Every time that two or more planets congregate in the night sky, fear mongers crank up the volume on their predictions of doom. They say the combined gravity of the planets will cause everything from earthquakes and storms to boils and hangnails.

Don’t listen to them.

All of the planets are so small or so far away that their short-term effects on Earth are negligible.

Jupiter, the largest and heaviest planet in the solar system, is only one-tenth of one percent as massive as the Sun. And, on average, it’s about five times farther. When combined, those numbers tell us that Jupiter’s gravitational tug on Earth is just one-25,000th as strong as the Sun’s. The pull of the other planets is even weaker. So even if you lined up all of the planets in the same direction from Earth, their combined pull would be insignificant.

That’s not the case on longer terms, though. The gravity of Jupiter and Venus change the shape of Earth’s orbit and the planet’s tilt on its axis. Mars may play a role as well. That influence creates cycles of warmer and colder climate. But the cycles play out over tens of thousands of years or longer – not over days, weeks, or even centuries.

Planetary alignments are common. In fact, there’s one right now. Mars, Saturn, and Mercury are close together in the dawn twilight. But they’re so low in the sky that they’re tough to see. We’ll have more about their alignment tomorrow.

Script by Damond Benningfield

The Coma galaxy cluster is like a cosmic iceberg. What you see is impressive. But what you don’t see is even more impressive.

The cluster is centered more than 300 million light-years away, and it spans 25 million light-years. It contains thousands of individual galaxies. Many of them are far bigger and heavier than our own galaxy, the Milky Way.

But in the 1930s, German astronomer Fritz Zwicky found something odd. He measured the motions of individual galaxies within the cluster. They were zipping along much too fast to be held in check by the gravity of the visible galaxies – they should all fly away from each other.

Zwicky concluded that something else was acting as a sort of gravitational “glue.” He called it dark matter – matter that couldn’t be seen, but that exerted a gravitational pull on the visible matter around it.

It took decades to confirm that finding. And even today, we don’t know what dark matter really is. The leading idea says it’s some type of subatomic particle. But despite many years of searching, no such particle has been found. All we know for sure is that dark matter accounts for about 85 percent of all the matter in the universe – the vast hidden depths of the cosmic iceberg.

The Coma Cluster is in Coma Berenices. The constellation is in the east at nightfall. It’s above brilliant Arcturus, the brightest star of Bootes, and to the lower left of Leo, the lion.

Script by Damond Benningfield

Astronomers love star clusters. All the stars in a cluster were born at the same time, from the same cloud of gas and dust. So any differences in the stars are the result of their evolution, which is a result of their mass. That makes it easier to learn what’s going on inside the stars.

One problem, though, is identifying which stars belong to a cluster. It takes detailed measurements of motion and brightness to separate members of the cluster from stars that just happen to line up in the same direction.

An example is the Coma star cluster, in Coma Berenices. The constellation is in the east at nightfall. Under dark skies, the cluster is a good target for binoculars.

The cluster is about 280 light-years away. But it spans dozens of light-years, so its stars are spread out. That makes it harder to pick out its members. And it takes big telescopes to pick out its fainter stars.

So despite decades of study, astronomers are still locking down the census of stars in the Coma cluster. A study about a decade ago confirmed eight small, faint members – the first of their kind known to belong to the cluster. And another study found that about a quarter of the stars in the cluster are binary or multi-star systems.

These discoveries bring the total number of stars in the Coma cluster to several dozen, with a few dozen more possibilities – members of a wide-spread stellar family.

More about Coma Berenices tomorrow.

Script by Damond Benningfield