William Lassell - brewer turned astronomer and his discoveries

Oct. 24, 1851 - William Lassell discovered two moons of Uranus, Umbriel and Ariel.

William Lassell was an English merchant and made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy.

He built an observatory at his house "Starfield" in West Derby, a suburb of Liverpool. There he had a 24-inch (610 mm) reflector telescope, for which he pioneered the use of an equatorial mount for easy tracking of objects as the Earth rotates. He ground and polished the mirror himself, using equipment he constructed.

In 1846 Lassell discovered Triton, the largest moon of Neptune, just 17 days after the discovery of Neptune itself by German astronomer Johann Gottfried Galle. In 1848 he independently co-discovered Hyperion, a moon of Saturn. In 1851 he discovered Ariel and Umbriel, two moons of Uranus.

In 1850, Lassell made his first sighting of the dark inner ring of Saturn (called the crepe ring); he spent the entire night verifying the discovery only to find in his morning newspaper an article announcing William Bond’s discovery of the same phenomenon.

Umbriel is a moon of Uranus and consists mainly of ice with a substantial fraction of rock, and may be differentiated into a rocky core and an icy mantle

Ariel is the fourth-largest of the 27 known moons of Uranus

The crater Lassell on the Moon, a crater on Mars, the asteroid 2636 Lassell and a ring of Neptune are named in his honour. At the University of Liverpool the William Lassell prize is awarded to the student with the highest grades graduating the B.Sc. program in Physics with Astronomy each year.

Sources -

1. Encyclopædia Britannica
2. Journal for the History of Astronomy
3. Wikipedia
4. Pacific Science Center

Uranus smells like rotten eggs

TAKE A WHIFF  Uranus is a lovely robin’s egg blue in this image taken by the Voyager 2 spacecraft when it flew past in 1986. New measurements of the planet’s chemistry suggests it may smell like eggs, too — that is, really rotten eggs. 

Uranus’ upper clouds are made of hydrogen sulfide — the same molecule that gives rotten eggs their noxious odor.

Using a spectrograph on the Gemini North telescope in Hawaii, planetary scientist Leigh Fletcher and his colleagues detected the chemical fingerprint of hydrogen sulfide at the top of the planet’s clouds. This isn't a complete surprise: Observations from the 1990s showed hints of hydrogen sulfide lurking deeper in Uranus’ atmosphere. But the gas hadn’t been conclusively detected before.

The clouds aren’t just smelly — they can help nail down details of the early solar system. Uranus’ hydrogen sulfide clouds set it apart from the gas giant planets, Jupiter and Saturn, whose cloud tops are mostly ammonia.

Hydrogen sulfide freezes at colder temperatures than ammonia. So it’s more likely that frozen hydrogen sulfide ice crystals would have been abundant in the further reaches of the early solar system, where the crystals could have glommed onto newly forming planets. That suggests that ice giants Uranus and Neptune were born farther from the sun than Jupiter and Saturn.

Fletcher is far from repelled by the malodorous clouds. He and other planetary scientists want to send a spacecraft to the ice giants — the first since the Voyager spacecraft visited in the 1980s — to find out more.

Source - ScienceNews

Read more on the Science Pole App

Citations - P. Irwin et al. Detection of hydrogen sulfide above the clouds in Uranus’s atmosphere. Nature Astronomy. Published online April 23, 2018. doi: 10.1038/s41550-018-0432-1.

We wouldn't be here but for the solstices. Be thankful!

December 21 was the winter solstice in the Northern Hemisphere - the shortest day in the year. The solstices occur on most planets because they do not spin upright, or perpendicular to their orbits.

The Earth, for example, slouches 23.5 degrees on a tilted axis (inclination). This leaves the planet’s North Pole pointed toward the North Star over relatively long periods of time, even as Earth makes its year long migration around the sun. That means the Northern Hemisphere will spend half the year tilted slightly toward the sun, bathing in direct sunlight during summer’s long, blissful days, and half the year cooling off as it leans slightly away from the sun during winter’s short, frigid days. December 21 marks the day when the North Pole is most tilted away from the sun.

But every planet slouches at different angles.

The axial tilt of Venus, for example, is so extreme — 177 degrees — that the planet is essentially flipped upside down with its South Pole pointing up. Perhaps counter-intuitively, that means that there’s very little tilt to its upside-down spin and its hemispheres will never dramatically point toward or away from the sun. As such, the sun’s dance across the sky will remain relatively stable — shifting by a mere six degrees over the course of a Venusian year.

The axial tilt of Venus is so extreme that the planet is essentially flipped upside down with its South Pole pointing up

Had we evolved on Venus, it’s likely that we would not have noticed solstices or seasons at all.

The same can’t be said for Uranus!

An axial tilt of 98 degrees causes the ice giant to spin on its side. So, whereas one of Earth’s poles leans slightly toward the sun at solstice, one of Uranus’s poles points almost directly toward the sun at solstice — as though poised to make a perfect bulls eye. That means that one hemisphere will bask under the sun both day and night, while the other will experience a frigid and dark winter and not catch a glimpse of the sun for that entire season.

Two images of the same view of Uranus made by NASA’s Voyager 2 in 1986. The false-color image on the right shows how Uranus’s pole points towards the sun, its axis tilting at 98 degrees

Such a tilt on Earth would mean that the Arctic Circle didn’t begin 66 degrees north of the Equator, but at the Equator itself. All of North America, Europe, Asia and half of Africa would spend winters in permanent darkness and summers under constant sunlight. And on Uranus, which takes 84 Earth years to orbit the sun, these seasons last for decades.

But the king of extreme seasons is Pluto.

When NASA’s New Horizons spacecraft arrived at the dwarf planet in 2015, scientists discovered a unique world overflowing with surface features that look like networks of drainage channels and even a frozen lake. But given Pluto’s low atmospheric pressure and chilly surface temperature, liquids cannot flow across the surface — at least not today.

Scientists now have an explanation: seasons in Pluto’s past pushed atmospheric pressure high enough to allow liquids of methane and nitrogen to flow and pool on the surface.

A changing axial tilt is the biggest driver of wildly varying seasons on Pluto. Over the course of 4 million years, Pluto’s inclination shifts back and forth between 102 and 126 degrees, causing its equivalent of an Arctic Circle to grow and shrink. That occasionally creates seasons where the atmospheric pressure is high enough that liquid methane and nitrogen can flow.

Although, astronomers remain uncertain how a planet’s seasons might affect its likelihood to host life, it is believed that such dramatic swings — like those on Pluto — are likely a hindrance because they can make a planet unfit to live on for long stretches of time. Life needs a continuously habitable zone to thrive. Similarly, astronomers have long suspected that life would likely not survive on Earth should it have an axial tilt more akin to Uranus.

So, as the sun reaches its farthest point in the sky on December 21, be grateful. Never will the sun dip so far below the horizon that it plunges half of the globe into a months long night and the other half into an equally long summer. Nor does Earth’s tilt change drastically over millions of years, thanks to the influence of the moon. Instead, the sun appears to trot back and forth between the extremes, like the pendulum of a great clock, keeping the planet cozy while steadily counting off its years.

Source - The New York Times