Jupiter was appropriately named after the king of the gods. It’s massive, has a powerful magnetic field, and more moons that any planet in the Solar System. Though it has been known to astronomers since ancient times, the invention of the telescope and the advent of modern astronomy has taught us so much about this gas giant.
In short, there are countless interesting facts about this gas giant that many people just don’t know about. And we here at Universe Today have taken the liberty of compiling a list of ten particularly interesting ones that we think will fascinate and surprise you. Think you know everything about Jupiter? Think again!
1. Jupiter Is Massive:
It’s no secret that Jupiter is the largest planet in the Solar System. But this description really doesn’t do it justice. For one, the mass of Jupiter is 318 times as massive as the Earth. In fact, Jupiter is 2.5 times more massive than all of the other planets in the Solar System combined. But here’s the really interesting thing…
Jupiter is the largest planet in our Solar System, with 2.5 times the mass of all the other planets combined. Credit: NASA
If Jupiter got any more massive, it would actually get smaller. Additional mass would actually make the planet more dense, which would cause it to start pulling it in on itself. Astronomers estimate that Jupiter could end up with 4 times its current mass, and still remain about the same size.
2. Jupiter Cannot Become A Star:
Astronomers call Jupiter a failed star, but that’s not really an appropriate description. While it is true that, like a star, Jupiter is rich in hydrogen and helium, Jupiter does not have nearly enough mass to trigger a fusion reaction in its core. This is how stars generate energy, by fusing hydrogen atoms together under extreme heat and pressure to create helium, releasing light and heat in the process.
This is made possible by their enormous gravity. For Jupiter to ignite a nuclear fusion process and become a star, it would need more than 70 times its current mass. If you could crash dozens of Jupiters together, you might have a chance to make a new star. But in the meantime, Jupiter shall remain a large gas giant with no hopes of becoming a star. Sorry, Jupiter!
3. Jupiter Is The Fastest Spinning Planet In The Solar System:
For all its size and mass, Jupiter sure moves quickly. In fact, with an rotational velocity of 12.6 km/s (~7.45 m/s) or 45,300 km/h (28,148 mph), the planet only takes about 10 hours to complete a full rotation on its axis. And because it’s spinning so rapidly, the planet has flattened out at the poles a little and is bulging at its equator.
In fact, points on Jupiter’s equator are more than 4,600 km further from the center than the poles. Or to put it another way, the planet’s polar radius measures to 66,854 ± 10 km (or 10.517 that of Earth’s), while its diameter at the equator is 71,492 ± 4 km (or 11.209 that of Earth’s). This rapid rotation also helps generate Jupiter’s powerful magnetic fields, and contribute to the dangerous radiation surrounding it.
4. The Clouds On Jupiter Are Only 50 km Thick:
That’s right, all those beautiful whirling clouds and storms you see on Jupiter are only about 50 km thick. They’re made of ammonia crystals broken up into two different cloud decks. The darker material is thought to be compounds brought up from deeper inside Jupiter, and then change color when they reacted with sunlight. But below those clouds, it’s just hydrogen and helium, all the way down.
Image of Jupiter’s Giant Red Spot, taken on March 5th, 1979. Credit: NASA GSFC/NASA/JPL
5. The Great Red Spot Has Been Around For A Long Time:
The Great Red Spot on Jupiter is one of its most familiar features. This persistent anticyclonic storm, which is located south of its equator, measures between 24,000 km in diameter and 12–14,000 km in height. As such, it is large enough to contain two or three planets the size of Earth’s diameter. And the spot has been around for at least 350 years, since it was spotted as far back as the 17th century.
The Great Red Spot was first identified in 1665 by Italian astronomer Giovanni Cassini. By the 20th century, astronomers began to theorize that it was a storm, one which was created by Jupiter’s turbulent and fast-moving atmosphere. These theories were confirmed by the Voyager 1 mission, which observed the Giant Red Spot up close in March of 1979 during its flyby of the planet.
However, it appears to have been shrinking since that time. Based on Cassini’s observations, the size was estimated to be 40,000 km in the 17th century, which was almost twice as large as it is now. Astronomers do not know if or when it will ever disappear entirely, but they are relatively sure that another one will emerge somewhere else on the planet.
6. Jupiter Has Rings:
When people think of ring systems, Saturn naturally comes to mind. But in truth, both Uranus and Jupiter have ring systems of their own. Jupiter’s were the third set to be discovered (after the other two), due to the fact that they are particularly faint. Jupiter’s rings consist of three main segments – an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring.
A schema of Jupiter’s ring system showing the four main components. For simplicity, Metis and Adrastea are depicted as sharing their orbit. Credit: NASA/JPL/Cornell University
These rings are widely believed to have come from material ejected by its moons when they’re struck by meteorite impacts. In particular, the main ring is thought to be composed of material from the moons of Adrastea and Metis, while the moons of Thebe and Amalthea are believed to produce the two distinct components of the dusty gossamer ring.
This material fell into orbit around Jupiter (instead of falling back to their respective moons) because if Jupiter’s strong gravitational influence. The ring is also depleted and replenished regularly as some material veers towards Jupiter while new material is added by additional impacts.
The first motion sensor was invented in the year 1950 by Samuel Bango named as a burglar alarm. He applied the basics of a radar to ultrasonic waves – a frequency to notice fire or robber and that which human beings cannot listen to. The Samuel motion sensor is based on the principle of “Doppler Effect”. Currently, most of the motion sensors work on the principle of Samuel Bango’s detector. Microwave and infrared sensors used to detect motion by the changes in the frequencies they produce. To understand the working of motion sensor, you first need to know the working of a camera. The camera uses an image sensor and the lens direct light to – when the light strikes the image sensor each pixel records how much light it’s getting. That outline of light and dark areas in the pixels becomes the entire video image.
Motion sensors are applicable for security systems which are used in offices, banks, shopping malls, and also as intruder alarm at home. The existing motion detectors can stop serious accidents by detecting the persons who are closest to the sensor. We can monitor motion detectors in public places. The main part of the motion detector circuit is the dual IR reflective sensor.
What is a Motion Sensor?
A motion sensor is a device that notices moving objects, mainly people. A motion sensor is frequently incorporated as a component of a system that routinely performs a task or else alert a user of motion in a region. These sensors form a very important component of security, home control, energy efficiency, automated lighting control, and other helpful systems. The main principle of motion sensor is to sense a burglar and send an alert to your control panel, which gives an alert to your monitoring center. Motion sensors react to different situations like movement in your living room, doors, windows being unbolt or closed and also these sensors can.
Motion Sensor
Activate a doorbell when someone comes close to the front door.
These sensors give you an alert whenever kids enter into some restricted areas in the home such as medicine cabinet, the basement or workout room.
Conserve energy by using this sensor lighting in empty spaces.
Types of Motion Sensors
There various kinds of motion sensors are available in the market, which has their ups and downs. They are namely PIR, Ultrasonic, Microwave, Tomographic and combined types.
Types of Motion Sensors
Passive Infrared (PIR) Sensor
All warm blooded animals produce IR radiation. Passive infrared sensorsinclude a thin Pyroelectric film material, that responds to IR radiation by emitting electricity. This sensor will activate burglar alarm whenever this influx of electricity takes place. These sensors are economical, don’t use more energy and last forever. These sensors are commonly used in indoor alarms.
Passive Infrared Sensor
Ultrasonic Sensor
Ultrasonic sensor can be active (or) passive, where passive ones pay attention for particular sounds like metal on metal, glass breaking. These sensors are very sensitive, but they are frequently expensive and prone to fake alarms. Active ones generate ultrasonic wave (sound wave) pulses and then determine the reflection of these waves off a moving object. Animals like cats, dogs, fishes can hear this sound waves, so an active ultrasonic alarm might unsettle them.
Ultrasonic Sensor
Microwave Sensor
These sensors generate microwave pulses and then calculate their reflection off of objects, in order to know whether objects are moving or not. Microwave sensors are very sensitive, but sometimes these can be seen in nonmetallic objects which can be detected moving objects on the outside of the target range. It consumes a lot of power, so these sensors are frequently designed to cycle ON & OFF. This makes it feasible to acquire past them, if you know the cycles. Electronic guard dogs utilize microwave sensors.
Microwave Sensor
Tomographic Sensor
These sensors generate radio waves and detect when those waves are troubled. They can notice through walls and objects, and are frequently placed in a way that makes a radio wave net that cover ups large areas. These sensors are expensive, so they are normally used in warehouses, storage units and also in other situations that need a commercial level of security.
Tomographic Sensor
Combined types of Motion Sensors
Some types of motion detectors mix some sensors in order to decrease fake alarms. But, dual sensors are only activated when both kinds sense motion. For instance, a dual microwave or PIR sensor will start out on the passive infrared sensor setting, because that consumes less energy. When the passive infrared sensor is tripped, the microwave division will turn ON; then, if the remaining sensor also tripped, the alarm will generate sound. This combined type is great for neglecting fake alarms, but tuns the possibility of missing real ones.
Combined types of Motion Sensors
Thus, this is all about the different types of motion sensors which include Passive Infrared Sensor, Ultrasonic Sensor, Microwave Sensor, Tomographic Sensor and Combined types. We hope that you have got a better understanding of this concept. Furthermore, any queries regarding this concept or to implement sensor based projects, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, What are the applications of motion sensors?
The Moon (or Luna) is the Earth’s only natural satellite and was formed 4.6 billion years ago around some 30–50 million years after the formation of the solar system. The Moon is in synchronous rotation with Earth meaning the same side is always facing the Earth. The first unmanned mission to the Moon was in 1959 by the Soviet Lunar Program with the first manned landing being Apollo 11 in 1969.
Moon Profile
Diameter:
3,475 km
Mass:
7.35 × 10^22 kg (0.01 Earths)
Orbits:
The Earth
Orbit Distance:
384,400 km
Orbit Period:
27.3 days
Surface Temperature:
-233 to 123 °C
Size of the Moon Compared to the Earth
Facts about the Moon
The dark side of the moon is a myth. In reality both sides of the Moon see the same amount of sunlight however only one face of the Moon is ever seen from Earth. This is because the Moon rotates around on its own axis in exactly the same time it takes to orbit the Earth, meaning the same side is always facing the Earth. The side facing away from Earth has only been seen by the human eye from spacecraft.
The rise and fall of the tides on Earth is caused by the Moon. There are two bulges in the Earth due to the gravitational pull that the Moon exerts; one on the side facing the Moon, and the other on the opposite side that faces away from the Moon, The bulges move around the oceans as the Earth rotates, causing high and low tides around the globe.
The Moon is drifting away from the Earth. The Moon is moving approximately 3.8 cm away from our planet every year. It is estimated that it will continue to do so for around 50 billion years. By the time that happens, the Moon will be taking around 47 days to orbit the Earth instead of the current 27.3 days.
A person would weigh much less on the Moon. The Moon has much weaker gravity than Earth, due to its smaller mass, so you would weigh about one sixth (16.5%) of your weight on Earth. This is why the lunar astronauts could leap and bound so high in the air.
The Moon has only been walked on by 12 people; all American males. The first man to set foot on the Moon in 1969 was Neil Armstrong on the Apollo 11 mission, while the last man to walk on the Moon in 1972 was Gene Cernan on the Apollo 17 mission. Since then the Moon has only be visited by unmanned vehicles.
The Moon has no atmosphere. This means that the surface of the Moon is unprotected from cosmic rays, meteorites and solar winds, and has huge temperature variations. The lack of atmosphere means no sound can be heard on the Moon, and the sky always appears black.
The Moon has quakes. These are caused by the gravitational pull of the Earth. Lunar astronauts used seismographs on their visits to the Moon, and found that small moonquakes occurred several kilometres beneath the surface, causing ruptures and cracks. Scientists think the Moon has a molten core, just like Earth.
The first spacecraft to reach the Moon was Luna 1 in 1959. This was a Soviet craft, which was launched from the USSR. It passed within 5995 km of the surface of the Moon before going into orbit around the Sun.
The Moon is the fifth largest natural satellite in the Solar System. At 3,475 km in diameter, the Moon is much smaller than the major moons of Jupiterand Saturn. Earth is about 80 times the volume than the Moon, but both are about the same age. A prevailing theory is that the Moon was once part of the Earth, and was formed from a chunk that broke away due to a huge object colliding with Earth when it was relatively young.
The Moon will be visited by man in the near future. NASA plans to return astronauts to the moon to set up a permanent space station. Mankind may once again walk on the moon in 2019, if all goes according to plan.
During the 1950’s the USA considered detonating a nuclear bomb on the Moon. The secret project was during the height cold war was known as “A Study of Lunar Research Flights” or “Project A119” and meant as a show of strength at a time they were lagging behind in the space race.
Open this linkA galaxy is a collection of stars and interstellar material held together by gravity. The galaxy our Sun lives in is called the Milky Way or the Galaxy (note the capital 'G'). The name `Milky Way' comes from the band of light that is seen overhead on very dark nights. The ancients called it the Celestial River. Galileo showed that the band is actually an edge-on concentration of stars seen looking through the disk of our Galaxy from the inside.
That same band looks very different when imaged at different wavelengths. For example, below is an image of the sky in the near-IR, sensitive to giant stars and dust.
The same region imaged in gamma-rays shows where all the neutron stars and x-ray binaries are found
The x-ray picture of our Galaxy shows where the hot supernova remnants are found (notice the partial arcs)
A deep optical picture shows where the dark nebula are found near the axis of the disk.
An image in the far-IR shows the concentration of old stars in the center of the Galaxy (called the bulge)
An an image taken at the 21-cm wavelength of neutral hydrogen shows how neutral gas avoids the center of the Galaxy and is found mostly out in the arms.
Size of the Milky Way:
Mapping of the Galaxy using star counts was shown to be ineffective due to the extinction of starlight by the interstellar medium.
A Harvard astronomer, H. Shapley, mapped the in the Galaxy's halo to see where the Sun was with respect to the Galactic center. The distance to a globular cluster is found by main sequence fitting, where a HR diagram of a cluster is made and `slide' up and down to match the globular cluster main sequence luminosity to the absolute luminosity of the main sequence of nearby stars. The difference between the apparent and absolute luminosity determines the distance to the globular cluster.
When Shapley did this for 150 globular clusters he had the following plot.
The globular clusters orbit the center of the Galaxy, so where their centroid is on the plot is the Galactic center. The Sun is shown to be off center from the Galactic center by about 8 kiloparsecs or 25,000 light-years.
Later mapping of variable stars, neutral hydrogen radio maps and star clusters gives us our current view of the shape of our Galaxy shown below.
The key components of our Galaxy is a bulge of old stars in the center, a disk of stars and gas and a halo of globular clusters. The disk of our Galaxy is whirlpool shaped with numerous spiral arms spanning out from the center of the Galaxy. In the very center of the bulge of our Galaxy lies a nucleus, possibly a million solar mass black hole.
Notice that the total size of the Milky Way is about 50,000 light-years in radius, with the Sun a little over halfway from the center. Since the Galaxy is similar in shape to the solar system, we use a Galactic coordinate system where the plane of the disk forms the galactic equator. Angular distance from the center of the Galaxy eastward is galactic longitude, angular distance above or below the plane is galactic latitude
The orbital period of an object is just how far an object traveled divided by its velocity. In a circular orbit, how far is the circumference of the orbit such that the period, P, is
P = 2 π r/v
where r is the distance from the center and v is the velocity.
Since the Sun orbits the center of the Galaxy, we can use this knowledge to determine the mass of the Galaxy. Remember that Kepler's 3rd law states that the sum of the masses of two objects in orbit around each other is given by
MGalaxy + MSun = r3/P2
Notice that the mass of the Sun is really, really small compared to the mass of the Galaxy. SoMGalaxy + MSun becomes just MGalaxy.
Rotation Curve of Galaxy:
The orbital period of the Sun around the Galaxy gives us a mean mass for the amount of material inside the Sun's orbit. But a detailed plot of the orbital speed of the Galaxy as a function of radius reveals the distribution of mass within the Galaxy. The simplest type of rotation is wheel rotation shown below.
Rotation following Kepler's 3rd law is shown above as planet-like or differential rotation. Notice that the orbital speeds falls off as you go to greater radii within the Galaxy. This is called a Keplerian rotation curve.
To determine the rotation curve of the Galaxy, stars are not used due to interstellar extinction. Instead, 21-cm maps of neutral hydrogen are used. When this is done, one finds that the rotation curve of the Galaxy stays flat out to large distances, instead of falling off as in the figure above. This means that the mass of the Galaxy increases with increasing distance from the center.
The surprising thing is there is very little visible matter beyond the Sun's orbital distance from the center of the Galaxy. So the rotation curve of the Galaxy indicates a great deal of mass, but there is no light out there. We call this the dark matter problem, and states that the halo of our Galaxy is filled with a mysterious dark matter of unknown composition and type.
At a first glance the two satellite images of Image 1.1 are indistinguishable, showing lights shining brightly in highly populated areas and dark spaces that mark vast uninhabited forests and oceans. Yet, upon closer inspection we notice differences: Toronto, Detroit, Cleveland, Columbus and Long Island, bright and shining in (a), have have gone dark in (b). This is not a doctored shot from the next Armageddon movie but represents a real image of the US Northeast on August 14, 2003, before and after the blackout that left without power an estimated 45 million people in eight US states and another 10 million in Ontario.
Image 1.1 2003 North American Blackout
Satellite image on Northeast United States on August 13th, 2003,at 9:29pm (EDT), 20 hours before the 2003 blackout.
The same as above, but 5 hours after the blackout.
The 2003 blackout is a typical example of a cascading failure. When a network acts as a transportation system, a local failure shifts loads to other nodes. If the extra load is negligible, the system can seamlessly absorb it, and the failure goes unnoticed. If, however, the extra load is too much for the neighboring nodes, they will too tip and redistribute the load to their neighbors. In no time, we are faced with a cascading event, whose magnitude depends on the position and the capacity of the nodes that failed initially.
Cascading failures have been observed in many complex systems. They take place on the Internet, when traffic is rerouted to bypass malfunctioning routers. This routine operation can occasionally create denial of service attacks, which make fully functional routers unavailable by overwhelming them with traffic. We witness cascading events in financial systems, like in 1997, when the International Monetary Fund pressured the central banks of several Pacific nations to limit their credit, which defaulted multiple corporations, eventually resulting in stock market crashes worldwide. The 2009-2011 financial meltdown is often seen as a classic example of a cascading failure, the US credit crisis paralyzing the economy of the globe, leaving behind scores of failed banks, corporations, and even bankrupt states. Cascading failures can be also induced artificially. An example is the worldwide effort to dry up the money supply of terrorist organizations, aimed at crippling their ability to function. Similarly, cancer researchers aim to induce cascading failures in our cells to kill cancer cells.
The Northeast blackout illustrates several important themes of this book: First, to avoid damaging cascades, we must understand the structure of the network on which the cascade propagates. Second, we must be able to model the dynamical processes taking place on these networks, like the flow of electricity. Finally, we need to uncover how the interplay between the network structure and dynamics affects the robustness of the whole system. Although cascading failures may appear random and unpredictable, they follow reproducible laws that can be quantified and even predicted using the tools of network science.
The blackout also illustrates a bigger theme: vulnerability due to interconnectivity. Indeed, in the early years of electric power each city had its own generators and electric network. Electricity cannot be stored, however: Once produced, electricity must be immediately consumed. It made economic sense, therefore, to link neighboring cities up, allowing them to share the extra production and borrow electricity if needed. We owe the low price of electricity today to the power grid, the network that emerged through these pairwise connections, linking all producers and consumers into a single network. It allows cheaply produced power to be instantly transported anywhere. Electricity hence offers a wonderful example of the huge positive impact networks have on our life.
Being part of a network has its catch, however: local failures, like the breaking of a fuse somewhere in Ohio, may not stay local any longer. Their impact can travel along the network’s links and affect other nodes, consumers and individuals apparently removed from the original problem. In general interconnectivity induces a remarkable non-locality: It allows information, memes, business practices, power, energy, and viruses to spread on their respective social or technological networks, reaching us, no matter our distance from the source. Hence networks carry both benefits and vulnerabilities. Uncovering the factors that can enhance the spread of traits deemed positive, and limit others that make networks weak or vulnerable, is one of the goals of this book.
The Indian National Satellite (INSAT) system is one of the largest domestic communication satellite systems in Asia-Pacific region with nine operational communication satellites placed in Geo-stationary orbit. Established in 1983 with commissioning of INSAT-1B, it initiated a major revolution in India’s communications sector and sustained the same later. GSAT-17 joins the constellation of INSAT System consisting 15 operational satellites, namely - INSAT-3A, 3C, 4A, 4B, 4CR and GSAT-6, 7, 8, 9, 10, 12, 14, 15, 16 and 18.
The INSAT system with more than 200 transponders in the C, Extended C and Ku-bands provides services to telecommunications, television broadcasting, satellite newsgathering, societal applications, weather forecasting, disaster warning and Search and Rescue operations.
Earth, third planet from the Sun and the fifth largest planet in the solar system in terms of size and mass. Its single most outstanding feature is that its near-surface environments are the only places in the universe known to harbour life. It is designated by the symbol ♁. Earth’s name in English, the international language of astronomy, derives from Old Englishand Germanic words for ground and earth, and it is the only name for a planetof the solar system that does not come from Greco-Roman mythology.
EarthA composite image of Earth captured by instruments aboard NASA's Suomi National Polar-orbiting Partnership satellite, 2012.early 17th century soon showed various other planets to be globes as well. It was only after the dawn of thespaceage, however, when photographs from rockets and orbitingspacecraftfirst captured the dramatic curvature of Earth’shorizon, that theconceptionof Earth as a roughly spherical planet rather than as a flat entity was verified by directhumanobservation. Humans first witnessed Earth as a complete orb floating in the inky blackness of space in December 1968 whenApollo8 carried astronauts around theMoon. Robotic space probes on their way to destinations beyond Earth, such as theGalileoand theNear Earth Asteroid Rendezvous(NEAR) spacecraft in the 1990s, also looked back with their cameras to provide other unique portraits of the planet.
Guided missiles work by tracking the location of the moving target in space by certain methods (eg. using a radar or following its heat signature), chasing it down and then finally hitting it with accuracy. Guided systems in missiles can be of various types, which serve different operational purposes.
Missiles have been around for quite some time now. In fact, humans have been using missiles – in various forms – for centuries. However, just as it happens with everything else, the technology of missiles has also improved dramatically over the past century. On today’s high-tech battlefields, we have guided missiles packed with explosive warheads that have become the devastating weapon of choice to destroy targets swiftly and with amazing accuracy.
In this article, we’re going to explain how guided missiles work and how they follow moving targets in non-straight trajectories to hit them with incredible precision.
A missile (used for the purposes of warfare) is basically a flying bomb that strikes its target with incredible precision. Earlier, satellites were simply larger and more powerful versions of regular bullets; they followed a relatively straight trajectory to hit their target, i.e., they didn’t have a system that could ‘guide’ them. However, thanks to technological development, there are now dedicated guidance systems in missiles that make them ‘pursue’ their chosen target until a hit is achieved.
The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupitercontains most of the rest).
It is often said that the Sun is an "ordinary" star. That's true in the sense that there are many others similar to it. But there are many more smaller stars than larger ones; the Sun is in the top 10% by mass. The median size of stars in our galaxy is probably less than half the mass of the Sun.
The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol.
The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.
The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets. The differential rotation extends considerably down into the interior of the Sun but the core of the Sun rotates as a solid body.
Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme. The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At the center of the core the Sun's density is more than 150 times that of water.
The Sun's power (about 386 billion billion mega Watts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation.
The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. Sunspots are caused by complicated and not very well understood interactions with the Sun's magnetic field.
A small region known as the chromosphere lies above the photosphere.
