Night Sky Viewer &
NOAA Orbit Tracker

You are holding two instruments. The Night Sky Viewer is an interactive planetarium that puts the entire visible sky on your screen, then lets you punch through to real photographic imagery from the world's greatest telescopes. The NOAA Orbit Tracker follows the Joint Polar Satellite System constellation in real time as it circles the Earth every 101 minutes, scanning the planet with infrared eyes.

What makes these different from a typical star chart or satellite map: when you zoom in on a nebula, you are looking at actual photographic plates from the Digitized Sky Survey, or deep exposures from Hubble, or infrared light captured by 2MASS. When you track NOAA-21, you are watching real SGP4-propagated orbital mechanics computed from today's Two-Line Element sets. These are not illustrations. This is the data.

The sky looks different from every point on Earth, so the first thing the viewer needs to know is where you are standing. You have three ways to tell it. When the location changes, the entire sky redraws to show what is actually above your horizon right now.

The 3x3 compass grid below the location input points your view toward any cardinal or intercardinal direction. South is selected by default because most interesting objects transit through the southern sky (if you are in the Northern Hemisphere). Click N, NE, E, SE, SW, W, or NW to swing your view. The center dot represents zenith -- straight up.

Each click immediately re-renders the planetarium. The current direction is shown in the info bar at the bottom of the screen.

The planetarium is powered by VirtualSky by Stuart Lowe (Las Cumbres Observatory). It renders stars by apparent magnitude, draws constellation stick figures, plots the planets at their current positions, and shows the ground and horizon. Drag to pan, scroll to zoom, and use the controls panel to toggle overlays and adjust settings.

The Projection dropdown changes how the spherical sky gets flattened onto your rectangular screen. Each one is useful for different things:

• Stereographic (horizon) -- The default. Shows the sky as you would see it standing outside and looking in one direction. The horizon is at the bottom, zenith is up. This is the most natural view.
• Fisheye (wide angle) -- A wider field of view with barrel distortion, like looking through a security camera. Good for getting a sense of the whole visible sky at once.
• Polar (zenith up) -- Centers on the point directly overhead. Constellations near zenith are shown undistorted; the horizon wraps around the edges.
• Lambert (all-sky) -- An equal-area projection of the entire hemisphere. Every constellation gets fair representation, though shapes distort near the edges.
• Orthographic -- The sky as seen from infinitely far away. Clean and geometric.
• Mollweide (full map) -- Shows the entire celestial sphere in an ellipse, like a world map projection. Both hemispheres visible at once.
• Free Look (drag anywhere) -- Unlocks the view from the horizon. Drag to look anywhere on the celestial sphere. Ground and cardinal points are disabled automatically since they do not apply in this mode.

The Objects section gives you checkboxes for everything the planetarium can draw:

These overlays help you navigate the coordinate systems astronomers use:

Live mode (checkbox, default on). When checked, the sky updates in real time. The clock ticks, the stars drift, the planets creep along.

When you click any time button, Live mode automatically disengages:

The current simulated date and time are displayed below the buttons. Use the time controls to preview tonight's sky before you go outside, or check what was visible last night.

Click the "Advanced Settings" expander to reveal three sliders and a color scheme selector:

Star Magnitude (range 1-8, default 5). This controls how faint the faintest visible stars are. Magnitude 5 approximates what a dark suburban sky shows. Crank it to 8 to see thousands more stars. Drop it to 1 or 2 for a minimalist view showing only the brightest.

Field of View (range 20-120 degrees, default 60). How wide your view is. 60 degrees is roughly what your eyes see when you look in one direction. Go to 120 for a panoramic sweep. Narrow it to 20 for a telephoto-like zoom on one patch of sky.

Star Size (range 0.5x-2.0x, default 1.0). A cosmetic multiplier on how large the star dots render. Useful on high-DPI screens or if you want the planetarium to feel bolder.

Color Scheme. Normal gives you white stars on a dark sky. Negative inverts everything -- dark stars on a white background -- useful for printing star charts.

Below the Advanced Settings, a Rise / Set Times panel lets you pick any solar system object from a dropdown -- Sun, Moon, Mercury, Venus, Mars, Jupiter, or Saturn. Select one and the app fetches its rise, transit, and set times for today, plus draws an altitude-over-time chart showing the object's arc across your sky. The horizon line is highlighted in amber at zero degrees. This is enormously helpful for planning: "When does Jupiter clear the trees tonight?"

The telescope interface provides these controls:

• Search box -- Type any object name or catalog number and press Enter or click Go. The viewer resolves the name through SIMBAD and flies to those coordinates.
• Catalog toggles -- Messier (red circles), NGC (green squares), Star Names (yellow crosses). Overlays reload when you pan to a new region.
• Survey dropdown -- Switch between DSS2, SDSS, PanSTARRS, Hubble, 2MASS, GALEX, Fermi, ROSAT, and more. See the Sky Surveys section for details on each.
• Zoom buttons -- Click + Zoom to halve the field of view (zoom in). Click - Zoom to double it (zoom out). You can also scroll your mouse wheel. At maximum zoom you can reach sub-arcsecond scales.
• Fullscreen button -- Expands the telescope view to fill your entire screen. Press Escape or click the X to exit.
• Coordinate display -- RA/Dec updates in real-time as you pan across the sky.

When the telescope identifies an object -- either from a right-click, a search, or clicking a catalog marker -- a detailed info panel appears below the viewer. It shows:

• Object name and type (galaxy, nebula, star cluster, etc.)
• Visual magnitude with a human-readable description ("Visible to naked eye," "Binoculars needed," etc.) and all available photometric bands
• Spectral type for stars, with a plain-English translation ("G2V -- Yellow star, like our Sun")
• Distance in light years, computed from parallax when available
• Radial velocity -- whether the object is approaching or receding, and how fast
• Angular size for extended objects
• Coordinates in RA/Dec
• Nearby objects in the same field -- other cataloged items within the search radius
• Fun facts -- contextual notes based on object type ("Nebulae are stellar nurseries where new stars are born from clouds of gas and dust")

The Survey dropdown is one of the most powerful controls in the entire app. Each survey captured the sky in different wavelengths, at different depths, and at different resolutions. Switching surveys on the same object is like putting on different pairs of glasses -- optical shows what our eyes would see, infrared penetrates dust clouds, ultraviolet reveals hot young stars, X-ray and gamma-ray show the violent universe. The telescope view gives you access to all of these, plus additional surveys like DECaPS (Dark Energy Camera Plane Survey, focused on the galactic plane where star fields are crowded) and Mellinger (a wide-field visible light mosaic, good for context when you want to see where your object sits relative to the Milky Way).

The Observation Planner is a separate page (click the Observation Planner link in the header) built for planning real observing sessions. It includes:

• Tonight's Best -- Ranks every Messier and Caldwell object by visibility from your location right now. Each object card shows its name, type, constellation, magnitude, and current altitude/azimuth. Objects near transit get an "Optimal" badge. Filter by object type. The ranking algorithm accounts for your latitude, the object's current altitude, and the limiting magnitude for your Bortle class (light pollution level).
• Object Checklists -- The complete Messier catalog (110 objects) and Caldwell catalog (109 objects) as checklists with progress bars. Check off objects as you observe them. Your progress persists in local storage between sessions.
• Ephemeris Calculator -- Search for any object and get its current altitude, azimuth, and rise/transit/set times. A visual timeline shows the object's arc with twilight zones behind it.
• Angular Distance Calculator -- Enter two RA/Dec coordinates and get the angular separation in degrees, arcminutes, arcseconds, and Moon widths. Useful for star-hopping.
• Moon Phase Widget -- Shows the current Moon phase as an SVG illustration with illumination percentage, age in days, rise/set times, and the date of the next full Moon. The Moon is the number one factor in whether you will have a good deep sky night.
• Weather Forecast -- A 48-hour cloud cover forecast from Open-Meteo, rendered as a color-coded bar chart. Green means clear skies. Red means overcast. It automatically identifies good observing windows.
• Constellation Stories -- Mythology and lore for constellations, sorted by culture and category. Search or browse.
• Bortle Class Indicator -- Your site's light pollution level on a scale from 1 (pristine dark site) to 9 (inner-city). The limiting magnitude adjusts accordingly.

At the bottom of the Night Sky Viewer, a horizontal timeline bar shows the darkness conditions for the next 24 hours.

True astronomical darkness -- when the Sun is more than 18 degrees below the horizon -- is what you need for serious deep sky observing. The bar makes it obvious how much dark time you have.

Moon overlay: Hatched regions on the bar indicate when the Moon is above the horizon. Even during full night, a bright Moon washes out faint objects. The ideal observing window is the gap where the bar is black and there is no hatching.

Summary line: Above the bar, a one-line summary reads something like: "6.2h dark / 4.1h moonless / Waxing Gibbous." That tells you everything you need to plan your night in three numbers.

The Now marker: A thin amber vertical line marks the current time on the bar and updates every minute.

Red light mode shifts the entire interface to deep red tones. Every element -- text, backgrounds, buttons, the planetarium itself -- goes red.

Why astronomers use it: Your eyes take 20 to 30 minutes to fully adapt to darkness. White or blue light from a screen destroys that adaptation instantly. Red light, however, does not affect your rod cells (the ones responsible for night vision). Professional observatories use red lighting exclusively after dark. So do experienced amateur astronomers.

How to toggle it: Click the Red Light button in the top header bar. It has a small sun icon. Click it once to go red, click again to go back to normal. Your preference is saved in local storage, so if you enable it tonight, it will still be on when you come back tomorrow night. The Observation Planner has its own independent night mode toggle that works the same way.

The Joint Polar Satellite System is a constellation of three satellites -- NOAA-21 (launched 2022), NOAA-20 (launched 2017), and Suomi NPP (launched 2011) -- operated by NOAA and NASA. They fly in sun-synchronous polar orbits at about 824 km altitude, circling the Earth every 101 minutes. Each one carries the VIIRS instrument, which scans a 3,060 km wide swath below, imaging the entire planet twice per day in 22 spectral bands.

The default tab shows a polar azimuthal projection of the Earth with the selected satellite's current position marked as a colored, pulsing dot. A fading trail shows where it has been. A dashed prediction line shows where it is going, computed from the pre-fetched 3-hour track. The VIIRS swath is drawn as a translucent band around the ground track. A velocity vector arrow shows the direction of motion.

The orbital info panel (top-left) displays the satellite's inclination, altitude, orbital period, and current orbit number. The position panel (top-right) shows latitude, longitude, altitude in km, and velocity in km/s. Toggle buttons in the legend panel let you show or hide the swath, velocity vector, and day/night terminator independently.

In 2D modes, press M or click the P/E button to toggle between polar (azimuthal equidistant) and equirectangular (flat map) projections. Hover your mouse over the map and the bottom-right panel shows the geographic coordinates under your cursor.

Click the Constellation tab to see all three satellites simultaneously on the same map. Each is drawn with its own color and label. Click any satellite marker to select it. The position panel updates to show that satellite's data.

This view makes visible the elegant phasing of the constellation -- the satellites are spaced to maximize global coverage. Each point on Earth is observed multiple times per day. The ground tracks show the characteristic sinusoidal pattern of polar-orbiting sun-synchronous satellites.

Click the 3D Globe tab to see the satellite on a WebGL-rendered Earth powered by globe.gl. The satellite appears as a glowing dot above the surface with its trail arcing behind it and prediction ahead. The VIIRS swath projects onto the globe surface. You can drag to rotate, scroll to zoom.

This view is the best way to viscerally understand what a polar orbit looks like -- the orbital altitude (roughly 824 km) and how the Earth rotates beneath the orbit, creating the ground track pattern.

Click the Time Machine button at the bottom of the screen to open the playback panel. Set a start time, duration (1, 3, 6, or 24 hours), and playback speed (10x to 3600x). Hit Play and the tracker animates the satellite along its historical track. A scrub bar lets you drag to any point in the window. The day/night terminator updates to match the simulated time.

This is mesmerizing at 300x speed over a 24-hour window -- you watch the satellite weave back and forth across the poles while the Earth rotates beneath it.

The 24h Coverage tab draws the full 24-hour ground track for the selected satellite. This reveals the characteristic sinusoidal pattern of a polar orbit, and the progressive westward drift of each track as the Earth rotates beneath it. After 24 hours, the tracks nearly tile the globe -- that is the whole point of the JPSS orbit design.

A warning notes that SGP4 accuracy degrades beyond plus or minus 7 days from the TLE epoch.

The Night Sky Viewer's telescope mode queries SIMBAD (operated by CDS Strasbourg) through the backend API to resolve object names, search regions, and retrieve catalog data. When you right-click a star or search for an object, SIMBAD provides the name, type, spectral class, magnitudes, parallax, radial velocity, and angular size that appear in the info panel.

Search by object name, coordinates, or catalog identifier. Returns: object type, coordinates, magnitude, radial velocity, spectral type, proper motion, cross-identifications in other catalogs, and links to bibliography. This connects the visual sky exploration to the professional astronomical literature.

Quick-reference keyboard shortcuts for the Night Sky Viewer and NOAA Orbit Tracker. The planetarium supports mouse drag to pan and scroll wheel to zoom. The Orbit Tracker has its own set of keys for navigation and playback.

This project stands on the shoulders of extraordinary open-source work and open data:

VirtualSky by Stuart Lowe, Las Cumbres Observatory. The planetarium engine that renders the interactive sky.

Aladin Lite by the Centre de Donnees astronomiques de Strasbourg (CDS). The telescope viewer that streams HiPS sky survey tiles. The same technology used by professional astronomers worldwide.

Skyfield by Brandon Rhodes. The Python library that computes satellite positions, rise/set times, and twilight calculations on the backend.

CelesTrak maintained by Dr. T.S. Kelso. The source for current Two-Line Element sets that make satellite tracking possible.

SIMBAD by CDS Strasbourg. The astronomical database that resolves object names and provides catalog data for the telescope info panel.

SGP4 orbital propagation, based on the work of David Vallado. The algorithm that predicts where a satellite will be given its TLE.

Data sources: NASA (Hubble, Fermi, GALEX), ESA, NOAA (JPSS satellite operations), EUMETSAT, Sloan Digital Sky Survey, PanSTARRS (University of Hawaii), 2MASS (UMass/IPAC), ROSAT, the Digitized Sky Survey (STScI/AAO/UK-PPARC).

Chart.js for the rise/set altitude plots and weather charts. D3.js for the orbital map projections. globe.gl for the 3D Earth view.