|Season 3, Episode 17|
|The Trial of Kal-El||The Swarm|
Nova Day is the seventeenth episode of Supergirl Season 3 and the 59th episode overall. It is the second part of the 5-part TRIAL storyline, focusing on the political strife on New Krypton.
A PLANETARY CELEBRATION- During Nova Day, an annual religious holiday where all crime can be absolved by the Mediator Guild, the trial ceases. During the festivities, Zod's assassin strikes and Kara pursues him. Karen informs Kara that Lena stowed away on Astra's ship. Kal-El shows compassion for an enemy. Lesla-Lar returns to New Krypton with a deadly agenda, while Alura finally falls out with her family.
- Melissa Benoist as Kara Danvers/Supergirl
- Chyler Leigh as Alex Danvers (hallucination)
- Katie McGrath as Lena Luthor
- Laura Benanti as Alura Zor-El/Astra In-Ze
- Tyler Hoechlin as Kal-El
- Floriana Lima as Maggie Danvers (credit only)
- Zachary Quinto as General Dru-Zod
- Odette Annable as Samantha Arias/Reign
- Chris Vance as Non
- Tracy Spiridakos as Lesla-Lar
- Michael Rosenbaum as Lex Luthor (credit only)
- Chad Lowe as Thomas Coville (hallucination)
- Paige Turco as Lara Van-El
- Casper Crump as Vandal Savage (Earth 2)
- Jenna Dewan-Tatum as Lucy Lane (credit only)
- Lauren German as President Veronica Banks (credit only)
- with Claire Holt as Karen Starr
- and David Harewood as J'onn J'onzz (credit only)
- Gregg Henry as Ral-Dar
- Georgina Campbell as Lieutenant Asha Del-Nar
- with Harry Lennix as Commander Gor
- and Amy Acker as Brainiac
- Antagonists: Ral-Dar, Lesla-Lar
- Maggie, Lucy, Lex, Banks, and J'onn do not appear in this episode. Alex and Coville only appear as hallucinations.
- 3rd episode this season in which Earth does not appear.
- Lena and Kara interact for the first time since Brave Enough.