Agulhamagnetica - AGULHA MAGNÉTICA

Ajuste e manutenção

Beautiful views of the Transit of Mercury across the sun. HAPPENING NOW. 

Cool!! This is the Han Dynasty Compass.

Farewell to the Van Allen Probes

After seven years of studying the radiation around Earth, the Van Allen Probes spacecraft have retired.

Originally slated for a two-year mission, these two spacecraft studied Earth’s radiation belts — giant, donut-shaped clouds of particles surrounding Earth — for nearly seven years. The mission team used the last of their propellant this year to place the spacecraft into a lower orbit that will eventually decay, allowing the Van Allen Probes to re-enter and burn up in Earth’s atmosphere.

Earth’s radiation belts exist because energized charged particles from the Sun and other sources in space become trapped in our planet’s huge magnetic field, creating vast regions around Earth that teem with radiation. This is one of the harshest environments in space — and the Van Allen Probes survived more than three times longer than planned orbiting through this intense region.

The shape, size and intensity of the radiation belts change, meaning that satellites — like those used for telecommunications and GPS — can be bombarded with a sudden influx of radiation. The Van Allen Probes shed new light on what invisible forces drive these changes — like waves of charged particles and electromagnetic fields driven by the Sun, called space weather. 

Here are a few scientific highlights from the Van Allen Probes — from the early days of the mission to earlier this year:

The Van Allen belts were first discovered in 1958, and for decades, scientists thought there were only two concentric belts. But, days after the Van Allen Probes launched, scientists discovered that during times of intense solar activity, a third belt can form.

The belts are composed of charged particles and electromagnetic fields and can be energized by different types of plasma waves. One type, called electrostatic double layers, appear as short blips of enhanced electric field. During one observing period, Probe B saw 7,000 such blips repeatedly pass over the spacecraft in a single minute!

During big space weather storms, which are ultimately caused by activity on the Sun, ions — electrically charged atoms or molecules — can be pushed deep into Earth’s magnetosphere. These particles carry electromagnetic currents that circle around the planet and can dramatically distort Earth’s magnetic field.

Across space, fluctuating electric and magnetic fields can create what are known as plasma waves. These waves intensify during space weather storms and can accelerate particles to incredible speeds. The Van Allen Probes found that one type of plasma wave known as hiss can contribute greatly to the loss of electrons from the belts.

The Van Allen belts are composed of electrons and ions with a range of energies. In 2015, research from the Van Allen Probes found that, unlike the outer belt, there were no electrons with energies greater than a million electron volts in the inner belt.

Plasma waves known as whistler chorus waves are also common in our near-Earth environment. These waves can travel parallel or at an angle to the local magnetic field. The Van Allen Probes demonstrated the two types of waves cannot be present simultaneously, resulting in greater radiation belt particle scattering in certain areas.

Very low frequency chorus waves, another variety of plasma waves, can pump up the energy of electrons to millions of electronvolts. During storm conditions, the Van Allen Probes found these waves can hugely increase the energy of particles in the belts in just a few hours.  

Scientists often use computer simulation models to understand the physics behind certain phenomena. A model simulating particles in the Van Allen belts helped scientists understand how particles can be lost, replenished and trapped by Earth’s magnetic field.

The Van Allen Probes observed several cases of extremely energetic ions speeding toward Earth. Research found that these ions’ acceleration was connected to their electric charge and not to their mass.

The Sun emits faster and slower gusts of charged particles called the solar wind. Since the Sun rotates, these gusts — the fast wind — reach Earth periodically. Changes in these gusts cause the extent of the region of cold ionized gas around Earth — the plasmasphere — to shrink. Data from the Van Allen Probes showed that such changes in the plasmasphere fluctuated at the same rate as the solar rotation — every 27 days.

Though the mission has ended, scientists will use data from the Van Allen Probes for years to come. See the latest Van Allen Probes science at nasa.gov/vanallen.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

MAGNETIC COMPASS ADJSTMENT

Celestial Mechanics Around the Solar System During December 2019

The dance of planets, moons and spacecraft around the solar system creates a host of rare alignments in late December 2019. Here’s what’s coming up.

Dec. 21: Winter solstice in the Northern Hemisphere

Dec. 21 is the 2019 winter solstice for the Northern Hemisphere. A solstice marks the point at which Earth’s tilt is at the greatest angle to the plane of its orbit, also the point where half of the planet is receiving the longest stretch of daylight and the other the least. There are two solstices a year, in June and December: the summer and winter solstices, respectively, in the Northern Hemisphere.

The winter solstice is the longest night of the year, when that hemisphere of Earth is tilted farthest from the Sun and receives the fewest hours of sunlight in a given year. Starting Dec. 21, the days will get progressively longer until the June solstice for those in the Northern Hemisphere, and vice versa for the Southern Hemisphere.  

Dec. 26: Annular solar eclipse visible in Asia

On Dec. 26, an annular solar eclipse will be visible in parts of Asia. During an annular eclipse, the Moon’s apparent size is too small to completely cover the face of the Sun, creating a “ring of fire” around the Moon’s edge during the eclipse.

Credit: Dale Cruikshank

Solar eclipses happen when the Moon lines up just right with the Sun and Earth. Though the Moon orbits Earth about once a month, the tilt in its orbit means that it’s relatively rare for the Moon to pass right in line between the Sun and Earth — and those are the conditions that create an eclipse. Depending on the alignment, the Moon can create a partial, total or annular solar eclipse.

On Dec. 26, the Moon will be near perigee, the point in its orbit when it’s farthest from Earth. That means its apparent size from Earth is just a bit smaller — and that difference means that it won’t completely cover the Sun during the Dec. 26 eclipse. Instead, a ring of the bright solar surface will be visible around the Moon during the point of greatest eclipse. This is called an annular eclipse.

It is never safe to look directly at an annular solar eclipse, because part of the Sun is always visible. If you’re in the path of the annular eclipse, be sure to use solar viewing glasses (not sunglasses) or another safe viewing method to watch the eclipse.

Dec. 26: Parker Solar Probe flies by Venus

After the eclipse, more than 100 million miles away from Earth, Parker Solar Probe will pull off a celestial maneuver of its own. On Dec. 26, the spacecraft will perform the second Venus gravity assist of the mission to tighten its orbit around the Sun.

During the seven gravity assists throughout the mission, Parker Solar Probe takes advantage of Venus’s gravity to slow down just the right amount at just the right time. Losing some of its energy allows the spacecraft to be drawn closer by the Sun’s gravity: It will fly by the Sun’s surface at just 11.6 million miles during its next solar flyby on Jan. 29, 2020. During this flyby, Parker Solar Probe will break its own record for closest-ever spacecraft to the Sun and will gather new data to build on the science already being shared from the mission.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

An Example of the Coordination of Magnetic Field Lines from a Bar Magnet.