HOW TO SPOT ARCTURUS

WHEN: SPRING

The star Arcturus is an iconic sight in the spring night sky. It’s easy to locate by extending the arc of the handle of the Saucepan (aka Plough) away from the pan. Arcturus lies on this curve, shining with a noticeable orange hue.

For those of us who live in the northern hemisphere, it’s an important object, being the brightest night-time star in this half of the sky. The brightest night-time star is Sirius, in Canis Major (the Great Dog), but this lies in the southern half of the sky. The northern and southern celestial hemispheres are separated by the celestial equator, which represents the projection of Earth’s equatorial plane into the sky.

Arcturus sits towards the southern end of a large, kite-shaped pattern representing the body of the constellation Boötes, the Herdsman. The kite asterism is about as high as the Plough is long, with Arcturus sitting at the pointed, bottom end. If you can identify the kite shape, look out for a small but distinctive semi-circle of stars off the kite’s eastern (left) ‘shoulder’. This is the constellation of Corona Borealis, the Northern Crown, another defining pattern of the Northern Hemisphere’s springtime night sky.

Occasionally you may see a dim star appear within Corona Borealis. This is R Coronae Borealis, an irregular variable star, which, when brightest, just peaks above the threshold of naked-eye visibility from a dark site. R Coronae Borealis is a carbon star, which occasionally releases clouds of carbon into the space around it. When this cools to form soot, it blocks the star’s light making it appear to dim. For this reason, R Coronae Borealis is known as the Dust Puff Star. At its dimmest, you’d need a large telescope to even glimpse it.

JACOB BURNETT, PETERBOROUGH

HOW CUTE ARE BABY SHARKS IN REAL LIFE?

That all hinges on what you consider to be cute. Depending on the species, a newborn shark can be anything from an adorable, hand-sized tiddler, like the small-spotted catsharks that hatch from ‘mermaid’s purse’ egg cases, or they can emerge directly from their mothers, with bodies as long as your outstretched arms. This is the case with sand tiger sharks, and how these baby sharks get so big is rather shocking.

Sand tigers are one of many species of sharks in which fertilised eggs hatch inside the female, then develop in her uterus. It’s quite common for unborn shark embryos to feed on unfertilised eggs, which happens in more than a dozen species. Sand tiger shark embryos go further – ultrasound scans of a pregnant sand tiger shark detected embryos swimming between the two prongs of her uterus, presumably hunting for more baby sharks to eat.

After a year-long gestation, a female sand tiger gives birth to one or two enormous pups, the winners of a prolonged intrauterine battle. Being so big at birth means they’re safe from a lot of predators, but, sadly, makes them vulnerable to getting caught in fishing nets. Sand tiger sharks are critically endangered of going extinct.

To find out more about why unborn sand tigers eat each other, researchers studied the bodies of sharks snagged in nets around South Africa. The pregnant female sand tiger sharks that were caught, varied in the number of embryos they were carrying. Those that were further along in their pregnancy had fewer unborn babies because the game of shark-eat-shark had been playing out for longer.

Sequencing the DNA from the unborn pups, scientists worked out the paternity of each embryo. Female sand tigers, as many sharks do, mate with multiple males within the same breeding season and so their eggs can be fertilised by different fathers. DNA tests showed that in litters of five, six or seven, the embryos came from at least two fathers. Meanwhile, the litters of just two pups were the offspring of the same father.

It’s not clear why, but it seems the offspring of one male shark tend to have an edge over their half-siblings and emerge victorious. It’s possible they’re first to be fertilised and get biggest first, priming them to devour their siblings. It could also be a strategy females employ to pick good mates. A female doesn’t need to be choosy and fend off the advances of all the males that want to mate with her, because the highest quality sperm will likely produce the fittest embryos, which will then be most likely to survive inside her and swim off into the ocean. HS