Spectral class or spectral classification is the manner of organization in astronomy that deals with classifying stars according to brightness or luminosity, or through the spectrum or color of the star’s chromospheres.

In learning how to classify stars, the best way to check is through color. In this classification, there are different levels of a star’s chromospheres colors. This is none other than the Blue, Blue-White, White, Yellow-White, Yellow, Orange and Red. This is known as the O, B, A, F, G, K, and M classes. Furthermore, a certain star’s color determines its age. When the star has a blue hue, it clearly means that the star is still young. The oldest and most probably dying star is the M or red colored stars. To better easily understand the color levels, it is usually interpreted as “Oh, Be A Fine Guy/Girl, and Kiss Me”. Adding on this, the levels also determine how hot and bright the star is, with blue as the hottest and red as the coolest and dimmest of all stars.

This type of classification may be old, but it is the basic of other stellar classifications used. The current system used is the Morgan-Keenan System, which classifies a star also by spectrum type, though it is based on a 0 to 9 scale.

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Most celestial bodies can be observed as entities resembling a definite shape when the proper equipment is used. The Sun, when viewed under a solar filter resembles a great big ball without the harmful rays. Most of the stars can be viewed the same way, where it can be seen as a sphere. However, numerous astronomers have detected that the intensity of the image formed by a star slowly diminishes from the center going to out towards the edge of the sphere. These edges are often referred to as limbs and the phenomenon is called limb darkening.

Limb darkening can occur as a result of two effects. The first is caused by the decreasing density of the star as the distance increases from the center, diminishing the intensity seen around the limbs. The second is when the star’s temperature decreases as the distance from the center increases because the radiation that is coming from the star is in fact a function of temperature. These two effects cause the edges of a particular star to darken at the limbs and the center can be observed as the most intense part of the star.

Limb darkening can be calculated using angular measurements associated with the observer and the star being observed.

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Photo by: Dim Grits Creative Commons

A variable star is a star which has varying brightness as viewed from earth. The brightness can change in a matter of seconds or even years, and the intensity of brightness can vary from as low as thousandth of a magnitude, which can only be seen by a powerful telescope, to as great as 20 magnitudes that can be seen by the naked eye.

Variable stars are classified as either intrinsic or extrinsic, depending on the cause of the variations in brightness. Intrinsic variable stars are those whose fluctuations in brightness are caused by the physical changes occurring in the star itself. It is further divided into subtypes: Pulsating, Eruptive, and Cataclysmic.

The variation may be caused by the pulsation or eruption in the star. Pulsating variable stars actually shrink or swell because of the forces inside the star. In Eruptive variable star, there are flares or ejections from the star, which cause the fluctuations. Another subtype of intrinsic variable star is the cataclysmic variable wherein there is an outburst of stellar material into space causing intense brightness. Supernovas are popular examples.

The second type of variable star, the extrinsic type is primarily caused by the eclipse of one star to another in a binary system. It may also be caused by the stellar rotation. The variability in rotating variable occurs when the star rotates and the side that is seen from the earth is the darker side of the star.

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Light pollution

Pollution happens during the production of artificial light. There are several scientific meanings of Light pollution. These include:

• Light pollution is the adjustment of light due to artificial light resources.
• Light pollution is the excessive production of artificial light which adversely affect the light levels.

All these refers to the introduction of man-made structures that produce artificial light.

What light pollution does is that it reduces the visibility in the evening sky. It does not allow people to appreciate the beauty of the heavens. It also disrupts astronomers in their study of space. Such pollution is known to distract existing ecosystems not to mention negative health effects.

This type of pollution is one of the consequences of the industrial revolution. As cities become more and more urbanized, one may observe a heightened degree of Light pollution. This is a very dangerous predicament in our ever-developing world.

What is Light Pollution?

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Luminosity can be interpreted in two ways. The most common manifestation of this event is when stars are seen at night. Stars emit light in the visible part of the electromagnetic spectrum, allowing observers to see stars by simply looking up the sky. The other manifestation is radiation and is not easily observed but still make up the total energy emitted by a star. Astronomers calculate luminosity using either a star’s apparent or bolometric magnitude.

A star’s luminosity can tell astronomers about its different characteristics. With this parameter, astronomers can quantify a star’s temperature or hotness, their size or their ability to support life just like our Sun. The energy emitted by a star greatly contributes to our present knowledge about the universe today.

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Observation centers use varying scales to indicate sky transparency. Some observatories use the 6-color scale where dark-blue equates excellent sky transparency, medium blue stands for above-average, light blue is for average, pale blue is for poor sky transparency, grey is for very poor transparency and white for a cloudy sky. Others use 1-7 scale, using the presence or quality of clouds and the types of celestial bodies that can be observed (such as the Milky Way and certain constellations) to designate transparency levels.

Note that transparency and atmospheric conditions are not the sole reasons why objects appear dim. Your equipment's magnification, resolving and light-gathering abilities are also important. Nonetheless, if you are an amateur sky observer or astronomer, it is important to consider transparency-related forecasts

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