StarDate

Earth passed by Jupiter yesterday. Now, we’re beginning to leave the giant planet behind. We’ll loop past it again early next year. That passage is known as opposition – Jupiter lines up opposite the Sun in our sky. It’s closest to us then, so it shines brightest for the year. And it’s in view all night. Jupiter is much farther from the Sun than Earth is, so it takes about 12 years to complete a single orbit. Earth follows a much shorter path around the Sun, and it moves faster. So it passes Jupiter every 13 months. As we approach Jupiter, the planet stops its normal eastward motion against the background of stars. For a while, it moves backward – a period known as retrograde. Jupiter itself doesn’t change direction. Instead, the shift is a result of our changing viewing angle. It’s like passing a car on the highway. For a little bit, the other car looks like it’s moving in reverse compared to the background of buildings and trees. As the gap opens, though, it appears to resume its forward motion. Jupiter will reach that point on March 11th – shifting gears as it circles the Sun. Jupiter looks like a brilliant star – brighter than any other planet or star in the night sky now. The twin stars of Gemini are close by. Pollux, the brighter twin, is close to the left of Jupiter at nightfall. Castor is farther to the upper left. The whole group soars high across the south during the night. Script by Damond Benningfield

The closer we look at the worlds of the solar system, the more places we see that could be homes for life. Some of those worlds orbit Jupiter, the largest planet in the solar system. Jupiter itself isn’t on the list. It’s a big ball of gas with no solid surface. There has been speculation that large organisms could float through its skies. But that’s considered a long shot. It’s more likely that life could inhabit some of Jupiter’s moons. The leading candidate is Europa. It’s about the same size as our own moon. A deep ocean of liquid water probably lies below its icy crust. Plumes of hot water may squirt into the bottom of the ocean. The plumes would contain a variety of compounds – perhaps including the chemistry of life. So Europa has the right combination of water, heat, and chemistry to support life – at least microscopic life. Europa isn’t the only Jovian moon with a deep ocean. The largest moon, Ganymede, may have more liquid water than all Earth’s oceans combined. One other big moon may have an ocean as well. But the crusts of these moons are much thicker than Europa’s. So even if their oceans are inhabited, it’ll be much harder for us to find evidence of life. Look for Jupiter in the eastern sky in early evening, and arcing high across the sky later on. It looks like a brilliant star. Through binoculars, its big moons look like tiny stars quite close to the planet. More about Jupiter tomorrow. Script by Damond Benningfield

Jupiter looks like it’s wearing zebra stripes. Bands of clouds that run parallel to the equator alternate between bright and dark – zebra stripes. Each one is thousands of miles wide. The stripes are a result of Jupiter’s composition and its rotation. It’s basically a ball of gas – it’s made almost entirely of hydrogen and helium. And even though it’s 11 times the diameter of Earth, it spins on its axis in less than 10 hours. That forces the clouds that top its atmosphere into bands that stretch from east to west. The bands alternate between belts and zones. The belts are darker – probably because they allow us to see deeper into the atmosphere. The zones are topped by the highest clouds. The clouds are made of frozen ammonia, which looks bright white. The belts don’t have that layer. Instead, we’re seeing clouds in the next layer down. Those clouds are made of water and other compounds, which are darker. The stripes are flanked by jet streams that blow in alternating directions. They can roar at hundreds of miles per hour. They keep the belts and zones separated – maintaining the zebra stripes on this giant planet. Jupiter is at its best this week. It’s in view all night, and it shines brightest for the year. It looks like a brilliant star. It’s low in the eastern sky in early evening, and climbs high across the sky later on. The stripes are easily visible through just about any telescope. Script by Damond Benningfield

If today is your birthday, then Happy Birthday! The next one is just one year away – 365 sunrises and sunsets. If today is your birthday and you happen to be from Jupiter – well, Happy Birthday, and … we’re sorry. Your next one is almost 12 Earth years away – almost 10,500 sunrises and sunsets. The Jovian year is so long for a couple of reasons. First, the planet is more than five times farther from the Sun than Earth is. So its path around the Sun is more than five times longer than Earth’s. The second reason is the laws of orbital motion. The farther a planet is from the Sun, the slower its orbital speed. At Jupiter’s great range, it moves at less than half the speed of Earth. Ergo, one Jovian year lasts almost 12 Earth years. But to get all those sunrises and sunsets, you also have to factor in the length of a Jovian day. Although Jupiter is 11 times the diameter of Earth, it spins in a hurry – a day lasts less than 10 hours. Add it all up, multiply, divide, and carry the two, and – well, it’s a lot of days between birthdays on the Sun’s largest planet. Jupiter is especially vibrant now. It reaches opposition this weekend – it lines up opposite the Sun in our sky. It rises around sunset and is in view all night. The planet is also closest to us, so it shines at its brightest. In fact, in all the night sky right now, only the Moon outshines it. More about Jupiter tomorrow. Script by Damond Benningfield

Stars are born when giant clouds of gas and dust break apart and collapse. And if that’s all there was to it, the Milky Way Galaxy would give birth to a couple of hundred stars every year. Instead, thanks to feedback from the stars themselves, it makes only a few. Feedback is a process that clears away the material for making stars, but can also trigger the birth of more stars. Young stars, for example, produce winds and jets that blow away the gas and dust around them. Since stars are born in clusters, many youngsters can be sweeping away the star-making material at the same time. That pares back the number of stars that can be born in a cluster. Mature stars add to the feedback – not only with winds, but also with radiation. Hot stars generate a lot of ultraviolet energy. It vaporizes tiny particles of dust – eliminating possible building blocks for new stars. The heaviest stars explode as supernovas. These blasts can clear out the space for light-years around, creating big, empty bubbles. And supernovas also accelerate subatomic particles around them to almost the speed of light. These “cosmic rays” help to sweep away the raw material for making more stars. But supernovas can also enhance the birth rate. Their shock waves can cause distant clouds of gas and dust to collapse to form stars. So feedback is a complex process – one that both aids and hinders the birth of new stars. Script by Damond Benningfield