Everett (Station 9447659): High 3.37m at 4:51 AM, Low 0.77m at 10:59 AM, High 3.01m at 5:04 PM, Low 0.72m at 10:57 PM. With the Moon nearly full, tidal range is near its spring maximum.
Planets Visible Tonight
Evening Sky — March 31, 2026
From Mukilteo at 47.9°N, the evening sky after sunset (7:39 PM) offers:
| Planet | Visibility | Notes |
|---|---|---|
| Venus | Morning star (pre-dawn) | Brightest object after Moon, low east before sunrise |
| Mars | Evening, west | In Gemini, dimming as Earth moves away |
| Jupiter | Evening, west-southwest | Setting earlier each night, in Taurus |
| Saturn | Not visible (conjunction) | Too close to Sun this month |
Approximate visibility from 47.9°N latitude. Actual visibility depends on atmospheric conditions and obstructions. The nearly-full Moon will wash out fainter objects tonight.
All Planets — Current Positions
| Planet | Distance from Sun | Distance from Earth | Magnitude | Constellation | Status |
|---|---|---|---|---|---|
| Mercury | 0.39 AU | ~1.2 AU | +0.5 | Pisces | Lost in twilight |
| Venus | 0.72 AU | ~1.4 AU | -4.0 | Aquarius | Morning star, brilliant |
| Mars | 1.52 AU | ~1.6 AU | +1.2 | Gemini | Evening, fading |
| Jupiter | 5.20 AU | ~5.8 AU | -2.1 | Taurus | Evening, prominent |
| Saturn | 9.54 AU | ~10.4 AU | +1.0 | Pisces | Solar conjunction |
| Uranus | 19.19 AU | ~20.0 AU | +5.8 | Taurus | Binocular object, near Jupiter |
| Neptune | 30.07 AU | ~30.9 AU | +7.9 | Pisces | Telescope required |
Distances and magnitudes are approximate for late March 2026. Inner planet positions change rapidly; outer planets shift slowly.
Celestial Mechanics — The Math Behind the Sky
Why the Moon Appears to Change Size
The Moon's orbit is elliptical (eccentricity 0.0549). At perigee (~363,300 km) its angular diameter is 33.5 arcminutes; at apogee (~405,500 km) it shrinks to 29.4 arcminutes — a 14% difference. "Supermoons" occur when full moon coincides with perigee.
Angular diameter formula: θ = 2 × arctan(R / d) ≈ 2R/d radians, where R = 1,737.4 km and d is the distance.
Synodic vs. Sidereal Month
The sidereal month (27.322 days) is the time for the Moon to orbit 360° relative to the stars. The synodic month (29.531 days) is the time between identical phases (e.g., full moon to full moon). The synodic month is longer because Earth has moved ~27° around the Sun during one lunar orbit, so the Moon needs ~2.2 extra days to "catch up" to the same Sun-Earth-Moon geometry.
Lagrange Points & the JWST Connection
The Sun-Earth system has five Lagrange points where gravitational and centripetal forces balance. L1 (sunward, 1.5M km) hosts DSCOVR/SOHO for solar monitoring. L2 (anti-sunward, 1.5M km) hosts JWST and Gaia. L4/L5 (60° ahead/behind Earth) collect Trojan dust.
The Earth-Moon system also has Lagrange points. Earth-Moon L2 (behind the far side) is where the Queqiao relay satellite operates for Chang'e missions. A future relay at EM-L2 could eliminate the communication blackout that Artemis II will experience during the far-side flyby.
Formula for L1/L2 distance: r ≈ R × (m2 / 3m1)1/3, where R is the orbital radius and m1, m2 are the two masses.
Sphere of Influence
The Moon's gravitational sphere of influence extends ~66,000 km from its center. Inside this boundary, the Moon's gravity dominates over Earth's for trajectory calculations. Artemis II enters this sphere on Day 3-4 outbound, and the free-return trajectory uses the Moon's gravity to redirect the spacecraft homeward without an engine burn.
Formula: rSOI = a × (mMoon/mEarth)2/5 = 384,400 × (0.0123)0.4 ≈ 66,183 km
Orbital Resonances in the Solar System
Orbital mechanics produces elegant integer ratios throughout the solar system. These resonances stabilize (or destabilize) orbits over millions of years:
| Bodies | Ratio | Type | Effect |
|---|---|---|---|
| Moon (rotation:orbit) | 1:1 | Spin-orbit | Tidal locking, same face to Earth |
| Mercury (rotation:orbit) | 3:2 | Spin-orbit | 3 rotations per 2 orbits |
| Io:Europa:Ganymede | 1:2:4 | Laplace | Mutual tidal heating (Io volcanism) |
| Pluto:Neptune | 2:3 | Mean-motion | Prevents close approaches |
| Jupiter:Saturn | ~2:5 | Near-resonance | Grand Tack migration theory |
Data Sources
| Source | Data | Update Frequency |
|---|---|---|
| USNO (aa.usno.navy.mil) | Sun/Moon rise/set, twilight, phase | Daily |
| sunrise-sunset.org | Sun times, day length, twilight | Daily |
| NOAA SWPC | Kp index, solar wind, aurora forecast | 5 minutes |
| NOAA Tides | Tide predictions (Station 9447659) | Daily |
| JPL Horizons | Moon distance, planetary ephemeris | On demand |
| NOAA DSCOVR/EPIC | Earth imagery from L1 | Hourly (when available) |
Deep Research — Science & Education Hub
Artemis II Mission
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