StarDate

Griffith J. Griffith was an interesting character. A native of Wales, he emigrated to the United States as a teenager and made his way to California. He became a newspaper reporter, then a mining consultant, which made him rich. He donated 3,000 acres of land to the City of Los Angeles for a park that today bears his name. And he tried to give money for a public observatory and more. But that wasn’t accepted until after his death — thanks to the fact that he’d shot his wife.

Griffith wasn’t the only astronomy benefactor with a scandalous background. In 1892, Charles Yerkes agreed to fund a new observatory for the University of Chicago.

Years earlier, Yerkes had been convicted of larceny. He’d later taken over most of Chicago’s street railway system, which he supported with bribes and other nefarious means. When he found himself unable to get credit, he agreed to pay for what’s now known as Yerkes Observatory to gain public support and respect.

Griffith already commanded respect when he shot his wife, in 1903. Testimony showed that he had paranoid delusions about her and others. He was convicted, but sentenced to only two years in prison.

After prison, Griffith tried to donate an observatory and a Greek theater. Los Angeles declined. When Griffith died — 100 years ago today — he left money in his will for both. Eventually, they were accepted. Griffith Observatory opened to the public in 1935 — and is still going strong today.

Script by Damond Benningfield

Vega, one of the brightest stars of summer nights, stands high in the east as darkness falls this evening. It’s the brightest member of the Summer Triangle, a wide pattern that’s easy to pick out even through the murky skies of a city.

Vega looks so bright in part because it’s only 25 light-years away. In other words, the light we see from the star tonight actually began its journey across the galaxy 25 years ago. By astronomical standards, that’s just down the street. Even so, if you want to go to Vega, be sure to stock up on snacks — it’ll be a long trip.

Traveling at highway speeds of 70 miles per hour, it would take about 250 million years to get there. Change highway speeds to airline speeds, and you’re still talking 30 million years. And even at the speed of the fastest spacecraft ever launched from Earth, you wouldn’t get to Vega for 400 thousand years.

Once you got to Vega, though, you’d have an interesting view. From Earth, we’re looking almost straight down at one of the star’s poles. A broad disk of gas and dust encircles Vega — a disk that may contain icy comets, rocky asteroids, and perhaps even some planets.

The disk is quite faint compared to the star. But from the inside of a rocketship, with no atmosphere between you and the system, you could simply block out Vega’s light with your hand. This mini-eclipse would let you see the spread-out disk, glowing faintly in the light of brilliant Vega.

Script by Damond Benningfield

The death of a star like the Sun is majestic and beautiful. For a while, the star surrounds itself with an iridescent cocoon of hot gas and dust. Until it dissipates into interstellar space, the cocoon shines brightly enough to see across thousands of light-years.

One of the best-known examples is in the constellation Lyra, the harp. Its brightest star, Vega, is in the east as darkness falls. The remains of a star that was once like Vega stand to its lower right: the Ring Nebula.

You need a telescope to see the nebula, but only because it’s thousands of light-years away. If you moved it to the distance of our closest stellar neighbors, it would outshine all the stars in the night sky. And it would be so big that you’d need your whole hand to cover it up.

The nebula began forming thousands of years ago. As the star aged, changes in its core caused its outer layers to puff outward. Eventually, those layers of gas were pushed off the star and out into space. That left behind only the hot, dense core — a white dwarf. Ultraviolet energy from the white dwarf lights up the surrounding gas like a fluorescent bulb.

Today, the nebula is more than a light-year wide. Seen from Earth, it looks like a pool of blue-green water surrounded by a yellow and pink ring. But it’s actually shaped like a barrel or an hourglass, and we’re looking at it from the top — a beautiful view of a final blaze of glory for a once-mighty star.

Script by Damond Benningfield

On average, Earth is 93 million miles from the Sun. Over the course of a year, though, that distance changes. Right now, for example, we’re a million-and-a-half miles farther than average. In fact, tomorrow we’ll be farthest from the Sun for the entire year.

The distance changes because Earth’s orbit looks like a flattened circle. The amount it’s “flattened” is called its eccentricity. Earth’s eccentricity is about 1.7 percent. So our distance from the Sun ranges from 1.7 percent closer to 1.7 percent farther than average.

The eccentricity isn’t constant. It varies over a period of a hundred thousand years. The change is caused by the tug of the other planets — especially Jupiter and Saturn, the heaviest planets.

During that long period, the eccentricity ranges from near zero to almost six. Earth’s average distance to the Sun doesn’t change, though, and neither does the length of its year.

One thing that does change is the amount of solar energy that strikes Earth. When the orbit is most eccentric, solar energy varies by about 25 percent over the course of a year. That’s compared to just seven percent today. So the hemisphere that’s having summer when Earth is closest to the Sun would have hotter summers and colder winters than the other hemisphere.

Right now, Earth’s orbit is getting less eccentric. In tens of thousands of years, it’ll be close to a perfect circle — and the distance to the Sun will remain almost constant.

Script by Damond Benningfield

One of nature’s most beautiful cycles takes its next step today, with a total solar eclipse. The Moon will line up between Earth and the Sun, blocking the Sun from view. The total eclipse will be visible only from a narrow path. It begins east of New Zealand, crosses the Pacific Ocean, then sweeps across Chile and Argentina. Totality — when the Sun is completely hidden from view — will last up to four and a half minutes.

The eclipse is part of a cycle called Saros 127. It began in the year 991, and will end in 2452.

A Saros is a series of alignments of three different cycles of the Moon. The cycles overlap every 18 years, 11 days, and 8 hours, creating a new eclipse.

The details of each succeeding eclipse in a Saros are similar. The Moon is about the same distance from Earth, for example, and the eclipses happen at the same time of year. Because of the extra eight hours, though, each one takes place a third of the way around Earth from the previous one. So the next eclipse in this cycle will slide across Australia.

A cycle begins with a partial eclipse. With each following eclipse, the Moon covers more of the solar disk, peaking with dozens of total eclipses. Then the Moon slides in the opposite direction, creating more partial eclipses.

Different alignments of Sun, Moon, and Earth create different Saros cycles. So about 40 are under way at any time — giving us two or more solar eclipses every year.

Script by Damond Benningfield

Starting at 3 p.m. EDT
 

Our view of the center of the Milky Way isn’t good. The galaxy’s core lies behind heavy clouds of dust, which absorb most of the light from the stars behind them. But there are a few tiny “windows” in the dust. They provide pinhole views of the galaxy’s “bulge” — the congregation of mostly old stars in the Milky Way’s heart.

The best known of those pinholes is Baade’s Window. It’s close to Gamma Sagittarii, one of the brightest stars of Sagittarius.

The window was discovered in the 1940s by Walter Baade, who was looking for a way to locate the center of the galaxy. He found an especially bright patch in the summer Milky Way — the hazy band of light that outlines the galaxy’s disk. That patch is about twice as wide as the Moon, and it provides a view of the southern part of the bulge — less than 2,000 light-years from the center of the galaxy.

Baade used a class of pulsating stars to measure the distance to the bulge — about 27,000 light-years. Most of the stars in the bulge are quite old — about 10 billion years. And astronomers have even found planets orbiting a few of those stars — in the busy center of our home galaxy.

Sagittarius is low in the southeast as night falls. Its stars form the outline of a teapot. Gamma Sagittarii is at the top of the spout. Baade’s Window is just to the upper right of the star. Binoculars reveal a bright patch of stars, with a star cluster right in the middle.

Script by Damond Benningfield

A flash of lightning across the night sky is one of nature’s most awe-inspiring sights. But it’s a lot more complicated than it looks. There can be flashes of light above the clouds, too. And there may even be a connection between lightning and exploding stars.

Lightning is triggered when there’s a difference in the electric charge at the top and bottom of a cloud, or between a cloud and the ground. When the difference gets big enough, there’s a discharge, so current flows between the oppositely charged regions. That heats the air, causing it to expand rapidly and create thunder.

In recent decades, scientists have found that other fireworks accompany lightning strikes. “Blue jets” can shoot many miles upward from the cloudtops. Higher still are faint red streamers called sprites. And instruments in space have detected flashes of powerful gamma-rays.

Some research has also suggested a link with cosmic rays. These are the nuclei of heavy atoms blasted into space by exploding stars and other powerful events. When they hit the atmosphere they split apart, triggering showers of other particles. As the particles zip toward the ground, they ram into atoms and molecules in the atmosphere, creating more charged particles. This torrent may create the pathway for a lightning strike.

The idea hasn’t been confirmed, though. So we can’t be sure if lightning has a “cosmic” connection.

Script by Damond Benningfield

The closest planet to the Sun is Mercury. It’s the smallest planet in the solar system — a little ball of metal and rock that’s blasted by the Sun’s fury.

Many other star systems, though, have planets that are much closer in than Mercury is. And some of those worlds are mammoth — they can be many times bigger and heavier than Jupiter, the giant of the solar system.

Such worlds are known as hot Jupiters. They’re as little as a few million miles from their parent stars. At that range, such a planet’s upper atmosphere can be heated to hundreds or even thousands of degrees. And it’s generally locked so that one hemisphere of the planet always faces the star, just as one side of the Moon always faces Earth.

Hot Jupiters may form much farther out, then move closer to their stars. The heat and winds from a star should vaporize planet-making material that’s close in, and blow it far away. That wouldn’t leave enough gas and dust to make a giant world.

Some recent research, though, suggests that some hot Jupiters — and perhaps most of them — form right where they’re seen today. Such worlds would grow from massive “seeds” — big balls of rock and metal known as super-Earths. Such planets have been found in many star systems, and many of them are quite close to their stars. Once a super-Earth forms, it should quickly sweep up any leftover gas and dust, growing to gigantic proportions — making a hot Jupiter.

Script by Damond Benningfield

As astronomers have discovered more planets in other star systems, they’ve gotten more surprises. One of the biggest is a class of planets unlike anything in the solar system. “Super-Earths” are heavier than our own planet, and a little bigger. And they’re quite common. Current catalogs list hundreds of them.

In our own solar system, there are two classes of planets: small and rocky, like Earth, and big and “gassy,” like Jupiter. Super-Earths fall between those extremes. There’s no formal definition for them. But a general definition is any planet between roughly 2 and 10 times the mass of Earth.

Depending on the distance from their parent stars, such worlds could take several forms. They could be mainly rock and metal, like Earth. They could have a massive core that’s surrounded by a thick atmosphere, or that’s topped by global oceans. Or they could have a smaller core surrounded by thick layers of hydrogen and helium gas.

The closest super-Earth may be just four and a quarter light-years away. Proxima Centauri b orbits the nearest star to the Sun. Astronomers haven’t been able to nail down the planet’s mass. It could be about as heavy as Earth. But it could also be a few times heavier, putting it solidly in the super-Earth category.

The planet is far enough from its star that it may be too cold for life. But there’s enough uncertainty about conditions that life can’t be ruled out — a “super” possibility for a super-Earth.

Script by Damond Benningfield

Earth-sized planets are elusive. Of the thousands of worlds discovered in other star systems, only a couple of hundred are within about 20 percent of Earth’s diameter. And fewer than a dozen are within 20 percent of Earth’s mass, which is how astronomers categorize planets.

That could be because Earth-sized planets are fairly small and lightweight. That makes them tougher to find than big, heavy planets similar to Jupiter and Saturn. Or perhaps it’s because Earth-sized worlds just aren’t that common. It’ll take a lot more planet discoveries to let us know for sure.

Planets that are similar to Earth’s size and mass probably are built a lot like Earth, too. They’re probably dense balls of rock and metal. Whether they have conditions like Earth depends on several factors, including the type of star they orbit and how far from the star they are.

As an example, consider the closest Earth-sized planet, which appears to orbit a star that’s 12 light-years away. Known as GJ 273c, the planet is about 20 percent heavier than Earth. It’s so close to its parent star, though, that surface conditions are much too hot for life like that on Earth.

Finding an Earth-sized planet with Earth-like conditions is the prize goal for planet hunters. Such worlds are considered the best places to look for signs of life — planets that could be “twins” to our own life-filled world.

We’ll have more about exoplanets tomorrow.

Script by Damond Benningfield