Tuesday April 15, 2014
Cassini Spots a New Object in Saturn's Rings
If you're out stargazing over the next few months, at some point, you will notice the planet Saturn. On these April nights, it's rising late in the evening (right now around 10 p.m. or thereabouts), so you have to stay up to find it. But, it's well worth the look. The rings alone give this planet an otherworldly and fascinating appearance.
Those of us who gaze at Saturn from our backyards aren't the only ones watching this planet. The Cassini spacecraft, which has been studying the Saturn system since 2004, has been our eyes, ears, and planetary science exploring, sending back incredible images and data. It has sent the Huygens probe to the surface of Saturn's largest moon, Titan, returning amazing information about this weird world. Cassini has also found an ocean of salty water beneath the icy surface of the moon Enceladus, mapped the rings, and shown us the beauty of Saturn's ever-changing cloud tops. Recently, it documented the formation of a small icy object within one of the planet's outermost rings. It could be a new moon, forming from the chunks of ice that orbit Saturn and form its rings.
A possible new moon of Saturn, discovered as part of a disturbance in Saturn's outermost A ring. Courtesy NASA/JPL-Caltech/Space Science Institute.
The object shows up in images taken with Cassini's narrow angle camera on April 15, 2013, and shows disturbances at the very edge of the A ring. One of these disturbances is an arc about 20 percent brighter than its surroundings, 750 miles (1,200 kilometers) long and 6 miles (10 kilometers) wide. Scientists also found unusual features in the usually smooth profile at the ring's edge. It's likely that the arc and its features are caused by the gravitational effects of a nearby object.
The object is not expected to grow any larger, and may even be falling apart. However, its formation process and outward movement may be a big help to planetary scientists as they seek to understand how Saturn's icy moons, including Titan and Enceladus, may have formed in ancient rings that were once much more massive than the set we see today. It also provides insight into how Earth and other planets in our solar system may have formed and migrated away from our star, the Sun.
The object, which scientist have nicknamed Peggy, is too small to be seen in images so far. Scientists estimate it is probably no more than about a half mile (about a kilometer) in diameter. For perspective, Saturn's icy moons range in size depending on their proximity to the planet. The more distant they are from Saturn, the bigger they are. Many of the moons and particles in the rings are made mostly of ice. Based on these facts, and other characteristics of the moons and rings, researchers recently proposed that Saturn's icy moons formed from ring particles and then moved outward, away from the planet, merging with other moons on the way. This discovery of a tiny moon, possibly as it is forming, is an important step in verifying this theory.
The more rings scientists study, the more they learn about these ephemeral (short-lived phenomena). It is possible the process of moon formation in Saturn's rings has ended with Peggy. This is because Saturn's rings are very likely too depleted to make more moons. Ring system formation (and destruction) is an exciting and incomplete story in the history of the solar system. The current theory is that Saturn's rings were once much more massive, and had enough material to create many moons as ring particles collided.
The Cassini mission has been a very successful exploration of the Saturn system. As such, it has been extended several times. Its current official mission, now known as the Cassini Solstice Mission, was last extended in 2010 for several more years and will allow the spacecraft to study the system up through Saturn's summer solstice in May 2017. This will mark one complete set of seasons on Saturn that the mission will have studied, giving planetary scientists an incredible amount of information about this planet, its moons, and rings.
Friday April 11, 2014
How the April 14-15, 2014 lunar eclipse could look during totality. The Moon will be near the bright star Spica. Created by Carolyn Collins Petersen using Stellarium open source software. Click image for a larger version.)
Experience a Total Lunar Eclipse!
On April 15th, in the wee hours of the morning, you have a chance to see one of nature's most awe-inspiring events: a total lunar eclipse. People are referring to this one as a Blood Moon because at totality (the darkest part of the eclipse), the Moon will appear a deep red color. Observers across the Americas, and parts of the Pacific will able to witness it beginning late Monday night April 14 into the early morning of April 15th. (For a complete list of what locations on Earth will see this eclipse, check out NASA's Eclipse Web page.)
What You Will See
So, what is a lunar eclipse? These rare events happen at Full Moon, when the Moon moves into Earth's shadow as it orbits our planet. The entire eclipse takes almost 6 hours (5 hours 43 minutes). First, it slips into the penumbra at the western edge of the shadow. At first, you won't notice much because the Moon is still quite bright. Then, about an hour later, the Moon will begin entering the umbra, the darkest part of Earth's shadow. This is when you will start to notice the Moon slowly taking on color -- anywhere from a ruddy brown to a coppery red. The Moon will spend just over an hour (1 hour 17 minutes) in the umbra. Then it will slowly move out into the eastern part of the penumbra, and finally exit Earth's shadow completely.
When Should I Look?
Here's a short timeline of events. Times are approximate.
The eclipse begins at 4:53 AM UT (April 15) 12:53 AM EDT, 11:53 AM CDT (April 14th), Â 10:53 PM MDT, 9:53 PM PDT, 6:53 PM Hawai'i time.
Totality begins at 7:08 AM UT (April 15), 3:08 AM EDT, 2:08 AM CDT, 1:08 AM MDT, 12:08 AM PDT, 9:08 PM Hawai'i (April 14)
Totality ends at 8:23 AM UT (April 15), 4:23 AM EDT, 3:23 AM CDT, 2:23 AM MDT, 1:23 AM PDT, 10:23 PM Hawai'i (April 14)
Eclipse ends at 10:35 AM UT (April 15), 6:36 AM EDT (below horizon), 5:35 AM CDT, 4:35 AM MDT, 3:35 AM PDT, 12:35 AM Hawai'i
A timeline of the April 14-15, 2014 lunar eclipse, based on data from NASA. Click image for a larger version.
Monday April 7, 2014
How Black Holes Grow
For the past few years, astronomers have been watching with great interest as a cloud of gas called G2 gets ever closer to the black hole at the center of the Milky Way Galaxy. The cloud (shown in the image at left) is headed directly into Sagittarius A* (Sgr A* for short) and will get caught up in the accretion disk of material surrounding and feeding into our black hole. The collision is already starting to occur, although the largest mass of the cloud has not yet arrived at the disk. But, the outer edges are starting to feel the pull of the black hole and that is providing a unique opportunity for astronomers to watch as a black hole swallows up material.
It could be quite an interesting sight. One common view of black holes and how they consume nearby objects suggests that as a cloud or other object moves through the accretion disk toward the black hole, it gets stretched out. This is because the gravity of the black hole pulls on the closest parts of the object first. One popular illustration shows an astronaut going feet-first into the black hole and getting stretched thinner and thinner. That process, nicknamed "spaghettification", eventually tears the object apart. So, observers will be on the lookout for evidence as the cloud begins to disintegrate under the black hole's voracious gravitational pull.
Astronomers can already tell that the cloud's edges are starting to shred as they get close to the accretion disk. In addition, temperatures in the cloud are rising. For that reason, the Swift X-Ray satellite and the Chandra X-Ray Observatory are both monitoring the Sgr A* region, to catch the rise in x-ray emissions as the cloud is heated up during its its death march into the black hole.
Friday April 4, 2014
I've been a stargazer since I was a child, and continue to go out and explore the sky when the conditions are right. Skygazing is an easy pastime, and a rewarding one. Want to check out the planets Mars, Jupiter and Saturn? See the Moon turn red? Experience a meteor shower? They're all available on April evenings after the sky gets dark. You don't need any special equipment, but if you do have binoculars or a small telescope, use them. Here's a list of ten great sky sights for April for you to search out. Go to About.com's star chart page to make a sky map for your location and let's do some stargazing!
- Jupiter. The famed astronomer Galileo Galilei had only a small telescope to study this giant planet, but the four moons he saw changed our view of the solar system. These small worlds, the Galilean satellites are easy to spot with a good pair of binoculars and look even better through a telescope. Jupiter is the brilliant shining dot in the constellation Gemini, the Twins.
- Mars. The Red Planet is easy to spot with the naked eye this month. Just look for a brilliant reddish dot in the constellation Virgo late in the evening, well above the eastern horizon. It's not too far from the bright star Spica.If you happen to have a good-sized telescope, you might be able to make out some surface markings on Mars.
- The Moon. Want a great observing target throughout the month? Check out the Moon. The dark areas on heavily cratered surface are called "maria", which is Latin for "seas". You will also see some bright areas marked by splashy-looking rays. These are craters and the rays are where the material gouged out by long-ago impacts spread out across the surface.
- A Total Lunar Eclipse. On the evening of April 14th into the morning of the 15th, watch as the Moon passes through Earth's shadow in a total lunar eclipse. It will gradually get dark as it moves through the penumbra. Later, the Moon will pass into the umbra - the darkest part of Earth's shadow. It will look darker and probably turn a coppery red color. The eclipse will be visible throughout North and South America, and parts of the lower Pacific basin, including Australia. Read More...