Original sentence: Originally believed to be a typical nova eruption, it was then realized to be something completely different.V838 Monocerotis (V838 Mon) is a variable star in the constellation Monoceros about 20,000 light years (6 kpc) from the Sun
Edited sentence: Originally believed to be a typical nova eruption, it was quickly realized to be something completely different.V838 Monocerotis (V838 Mon) is an enigmatic variable star in the constellation Monoceros about 20,000 light years (6 kpc) from the Sun