astronomical unit (AU)

An astronomical unit, shortened to AU, is defined as the average distance between the Earth and Sun. One AU is equal to 214.94 solar radii (Or if you prefer, 1.496E+11m). Good thing they abbreviated it.

bow shock

Bow shock is defined as shock waves without collisions. They are found in front of a planetary magnetosphere(see definition below)- which is basically the place where the supersonic(speed greater than the speed of sound as found in given values) rhythm of the solar wind slows to a subsonic (speed less than the speed of sound as found in given values) flow, due to the planetary magnetic field. How cool is that?

chromosphere

The chromosphere is the layer of the sun’s atmosphere on top of the photosphere and beneath the transition region and the corona. From it come the most powerful lines in the solar spectrum, which includes the Balmer alpha line of hydrogen and the H and K lines of calcium. The Chromosphere is the source of the red ( or if you prefer more technical terms, chromium) color that is sometimes seen around the Moon’s rim during total solar eclipses.

convection

Convection is the main transport of plasma (or if you must have simpler terms, gas) from one place to another. This process takes place because of or in response to mechanical forces (like, say, interaction with the solar wind) or some electromagnetic forces.

corona

The corona just happens to be the outermost layer of the sun’s atmosphere, and is characterized by low densities (like…oh let’s say <10E+9 per cubic cm or 10E+15 per cubic m and even high temperatures such as (>10E+6 K). The corona can’t be seen from the Earth except during a total eclipse of the Sun or if you use of a special telescope called a coronagraph in order to see it. Too bad.

coronal mass ejection (CME)

A CME is a short-lived discharge of plasma from or through the sun’s corona. Wow! CMEs are sometimes but not always compared with emitting prominences, disappearing solar filaments, and flares.

cosmic ray

Cosmic ray particles have been shown to be ions of a familiar sort--mostly hydrogen, some helium, diminishing amounts of carbon, oxygen etc. and even a few atoms of iron and of heavier elements, similar to those found on the Sun. A cosmic ray is none other than the electromagnetic radiation of really really high frequency and energy. Sounds scary. You probably didn’t know that they usually interact with the atoms of the atmosphere before reaching the Earth’s surface. And some cosmic rays come from OUTSIDE the solar system while others come from the Sun and pass through some of the corona’s holes.

geomagnetic activity

Well geomagnetic activity is defined as natural, short-term variations and confusion in the geomagnetic field. This happens because of interactions of the geomagnetic field and the magnetosphere combined with the solar wind and other energy products of solar activity.

granulation

Did you know that granulation is the cellular structure of the photosphere? Well, it is also visible at really really high spatial resolution. Individual or distinct granules represent the tops of teeny tiny convection cells. They are normally 200 to 2000 kilometers in diameter. But they only last 8 to 10 minutes!

H alpha

The H alpha is surprisingly the very first atomic transition in the hydrogen Balmer series. It has a wavelength of about 656.3 nm. This is an absorption line of neutral hydrogen that happens to fall in the red part of the visible spectrum. This is also convenient for observing the sun. The H alpha line is used around the world for patrol observations of solar flares, filaments, prominences, and for studying the structure of active regions.

heliopause

The heliopause is simply the boundary surface that’s between the solar wind and the outer galactic medium.

Hale boundary

The Hale boundary just happens to be a great big magnetic inversion line of a specific magnetic orientation that is in the sun’s photosphere or across from a sector boundary in the solar wind. If the western (or the leading) side’s polarity of the boundary is the same as that of the closest pole of the sun at the beginning of a sunspot cycle, then the boundary is said to be "Hale." That’s where the name comes from. Let’s say, however, that the polarity is opposite. In that case the boundary would be called "anti-Hale." At the beginning of Cycle 22 (that took place in the year Nineteen hundred and eighty-seven, Common Era), the northern pole of the sun was negative and so in the northern hemisphere a Hale boundary separates a leading negative polarity region from a positive one that follows it. Because of this, the boundary that is between the leader spot and follower spot of an everyday sunspot group in either of the hemispheres is a Hale boundary, not an anti-Hale boundary.

heliosphere

After great scientific research and many years of studying, it has been concluded that the heliosphere is the magnetic cavity (or the giant bubble) that surrounds the Sun and planets. For a picture, see Sal’s page. The amazing heliosphere is also carved out of the galaxy (Which in case you didn’t know is called the Milky Way) by the solar wind.

high-speed stream

A high-speed stream is a feature of the solar wind that has values that are much greater than 600 km/s (and that is about DOUBLE the average solar wind values!). High-speed streams that begin in coronal holes are less dense than the ones that begin in the average solar wind.

interplanetary magnetic field

Simply stated, the interplanetary magnetic field is the magnetic field that is carried along with the solar wind.

ionosphere

The ionosphere is the region of the Earth's atmosphere that is ionized by the Sun's emissions.

magnetograph

A magnetograph is a special telescope that examines the color and polarization of the sun’s light so that it can measure the Sun’s magnetic field.

magnetopause

This is the definition for magnetopause. It is the boundary surface that lies between the solar wind and the magnetosphere. That is also where the magnetic field’s pressure of the object is equal to the dynamic pressure of the solar wind.

magnetotail

The magnetotail, as you can tell, is a tail. It is also a supplement of the magnetosphere in the opposite direction of the sun as a result of interaction with the solar wind. In the inside of the magnetotail, the field lines keep a roughly dipolar design. But at greater distances in the opposite direction of the sun, the field lines are stretched into northern and southern borders and are separated by a plasmasheet. There is also evidence for traces of the Earth's magnetotail as far as 1000 Earth radii downstream. Cool, huh?

penumbra

The penumbra (or penumbrae) is a sunspot area. It can possibly surround the darker umbra or umbrae. In its developed form it has linear bright and dark elements coiled from the sunspot umbra.

plasma

Plasma is any ionized gas that conducts electricity and is affected by magnetic fields.

sector boundary

The sector boundary takes place in the solar wind, which is the area where demarcation takes place in between sectors.(By now I think you should all know what solar wind is!) A sector is a huge feature that can be told apart from other things by looking at the main direction of the magnetic field that goes on betweens all planets, toward the Sun (which happens to be a negative sector), or even away from the Sun, in the opposite direction (which happens to be a positive sector). The sector boundary that separates the fields of opposite polarities is usually pretty narrow, and it passes the Earth pretty quickly- within minutes to hours instead of the week or so that is needed for typical sectors to pass. The solar wind velocities in the boundary region are usually some of the lowest observed.

solar maximum

Solar maximum……let me tell you about it….This would be the month(s) that occur during the sunspot cycle when the very cool smoothed sunspot number reaches a maximum. One pretty recent solar maximum occurred in December 1979.

solar minimum

Solar minimum is basically the opposite of what the solar maximum is! Would you look at that! The solar maximum is pretty much the month(s) during the sunspot cycle when the smoothed sunspot number reaches a minimum. One pretty recent solar minimum occurred in September 1986.

solar wind

Well seeing as this is the topic of this website it must be worth telling about….So I suppose I could tell you…The solar wind is the outward flow of solar particles(which means they come from the sun) and magnetic fields from the Sun. Usually at 1 AU(Remember? That stands for astronomical unit), solar wind velocities are close to 375 km/s. At that same time, proton and electron densities are near 5 per cubic centimeters. The total intensity of what is called the interplanetary magnetic field is nominally 5 nT.

troposphere

The troposphere is is the lower part of the atmosphere that is characterized by decreasing temperature with height.

umbra

Basically, the umbra is defined as the dark core or cores (umbrae = plural) in a sunspot with penumbra, which is a penumbra with no sunspots.

ultraviolet ( or UV)

Ultraviolet is….get ready for this hard-to-grasp concept… electromagnetic radiation at wavelengths that are shorter than the violet end of visible light (which is 5 to 300 nm). Fortunately for us humans, the Earth’s atmosphere can pretty effectively block the transmission of most ultraviolet light. You should still use sunscreen though!

This glossary was compiled and edited by Christina Ray.

Special thanks to spaceweather.com for guidance and information on this topic.