SAN FRANCISCO: US President Donald Trump has left people astonished with his knowledge of space and the universe and has become a laughing stock yet again after he claimed that the moon is a part of Mars.

In a tweet on Friday, he said: "For all of the money we are spending, NASA should NOT be talking about going to the Moon - We did that 50 years ago. They should be focused on the much bigger things we are doing, including Mars (of which the Moon is a part), Defence and Science."

Trump's remarks came a day after NASA Administrator Jim Bridenstine told USA Today that US astronauts would not be able to make a lunar landing by 2024 unless Trump administration's $1.6 billion budget increase request is not approved by the US Congress.

As soon as Trump tweeted, people from around the world started trolling him with witty one-liners, jokes and memes.

"Sigh! His dad must have paid his way through astronomy class too!" wrote American long-distance runner Ryan Hill.