StarDate

A couple of the small worlds of the solar system will cross in front of two different stars on Sunday and Monday. One passage will be visible only from the other side of the world, while the other is well placed for viewers in North America.

Early tomorrow, the Moon will pass in front of Aldebaran, the leading light of Taurus, the bull, blocking the star from view. This “occultation” will be visible from parts of Asia, Africa, and Europe, but just barely — the Moon and Aldebaran stand so close to the Sun that they’re difficult to spot through the evening twilight.

And early Monday, Mercury will cross in front of the Sun. The Sun’s closest planet is so tiny, though, that it won’t block much of the sunlight. Instead, Mercury will look like a tiny dot tracking across the Sun’s disk. At least part of the transit will be visible across all of North America, although you don’t want to look at it directly — the Sun is just too bright. Instead, follow it online or at a local museum or planetarium.

In centuries past, astronomers used transits of Mercury, and especially of Venus, to measure the scale of the solar system. Watching transits from different points on the globe gave them a 3-D view, allowing them to plot the distances to the Sun and the transiting object. That showed that the Sun is about 93 million miles away — providing a good “yardstick” for measuring the scale of the solar system.

More about the transit of Mercury tomorrow.

Script by Damond Benningfield

A tiny black dot will cross the face of the Sun early Monday: Mercury, the Sun’s closest planet. The entire event — known as a transit — will be visible across the eastern half of the United States, with the rest of the country seeing most of it. Don’t look at it directly, though — the Sun is too bright. But many museums and planetariums will display it, and you can also watch it online.

During the latter half of the 19th century, astronomers hoped to use transits to find another solar system body: Vulcan.

Oddities in the orbit of Mercury suggested that the little planet was being pulled by the gravity of something even closer to the Sun. At first, astronomers thought it was a planet. Later, they decided it might be several large asteroids. Such bodies would be too close to the Sun to see directly, but they should occasionally transit the Sun. Observing a transit would yield the object’s size and its distance from the Sun.

In 1859, an amateur astronomer in France reported seeing something transiting the Sun, which the pros interpreted as Vulcan. Unfortunately, though, no one else saw it. Repeated attempts led to a few other sightings — but none was ever confirmed.

In 1915, it became clear why. Albert Einstein’s theory of gravity showed that the Sun warps the space around it. That accounts for the shift in Mercury’s orbit — without the need for another planet.

You can find out more about Vulcan in “The Hunt for Vulcan,” by Thomas Levenson. And we have an excerpt in the current issue of StarDate magazine. Subscription information at stardate.org

Script by Damond Benningfield

The strong man and the snake handler go head to head on spring and summer nights.

Rasalhague is the star that represents the head of Ophiuchus, the serpent bearer. And Rasalgethi is the head of Hercules, the strong man. Rasalhague climbs into good view in the east by around 10:30, with fainter Rasalgethi above it. They’re separated by only about five degrees — the width of three fingers held at arm’s length.

The names of the two stars come from ancient Arabic. The first part of each name, Ras, means “head.” And these aren’t the only stars named for the head of a constellation. Another is Rastaban — the head of Draco, the dragon, which is off to the upper left of Hercules. And yet another is Rasalas, the head of the lion, which is high in the southwest.

Rasalhague consists of two stars. One of them is more than twice as big and twice as massive as the Sun, while the other is much smaller than the Sun. The bigger star is actually nearing the end of its life, so it’s starting to undergo changes in its core. Over many millions of years, that’ll cause the star to grow much bigger and brighter.

Rasalgethi is already in that phase of life. It’s hundreds of times wider than the Sun, and thousands of times brighter. And it has not one companion, but two, both of which are also bigger and brighter than the Sun. They, too, eventually will puff up to giant proportions — but not until the current bright star has expired and faded from sight.

Script by Damond Benningfield

The first discovery of the Space Age was two intense radiation belts that encircle Earth. They’re called the Van Allen belts in honor of James Van Allen, the scientist who led the team that found them. And scientists are still learning about them today.

The belts contain electrically charged particles that are trapped by Earth’s magnetic field. Some of the particles come from the solar wind, while others are born from interactions between cosmic rays and Earth’s upper atmosphere.

The inner belt stretches from a few hundred to a few thousand miles above the planet. The outer belt extends far beyond that. And most of the time, there’s a gap of a few thousand miles between them.

But a pair of probes — also named for Van Allen — has found that the belts are quite dynamic — they expand, contract, and vibrate in response to storms on the Sun. At times, the gap between them can fill in, creating a single super-belt. The inner belt can expand to within just a couple of hundred miles of the surface. And the mixture of particles the belts contain can change.

Understanding the belts is important for space flight. Most satellites generally stay below the belts. But any craft that spends much time in the belts can receive a hefty jolt of radiation — enough to fry unprotected systems. So spacecraft operators need to know what to expect from the belts so they can shield their hardware — from one of the many hazards of space flight.

Script by Damond Benningfield

Mars is pushing into the pre-midnight sky, and getting brighter as it does so. In about three weeks, it’ll be rising at sunset, and putting on its brightest performance of the year. It’s already the third-brightest object in the night sky, after the Moon and the planet Jupiter. Mars will stay in third place, but it’ll grow almost twice as bright as it is tonight.

Mars is pumping up its appearance because Earth is getting ready to pass it by. Our planet is closer to the Sun than Mars is, so Earth follows a shorter path, and it moves faster along that path. The combination means that we pass Mars about every 26 months. And not surprisingly, when we’re closest, Mars shines brightest.

The planet also moves backwards against the dome of the sky as we move by it. It’s like passing another car on the highway. When the car is far ahead of you, it appears to move forward against the background of distant buildings and trees. As you pass it, though, it briefly appears to move backward against that background. The car is still moving forward, but because of the changing positions, it appears to move in reverse.

For a planet, “reverse” is known as retrograde. Mars will continue that westward motion for about three months, then resume its normal eastward motion in late July.

For now, look for bright orange Mars quite low in the southeast by 11 or 11:30. The star Antares is close below Mars, with the planet Saturn farther to its lower left.

Script by Damond Benningfield

Neutrinos are ghostly particles that almost never interact with matter. In fact, trillions of them shoot harmlessly through your body every second. They were created by nuclear reactions in the Sun’s core. But astronomers recently uncovered evidence that these aloof particles play a role in creating an element that helps fight cavities: fluorine.

In one way or another, stars create most of the chemical elements. But fluorine’s exact origin has long been mysterious. For one thing, the element is difficult to see in stars. But a recent survey detected a fluorine-containing gas — hydrogen fluoride — in 51 stars. It’s by far the largest number of Sun-like stars in which the element has been seen. The stars have so much fluorine that the researchers say it must have been made in powerful stellar explosions. It was expelled into space, then incorporated into new stars.

When a massive star explodes, it produces an enormous number of neutrinos. These are so energetic that a few defy their ghostly nature and smack into atoms of neon. Neon is just a little heavier than fluorine, and massive stars make a lot of it before they explode. When a neutrino shoots through such a star, it can knock a proton or neutron off the neon atom’s nucleus, creating fluorine.

Detection of fluorine in more stars is necessary to confirm this scenario. But if it’s right, it means you can thank neutrinos — which normally don’t do anything — for the cavities you never got.

Script by Ken Croswell, Copyright 2015

The modern western calendar tells us that summer arrives in the northern hemisphere this year on June 20th — the summer solstice. It’s the longest day of the year, and the Sun stands farthest north for the year as well.

In ages past, though, many calendars had a less direct link to the solstices and equinoxes. The seasons began not on these dates, but about halfway between them. Such dates are known as “cross-quarter” days. And in the calendars of the ancient British Isles, one of those days was commemorated on May 1st. In Ireland and Scotland it was known as Beltane, while in other regions it was known as May Day.

The rituals of Beltane celebrated the end of the cold, dark time of year and the beginning of the long, warm days of summer.

The centerpiece of Beltane was a village bonfire — or perhaps two bonfires. The fires themselves chased away the darkness and ushered in the light of summer. The flames and smoke were thought to have special protective powers, so villagers doused the fires in their homes, then relit them using a torch from the bonfire. They also paraded their livestock past the fires on the way to their summer fields — providing a bit of good luck for the start of the summer growing season.

These rituals were part of a deep connection to the cycles of nature, and especially the Sun — which warms and lights the summer no matter when the season officially kicks off.

Tomorrow: Dental hygiene from the stars.

Script by Damond Benningfield

Our solar system is heading into the aftermath of a stellar breakup — a stream of stars that split away from a big family of stars. One of the brightest members of the stream stands in the east at nightfall, and high overhead not long after midnight: Alphecca, the brightest star of Corona Borealis, the northern crown.

The stars in the stream once were members of a good-sized cluster. Today, though, the cluster’s been whittled down to only about a dozen stars, including five stars of the Big Dipper.

The cluster is being torn apart by the gravitational tug of other stars, plus giant clouds of gas and dust. Dozens of stars that once belonged to the cluster are now moving through the galaxy on their own, forming a stream that spans hundreds of light-years. The Sun is on the outskirts of the stream, but it’s moving in a different direction.

Astronomers are pretty sure of the origin of the stars in the stream because they still move in the same speed and direction as the cluster’s core. The stars are all about the same age, too, and they have the same chemical composition — good indications that they’re all members of the same stellar family.

Alphecca is 75 light-years away — about the same distance as the cluster’s core. It’s in a pretty semicircle of stars that’s about a third of the way up the eastern sky at sunset. Alphecca is at the center of the semicircle — a member of a big stellar family that’s heading off on its own.

Script by Damond Benningfield

Modern-day astronomy is suffering from an embarrassment of riches. Telescopes and satellites are producing so much data that astronomers can’t handle it all. It’s difficult just to store all those observations, much less pick through them for nuggets of information. And new projects in the years ahead will collect even more data — terabytes of it every day.

Much of the glut is produced by changes in technology. Just a few years ago, for example, electronic cameras recorded a few megapixels. Today, they’re in the hundreds of megapixels, and headed toward thousands of megapixels in the coming years.

And part of the glut comes from a profusion of surveys. Instead of looking at one or two objects in a given night, a telescope might look at hundreds of objects at the same time, gathering significant amounts of information on each one. And a telescope scheduled to come online in a few years will scan the entire sky every few nights. To see a single one of its images in full resolution, you’d need hundreds of big-screen TVs.

To handle all of those observations, astronomy is developing new software, or adapting software from other fields. These tools will “mine” the mounds of information for the best nuggets. They also will make it possible to search through older data sets for discoveries that might have been missed.

So the combination of new technology and big surveys could yield some amazing discoveries in the years ahead.

Script by Damond Benningfield

Some of the brightest stars in the night sky are in view early this evening. Sirius, the brightest of all, is low in the southwest as night falls. Bright orange Betelgeuse is well to its upper right, with Aldebaran closer to the lower right of Betelgeuse.

To the eye alone, these stars look changeless. Careful observations, however, show that Sirius moves in orbit with a small, faint companion. Bubbles of gas bigger than the Sun rise and fall across the surface of Betelgeuse. And Aldebaran changes brightness as the result of changes in its core.

All of these changes can help scientists understand how stars work, and how they evolve as they age. The fullest understanding requires observations made over years, decades, or even centuries — something known as “time-domain” astronomy.

And astronomers are putting more effort into that area — preserving observations made in prior years.

Many of those observations are in the form of glass plates. They can reveal how objects have moved, how they’ve changed in brightness, or how they’ve expanded. Harvard Observatory has digitized thousands of these images, some dating back to the mid-1800s, and other observatories are preserving their plates as well.

Some observations will be tougher to preserve — those that are archived on punch cards or magnetic tape, for example. Yet these, too, can help astronomers see how the universe changes from night to night.

More about astronomy technology tomorrow.

Script by Damond Benningfield