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ISS Spotting Guide

How to use pass predictions for successful ISS spotting and amateur radio communications

Understanding Pass Predictions

Each ISS pass prediction provides critical information to help you successfully spot the station or make amateur radio contact. Here's what each piece of data means:

Time Information

Rise Time
When the ISS first appears above your horizon. Start listening or watching at this time.
Max Elevation Time
When the ISS reaches its highest point. This is the best time for contact attempts.
Set Time
When the ISS disappears below your horizon. End of the pass.

Direction & Elevation

Azimuth (°)
Compass direction: 0°=N, 90°=E, 180°=S, 270°=W
Elevation (°)
Height above horizon: 0°=horizon, 90°=directly overhead
Direction
Cardinal direction (N, NE, E, SE, S, SW, W, NW)

Visual Guide: Reading the Sky

Elevation Angles

0°-10°
Very Low
Poor visibility
Weak signals
10°-30°
Low
Marginal
Basic operation
30°-60°
Good
Excellent visibility
Strong signals
60°-90°
Overhead
Best possible
Maximum signal

Compass Directions

N
0°
NE
45°
E
90°
SE
135°
S
180°
SW
225°
W
270°
NW
315°

For Visual Spotting

The ISS appears as a bright, fast-moving star. It's the third brightest object in the sky after the Sun and Moon when conditions are right.

1

Timing is Critical

Go outside 2-3 minutes before the rise time. The ISS moves quickly - passes typically last 2-8 minutes.

2

Find the Starting Point

Use the rise azimuth to determine where to look on the horizon. Face that compass direction and look low on the horizon.

3

Track the Path

The ISS will rise from the horizon, reach maximum elevation, then set in another direction. It moves as fast as a high-altitude aircraft.

4

Best Conditions

Look during evening or morning passes when the ISS is in sunlight but your location is in darkness. Clear skies required.

For Amateur Radio Operations

Using pass predictions for amateur radio contacts requires additional considerations beyond visual spotting.

Pre-Pass Setup

  • • Tune to the current ISS frequencies
  • • Point your antenna toward the rise azimuth
  • • Start listening 1-2 minutes before rise time
  • • Have your call sign and grid square ready

During the Pass

  • • Track the ISS with your antenna if possible
  • • Listen first - don't transmit immediately
  • • Account for Doppler shift (frequency change)
  • • Best signal strength at maximum elevation

Important Notes

• ISS amateur radio may not always be active - check ARISS status

• Crew schedules affect availability - they're not always at the radio

• Some passes may be for packet/digital modes instead of voice

Choosing the Best Passes

Excellent Passes

  • • Max elevation > 50°
  • • Duration > 5 minutes
  • • Evening or early morning
  • • Clear skies forecast

Good Passes

  • • Max elevation 20-50°
  • • Duration 3-5 minutes
  • • Acceptable weather
  • • Worth attempting

Poor Passes

  • • Max elevation < 20°
  • • Very short duration
  • • Midday passes (not visible)
  • • Probably skip these

Quick Reference

Essential Information

ISS Speed: 17,500 mph (28,000 km/h)
Orbit Time: ~90 minutes
Altitude: ~408 km (253 miles)
Brightness: Up to -4 magnitude

Hand Measurement

Use your hand at arm's length to estimate elevation:

• Fist width ≈ 10°
• Hand span ≈ 20°
• Finger width ≈ 2°