How much do you know about Space Weather? Try your hand at some of the questions below. The Glossary and Science Briefs have more information to help you out. Space Weather | The Sun | The Sun in Earth's Sky Space Weather Q: High energy particles from the Sun are a serious hazard to astronauts. What protects passengers on the Space Shuttle from deadly solar radiation? A: Earth's magnetic field deflects most (98%) of the energetic particles from the Sun. So long as astronauts are within Earth's magnetosphere, they are relatively safe (except during magnetic storms). Astronauts on the moon or traveling to Mars are in far greater danger. Q: Who was the first person in modern history to observe Sunspots? A: Galileo was the first person in modern history to observe and study Sunspots. Q: What terrestrial visual phenomenon is associated with magnetic storms? A: Auroras (Northern or Southern Lights) are more intense and more widespread during magnetic storms. Q: What is the name given to the constant outward stream of particles from the Sun? A: The Solar Wind is a gas of charged particles that blows outward from the Sun at a million miles per hour. Q: What was the Maunder Minimum? A: The Maunder Minimum was the period 1645 to 1710 when very few Sunspots were seen. It has been proposed that the decreased solar activity was responsible for unusually cold conditions during that period. Q: What is the average temperature of the solar photosphere? A: The mean solar photospheric temperature is around 10,832 degrees Fahrenheit (6000 degrees Celsius.) Q: A Sunspot has two distinct areas. What are their names? A: The dark center of a Sunspot is the umbra, the lighter area surrounding the umbra is the penumbra. Q: Name three effects of a magnetic storm. A: A magnetic storm affects HF communication, astronauts working in space, and produces aurora activity. Q: In what months are magnetic disturbances on Earth most probable? A: Magnetic disturbances are more probable around the equinox months. Q: What is the average geomagnetic field strength? A: The average strength of Earth's magnetic field at any point on the planet is roughly one gauss, or 10-4 Tesla. That's less than the magnetic field of a refrigerator magnet! The average magnetic field on the Sun's surface is also around one gauss, but the field strength in Sunspots can be 1000 times that. Q: What is the average length of a Sunspot cycle? A: The average length of a Sunspot cycle is 11 years. Q: What is the approximate delay between a coronal mass ejection and a geomagnetic storm on Earth? A: A magnetic storm may occur 2 to 4 days after a large solar flare or coronal mass ejection. Q: What is the approximate solar rotation period at Sunspot latitudes? A: At Sunspot latitudes, the Sun appears to rotate about once every 27 or 28 days. Q: What is a possible effect of a coronal mass ejection on Earth? A: A coronal mass ejection may be followed by a geomagnetic storm. Q: How powerful is a magnetic storm? A: A large magnetic storm generates about 5 terawatts of power ( 5 x 10^12 watts). This is about the same power capacity of the United States. Q: How powerful is a solar flare? A: A Solar Flare that lasts several hours is so powerful that it could provide the energy needs of the United States for about 10,000 years. Q: How high are auroras? A: Auroras form between 60 and 250 miles above Earth 's surface. The Sun Q: How many Earths can fit into the Sun? A: About 1,000,000. Q: How far away is the Sun? A: The Sun is 93 million miles (150 million kilometers) from Earth. This is pretty close by outer space standards, since the next closest star is 25 TRILLION miles (40 trillion kilometers) away! Q: How big is the Sun? A: Enormous! It may look small in the sky, but that's because it is so far away. It's about 800,000 miles (more than 1 million kilometers) across more than 100 Earths could fit across the Sun's face. Some stars are hundreds of times wider than the Sun! Q: What is the Sun made of? A: The Sun is mostly hydrogen gas, with some helium and traces of other elements found on Earth, such as carbon, oxygen, calcium and iron. Hydrogen is the most abundant element in the Universe. On Earth, hydrogen and helium are lighter than air - Helium gas is what makes party balloons float. Q: How do we know what the Sun is made of? A: By studying its light. Each of the hot gases in a star produces a unique "fingerprint" of light. By using an instrument called a spectroscope, astronomers can tell which gases are there. Most of what we know about the Sun and other stars comes from studying their light. Q: How hot is the Sun? A: Deep in the core, the temperature is an amazing 27 million degrees Fahrenheit (15 million degrees Celsius)! The surface of the Sun is almost 11,000 degrees Fahrenheit (6000 degrees Celsius). The Sun's outer atmosphere (corona) is about 2 million degrees Fahrenheit (1million degrees Celsius). Q: What makes the Sun shine? Is the Sun on fire? A: No, the burning that takes place in the Sun is different from fire we are used to experiencing on Earth. The Sun shines because the core produces tremendous amounts of energy by a process called nuclear fusion. Fire on Earth is caused by a chemical reaction. Q: How long does it take energy produced in the Sun's core to make its way to the surface? A: About 150,000 years. The nuclear fusion process in the Sun's core produces, among other things, gamma rays. These gamma rays are constantly absorbed and re-emitted as they move through the Sun, essentially bouncing in random directions. By the time this "random walk" takes them to the Sun's surface they have been transformed into visible light. This light escapes from the photosphere and arrives at Earth about 8 minutes later. Q: How old is the Sun? A: Our evidence shows that the Sun has been shining for nearly 5 BILLION years! That might sound like a long time, but it's less than half the age of the Universe, which is about 14 billion years old. Humans have only been around for a tiny part of that time. Q: Will the Sun ever become a black hole? A: No need to worry, our star will never become a black hole. Only stars that are a lot more massive than ours - meaning they have a lot more stuff in them - can end their days as black holes. Such a massive star eventually explodes as a Super Nova, leaving behind a black hole, which has gravity so powerful that not even light can escape. Q: How will our Sun end its days? A: Our Sun will end its days by expanding to the size of Earth's orbit and puffing off its outer layers. At that time we would call it a red giant star. Eventually, all that will remain is a tiny core (a white dwarf star) about the size of Earth. Earth will be burnt to a crisp, but this won't happen for about 5 BILLION years so don't start packing your bags for Alpha Centauri just yet!   The Sun in Earth's sky Q: Does the Sun go around Earth? A: No, Earth orbits around the Sun. It may seem the other way around because the Sun appears to travel across the sky from east to west each day. But this is just due to Earth's daily rotation toward the east. Q: How long does it take for our planet to go around the Sun? A: It takes one year for Earth to make one orbit around the Sun. Planets that are closer to the Sun take less time, and those that are farther away take more time to go around. Mars takes about two Earth years to go around the Sun. Q: Why do we have fewer daylight hours in winter than in summer? A: Because Earth's axis (the imaginary line that runs through the north and south poles) is tilted 23.5 degrees from the vertical toward a distant star called Polaris. This tilt causes the Sun to appear lower in the sky in winter months and higher in the sky in the summer months. If the Sun is lower in the sky in winter, then it spends less time above the horizon, resulting in fewer daylight hours and cooler temperatures. Q: Why does the Sun look bigger at Sunset? A: Your mind is playing tricks on you! The Sun looks bigger because of an optical illusion. When the Sun is near the horizon, it sometimes seems to be much bigger and closer than during the rest of the day. At Sunrise or Sunset, your brain has other objects to compare the Sun's size to, such as trees and buildings. Q: Why does the Sun look red/orange at Sunrise/Sunset? A: The Sun emits light of all colors that combine to make white light. At mid-day our atmosphere scatters the Sunlight to make the sky appear blue and the Sun a yellowish white. At Sunset, sunlight is scattered even more because it passes through more atmosphere to get to your eyes. More scattering means a redder color. The Sun's apparent color can also be affected by smoke or dust particles in the air which can enhance the scattering effect. Q: Why do the Sun and Moon seem to be the same size in the sky? A: The Sun is actually 400 times wider than the Moon, but it just so happens to be 400 times farther away in space, so it appears to be about the same size as the Moon. Because of this coincidence, the Moon sometimes completely blocks the Sun's light - an event called a total solar eclipse. Q: What is a solar eclipse? A: A solar eclipse occurs when the Sun, Moon, and Earth are lined up just right so that the Moon blocks the Sun's light and casts a shadow onto the Earth. Q: How can I view a solar eclipse? A: A Solar Eclipse occurs somewhere on Earth about every 18 months. Often they are only visible from remote places, so few people on Earth are able to view them. Sometimes the only place to see an eclipse is from a boat on the ocean! There are lots of web sites and magazines that contain information about upcoming eclipses and where you must go to view them. Visit www.exploratorium.edu/eclipse to learn more about eclipses and how to view them. Q: Are the Northern Lights related to Sunlight? A: The Northern Lights (or auroras) are not caused by the Sun's light but by tiny charged particles that constantly stream from the Sun. Auroras are caused when this stream of particles (called the solar wind) interacts with Earth's magnetic field and upper atmosphere (high above where airplanes fly). Auroras are always present in both the north and south polar regions of Earth. Whether we can see them depends on the time of year, cloud cover, and the intensity of solar activity. Storms from the Sun can enhance the brightness and dynamics of auroras.