321. Q. & A.s SCI. & TECH. – 19

Q. &  A.s  ‑‑‑  SCI.  &  TECH. – 19

500Q. Are all solar flares of the same intensity?

      Solar flares are not all the same intensity. In fact, there are many more low-intensity flares than high-intensity flares. The number of flares increases with decreasing intensity right on down to the limit of the sensitivity of the instruments that have been used to detect them.

501Q. How often do solar flares occur at solar minimum and at solar maximum, on a day-to-day basis?

 This depends upon the flare intensity.

At solar minimum, at an average rate of about one per day, the statistics of flares that were detected from 1980 through 1989 with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission show that flares occurred. There can be long periods of time at solar minimum when no detectable flares occur.

At solar maximum the average rate was as high as 20 per day (averaged over a 6 month interval). So the rate at solar maximum is roughly a factor of ten greater than at solar minimum. It is important to realize, however, that the flare rate is very irregular. Then a large active region can form and produce many flares in just a few days. The duration of a solar flare in the energetic hard x-rays is seconds to minutes This emission can last from minutes to hours.

502Q. What is the velocity of plasma from a solar flare as it heads toward Earth?

The electromagnetic radiation from flares travels at the speed of light and reaches the Earth in eight minutes. CMEs [Coronal mass ejections], on the other hand, travel at speeds from 100 to 1000 kilometers per second and take several days to reach the Earth.

503Q. One solar flare crippled the communications satellite Anik E1 permanently and temporarily interfered with other satellites - why weren't all affected equally?

      The sensitive components on Anik E1 were presumably not shielded well enough to withstand the large storm that occurred.

      The effects of the storm are not the same at all locations. It may be that Anik was damaged while other satellites were not because it just happened to be in a location where the effects of the storm were particularly intense.

      The Anik satellites are in high, geosynchronous orbits that expose them to the Earth's radiation belts. But other satellites are in similar orbits.

504Q. Do you know of any Web site that supplies daily information about solar flares?

MIGRAINES AGGRAVATE.

The same has been reported to the number of patients in Intensive Care Units and in Emergency Rooms. So, there is a DIRECT CORRELATION.

There is something called, "Monthly Chronogram", where the patient reports during one month the date and the hour of the "aggravations" of her/his disease.

505Q. What's the lifespan profile of sunspots?

The lifespan of a sunspot can be anywhere from less than an hour for a small spot to as long as several months.

506Q. Can flares erupt on any star's surface, or just the Sun's?

Flares do erupt on the surface of other stars. Most stars are in fact too far away for flares having the brightness of those that occur on the Sun to be observed.

507Q. Do flares have a measured effect on the ionosphere?

Solar flares do have an effect on the ionosphere. The evolution of the x-ray emission from a flare is mimicked in the ionosphere as a Sudden Ionospheric Disturbance (SID). This particularly affects radio communications at frequencies below around 30 MHz that depend upon the reflection of the signal off the ionosphere for long distance communications.

508Q. I would greatly appreciate it if you would tell me which specific types of ions or particles are emitted from a solar flare.

      The types of particles detected in space from solar flares reflect the composition of the solar corona.

      The corona is mostly hydrogen, so a lot of energetic protons and electrons are observed. Since the protons are heavier and more energetic than the electrons, they are of particular concern because of the damage they can do to astronauts and to electronic equipment.

      The next most abundant element is helium, which is observed along with its isotope helium-3.

      Heavier ions such as carbon, oxygen, silicon, iron, and many others are present at a much lower level.

509Q. What special precautions are taken aboard the space shuttle to prevent damage to their electronic components and how are the astronauts protected?

      The primary protection is the Shuttle orbit.

      The altitude of the Shuttle is typically 300-500 km  above sea level. This is well within the Earth's magnetic field and below the Earth's radiation belts (the van Allen belts).

      This magnetic field protects us from most of the charged particles from space, including from the Sun.

      Since these charged particles can travel along the Earth's magnetic field to lower altitudes at the poles, however, the Shuttle orbit also avoids the regions around the north and south poles.

      Manned missions to the Moon or Mars are much more dangerous, since these require leaving the protection of the Earth's magnetic field.
      Some high-energy charged particles ("cosmic rays") do penetrate down to the Shuttle orbit and to the surface of the Earth.

      Therefore, the risk of damage is higher at the Shuttle orbit than at the surface of the Earth. The Shuttle shroud does provide protection, but not from the highest energy particles.

      The Shuttle astronauts have in fact seen flashes resulting from the interaction of high-energy protons with their eyes. Nevertheless, the increased health risk is not unacceptably high.

510Q. How does the sun burn?  Is there oxygen in space?   Isn't that needed for fire?

The burning in a fire is a chemical reaction, requiring oxygen. If such a chemical reaction were responsible for the heat of the Sun, the Sun would have lasted for less than 100 million years. We know, however, that the Sun must be several billion years old. Therefore, a greater source of energy is required.

511Q. Do all of the stars have names?

No, only about 250 of the brighter stars have names.

512Q. How did the stars get their names?

The Babylonians were probably the first historical people to name the stars. Most of the names which have come down to us are Arabic, with some Persian, Greek, Latin and Babylonian names. Most of the Latin names are modern. The names of the stars came to us about 2,000 years ago. Some of them came 500 years ago.

513Q. What star is nearest the Earth?

The Sun is the nearest the Earth. The mean distance of the Sun from the Earth is 150 million kilometres. The distance from the Earth to the second nearest star, Proxima Centauri, is about 4.2 light years from the Sun. That distance translates into 40 billion (40,000,000,000,000) kilometres.

514Q. What is a parsec?

The word "parsec" is made up of the parts of the words "parallax" and "second". It means the distance from the Earth to a star whose parallax is one second of arc. There is no star as near as one parsec, for the parallax of the nearest star is 0.75". A parsec is 3.26 light years.

515Q. How many stars can we see on a clear night?

A man can see between 3,500 and 4,000 stars.

516Q. Why are some stars brighter than others?

In general, a star's brightness depends upon its distance from us, its temperature and its size. With stars of the same size and temperature, the nearer stars will appear to be the brighter. With stars at the same distance and of the same size, the hotter stars will be the brighter. With stars at the same distance and the same temperature, the larger stars will appear brighter.

517Q. What does magnitude mean?

Magnitude is the measure of the brightness of a star or of any luminous body in the heavens.

518Q. Do the stars have colour?

Yes. The colours most often seen in the stars are red, orange, yellow, white and blue. There are some violet stars and a few green stars.

519Q. Do the colours of the stars have any significance?

Yes. Colours indicate star temperatures; they also tell which of the elements make up the stars. As a rule, the blue and the white stars are the hottest, while the red stars are cooler stars.

520Q. How hot are stars?

The hottest stars have a surface temperature about 45,000°C. The coolest visible stars are about 200°C at their surfaces. The inside temperatures of all stars must be measured in the millions of degrees.

521Q. How do we know the temperature of a star?

An instrument called a thermocouple indicates the amount of radiation we receive from a star. If the star's distance is known, its temperature can be calculated. The spectroscope will tell us of the behavior of the atoms that make up a star, and the laboratory gives us a criterion for the behavior of atoms of various elements at various temperatures. It is possible to estimate very closely the temperature of any star whose spectrum can be studied.

522. How big are stars?

The smallest known stars are about the size of planets. The largest stars are hundreds of times the diameter of the Sun.

523Q. Are the giants massive stars?

A giant star is one whose diameter is between 10 times the diameter of the Sun and 100 times its diameter.

The largest star masses known are only 100 times the mass of the Sun, and such stars are very rare. The giants are large, cool stars, whose masses are about the mass of the Sun and go from 10 and sometimes 20 times of the Sun's mass.

524Q. Are the giant stars hot stars?

Not as a rule, at least at their surface. There are very few hot stars that are larger than 10 times the diameter of the Sun.

525Q. What is a supergiant star?

Stars which are larger than giants are supergiant stars. A supergiant star is one whose diameter is more than 100 times the diameter of the Sun.