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    • By NASA
      4 min read
      Don’t Make Me Wait for April 8!
      Can’t wait to see the Moon block the Sun on April 8? Neither can we. But we have good news – if you want to see an incredible cosmic alignment, you can catch one right now! Exoplanets, asteroids, and other objects regularly pass in front of stars and block their light. Observing these events is easier than you might think – and it can be a fantastic way to contribute to NASA science.
      The Baily’s Beads – the bright spots of light on the lower left of the Moon – seen here are the last rays of sunlight that shone through the low spots or valleys on the Moon’s rugged surface as the Moon made its final move over the Sun during the total solar eclipse on Aug. 21, 2017, above Madras, Oregon. Baily’s Beads will appear on the opposite side of the Moon as it begins to move away from the Sun following totality. NASA/Aubrey Gemignani There are three main kinds of cosmic alignments that temporarily block our view of a star. Each one can help us pick out fine details about astronomical objects that can’t be observed any other way.
      Eclipse – when one object blocks another that’s apparently similar in size.
      Occultation – when a relatively big object completely blocks an apparently smaller object.
      Transit – when an apparently small object passes in front of a larger star, blocking some but not all of its light.
      You’ll notice that we use the word “apparently” in each of those definitions. That’s because what matters is how big the object looks from our perspective, not how big it actually is.
      Now let’s look at some science projects you can get involved in that observe these phenomena.
      Eclipses help scientists see faint objects next to bright objects. Just like you might raise your hand to block light from your car’s headlight while you search the ground for your keys, eclipses block the overpowering light from a star so objects around it can be viewed more easily. This is what the Eclipse Megamovie project, the Dynamic Eclipse Broadcast Initiative, and Citizen CATE 2024 are doing: taking advantage of the Moon blocking the fierce sunlight so they can see what’s happening right around the Sun. These projects invite you to help them use this method to study the Sun’s faint corona. Eclipses and occultations can also tell us about the relative sizes and shapes of objects. This is how Sunsketcher will harness the April 8 eclipse. With your help, they will use our precise knowledge of the size and topography of the Moon to vastly improve estimates of the shape of the Sun. At the very beginning and end of totality, viewers will see Baily’s Beads – bright spots of light around the Moon’s edge where rays of sunlight slip through the valleys between the mountains on the Moon’s surface just before and after totality. The SunSketcher app will capture images of these beads along with precise time and location data of each observation. Following the eclipse, the SunSketcher team will use the collected observations to calculate the shape of the Sun.
      When a planet passes directly between a star and its observer – what astronomers call a transit – the planet dims the star’s light by a measurable amount. The graph in the lower left shows a real time visualization of the strength of the light signal from the star.
      NASA When an object transits – or passes in front of – a star, the star’s light dims. Measuring changes in starlight to search for these transits has revealed thousands of exoplanets (planets orbiting other stars) in recent years. You can join the search today! Three NASA citizen science projects are focused on investigating exoplanets using transits.
      Planet Hunters TESS invites everyone to look for traces of transiting planets in the changing light of distant stars. The most promising of these signals indicate “exoplanet candidates” to be confirmed through additional observations. This project, hosted on the Zooniverse platform, can be done on a smartphone or a computer. Exoplanet Watch is a community of people who use their own telescopes or a shared community robotic telescope to observe exoplanet candidates to better predict the next time the objects will transit. This project requires an internet-connected computer. UNITE, like Exoplanet Watch, is a community of folks using their telescopes to observe exoplanet candidates. This community uses Unistellar telescopes, which operate on a standard, user-friendly system. The UNITE and Exoplanet Watch teams often share data and collaborate! Whichever events you observe, or whichever projects you choose to contribute to, we’re sure you’ll find yourself marveling at our presence on this wonderful planet in this mysterious universe. You don’t have to wait until April 8!
      by Sarah Kirn and Marc J. Kuchner
      NASA Citizen Science
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      Last Updated Mar 28, 2024 Related Terms
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    • By Amazing Space
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    • By NASA
      The asteroid Dimorphos was captured by NASA’s DART mission just two seconds before the spacecraft struck its surface on Sept. 26, 2022. Observations of the asteroid before and after impact suggest it is a loosely packed “rubble pile” object.NASA/Johns Hopkins APL After NASA’s historic Double Asteroid Redirection Test, a JPL-led study has shown that the shape of asteroid Dimorphos has changed and its orbit has shrunk.
      When NASA’s DART (Double Asteroid Redirection Test) deliberately smashed into a 560-foot-wide (170-meter-wide) asteroid on Sept. 26, 2022, it made its mark in more ways than one. The demonstration showed that a kinetic impactor could deflect a hazardous asteroid should one ever be on a collision course with Earth. Now a new study published in the Planetary Science Journal shows the impact changed not only the motion of the asteroid, but also its shape.
      DART’s target, the asteroid Dimorphos, orbits a larger near-Earth asteroid called Didymos. Before the impact, Dimorphos had a roughly symmetrical “oblate spheroid” shape – like a squashed ball that is wider than it is tall. With a well-defined, circular orbit at a distance of about 3,900 feet (1,189 meters) from Didymos, Dimorphos took 11 hours and 55 minutes to complete one loop around Didymos.
      “When DART made impact, things got very interesting,” said Shantanu Naidu, a navigation engineer at NASA’s Jet Propulsion Laboratory in Southern California, who led the study. “Dimorphos’ orbit is no longer circular: Its orbital period” – the time it takes to complete a single orbit – “is now 33 minutes and 15 seconds shorter. And the entire shape of the asteroid has changed, from a relatively symmetrical object to a ‘triaxial ellipsoid’ – something more like an oblong watermelon.”
      This illustration shows the approximate shape change that the asteroid Dimorphos experienced after DART hit it. Before impact, left, the asteroid was shaped like a squashed ball; after impact it took on a more elongated shape, like a watermelon.NASA/JPL-Caltech Dimorphos Damage Report
      Naidu’s team used three data sources in their computer models to deduce what had happened to the asteroid after impact. The first source was aboard DART: The spacecraft captured images as it approached the asteroid and sent them back to Earth via NASA’s Deep Space Network (DSN). These images provided close-up measurements of the gap between Didymos and Dimorphos while also gauging the dimensions of both asteroids just prior to impact.
      The second data source was the DSN’s Goldstone Solar System Radar, located near Barstow, California, which bounced radio waves off both asteroids to precisely measure the position and velocity of Dimorphos relative to Didymos after impact. Radar observations quickly helped NASA conclude that DART’s effect on the asteroid greatly exceeded the minimum expectations.
      The third and most significant source of data: ground telescopes around the world that measured both asteroids’ “light curve,” or how the sunlight reflecting off the asteroids’ surfaces changed over time. By comparing the light curves before and after impact, the researchers could learn how DART altered Dimorphos’ motion.
      As Dimorphos orbits, it periodically passes in front of and then behind Didymos. In these so-called “mutual events,” one asteroid can cast a shadow on the other, or block our view from Earth. In either case, a temporary dimming – a dip in the light curve – will be recorded by telescopes.
      See the DART impact with NASA’s Eyes on the Solar System “We used the timing of this precise series of light-curve dips to deduce the shape of the orbit, and because our models were so sensitive, we could also figure out the shape of the asteroid,” said Steve Chesley, a senior research scientist at JPL and study co-author. The team found Dimorphos’ orbit is now slightly elongated, or eccentric. “Before impact,” Chesley continued, “the times of the events occurred regularly, showing a circular orbit. After impact, there were very slight timing differences, showing something was askew. We never expected to get this kind of accuracy.”
      The models are so precise, they even show that Dimorphos rocks back and forth as it orbits Didymos, Naidu said.
      Orbital Evolution
      The team’s models also calculated how Dimorphos’ orbital period evolved. Immediately after impact, DART reduced the average distance between the two asteroids, shortening Dimorphos’ orbital period by 32 minutes and 42 seconds, to 11 hours, 22 minutes, and 37 seconds.
      Over the following weeks, the asteroid’s orbital period continued to shorten as Dimorphos lost more rocky material to space, finally settling at 11 hours, 22 minutes, and 3 seconds per orbit – 33 minutes and 15 seconds less time than before impact. This calculation is accurate to within 1 ½ seconds, Naidu said. Dimorphos now has a mean orbital distance from Didymos of about 3,780 feet (1,152 meters) – about 120 feet (37 meters) closer than before impact.
      “The results of this study agree with others that are being published,” said Tom Statler, lead scientist for solar system small bodies at NASA Headquarters in Washington. “Seeing separate groups analyze the data and independently come to the same conclusions is a hallmark of a solid scientific result. DART is not only showing us the pathway to an asteroid-deflection technology, it’s revealing new fundamental understanding of what asteroids are and how they behave.”
      These results and observations of the debris left after impact indicate that Dimorphos is a loosely packed “rubble pile” object, similar to asteroid Bennu. ESA’s (European Space Agency) Hera mission, planned to launch in October 2024, will travel to the asteroid pair to carry out a detailed survey and confirm how DART reshaped Dimorphos.
      More About the Mission
      DART was designed, built, and operated by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, for NASA’s Planetary Defense Coordination Office, which oversees the agency’s ongoing efforts in planetary defense. DART was humanity’s first mission to intentionally move a celestial object.
      JPL, a division of Caltech in Pasadena, California, manages the DSN for NASA’s Space Communications and Navigation (SCaN) program within the Space Operations Mission Directorate at the agency’s headquarters in Washington.
      NASA’s Asteroid-Striking DART Mission Team Has JPL Members Classroom Activity: How to Explore an Asteroid NASA’s Planetary Radar Captures Detailed View of Oblong Asteroid News Media Contacts
      Ian J. O’Neill
      Jet Propulsion Laboratory, Pasadena, Calif.
      818-354-2649
      ian.j.oneill@jpl.nasa.gov
      Karen Fox / Charles Blue
      NASA Headquarters
      karen.c.fox@nasa.gov / charles.e.blue@nasa.gov
      2024-029
      Share
      Details
      Last Updated Mar 19, 2024 Related Terms
      DART (Double Asteroid Redirection Test) Asteroids Jet Propulsion Laboratory Modeling Near-Earth Asteroid (NEA) Planetary Defense Planetary Defense Coordination Office Explore More
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