A telescope is an instrument used to observe objects from afar. The word is derived from Greek words tele and skopein which means “far” and “to see” respectively. Contrary to popular belief, it was not ‘invented' by Galileo. There has been evidence of a refracting telescope that has been in use in the Netherlands during 1608 and its development was credited to spectacle makers Hans Lippershey and Zacharias Janssen, and a third person Jacob Metius. However, it was Galileo who improved on the devices soon after so they can be used for exploring the heavens.

A telescope works by collecting electromagnetic radiation, which on earth-speak means visible light. However, with the development of space technology, there has risen the capability to utilize the full range of the electromagnetic spectrum and use the radio band. The first radio telescope was used in 1937 and there have been subsequent development of telescopes that can work with other wavelengths such as gamma rays.

Photo by: Mike Peel Creative Commons

A telescope has A telescope has three major capabilities – the ability to magnify, the ability to resolve images and create sharp images and the most important being the ability to collect light so it ‘sees' better (which is also the reason why your pupils enlarge when the room is dark or when it's nighttime). The part of a telescope which collects light is the ‘objective'. The objective of a refractor telescope is a glass lens and a reflector telescope uses a (surprise, surprise) mirror.

The first telescopes used to observe the heavens where refractor telescopes and they were subject to problems of chromic aberration or color distortion and spherical aberration among others. It wasn't until 1668 that the first practical reflecting telescope was developed by no other than Sir Isaac Newton with the idea that parabolic mirrors can reduce aberration and more than a hundred years after, achromatic lenses where developed and the rest, as they say, is history.

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Setting circles are disks used on various telescopes outfitted with an equatorial mount to aid in the
search for astronomical objects anywhere in the sky by referencing equatorial coordinates used in the star charts. It functions by attaching those graduated disks to the right ascension and to the declination axis within the equatorial mount. The disk positioned on the right ascension will be graduated by time, through hours, and even minutes and seconds.

A declination disk on the other hand is graduated into degrees, and then minutes and seconds. Locating any object on the celestial sphere through setting circles is just similar to searches on a terrestrial map using the longitude and latitude values. Some variations on the right ascension circle provide a northern hemisphere scale and southern hemisphere scale.

Today’s applications of setting circles play an important role in astronomy. Research telescopes benefit much from the large diameters of these disks. When combined with a vernier scale, any telescope can be greatly enhanced with its arc minute accuracy.

Portable telescopes are very useful especially with amateur astronomy. And when equipped with such disks, the setup will normally require polar alignment, which is the alignment related either to the northern celestial pole or to that of the southern celestial pole. Setting the right ascension disk after polar alignment is also required. Observers make use of a calculator or any known star in the sky to synchronize the right ascension disk with the sidereal time.

All these functions make setting circles an important component when searching the sky for anything.

Using a Telescope with Setting Circles

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These illuminated reticles are actually needed to accurately align telescopes. It also has a grid of patterns placed in the eyepiece of an optical instrument and is also used to establish a scale or position. A reticle control would allow manual rotation of the reticle for use when it comes to lunar surface alignments. Crossing by the line on the star image defines a plane containing the star. Crossing of the other line defines another plane containing the same star or a different one.

The intersection of these planes forms a line that defines a direction of the star. To define the internal orientation of the particular star being viewed, sightings on at least two stars are required. Each star sighting requires the same procedure. Multiple reticle crossings and their corresponding marks can be made on either or both stars to improve the accuracy of the sightings. Upon completion of the second star sighting, the guide computer would then calculate its orientation with respect to a predefined reference coordinate system.

Centering stars without a reticle would be very difficult. It would be best to select the best reticle for your telescope to make sure that finding the stars and centering it would be easier.

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Currently there are seven main types of stars based on their temperature, O, B, A, F, G, K, M. Depending on their mass and stage of development however; stars may be classified as either dwarf stars or giants. Based on this grouping, scientists have found out that the most common stars in outer space are what they call red dwarf stars.

Red dwarf stars get their name because of their relatively smaller size and mass than the sun. These stars are known to have only a little less of the half of the weight of the sun. Their small size enables them to live for a very long time because they burn their fuel very slowly. However, because they burn only a little bit of fuel, red dwarf stars are also cooler compared to other stars and thus isn’t able to shine as brightly. Typically these stars only have a temperature below 4,000 K resulting in a faint light.

Though quite numerous in outer space, it will be very hard to see red dwarf stars in the night sky because of their small size and the faint glow that they give off. Probably the most popular red dwarf is the Proxima Centauri.

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Currently there are different types of radiometers, each with its own way of detecting and measuring electromagnetic wavelength, but the most popular model still remains to be the Crookes radiometer. Made in 1873 by a physicist named Edward Crooks, this model is one of the earliest to have been used. It is made of a spindle fitted with a rotor and a set of vanes inside a partial vacuum. The vanes, which are painted silver on one side and black on the other, rotate upon exposure to light. This motion is commonly explained by physicists as the result of the heat generated upon absorption of the blackened side of the vanes of the photons from the light. The Crookes radiometer is used to provide a quantitative measurement of electromagnetic radiation. In principle, the more intense the light is that hits the vanes, the faster the rotation will be.

But as popular as the Crookes radiometer is, its use has been usurped by newer models such as the MEMS and Nichols radiometer which tend to be more diverse and sensitive in measuring electromagnetic radiation.

Crookes Radiometer

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The first convex lenses to be used in refracting telescopes were designed and made by a Dutch optician named Hans Lippershey in 1608. What he discovered about how looking through a concave and convex lens positioned in front of each other can make distant objects look very much nearer paved the way for the use of these lenses in telescopes. Just a year later, the first refracting telescope to be used in the study of space was made by Galileo Galilee. It was through this device that he was able to map the surface of the moon and to discover four of the moons circling Jupiter.

But how exactly does a seemingly simple device enable you to peer into outer space? Well for starters, refracting telescopes basically have two parts that function to gather and collect light – the objective lens and the eyepiece. The objective focuses the light by bending it into a focal point. This focal point is where the image is formed. Once the person looks into the eyepiece, a concave lens will gather and focus more light than the eye could so that a magnified image can be seen.

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Parallax provides astronomers with a simple method of calculating the distance of many celestial objects. As the Earth revolves around the Sun, celestial objects seem to be located at different positions when observed month after month. When a star is observed during June and December, observers can make use of two different viewpoints or lines of sight to the star to measure the distance. These two lines of sight intersect at the star being observed, forming an angle and half of this angle is the parallax. Typically, the distance is measured in parsecs by getting the inverse of the observed parallax measured in arc seconds.

There are different kinds of parallax, namely, stellar, solar, lunar, diurnal, and dynamic or moving cluster. It is important to keep in mind that parallax decreases with distance and can only be used to measure celestial objects at a maximum distance of 100 parsecs. The use of this concept in astronomy is extended with much precision through the use of the Hipparcos satellite.

Geometric Technique – Parallax

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The angle between a certain rotational axis of an object and the specific perpendicular line in regards to the object’s orbital plane is better known as its obliquity. In the solar system, the axial tilt of the earth is known formally as the obliquity of the ecliptic, since the name of the planet’s orbital plane is called the ecliptic plane. In formulas, it is represented by the Greek Character “Ε” or epsilon.

Apart from this, a planet’s axial tilt causes the seasons like spring or winter. This is due to the change of orientation of a planet’s obliquity, though the actual angular degree of tilt does not change, and the rotation moves until it reaches 360 degrees or one complete revolution. Thus, specifying which season it is now.

The planet earth has an approximate axial tile of 23.4 degrees. The axis stays tilted in the direction pointing to the stars for the entire year. This implies that a certain hemisphere — or half of the earth is in the direction towards the sun, half a year or half an orbit later, the other half will be now in the sun’s direction. Also, the current hemisphere that is facing the sun tends to have longer hours of sunlight.

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Not only does astronomy cover different branches of science, it also borrows concepts in fiber optics as well. Objective (optics) is also taken into account when it comes to science, or in this case, astronomy.

Objective (optics) means the optical part of a scientific instrument such as a telescope or microscope, that is responsible for gathering light from the observed specimen and makes sure that these light rays are then focused at different levels to produce the real image.

In space studies, Objective (optics) is the optical part of the telescope. It is the lens located at the end of the refractor or simply put, is the front end of the telescope, where people usually set and focus at a fixed point in the sky or at a long distance. This is not to be confused with the other end of the telescope, where people usually take a look on the area being fixed upon. The light gathering capability and the maximum distance it can take is dictated by the diameter or size of the lens. This means that the bigger the objective lens a certain telescope has, it means that the dimmer the object it is focused on and more details can be shown or seen.

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When measuring rotation for solid objects, examples of which are rocky planets and asteroid, the rotation would be considered as a single value. For gaseous or fluid bodies, such as stars and gas giant planets, the period of rotation is different from the equator to the poles because of the differential rotation. The rotation for a gas product is its Rotation period as determined by the rotation of the planets magnetic field.

Earth’s rotation is relative to the Sun which is 86,400 seconds of solar time. Each of these is a little longer than the SI second because of the fact that the Earth’s solar day is longer than it was during the 19th century. The mean solar second between 1750 and 1892 was chosen in 1895 by Simon Newcomb as the independent unit of time in his Tables of the Sun.

These tables were used to calculate the world's ephemerides between 1900 and 1983, so this second became known as the ephemeris second. The SI second was made equal to the ephemeris second in 1967. While the planet rotates, it is also moving around the Sun. This changes the apparent position of the Sun among the stars, and as a result, it does not move around the sky in quite the same period of time that the stars do.

Sunchronous Rotation

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