How to Look Up Orion's Coordinates Using JPL Horizons ===================================================== There's no login required — JPL Horizons is a free, public system with no account needed. Here are the instructions: 1. Go to https://ssd.jpl.nasa.gov/horizons/app.html in your web browser. 2. Set the Target Body. Click the "Edit" button next to Target Body. In the search box type "Artemis II" or enter the object number -1024. Select "Artemis II (spacecraft) (Integrity)" from the results. 3. Set your Observer Location. Click "Edit" next to Observer Location. You can type a city name (e.g., "London, UK"), enter geographic coordinates (longitude, latitude, altitude), or use an observatory code (e.g., 675 for Palomar). This gives you topocentric coordinates specific to your location, including altitude and azimuth so you know exactly where to point. 4. Set the Time Span. Click "Edit" next to Time Specification. Enter your start and stop times in UTC (e.g., Start: 2026-04-02 20:00, Stop: 2026-04-03 06:00). Set the Step Size — use small intervals like 5 min or 10 min for close passes when the spacecraft moves quickly, or 1 h to 4 h for the cruise phases. 5. Choose what data you want. Click "Edit" next to Table Settings. The most useful quantities are: 1, 2 — Right Ascension and Declination (where to point your telescope) 4 — Azimuth and Elevation (compass direction and height above your horizon) 9 — Visual magnitude (will show "n.a." for this spacecraft, so use Molczan's estimates instead) 20 — Range in AU (multiply by 149,598 to get km) 23 — Solar elongation (how far from the Sun in the sky; higher is better for observing) 6. Generate the ephemeris. Click "Generate Ephemeris." The results table shows the spacecraft's sky position at each time step. Negative elevation values mean the spacecraft is below your horizon. Quick tips: - The ephemeris data only begins about 3.5 hours after launch (after ICPS separation), so there is no data before that point. - Horizons does not provide magnitude estimates for this spacecraft. Use the range (delta) column and cross-reference with the Molczan magnitude table at the end of this document. - If the elevation column shows the spacecraft above your horizon during nighttime hours, you have a potential observation window. - You can also access the system via its API for batch queries: https://ssd.jpl.nasa.gov/api/horizons.api Molczan Magnitude Estimates for Artemis II ========================================== Since Horizons does not provide magnitude estimates for the Artemis II spacecraft, satellite observer Ted Molczan has produced rough estimates based on published NASA dimensions. To estimate how bright the spacecraft will appear, find the range (delta) from your Horizons output and look up the corresponding magnitude in the table below. Standard magnitudes (at 1000 km range, 90 deg phase angle): Orion spacecraft (crew + service module): 4.6 ICPS + spacecraft adapter: 3.9 (subtract 0.7 from table) Estimated uncertainty: +/- 2 magnitudes Range (AU) Range (km) Mag (100% Ill.) Mag (50% Ill.) ---------- ---------- --------------- -------------- 0.00001 1,496 4.2 5.5 0.00002 2,992 5.7 7.0 0.00003 4,488 6.6 7.9 0.00004 5,984 7.2 8.5 0.00005 7,480 7.7 9.0 0.00006 8,976 8.1 9.4 0.00007 10,472 8.5 9.7 0.00008 11,968 8.7 10.0 0.00009 13,464 9.0 10.2 0.00010 14,960 9.2 10.5 0.00020 29,920 10.7 12.0 0.00030 44,879 11.6 12.9 0.00040 59,839 12.2 13.5 0.00050 74,799 12.7 14.0 0.00060 89,759 13.1 14.4 0.00070 104,719 13.5 14.7 0.00080 119,678 13.7 15.0 0.00090 134,638 14.0 15.2 0.00100 149,598 14.2 15.5 0.00110 164,558 14.4 15.7 0.00120 179,517 14.6 15.9 0.00130 194,477 14.8 16.0 0.00140 209,437 15.0 16.2 0.00150 224,397 15.1 16.3 0.00160 239,357 15.2 16.5 0.00170 254,316 15.4 16.6 0.00180 269,276 15.5 16.7 0.00190 284,236 15.6 16.9 0.00200 299,196 15.7 17.0 0.00210 314,156 15.8 17.1 0.00220 329,115 15.9 17.2 0.00230 344,075 16.0 17.3 0.00240 359,035 16.1 17.4 0.00250 373,995 16.2 17.5 0.00260 388,954 16.3 17.5 0.00270 403,914 16.4 17.6 These values are for the Orion capsule. For the ICPS upper stage (if tracked separately), subtract 0.7 magnitudes (i.e., it is brighter). For reference: Naked eye limit (dark sky) ~6.0 to 6.5 7x50 binoculars ~9 to 10 6-inch (150mm) telescope ~13 8-inch (200mm) telescope ~14 12-inch (300mm) telescope ~15 16-inch (400mm) telescope ~16 Credit: Ted Molczan, via SeeSat-L mailing list