Easy Science

A lot of moons or no moons at all? We on Earth have just one moon, but some planets have dozens of them. Others don’t have any. Which planets have moons, and which don’t? Let’s go in order from the sun. Mercury and Venus Up first are Mercury and Venus. Neither of them has a moon. Because Mercury is so close to the sun and its gravity, it wouldn’t be able to hold on to its own moon. Any moon would most likely crash into Mercury or maybe go into orbit around the sun and eventually get pulled into it. Why Venus doesn’t have a moon is a mystery for scientists to solve. Earth (That's us!) Up next is Earth, and of course we have one moon. Mars Mars has two moons. Their names are Phobos and Deimos. Don’t you wish our moon had a cool name like that? Jupiter Next are the giant outer planets. They have lots of moons. Jupiter, for instance, has 53 moons! The most well-known are Io (pronounced  eye-oh ), Europa, and Callisto. Jupiter also has the biggest moon in

If it's time for a meteor shower, you won't need a telescope, binoculars, or a high mountain to have a "star gazing" party. You might need a warm sleeping bag and an alarm clock to wake you in the middle of the night. But then just lying down in your own back yard will put you in the perfect spot to enjoy a great show. What is a meteor shower? A meteor is a space rock—or meteoroid—that enters Earth's atmosphere. As the space rock falls toward Earth, the resistance—or drag—of the air on the rock makes it extremely hot. What we see is a "shooting star." That bright streak is not actually the rock, but rather the glowing hot air as the hot rock zips through the atmosphere. When Earth encounters many meteoroids at once, we call it a meteor shower. Why would Earth encounter many meteoroids at once? Well, comets, like Earth and the other planets, also orbit the sun. Unlike the nearly circular orbits of the planets, the orbits of comets are usuall

Asteroids are small, rocky objects that orbit the sun. Although asteroids orbit the sun like planets, they are much smaller than planets. A close-up image of the asteroid Ida taken by NASA's Galileo spacecraft. There are lots of asteroids in our solar system. Most of them live in the main  asteroid belt —a region between the orbits of Mars and Jupiter. Most asteroids in our solar system can be found in the asteroid belt, between Mars and Jupiter. Asteroids hang out in other places, too. For example, some asteroids are found in the orbital path of planets. This means that the asteroid and the planet follow the same path around the sun. Earth and a few other planets have asteroids like this. Where did asteroids come from? Asteroids are left over from the formation of our solar system. Our solar system began about 4.6 billion years ago when a big cloud of gas and dust collapsed. When this happened, most of the material fell to the center of the cloud and formed the s

A  supernova  is the biggest explosion that humans have ever seen. Each blast is the extremely bright, super-powerful explosion of a star. An illustration of one of the brightest and most energetic supernova explosions ever recorded .  What causes a supernova? One type of supernova is caused by the “last hurrah” of a dying massive star. This happens when a star at least five times the mass of our sun goes out with a fantastic bang! Massive stars burn huge amounts of nuclear fuel at their  cores , or centers. This produces  tons of energy , so the center gets very hot. Heat generates pressure, and the pressure created by a star’s nuclear burning also keeps that star from collapsing. A star is in balance between two opposite forces. The star’s gravity tries to squeeze the star into the smallest, tightest ball possible. But the nuclear fuel burning in the star’s core creates strong outward pressure. This outward push resists the inward squeeze of gravity. What holds stars t

We live on a planet called Earth that is part of our solar system. But where is our solar system? It’s a small part of the Milky Way Galaxy. A  galaxy  is a huge collection of gas, dust, and  billions  of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a  supermassive black hole  in the middle.   When you look up at stars in the night sky, you’re seeing other stars in the Milky Way. If it’s really dark, far away from lights from cities and houses, you can even see the dusty bands of the Milky Way stretch across the sky. There are many galaxies besides ours, though. There are so many, we can’t even count them all yet! The  Hubble Space Telescope  looked at a small patch of space for 12 days and found 10,000 galaxies, of all sizes, shapes, and colors. Some scientists think there could be as many as  one hundred billion galaxies in the universe. Some galaxies are spiral-shaped like ours. They have curved arms that ma

What causes the seasons? It's all about Earth's tilt! Many people believe that Earth is closer to the sun in the summer and that is why it is hotter. And, likewise, they think Earth is farthest from the sun in the winter. Although this idea makes sense, it is  incorrect. It is true that Earth’s orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is closer to the sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the sun and summer when it is farthest away! Compared with how far away the sun is, this change in Earth's distance throughout the year does not make much difference to our weather. There is a different reason for Earth's seasons. Earth's axis is an imaginary pole going right through the center of Earth from "top" to "bottom." Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why e

Constellations and their symbols Some curious symbols ring the outside of the  Star Finder . These symbols stand for some of the constellations in the zodiac. What is the zodiac and what is special about these constellations? Imagine a straight line drawn from Earth through the Sun and out into space way beyond our solar system where the stars are. Then, picture Earth following its orbit around the Sun. This imaginary line would rotate, pointing to different stars throughout one complete trip around the Sun—or, one year. All the stars that lie close to the imaginary flat disk swept out by this imaginary line are said to be in the zodiac. The constellations in the zodiac are simply the constellations that this imaginary straight line points to in its year-long journey. A long history of looking to the stars In ancient times, astronomers did not fully understand how Earth, the Sun, and the stars moved. Nor did they have any idea the Universe is so vast. But they were keen ob

What's so special about a supermoon? Turns out, it's a bit more subtle than it sounds—but for the interested observer, there's plenty to see. The name “supermoon” was coined by an astrologer in 1979 and is often used by the media today to describe what astronomers would call a perigean ( pear-ih-jee-un ) full moon: a full moon occurring near or at the time when the Moon is at its closest point in its orbit around Earth. The term gives preference to the geometric alignment of Sun-Earth-Moon and allows the occurrence of perigee into a wider time period than the actual instant of perigee (up to about two weeks, which is almost half of the Moon’s orbit). For those looking carefully, there are several things worth noting. Take a look at the lunar images from November 2016 below: Which of these views of the Moon is a SuperMoon? Both! This is a size comparison of the Moon on the “supermoon” night of November 13-14, 2016. On the left, the Moon was nearer the horizon,

An  eclipse  happens when a planet or a moon gets in the way of the sun’s light. Here on Earth, we can experience two kinds of eclipses:  solar eclipses  and  lunar eclipses . What’s the difference? Solar Eclipse A  solar eclipse  happens when the moon gets in the way of the sun’s light and casts its shadow on Earth. That means during the day, the moon moves over the sun and it gets dark. Isn’t it strange that it gets dark in the middle of the day? This  total eclipse  happens about every year and a half somewhere on Earth. A partial eclipse, when the moon doesn’t completely cover the sun, happens at least twice a year somewhere on Earth. But not everyone experiences every solar eclipse. Getting a chance to see a total solar eclipse is rare. The moon’s shadow on Earth isn’t very big, so only a small portion of places on Earth will see it. You have to be on the sunny side of the planet when it happens. You also have to be in the path of the moon’s shadow. On average,

The Earth’s axis is tilted by 23.4 degrees and so the plane of the Earth’s equator is tilted with respect to the plane of the Earth’s orbit around the Sun – sometimes referred to as the ecliptic. This means that during the Northern Hemisphere summer, the Sun illuminates the Northern Hemisphere more than the Southern Hemisphere. During this time we receive more hours of sunlight and the longest day is known as the summer solstice. During the winter, the Sun illuminates the Southern Hemisphere more than the Northern Hemisphere because the North Pole is titled away from the Sun. During this time we receive fewer hours of sunlight and the shortest day (and longest night) is known as the  winter solstice . But at two points in the year the Sun will illuminate the Northern and Southern Hemispheres equally – these are known as the equinoxes: the  autumnal equinox  in October and vernal equinox in March. It’s the moment in which the plane of Earth's equator passes through the centr