| Abbreviation | Definition |
|---|---|
| ICV | Illumination Chromacity Variation |
| IDIA | Institute for Data Intensive Astronomy |
| IDMP | International Daylight Measurement Program |
| IDT | Inter Dimensional Travel |
| IETI | Invitation to ExtraTerrestrial Intelligence |
| IFA | Institute for Astronomy |
| IFAS | Irish Federation of Astronomical Societies |
| IFO | Identified Flying Object |
| IG | Inter-Galactic |
| IGRB | Isotropic Gamma Ray Background |
| ILOC | International Lunar Occultation Center |
| ILRT | intermediate-luminosity red transients |
| IMAGE | Imager for Magnetopause to Auroral Global Exploration |
| IMBH | Intermediate Mass Black Hole |
| IMO | International Meteor Organization |
| IMOA | International Museum of Astronomy |
| INAO | Indian National Astronomy Olympiad |
| INFOL | Ingredient Necessary FOr Life |
| ING | imagining new gastronomy |
| INS | Inertial Navigation System |