Positive: Northern Hemisphere (e.g., 42.0 for New York)
Negative: Southern Hemisphere (e.g., -33.9 for Sydney)
Observer Longitude
Range: -180° to +180°
Positive: Eastern Hemisphere
Negative: Western Hemisphere
Observation Date
Date for the observation session. Calculations cover the entire night from sunset to sunrise.
GPS Location
Click "Use My Location" for automatic coordinate detection.
Understanding Sky Direction Parameters
The Object Finder uses a celestial coordinate system to locate objects in the sky. Three parameters work together to define your search area:
1. Azimuth (Compass Direction)
Range: 0° to 360°
Azimuth is the compass direction measured clockwise from North. Think of it as looking at the sky from above.
Azimuth: View From Above (Looking Down at Observer)
Looking down from above, azimuth sweeps clockwise from North (0°) through East (90°), South (180°), and West (270°).
Interactive Compass
Use the visual compass rose in the app to click and select your azimuth direction instead of typing degrees.
3D Sky Preview
The Object Finder features a real-time 3D sky preview that shows the exact search area BEFORE you click "Find Objects". This interactive hemisphere visualization updates instantly as you adjust azimuth, altitude range, and search radius parameters. Drag to rotate the view, scroll to zoom. The camera position is preserved as you change parameters, so you can explore from your preferred angle. The bounded search patch appears as a colored area on the hemisphere, showing you precisely which part of the sky will be searched.
2. Altitude Range (Elevation Angle)
Min Altitude: 0° to 85°Max Altitude: 5° to 90°
The Object Finder uses an altitude range to define the vertical bounds of your search area. Instead of searching at a single elevation, you specify minimum and maximum altitudes to create a bounded patch in the sky.
Min Altitude
The lower boundary of your search area. Objects below this altitude will not be included in results.
Max Altitude
The upper boundary of your search area. Objects above this altitude will not be included in results.
5° Minimum Gap
The system enforces a minimum 5° gap between min and max altitude to ensure a usable search area. When you adjust one slider, the other may automatically adjust to maintain this gap.
Altitude: Side View (Elevation from Horizon)
From the observer's position: 0° = horizon (looking straight ahead), 45° = halfway up, 90° = zenith (straight overhead).
Altitude Range Examples:
30°-35° = Narrow low-altitude band (5° span, more atmospheric extinction)
20°-40° = Moderate elevation band (20° span)
45°-60° = Mid-sky band (15° span, good imaging conditions)
60°-75° = High altitude band (15° span, excellent conditions)
85°-90° = Near-zenith band (5° span at minimum gap, optimal conditions)
3. Search Area Radius
Range: 1° to 90°
The search radius defines how far left and right from your target azimuth to search. Combined with the min/max altitude range, this creates a bounded rectangular patch on the sky hemisphere.
How the Bounded Search Area Works
Your search area is defined by four boundaries:
Left boundary: Target azimuth - search radius
Right boundary: Target azimuth + search radius
Bottom boundary: Minimum altitude
Top boundary: Maximum altitude
Visualize Your Search Area
The 3D Sky Preview shows this bounded rectangular patch in real-time. Watch it update as you adjust the search radius and altitude range to see exactly which part of the sky will be searched.
Search Area: Interactive 3D Sky Hemisphere
Interactive 3D visualization - Drag to rotate, scroll to zoom. The hemisphere shows the sky dome from the observer's perspective. Different colored patches show search areas with varying radii: 15° (red/narrow), 30° (yellow/standard), and 60° (green/wide). Each patch is bounded by min/max altitude (30°-40°) and extends ±radius from the target azimuth (South/180°). Toggle patches on/off using the legend.
Search Radius Guide:
10-15° = Narrow azimuth range for specific target framing (±10-15° from center)
20-30° = Typical wide-field imaging area (±20-30° from center)
40-50° = Large region survey (±40-50° from center)
60°+ = Very broad exploration of entire sky area (±60°+ from center)
Putting It All Together
These three parameters work together to define a bounded rectangular search area on the sky hemisphere:
Complete Example: South at 25°-50° altitude range, 30° search radius
Interactive 3D example - Drag to rotate, scroll to zoom. This shows all parameters working together: Azimuth (South/180°) sets the compass direction, Min/Max Altitude (25°-50°) defines the vertical bounds (25° vertical span), and Search Radius (30°) defines how far left and right to search (±30° in azimuth). The yellow rectangular area on the hemisphere shows the bounded search patch - note how it's clearly bounded by min altitude at the bottom (25°), max altitude at the top (50°), and extends from 150° to 210° in azimuth (±30° from South). The blue diamond marks the center of the patch.
Practical Examples
Example 1: Imaging the Milky Way Core (Northern Hemisphere Summer)
Azimuth: 180° (South)
Min Altitude: 20°, Max Altitude: 40° (low to mid sky band)
Search Radius: 45° (wide field to capture the region) → Finds objects in the southern Milky Way region within a 20° vertical band
Example 2: Overhead Targets at Zenith
Azimuth: 0° (any direction - doesn't matter at zenith)
Min Altitude: 85°, Max Altitude: 90° (near-zenith band at minimum gap)
Search Radius: 30° (moderate area around zenith) → Finds objects passing directly overhead (best conditions, minimal extinction)
Example 3: Eastern Sky in Early Evening
Azimuth: 90° (East)
Min Altitude: 30°, Max Altitude: 60° (low to high elevation band)
Search Radius: 30° (standard wide field) → Finds objects rising in the east across a 30° vertical range
Example 4: Exploring the Northern Sky
Azimuth: 0° (North)
Min Altitude: 50°, Max Altitude: 75° (high in the sky)
Search Radius: 60° (very large survey) → Broad search of northern circumpolar region across 25° vertical span
Pro Tips
Use the 3D Sky Preview! Watch the bounded search area update in real-time as you adjust parameters
Start with azimuth to pick your compass direction (use the interactive compass)
Set min/max altitude to define your vertical search boundaries (minimum 5° gap enforced)
Adjust search radius to control azimuth spread (±radius from target direction)