Taking a break from magnetic fields, I wanted to talk about a very rare event that started taking place on Tuesday, April 15, 2014. The first of four lunar eclipses took place that night. This is a rare event as this tetrad of eclipses will occur six months apart from each other; the first one on April 15, 2014, the next on October 8, 2014, the third on April 4, 2015, and the last one on September 28, 2015. All of the eclipses will be visible from North America.
All these eclipses will be total eclipses. That is when the entire moon is completely engulfed in the Earth’s shadow. This is the most spectacular eclipse as the whole moon turns a bright red, reminiscent of a sunset. This is also called the blood moon. The next kind of eclipse is a partial eclipse. This is when the Moon crosses into the Earth’s umbra, but is not completely consumed by it. The last and least noticeable is a prenumbral eclipse. The Moon enters the Earth’s prenumbra, but doesn’t cross into the umbra. This is a very subtle eclipse. The most one will notice is a drop in brightness. Luckily for us, all the eclipses during this tetrad of eclipses will make the moon glow red. But why red?
That is because, when the sun obstructs the Earth, most of the light is being blocked, but the light hitting the atmosphere is bending towards the Moon. While that occurs, the atmosphere is also scattering the shorter wavelengths of the spectrum into the atmosphere, leaving behind the red wavelength, which is the longest and the least likely to scatter. This is why the moon looks red during a lunar eclipse, and this is why sunsets are red.
Unlike a solar eclipse, this eclipse is safe to view without any eye protection, and it is visible across a whole continent, whereas solar eclipses are visible in a thin, 250 km region during its path. That will be another post…
We ended the previous post with mentioning that Earth is not the only planet with a magnetic field. All the planets, with the exception of Venus and Mars, produce magnetic fields.
Mercury, the closest planet to the sun, and one of the smallest planets in the solar system, has a magnetic field. It is thought that Mercury’s large core is doing the geodynamo process to produce the magnetic field, however, it has not been confirmed yet, and there are other ideas floating around. Mercury’s magnetic fields are only 1% the strength of the Earth’s, however, it is strong enough to repel solar flares. Currently, the MESSENGER probe orbiting mercury is working to learn more about Mercury’s magnetic field using a variety of instruments. Of the inner planets, Venus and Mars are the only planets that do not produce magnetic fields.
Mercury’s magnetic fields with MESSENGER’s orbit.
Venus is similar to Earth in some ways; however, it doesn’t produce a magnetic field. While our knowledge of Venus is incomplete, there are a few conjectures as to why that is. The first one is that the core has solidified and there is no convective outer core to convect any conductive fluids, and thus no magnetic field could be produced. Another conjecture is that, since the planet went through a major resurfacing event, the crust has effectively sealed the core in, and the core became heated to a uniform temperature which doesn’t promote convection. Another theory is that in addition to the lack of convection, Venus is also rotating so slowly (243 days/Venus Day)- it isn’t moving fast enough to produce any magnetic fields. Since Venus doesn’t have a magnetic field, and any solar flare will interact with the ionosphere directly, the ionosphere will slow the flare down and redirect the flow of charged particles. Since the atmosphere is dense, and Venus’ winds are intense, the ionosphere will prevent the charged particles from reaching its surface. Despite all we have learned about Venus, these theories are still conjecture, and it will be difficult to find answers due to Venus’ harsh conditions. We have more complete information about Mars, however.
Venus’, Earth’s, and Mars’ interactions with Solar Flares
Mars is different, in many ways, from Venus and Earth, but like Venus, it doesn’t have a magnetic field. It has an ionosphere present, but the atmosphere is quite weak; therefore, the planet isn’t protected by any solar flares. Its mantle is presumed to be inactive, and its core is already small, having never accumulated enough iron, therefore convection in the core stopped and the magnetic field ceased to exist. However, there are traces of a magnetic field in Mars’ past found frozen into the rocks on Mars that are over 4 billion years old. There is a theory that Mars’ magnetic field was destroyed when a large asteroid impact interrupted the convective process of Mars, which stopped the production of the magnetic field. It is under debate, though, as some might consider that Mars’ geodynamo process ended when the core cooled enough to stop the convection process on its own. It makes sense since Mars is smaller, and lighter. It would take a shorter amount of time to cool down than Earth would. Since the magnetic field ceases to exist, the solar flares were able to strip away Mars’ outer atmosphere and kill any life on Mars. Unlike some inner planets, all the outer planets have magnetic fields.
The magnetic fields of the outer planets
All the gas giants have magnetic fields, with Jupiter having the strongest magnetic fields of them all. The magnetic field works much like Earth’s, with the geodynamo process originating from its metallic hydrogen outer core and its fast rotation period. However, it is 100 times larger and extends 20,000 greater than Earth’s magnetic field. Some say that the tail of the magnetic field extends as far as the orbit of Saturn. It’s so big that it begins to repel a solar flare 3 million kilometres away from Jupiter. However, because of its larger distance from the sun, the intensity of the solar wind is 4% that of the Earth’s. This means, less effort is needed to repel it. Much like Earth, Jupiter has a set of radiation belts that trap any charged particles heading towards it. It is 1000 times stronger than Earth’s radiation belts. In addition, the magnetic fields also receive particles from its innermost moon, Io. The sulphur, and oxygen Io emits from its volcanoes create a ring of gas that interacts with the magnetic field and collects it, which creates a gas torus. Spacecraft visiting Jupiter will need to overcome the intense radiation present in its magnetic fields.
Saturn’s magnetic field is the second largest in the whole solar system. It works a lot like Jupiter’s, but it is only half of its strength. This is because; the metallic hydrogen outer core that conducts the geodynamo process is smaller than Jupiter’s. When the magnetic fields interact with the solar flare, they interact from 20 Saturn radii away, and its tail extend much farther than that. The magnetosphere has many taurii, originating from Enceladus, and Titan. Enceladus ejects a large amount of water vapour into space. The water vapour ionizes and rotates with the magnetic field. Eventually, it escapes through the magnetotail. Titan has a large amount of Nitrogen ion plasma and is released into Saturn’s inner magnetic fields. There might be other sources inside Saturn’s rings, inner moons, or the upper atmosphere. When the solar flare hits Saturn, much like Earth, aurorae are formed on Saturn spanning the whole spectrum of light. Spacecraft visiting here have to overcome its intense radiation as well here.
Uranus’ magnetic field is 0.1 times that of Saturn. Before Voyager 2 arrived there, no experiments took place there of its magnetic fields. They expected a magnetic field similar to the ones they knew, such as Earth’s. However, measurements revealed two major differences: Uranus’ magnetic fields aren’t in line with the center of the planet, and that it is tilted 59 degrees from the rotational axis. This means the magnetic field produced is asymmetric across the whole planet. One theory to suggest why it occurs is that, unlike the other planets where the magnetic fields are generated in their cores, Uranus’ magnetic fields is formed closer to the surface, such as in a water-ammonia ocean, where convective movement could take place. Since the magnetic axis is highly inclined with respect to the rotational axis, the magnetotail would be wound into a corkscrew shape. In addition, the radiation belts are mostly made of Hydrogen ions, which suggest that there are no taurii present from any of its moons. However, despite its differences, its magnetic fields are similar to Saturn’s magnetic fields.
Uranus and Neptune’s magnetic fields
Neptune is very similar to Uranus and is the only other planet to have similar magnetic fields to Uranus. Its magnetic field is titled relative to the rotational axis by 47 degrees and offset by 0.55 Neptune Radii. Comparing it to Uranus, it is likely that there is convective flow in a shell of conductive liquids that drives the geodynamo process. When the solar wind interact with Neptune’s magnetic fields, it starts to repel it at 34.9 Neptune Radii, and the magnetotail extends at least 72 Neptune radii, and probably farther. In addition, it is found that there are aurorae on Neptune, but much weaker than those of Earth. These results were verified by Voyager 2’s visit to the two ice giants.
However, one more celestial object has a magnetic field, and during an 11 year period, it produces noticeable black spots on it. Stay Tuned for the final segment.
Here are the astronomical events occurring in the month of April: (All times are given in UTC format)
April 8: Mars reaches opposition with a magnitude of -1.5.
April 12: Venus and Neptune come to a close conjunction with both planets being 0.7 degrees apart at 2:00 UTC.
April 15: A total lunar eclipse will occur at 7:47. It will be visible in the Americas.
April 17: The Moon will occult Saturn at ~7:19. It will be visible in South America.
April 29: An Annular Solar Eclipse will occur at 6:05. It will be visible from Australia, and from the South Indian Ocean. It will also be a unique, non-central eclipse.
RASC Toronto Centre Events (These times will be written as EST or EDT)
April 2: Dr. Amy Shaw, from York University, will speak about the OSIRIS-REx mission and its target asteroid Bennu. It will take place at the Ontario Science Centre. Parking is free after 6 pm, and it is free for the public.
April 5: There will be a Solar Observation Event at the Ontario Science Centre. It is free for the public. Go to http://www.rascto.ca for the GO/NO GO call.
Monday April 7 – 10: There will be a City Star Party, where people can look at the stars and planets without going outside of Toronto. A telescope is not necessary to attend. This event is free for the public. It will be located at either Bayview Village Park or at High Park. Go to http://www.rascto.ca for the GO/NO GO call.
On April 11-13, developers, engineers, and many others will take on 25 NASA-designed challenges and solve them using a variety of solutions with the help of a mentor. Anyone can attend, but registration is required. To register, go to: http://spaceappstoronto.com/ It will take place at the Ontario Science Centre.
April 12: Yuri’s night will take place. It is a global celebration of humanity’s journey into space. This night takes place every April 12th. This celebrates the the first human spaceflight, and the first space shuttle launch. The party features space-related activities, such as a mix of “techno and technology at a NASA Center”, to a gathering at a bar. To find a party, or to plan your own event, go to: http://yurisnight.net/#/starter
On April 22: Joseph Ivor Silk will speak about his work in cosmology. It is organized by the Canadian Institute for Theoretical Astrophysics. It will take place from 7:30 – 9:30 and will be located at the Koffler Building at 569 Spadina Avenue, Room 108.
April 23: The RASC monthly Recrational Astronomy night will take place at the Ontario Science Centre. There will be four lectures by Chris Vaughan, Guy Nason, and Ed Treijs. This event is free and open to the public. Parking after 6 pm is free. It will take place at the Ontario Science Centre.
April 26: The RASC Member’s night will take place. This month’s theme is “Catch a Falling Star – A New Meteor Shower”. Members can only attend, but we can sign you up there. It is free to attend. It will take place at the David Dunlap Observatory starting at 5:30 pm.
April 28 – May 1: This is the window for RASC’s Dark Sky Party that will take place at the Long Sault Conservation Area. It will start at 8 pm. This event is free and open to the public. Telescope are not necessary to attend. Go to http://www.rascto.ca for the GO/NO GO calls.