Mercury making rare transit across sun today1,117 views
PARIS: Astronomers on Monday were preparing for one of the highlights of the skywatchers’ year, when the Sun, Mercury and Earth all line up — a phenomenon that happens just a dozen or so times per century.
Mercury will be seen through telescopes as a black dot inching over the face of our star, providing a celestial spectacle — weather permitting — that will last seven and a half hours.
“At the start, Mercury will look as if it is nibbling at the edge of the Sun, and then it will very slowly cross its surface and leave the other side,” said Pascal Descamps of the Paris Observatory.
“It’s something rare, because it requires the Sun, Mercury and Earth to be in almost perfect alignment.”
The smallest recognised planet in the Solar System, Mercury completes an orbit every 88 days, and passes between the Earth and the Sun every 116 days.
But its orbit is tilted in relation to Earth’s, which means it usually appears — from our perspective — to pass above or below the Sun.
Thirteen times each century, however, the two orbits align such that even amateur astronomers can see the tiny planet tens of millions of kilometres (miles) away.
According to Britain’s Royal Astronomical Society (RAS), most of Western Europe, the western parts of North and West Africa, eastern North America, and most of South America will be able to view the entire transit, which will last from 1112 GMT to 1842 GMT.
The rest of north and south America, the eastern Pacific, the remainder of Africa and most of Asia, will see parts of the event.
Observers in east and southeast Asia and Australasia, however, will miss out entirely.
– Weird planet –
The closest planet to the Sun and a third the size of Earth, Mercury is one of the Solar System’s curiosities.
It is one of the four rocky planets of the inner Solar System but has no atmosphere and its metallic body is scarred by collisions from space rocks.
Daytime on Mercury is six times hotter than the hottest place on Earth, and nighttime can be more than twice as cold as the coldest place on our planet.
It rotates so slowly — three times for every two orbits — that, bizarrely, Mercury’s day is twice as long as its year.
The transit of Mercury was first recorded by French astronomer Pierre Gassendi. He observed it through a telescope in 1631, two decades after the instrument was invented.
German astronomer Johannes Kepler had correctly predicted that transit, but died in 1630 before he could witness the event.
The last Mercury lineup was 10 years ago, and the next will be in 2019, followed by 2032 and 2049.
“It is always exciting to see rare astronomical phenomena such as this transit of Mercury,” said RAS President Martin Barstow. “They show that astronomy is a science that is accessible to everyone.”
But be warned: looking directly at the phenomenon can result in permanent eye damage, as only a very small part of the Sun will be blocked out.
One option is to use a telescope or binoculars to project the image onto a white surface. Stargazers can also observe the event through a telescope with a strong filter or — most safely of all — on the Internet.
Mini Mercury facts
To brush up on your Mercury knowledge before the big day, here are some of the teeny planet’s highlights:
1. Mercury is the baby planet in the solar system. At just 4,880 km in diameter, it is the smallest of all planets (sorry, Pluto fans!) – that’s almost three times smaller than Earth and almost 30 times smaller than Jupiter for scale.
2. Mercury is orbiting 46 to 70 million kilometers away from the Sun, making it the closest planet with the most eccentric orbit (that’s a scientific term). One complete revolution takes about 88 days, meaning one Earth year is the equivalent to four years on Mercury.
3. However, counting solar days is much trickier if you are on Mercury. There, it takes 176 Earth days for the Sun to go around the sky once because of the so-called spin-orbit resonance. The orbit’s shape and the resonance result in an even weirder effect of the Sun actually slowing down, going backwards and then forward again. Can you imagine that?
4. Unfortunately, there’s a slim chance of anyone ever observing this show and staying alive, as Mercury being the closest planet to the Sun means it can get quite hot. Temperatures can reach as high as 427 degrees Celsius (800 degrees Fahrenheit). Meanwhile, on the side that’s not facing the sun, temps can drop as low as minus 173 °C (-279 °F). Brrr!
5. Mercury’s surface is covered in bumps and rocks thanks to its many impacts with meteorites over the millions of years. A topographic animation from NASA shows the planet’s highest and lowest points, ranging from its highest at 2.78 miles (4.48 km) to the lowest at 3.34 miles (5.38 km).
If you simply can’t catch 2016’s Mercury madness, make sure to mark your diary for the next opportunity on November 11, 2019. After that, you’ll be waiting until 2032.