A supermoon happens when a full moon occurs near the Moon's closest point to Earth in its orbit. Because it is closer, the Moon can appear a little larger and brighter than usual.
Why the difference can be subtle
Supermoons are real, but the visual difference is not always dramatic to the naked eye. Weather, horizon effects, and local viewing conditions can influence how impressive it looks.
Supermoon versus blue moon
A blue moon is about calendar timing. A supermoon is about the Moon's distance from Earth.
Both terms describe special Moon events, but they refer to different things.