91色情片

2GA52R4 A woman on the beach at Portrush, Co. Antrim, on Northern Ireland's north coast doing open water swimming in the Atlantic Ocean.

When sea swimming, is it better to enter quickly or to take your time?

The most important consideration when swimming in the sea is safety, say our readers 鈥� but it also depends on how cold the water is

2K6A82T Artist's concept of astronauts and human habitats on Mars.

What is the minimum number of people needed for a Martian settlement?

purebred beagle puppy is learning the world in first time; Shutterstock ID 566398009; purchase_order: -; job: -; client: -; other: -

This week鈥檚 new questions

New black hole discovered in New Zealand toilet

Tom Gauld on a disagreement about the nature of gravity

Twisteddoodles on a relatable test tube

Life

Artist’s tulip photos capture transience of life

Two seagulls above aircraft wing

Do winged animals ever suffer comparable mishaps to aircraft?

2R067KD The Great Sphinx is the oldest known monumental sculpture in Egypt. It was built more than 4,500 years ago to guard the pyramid of Khafre at Giza.

How long will it be until the pyramids in Egypt weather away?

B1PP5G Spiral Galaxy M74 i. Image shot 2008. Exact date unknown.

What makes galaxies spin in a certain direction? Part two

One reader wonders if the outer-points of a galaxy鈥檚 spirals precede or trail the rotation

This week鈥檚 new questions

Society

Why ‘existential humility’ may be the answer to today’s culture wars

How much hair is the right amount to cut off? Depends who you ask

Tom Gauld on the adventures of AI-Chessbot-5000