On Nov. 11, Earthlings will be treated to a rare cosmic event — a Mercury transit.
For about five and a half hours on Monday, Nov. 11 — from about 7:35 a.m. EST to 1:04 p.m. EST — Mercury will be visible from Earth as a tiny black dot crawling across the face of the Sun. This is a transit and it happens when Mercury lines up just right between the Sun and Earth.
Mercury transits happen about 13 times a century. Though it takes Mercury only about 88 days to zip around the Sun, its orbit is tilted, so it’s relatively rare for the Sun, Mercury and Earth to line up perfectly. The next Mercury transit isn’t until 2032 — and in the U.S., the next opportunity to catch a Mercury transit is in 2049!
How to watch
Our Solar Dynamics Observatory satellite, or SDO, will provide near-real time views of the transit. SDO keeps a constant eye on the Sun from its position in orbit around Earth to monitor and study the Sun’s changes, putting it in the front row for many eclipses and transits.
If you’re thinking of watching the transit from the ground, keep in mind that it is never safe to look directly at the Sun. Even with solar viewing glasses, Mercury is too small to be easily seen with the unaided eye. Your local astronomy club may have an opportunity to see the transit using specialized, properly-filtered solar telescopes — but remember that you cannotuse a regular telescope or binoculars in conjunction with solar viewing glasses.
Transits in other star systems
Transiting planets outside our solar system are a key part of how we look for exoplanets.
Our Transiting Exoplanet Survey Satellite, or TESS, is NASA’s latest planet-hunter, observing the sky for new worlds in our cosmic neighborhood. TESS searches for these exoplanets, planets orbiting other stars, by using its four cameras to scan nearly the whole sky one section at a time. It monitors the brightness of stars for periodic dips caused by planets transiting those stars.
This is similar to Mercury’s transit across the Sun, but light-years away in other solar systems! So far, TESS has discovered 29 confirmed exoplanets using transits — with over 1,000 more candidates being studied by scientists!
What’s Up for May? Two huge solar system highlights: Mercury transits the sun and Mars is closer to Earth than it has been in 11 years.
On May 9, wake up early on the west coast or step out for coffee on the east coast to see our smallest planet cross the face of the sun. The transit will also be visible from most of South America, western Africa and western Europe.
A transit occurs when one astronomical body appears to move across the face of another as seen from Earth or from a spacecraft. But be safe! You’ll need to view the sun and Mercury through a solar filter when looking through a telescope or when projecting the image of the solar disk onto a safe surface. Look a little south of the sun’s Equator. It will take about 7 ½ hours for the tiny planet’s disk to cross the sun completely. Since Mercury is so tiny it will appear as a very small round speck, whether it’s seen through a telescope or projected through a solar filter. The next Mercury transit will be Nov. 11, 2019.
Two other May highlights involve Mars. On May 22 Mars opposition occurs. That’s when Mars, Earth and the sun all line up, with Earth directly in the middle.
Eight days later on May 30, Mars and Earth are nearest to each other in their orbits around the sun. Mars is over half a million miles closer to Earth at closest approach than at opposition. But you won’t see much change in the diameter and brightness between these two dates. As Mars comes closer to Earth in its orbit, it appears larger and larger and brighter and brighter.
During this time Mars rises after the sun sets. The best time to see Mars at its brightest is when it is highest in the sky, around midnight in May and a little earlier in June.
Through a telescope you can make out some of the dark features on the planet, some of the lighter features and sometimes polar ice and dust storm-obscured areas showing very little detail.
After close approach, Earth sweeps past Mars quickly. So the planet appears large and bright for only a couple weeks.
But don’t worry if you miss 2016’s close approach. 2018’s will be even better, as Mars’ close approach will be, well, even closer.
You can find out about our #JourneytoMars missions at mars.nasa.gov, and you can learn about all of our missions at http://www.nasa.gov.
A quarter-century ago, the Solar and Heliospheric Observatory (SOHO) launched to space. Its 25 years of data have changed the way we think about the Sun — illuminating everything from the Sun’s inner workings to the constant changes in its outermost atmosphere.
SOHO — a joint mission of the European Space Agency and NASA — carries 12 instruments to study different aspects of the Sun. One of the gamechangers was SOHO’s coronagraph, a type of instrument that uses a solid disk to block out the bright face of the Sun and reveal the relatively faint outer atmosphere, the corona. With SOHO’s coronagraph, scientists could image giant eruptions of solar material and magnetic fields, called coronal mass ejections, or CMEs. SOHO’s images revealed shape and structure of CMEs in breathtaking detail.
These solar storms can impact robotic spacecraft in their path, or — when intense and aimed at Earth — threaten astronauts on spacewalks and even disrupt power grids on the ground. SOHO is particularly useful in viewing Earth-bound storms, called halo CMEs — so called because when a CME barrels toward us on Earth, it appears circular, surrounding the Sun, much like watching a balloon inflate by looking down on it.
Before SOHO, the scientific community debated whether or not it was even possible to witness a CME coming straight toward us. Today, SOHO images are the backbone of space weather prediction models, regularly used in forecasting the impacts of space weather events traveling toward Earth.
Beyond the day-to-day monitoring of space weather, SOHO has been able to provide insight about our dynamic Sun on longer timescales as well. With 25 years under its belt, SOHO has observed a full magnetic cycle — when the Sun’s magnetic poles switch places and then flip back again, a process that takes about 22 years in total. This trove of data has led to revolutions in solar science: from revelations about the behavior of the solar core to new insight into space weather events that explode from the Sun and travel throughout the solar system.
Data from SOHO, sonified by the Stanford Experimental Physics Lab, captures the Sun’s natural vibrations and provides scientists with a concrete representation of its dynamic movements.
The legacy of SOHO’s instruments — such as the extreme ultraviolet imager, the first of its kind to fly in orbit — also paved the way for the next generation of NASA solar satellites, like the Solar Dynamics Observatory and STEREO. Even with these newer instruments now in orbit, SOHO’s data remains an invaluable part of solar science, producing nearly 200 scientific papers every year.
Relatively early in its mission, SOHO had a brush with catastrophe. During a routine calibration procedure in June 1998, the operations team lost contact with the spacecraft. With the help of a radio telescope in Arecibo, the team eventually located SOHO and brought it back online by November of that year. But luck only held out so long: Complications from the near loss emerged just weeks later, when all three gyroscopes — which help the spacecraft point in the right direction — failed. The spacecraft was no longer stabilized. Undaunted, the team’s software engineers developed a new program that would stabilize the spacecraft without the gyroscopes. SOHO resumed normal operations in February 1999, becoming the first spacecraft of its kind to function without gyroscopes.
SOHO’s coronagraph have also helped the Sun-studying mission become the greatest comet finder of all time. The mission’s data has revealed more than 4,000 comets to date, many of which were found by citizen scientists. SOHO’s online data during the early days of the mission made it possible for anyone to carefully scrutinize a image and potentially spot a comet heading toward the Sun. Amateur astronomers from across the globe joined the hunt and began sending their findings to the SOHO team. To ease the burden on their inboxes, the team created the SOHO Sungrazer Project, where citizen scientists could share their findings.
Solar Orbiter just released its
first scientific data — including the closest images ever taken of the Sun.
Launched on February 9, 2020, Solar
Orbiter is a collaboration between the European Space Agency and NASA, designed
to study the Sun up close. Solar Orbiter completed its first close
pass of the Sun on June 15, flying
within 48 million miles of the Sun’s surface.
This is already closer to the
Sun than any other spacecraft has taken pictures (our Parker Solar Probe
mission has flown closer, but it doesn’t take pictures of the Sun). And over
the next seven years, Solar Orbiter will inch even closer to the Sun while tilting
its orbit above the plane of the planets, to peek at the Sun’s north and south
poles, which have never been imaged before.
Here’s some of what Solar
Orbiter has seen so far.
The Sun
up close
Solar Orbiter’s Extreme
Ultraviolet Imager, or EUI, sees the Sun in wavelengths of extreme ultraviolet
light that are invisible to our eyes.
EUI captured images showing “campfires”
dotting the Sun. These miniature bright spots are over a million times smaller
than normal solar flares. They may be the nanoflares, or tiny explosions, long thought
to help heat the Sun’s outer atmosphere, or corona, to its temperature 300
times hotter than the Sun’s surface. It will take more data to know for sure,
but one thing’s certain: In EUI’s images, these campfires are all over the Sun.
The Polar and Helioseismic
Imager, or PHI, maps the Sun’s magnetic field in a variety of ways. These
images show several of the measurements PHI makes, including the magnetic field
strength and direction and the speed of flow of solar material.
PHI will have its heyday later
in the mission, as Solar Orbiter gradually tilts its orbit to 24 degrees above
the plane of the planets, giving it a never-before-seen view of the poles. But
its first images reveal the busy magnetic field on the solar surface.
Studying
space
Solar Orbiter’s instruments don’t just focus on the
Sun itself — it also carries instruments that study the space around the Sun
and surrounding the spacecraft.
The Solar and Heliospheric Imager, or SoloHi, looks out the side of the Solar Orbiter spacecraft to see the solar wind, dust, and cosmic rays that fill the space between the Sun and the planets. SoloHi captured the relatively faint light reflecting off interplanetary dust known as the zodiacal light, the bright blob of light in the right of the image. Compared to the Sun, the zodiacal light is extremely dim – to see it, SoloHi had to reduce incoming sunlight by a trillion times. The straight bright feature on the very edge of the image is a baffle illuminated by reflections from the spacecraft’s solar array.
This first data release
highlights Solar Orbiter’s images, but its in situ instruments also revealed
some of their first measurements. The Solar Wind Analyser, or SWA instrument, made
the first dedicated
measurements of heavy ions — carbon, oxygen, silicon, and iron — in the solar
wind from the inner heliosphere.
Read more about Solar Orbiter’s
first data and see all the images on ESA’s website.
Astronomy is the scientific study of everything in outer space. Astronomers and other scientists know that stars many light-years away have no effect on the ordinary activities of humans on Earth.
Astrology, meanwhile, is something else. It’s the belief that the positions of stars and planets can influence human events. It’s not considered a science.
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 though 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.
What are Constellations?
A constellation is group of stars like a dot-to-dot puzzle. If you join the dots—stars, that is—and use lots of imagination, the picture would look like an object, animal, or person. For example, Orion is a group of stars that the Greeks thought looked like a giant hunter with a sword attached to his belt. Other than making a pattern in Earth’s sky, these stars may not be related at all.
Even the closest star is almost unimaginably far away. Because they are so far away, the shapes and positions of the constellations in Earth’s sky change very, very slowly. During one human lifetime, they change hardly at all.
A Long History of Looking to the Stars
The Babylonians lived over 3,000 years ago. They divided the zodiac into 12 equal parts – like cutting a pizza into 12 equal slices. They picked 12 constellations in the zodiac, one for each of the 12 “slices.” So, as Earth orbits the sun, the sun would appear to pass through each of the 12 parts of the zodiac. Since the Babylonians already had a 12-month calendar (based on the phases of the moon), each month got a slice of the zodiac all to itself.
But even according to the Babylonians’ own ancient stories, there were 13 constellations in the zodiac. So they picked one, Ophiuchus, to leave out. Even then, some of the chosen 12 didn’t fit neatly into their assigned slice of the pie and crossed over into the next one.
When the Babylonians first invented the 12 signs of zodiac, a birthday between about July 23 and August 22 meant being born under the constellation Leo. Now, 3,000 years later, the sky has shifted because Earth’s axis (North Pole) doesn’t point in quite the same direction.
The constellations are different sizes and shapes, so the sun spends different lengths of time lined up with each one. The line from Earth through the sun points to Virgo for 45 days, but it points to Scorpius for only 7 days. To make a tidy match with their 12-month calendar, the Babylonians ignored the fact that the sun actually moves through 13 constellations, not 12. Then they assigned each of those 12 constellations equal amounts of time.
So, we didn’t change any zodiac signs…we just did the math.
For more than seven hours on Monday, May 9, Mercury will be visible as a tiny black dot crossing the face of the sun. This rare event – which happens only slightly more than once a decade – is called a transit.
Although Mercury whips around the sun every 88 days – over four times faster than Earth – the three bodies rarely align. Because Mercury orbits in a plane 7 degrees tilted from Earth’s orbit, it usually darts above or below our line of sight to the sun. As a result, a Mercury transit happens only about 13 times a century. The last one was in 2006, and the next one isn’t until 2019.
When: On May 9, shortly after 7:00 a.m. EDT, Mercury will appear as a tiny black dot against a blazing backdrop, traversing the sun’s disk over seven and a half hours. Mercury will cross the edge of the sun (ingress) after 7:00 a.m. EDT. The mid-transit point will occur a little after 10:45 a.m. EDT, with egress around 2:30 p.m. EDT.
Where: Skywatchers in Western Europe, South America and eastern North America will be able to see the entirety of the transit. The entire 7.5-hour path across the sun will be visible across the Eastern U.S. – with magnification and proper solar filters – while those in the West can observe the transit in progress at sunrise.
Safety!
Unlike the 2012 Venus transit of the sun, Mercury is too small to be visible without magnification from a telescope or high-powered binoculars. Both must have safe solar filters made of specially-coated glass or Mylar; you can never look directly at the sun. We’re offering several avenues for the public to view the event without specialized and costly equipment, including images on NASA.gov, a one-hour NASA Television special, and social media coverage.
The Science…Why are Planetary Transits Important?
Transits like this allowed scientists in the 17th century to make the first estimates of Earth’s distance from the sun. Transit observations over the past few centuries have also helped scientists study everything from the atmosphere of Venus to the slight shifts in Mercury’s orbit that could only be explained by the theory of general relativity. Because we know Mercury’s size and location precisely, this transit will help scientists calibrate telescopes on solar observatories SDO, SOHO, and Hinode.
Transits can also teach us more about planets – both in and out of our solar system. The Venus transit in 2012 provided observations of the planet’s atmosphere. Transits are also the main way we find planets outside the solar system, called exoplanets.
The transit method looks for a drop in the brightness of a star when a planet passes in front of it. This method will not find every planet – only those that happen to cross our line of sight from Earth to the star. But with enough sensitivity, the transit method through continuous monitoring is a great way to detect small, Earth-size planets, and has the advantage of giving us both the planet’s size (from the fraction of starlight blocked), as well as its orbit (from the period between transits). Our Kepler/K2 mission uses this method to find exoplanets, as will the Transiting Exoplanet Survey Satellites, or TESS, following its launch in 2017/2018.
We will stream a live program on NASA TV and the agency’s Facebook page from 10:30 to 11:30 a.m. – an informal roundtable during which experts representing planetary, heliophysics and astrophysics will discuss the science behind the Mercury transit. Viewers can ask questions via Facebook and Twitter using #AskNASA.
In addition to the Mercury transit of the sun today, there are a few other things you should know about our solar system this week:
1. Mars, Ready for its Close-Up
Mars will soon be closer to Earth than it has been for 11 years, presenting a great opportunity for backyard sky watchers.
2. Fire and Ice
Our spacecraft have an even closer view of Mars, and that fact regularly leads to some intriguing discoveries. The latest: volcanoes may have erupted beneath an ice sheet there billions of years ago. The above image is a mineral map of part of the Martian surface.
3. Icy Hydra
Meanwhile, our New Horizons spacecraft has sent home the first compositional data about Pluto’s four small moons. The new data show the surface of Hydra is dominated by nearly pristine water ice–confirming hints that scientists picked up in images showing Hydra’s highly reflective surface.
4. Ceres, Ever Sharper
The mission director for our Dawn mission writes, “Ceres, which only last year was hardly more than a fuzzy blob against the stars, is now a richly detailed world, and our portrait grows more elaborate every day.”
5. Join us at Jupiter
Our Juno mission arrives at the giant planet on Jul. 4. Meanwhile, all amateur astronomers are invited to take part in a worldwide effort to identify potential observations for the spacecraft to make once it’s in orbit. Find out how to join HERE.
Want to learn more? Read our full list of the 10 things to know this week about the solar system HERE.
Our solar system was built on impacts — some big, some small — some fast, some slow. This week, in honor of a possible newly-discovered large crater here on Earth, here’s a quick run through of some of the more intriguing impacts across our solar system.
1. Mercury: A Basin Bigger Than Texas
Mercury does not have a thick atmosphere to protect it from space debris. The small planet is riddled with craters, but none as spectacular as the Caloris Basin. “Basin” is what geologists call craters larger than about 186 miles (300 kilometers) in diameter. Caloris is about 950 miles (1,525 kilometers) across and is ringed by mile-high mountains.
For scale, the state of Texas is 773 miles (1,244 kilometers) wide from east to west.
2. Venus: Tough on Space Rocks
Venus’ ultra-thick atmosphere finishes off most meteors before they reach the surface. The planet’s volcanic history has erased many of its craters, but like almost any place with solid ground in our solar system, there are still impact scars to be found. Most of what we know of Venus’ craters comes from radar images provided by orbiting spacecraft, such as NASA’s Magellan.
Mead Crater is the largest known impact site on Venus. It is about 170 miles (275 kilometers) in diameter. The relatively-flat, brighter inner floor of the crater indicates it was filled with impact melt and/or lava.
3. Earth: Still Craters After All These Years
Evidence of really big impacts — such as Arizona’s Meteor Crater — are harder to find on Earth. The impact history of our home world has largely been erased by weather and water or buried under lava, rock or ice. Nonetheless, we still find new giant craters occasionally.
This follows the finding, announced in November 2018, of a 19-mile (31-kilometer) wide crater beneath Hiawatha Glacier – the first meteorite impact crater ever discovered under Earth’s ice sheets.
If the second crater, which has a width of over 22 miles (35 kilometers), is ultimately confirmed as the result of a meteorite impact, it will be the 22nd largest impact crater found on Earth.
4. Moon: Our Cratered Companion
Want to imagine what Earth might look like without its protective atmosphere, weather, water and other crater-erasing features? Look up at the Moon. The Moon’s pockmarked face offers what may be humanity’s most familiar view of impact craters.
One of the easiest to spot is Tycho, the tight circle and bright, radiating splat are easy slightly off center on the lower-left side of the full moon. Closer views of the 53-mile (85 kilometer)-wide crater from orbiting spacecraft reveal a beautiful central peak, topped with an intriguing boulder that would fill about half of a typical city block.
5. Mars: Still Taking Hits
Mars has just enough atmosphere to ensure nail-biting spacecraft landings, but not enough to prevent regular hits from falling space rocks. This dark splat on the Martian south pole is less than a year old, having formed between July and September 2018. The two-toned blast pattern tells a geologic story. The larger, lighter-colored blast pattern could be the result of scouring by winds from the impact shockwave on ice. The darker-colored inner blast pattern is because the impactor penetrated the thin ice layer, blasting the dark sand underneath in all directions.
6. Ceres: What Lies Beneath
The bright spots in Ceres’ Occator crater intrigued the world from the moment the approaching Dawn spacecraft first photographed it in 2015. Closer inspection from orbit revealed the spots to be the most visible example of hundreds of bright, salty deposits that decorate the dwarf planet like a smattering of diamonds. The science behind these bright spots is even more compelling: they are mainly sodium carbonate and ammonium chloride that somehow made their way to the surface in a slushy brine from within or below the crust. Thanks to Dawn, scientists have a better sense of how these reflective areas formed and changed over time — processes indicative of an active, evolving world.
7. Comet Tempel 1: We Did It!
Scientists have long known we can learn a lot from impact craters — so, in 2005, they made one themselves and watched it happen.
On July 4, 2005, NASA’s Deep Impact spacecraft trained its instruments on an 816-pound (370-kilogram) copper impactor as it smashed into comet Tempel 1.
One of the more surprising findings: The comet has a loose, “fluffy” structure, held together by gravity and contains a surprising amount of organic compounds that are part of the basic building blocks of life.
8. Mimas: May the 4th Be With You
Few Star Wars fans — us included — can resist Obi Wan Kenobi’s memorable line “That’s no moon…” when images of Saturn’s moon Mimas pop up on a screen. Despite its Death Star-like appearance, Mimas is most definitely a moon. Our Cassini spacecraft checked, a lot — and the superlaser-looking depression is simply an 81-mile (130-kilometer) wide crater named for the moon’s discoverer, William Herschel.
9. Europa: Say What?
The Welsh name of this crater on Jupiter’s ocean moon Europa looks like a tongue-twister, but it is easiest pronounced as “pool.” Pwyll is thought to be one of the youngest features we know of on Europa. The bright splat from the impact extends more than 600 miles (about 1,000 kilometers) around the crater, a fresh blanket over rugged, older terrain. “Fresh,” or young, is a relative term in geology; the crater and its rays are likely millions of years old.
10. Show Us Your Greatest Hits
Got a passion for Stickney, the dominant bowl-shaped crater on one end of Mars’ moon Phobos? Or a fondness for the sponge-like abundance of impacts on Saturn’s battered moon Hyperion (pictured)? There are countless craters to choose from. Share your favorites with us on Twitter, Instagram and Facebook.
Follow, follow the Sun / And which way the wind blows / When this day is done 🎶 Today, April 8, 2024, the last total solar eclipse until 2045 crossed North America.