StarDate

The bright Moon is getting ready to run a gauntlet in the pre-dawn sky – a gauntlet of three planets. The planets align to the left of the Moon at first light tomorrow. The Moon will move past them over the following mornings.

The Moon is in its waning gibbous phase for the next few days. That means that sunlight illuminates more than half of the hemisphere that faces our way, but not the whole hemisphere.

The word “gibbous” comes from a Latin word that means “hump.” It indicates that the Moon looks like it has a hump on its back.

Over the next few days, though, the hump will be getting smaller – where the “waning” part of the title comes in. Tomorrow, the Moon will be about 80 percent full – the Sun will light up 80 percent of the lunar disk. For the following few days, though, that fraction will drop by about 10 percent per day. By Friday, only about 40 percent will be in sunlight. At that point, the Moon will be in its waning crescent phase. The crescent will grow thinner until the Moon disappears in the dawn twilight.

Watch the Moon as it grows thinner over the next few mornings – and passes by a beautiful array of planets. The brightest of the three worlds is Jupiter, the brightest object in the sky at that time other than the Moon. It’s to the left of the Moon tomorrow. Saturn stands close to the left of Jupiter, with orange Mars a good distance to their lower left.

We’ll have more about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

The sky offers two north poles. One is the celestial pole. It’s marked by Polaris, the North Star. Earth’s axis aims toward Polaris, so all the stars appear to rotate around it. And the star is in the same position in the sky all day and night — marking due north.

The north galactic pole moves around the sky. It stays in the same constellation, but the constellation turns around Polaris, so the pole moves, too.

This pole is based on the alignment of our home galaxy, the Milky Way.

Astronomers have devised a set of galactic coordinates. The “east-west” line is marked by the plane of the galaxy’s disk. You can get a rough idea of the plane by looking at the hazy band of light that outlines the Milky Way. A lane down the middle of that band generally looks darker than the rest of it — a pretty good marker of the galactic plane.

The east-west coordinates are centered on the heart of the galaxy, in Sagittarius — a galactic longitude of zero. That’s also the starting point for galactic latitude — the position north or south of the plane. The point 90 degrees north marks the north pole. It’s in Coma Berenices. Right now, it’s high in the southeast at nightfall, above the bright yellow-orange star Arcturus.

Since we’re looking away from the Milky Way’s disk, that region offers an unobstructed view beyond the Milky Way. In fact, it’s home to one of the most impressive galaxy clusters around — spreading out near the north galactic pole.

Script by Damond Benningfield

It’s big. It’s bright. And it’s doomed.

Antares is one of the most impressive stars in the galaxy. It’s at least 15 times as massive as the Sun, hundreds of times wider, and tens of thousands of times brighter. But that flashiness comes at a price. The star’s lifetime will be measured in millions of years versus billions of years for more sedate stars like the Sun.

When that lifetime is up, the star’s core will collapse, while its outer layers will blast into space as a supernova. The blast will push a mixture of chemical elements out into the galaxy — elements created in the star’s core during its short lifetime, or in the surrounding layers of gas during the explosion.

The collapsed core will most likely form a neutron star — a ball a couple of times the mass of the Sun but only a few miles in diameter. Most young neutron stars spin rapidly, beaming out pulses of energy, so they’re also known as pulsars. And they generate magnetic fields that can be millions of times stronger than Earth’s. That gives them yet another designation: magnetars.

Astronomers don’t know all the signs that herald an impending supernova, so they can’t be sure just when Antares will explode. All they know for sure is that it’s likely to happen within the next million years or so — and it could happen as early as tonight.

Look for bright orange Antares rising to the right of the Moon around 11 o’clock, and leading the Moon across the sky later on.

Script by Damond Benningfield

Vanguard 1 has been orbiting Earth for more than 60 years — longer than any other spacecraft. And it’s expected to stay in orbit until late in the 22nd century.

Just about every other spacecraft is expected to crash to Earth much sooner. Most will burn up in the atmosphere, or splash into the oceans. But a few will hit land, perhaps harming property or people.

The odds of such an impact are getting better all the time. More than 9,000 satellites have been sent into orbit, and about half are still there. And the number of satellites is expected to rise dramatically in the next few years.

There’s lots of other stuff up there, too — debris from exploded rocket stages, for example. These projectiles could damage or destroy spacecraft — creating more pieces of debris that could fall to Earth.

Some satellites are targeted to splash into a lonely region of the Pacific Ocean. But controlled re-entry adds to a mission’s cost.

Most commercial satellites are insured against the possibility that they’ll cause damage or injury when they hit the ground. And satellite operators are looking at ways to make it more likely that future craft will completely burn up in the atmosphere. But it’ll take a while to implement new designs.

So far, only six people are known to have been hurt by falling debris. As both Earth’s surface and Earth orbit get more crowded, though, we could see more such incidents in the decades ahead.

Script by Damond Benningfield

At the end of last year, a couple of thousand working satellites were orbiting Earth — watching the weather, tracking people and equipment, and studying the universe. Over the next few years, though, the number could increase by a factor of seven or eight. That could be good for business, but not so good for astronomy.

From the start of the Space Age, in late 1957, through last year, the world had launched about 9,000 satellites. Most of them have either stopped working or fallen back to Earth.

But two companies are ready to fill low Earth orbit with many more. SpaceX and OneWeb are launching thousands of small satellites into low orbits to provide high-speed internet service. OneWeb could launch a couple of thousand, while SpaceX has announced plans to launch up to 12,000.

For astronomy, though, that’s a problem. As the satellites pass across the sky at certain times of night, they reflect the Sun’s rays. So they create bright streaks of light on any pictures astronomers might be taking.

In February, the International Astronomical Union said it considers the satellites “worrisome.” The constellations of satellites, it said, “will have a negative impact on the progress of ground-based astronomy.”

SpaceX, which has already launched hundreds of satellites, is testing a new coating to make the craft darker. Even so, the view of the universe is likely to get a lot messier in the years ahead.

More about satellites tomorrow.

Script by Damond Benningfield

The two brightest objects in the night bracket the sky as darkness falls this evening. The almost-full Moon is in the southeast, with Venus, the “evening star,” setting half way around the sky, in the west-northwest.

About the only thing that can challenge the Moon’s brightness is a bolide — the brightest type of meteor. Such flashes are quite rare, though.

One other nightlight can at least challenge Venus, though — the International Space Station. It’s the biggest spacecraft ever built, so it’s especially brilliant — as bright as Venus.

Thousands of satellites are in orbit right now. Most of them are too small, too far, or too dark to see. But some of them are visible as they move across the sky. They’re in sight only for a while after sunset or before sunrise. They’re high enough then to be in sunlight, so they reflect that light down to Earth. But it’s dark at the surface, so we see them streaking across the sky.

The space station is the biggest and brightest. Hubble Space Telescope is a bright target, too. And so are the Iridium satellites — communication satellites in low orbits. They flare brightly when they catch the sunlight just right.

A couple of companies are beginning campaigns to launch thousands of new satellites. They, too, may be pretty bright — especially as they climb to their final orbits. That might be fun to watch — but not fun for astronomers. We’ll have more about that tomorrow.

Script by Damond Benningfield

There are quite a few celebrations of space at this time of year. Friday, for example, was International Space Day, while Saturday was Astronomy Day. And tomorrow is National Astronaut Day. The date was chosen because the first American astronaut, Alan Shepard, rocketed into space on May 5th of 1961.

And today celebrates some fictional accomplishments in space. It’s Star Wars Day. May the Fourth was picked as a pun on the line “may the force be with you.”

Star Wars Day started in Toronto almost a decade ago, and caught on around the world. In 2012, Boris Johnson — now prime minister of the United Kingdom — celebrated his election as mayor of London on Star Wars Day:

    JOHNSON: Thank you very, very much everybody, and may the fourth be with you!

In 2014, an astronaut beamed greetings from the International Space Station. And minor league baseball teams have worn Star Wars-themed uniforms on the date.

Some German astronomers may celebrate at their own version of R2-D2. In late 2018, Hubert Zitt and colleagues at Zweibrück Observatory repainted a 15-foot telescope dome to look like the droid. It became famous when Luke Skywalker himself — actor Mark Hamill — tweeted about it a few months later.

Of course, you don’t have to wait for specific dates to celebrate the universe and space exploration. Look up at the sky on any night, read a book, check out the latest pictures from Mars — or, yes, watch a movie. And may the fourth be with you.

Script by Damond Benningfield

A modest meteor shower is at its best the next couple of nights. At its peak, the Eta Aquarid shower might produce a couple of dozen meteors per hour. But the Moon is almost full now, so it’s in the sky until shortly before dawn. Its light will wash out all but a few of the “shooting stars.”

The moonlight demonstrates the importance of dark skies for viewing the subtleties of the night sky. Extra light knocks out our view not only of faint meteors, but of the Milky Way, the northern lights, and many other faint but beautiful sights.

We can’t do much about the bright Moon. But we can do something about artificial lights — the fixtures that light our streets, buildings, and homes.

Fixtures that shine much of their light into the sky aren’t very efficient. They don’t do a good job of lighting the ground, which is what most of them are supposed to do. And since they’re wasting a lot of their light, they’re also wasting energy. What’s more, the light in the sky can distract migrating birds, sea turtles, and other creatures. It can even create health problems for people.

Some cities and counties have banned inefficient outdoor lights. But individuals can help, too. Make sure that any outdoor lights are shining down, not up, and that they’re the right color — blue light is worse than warmer colors.

That can help keep the skies dark, enhancing the view of meteor showers and other wonders — at least when the Moon is out of sight.

Script by Damond Benningfield

Venus, the “evening star,” flirts with the tip of one of the bull’s horns for the next few weeks. The tip is represented by the star El Nath — a name that means “the butting one.” This evening, it’s a couple of degrees above Venus. Venus will draw a little closer over the coming nights, but won’t quite catch up to it. They’ll stay within a couple of degrees of each other, though, through the middle of the month.

El Nath is about 135 light-years away. Perhaps more interesting, though, is what lies beyond it. El Nath is the closest bright star to the galactic anti-center — the point exactly opposite the center of the Milky Way Galaxy.

The center is in Sagittarius, which will be in good view in a couple of months. That region of the galaxy is densely packed — stars and gas clouds galore.

But the anti-center faces the galaxy’s poorly populated outer regions. So the view of the Milky Way in that direction is thin — you need really dark skies to make it out.

The edge of the Milky Way’s disk is far beyond El Nath. Just how far isn’t certain, though. We’re about 27,000 light-years from the center of the galaxy. And most studies say it’s about 50,000 light-years from the center to the edge. That would put the edge about 25,000 light-years away.

Some recent work, though, has found a few straggler stars even farther out. Either way, it’s a long haul. Just head for El Nath and keep on going — to the edge of the galaxy.

Script by Damond Benningfield

For lunar colonies, nothing will be more important than water — and not just for drinking. It’ll supply oxygen for breathing, and oxygen and hydrogen to power their rockets. But there’s no liquid water anywhere on the Moon. There is a large amount of frozen water, but most of it is buried in craters at the poles.

NASA’s getting ready to test out some electronic “noses” designed to sniff out that water. They’ll be carried to the Moon on a pair of landers next year.

Last year, the Space Agency selected three companies to land scientific instruments on the Moon, although one of them quickly dropped out. And early this year, it picked 16 experiments for the probes to carry.

Most of the experiments are designed to help plan for astronauts to land on the Moon in a few years. Some will measure the level of radiation at the lunar surface, for example. Others will study how the landers change the surface. And one will test new solar cells that will power future missions.

Several of the instruments will look for evidence of water and other compounds that astronauts might be able to use, such as methane and carbon dioxide. The instruments will “sniff” out tiny amounts of these materials wafting just above the surface. The experiments will pioneer ways for explorers to “live off the land” — on the surface of the Moon.

Look for the Moon high in the sky at nightfall. Regulus, the star that marks the heart of the lion, stands just below it.

Script by Damond Benningfield