Photographic self-portraits have existed for as long as cameras have been in human hands. But what about selfies in space? On Twitter last year, NASA astronaut Edwin Buzz Aldrin, who famously became the second man to walk on the moon in July 1969, laid claim to a spaceflight first; taking the first selfie in space during the Gemini XII mission in 1966.

“For me, it needs to be digital to be a selfie.” argues Jennifer Levasseur, a director at the Smithsonian National Air and Space Museum. According to Levasseur, the concept of a selfie is directly linked to internet culture. “The thing that makes a selfie a selfie is sharing it.” she says.

Still, astronauts have been carrying cameras aboard space vehicles since the 1960s. In 1966, Aldrin used a Hasselblad camera designed specifically for space, with an extra-large trigger to accommodate the astronaut's thick gloves. Hasselblad also painted the first camera in space a matte black to reduce reflections in the orbiter window. But cameras used in space need to survive extreme conditions, like temperature swings from - 149° to 248°F, so Hasselblad painted later models silver.

Astronauts visiting the moon then had to take out the film magazines and leave their camera bodies behind when they returned to Earth, because early space missions were limited by a weight limit on the return trip. Then a big change in space camera technology came after the space shuttle Columbia broke apart on its return to Earth in 2003. Levasseur notes. “Fear that they’d never be able to bring film back from space and lose all that hard work” accelerated the push for digital, she says.

Today, astronauts also have access to internet and social platforms in space and can post true space selfies made using digital cameras. Similarly, space robots are participating in selfie culture, capturing remote pictures of themselves in space or on other planets and sending them back to Earth.

When you think of 3D-printing, you may think of small objects. But three companies are working together to print something much bigger. They’ re using a giant 3D printer to create what they say is the first two-storey 3D-printed house in the US.

Usually, 3D-printing involves a machine building something by putting down many layers of a material — often hot plastic. When the material hardens, the layers stick together to create a finished object. The method here is similar, but uses concrete.

Leslie Lok, who designed the house, says there are special challenges involved in printing a two-storey house. One of the biggest is the size of the machine needed for the building. The 3D printer in Houston is massive, weighing over 12 tons.

Ms. Lok says printing the house will take the massive machine about 330 hours. That’s about eight normal work weeks. But the team isn’t in a rush. “We are not trying to beat the clock,” says Hikmat Zerbe, who works for CIVE. Instead, they’ re using the house as a “big laboratory” to learn more about 3D-printing houses. They want to see how the concrete reacts “under different weather conditions”. They also want to figure out how to make 3D-printing faster and cheaper. Mr. Zerbe says that currently, 3D-printing a house with concrete costs more than building a house with wood.

With time, Mr. Zerbe expects the costs of 3D-printing houses to go down. He thinks printers will improve and make it easier to create more houses quickly. 3D-printed concrete houses are stronger and hold up better in serious storms than houses built with wood. This can save money in the long run. Since the machine is doing the building, fewer workers are needed, which also saves money.

Sometimes trees can be a little too respectful of one another’s boundaries. Or maybe they just stop growing when they get too close. The phenomenon is called crown (树冠) shyness-the tops of individual trees do not touch each other, creating a visible gap between the tree crowns.

Experts aren’t exactly sure why the naturally occurring phenomenon happens, but they’ve been studying it for decades and have a few theories. In 1955 a biologist Putz noticed that the trees, which grow close together, can rub against each other when the wind is strong enough. The resulting abrasion (磨损) helps form and maintain the shyness gaps. In 1986, this theory was backed up by Dr. Miguel Franco, who noticed that the branches of Picea sitchensis and Larix kaempferi trees suffered physical damage during abrasion, which killed the leading branches. The presence of broken tips at the points where branches meet lends support to the abrasion theory.

However, one Malaysian scholar suggests that shyness gaps result from the influences individual trees have on one another. Trees cannot move, so if they have nearby neighbors, they are forced to compete for resources, especially light. According to this theory, each tree forces its neighbors into a pattern that maximizes resource collection and minimizes harmful competition. Trees grow in the direction of light, so branches would naturally try to avoid other plants that could shade them or prevent their growth, creating a gap between the tree crowns.

Another possible reason for crown shyness is to prevent the spread of harmful insects, which could eat the tree’s leaves. Still someone believes the best scientific explanation so far is that the leaves of the tree release certain chemicals to stop other trees from growing too close.

The answer could be just one of the above, or a combination of more. But some species have been adapted to take advantage of crown shyness to grow into shapes that go well with nearby trees and therefore economic profits can be maximized out of the phenomenon.