But what is relativity all about and how was it able to answer these questions? We can begin with what Einstein came up with, the idea that if we are to believe that the natural laws of the universe are absolute and true then they must be true under all circumstances and at all times. According to him, this is only made possible when elements such as space, time, matter, and energy are altered or are changed constantly in order to present us with the same circumstance every time. Applying that to observations of the universe, he supposes that even empty space can contract or expand depending on the position of the person observing it.

In astronomy, relativity has found its place especially when observing or studying objects that move in a strong gravitational field as well as those that are moving near the speed of light.

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Parallax is the model of measuring these celestial bodies by observing their apparent direction at two different lines of sight, say one in January and the second in July. The intersection of these two lines of sight is the astronomical object itself and is half the angular measure of parallax. When the inverse value of parallax which is measured in arcseconds is taken, the distance in parsec is obtained for the particular celestial body being observed.

The use of parallax is the most basic calibration step in measuring distances in the field of astrophysics. However, the limitations of a telescope allow only the observations on astronomical objects that are up to 100 parsecs away from the Earth. The first successful attempt of measuring a celestial object by means of parallax was carried out by a German named Friedrich Wilhelm Bessel who made an observation on 61 Cygni. His trigonometric calculations are the basis for the calculation of parsecs.

About 4.85 x 10-6 pc is the equivalent of one astronomical unit and one parsec is equal to 3.262 light-years. The concept of parallax and distances in parsecs remain to be one of the most useful ideas in astronomy.

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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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Tropical year is the mean interval between one vernal equinox to another vernal equinox, meaning, it is the length of time when the sun returns to its original position along its ecliptic or path on the celestial sphere after a cycle of seasons as viewed from the Earth.

The movement of the sun is the reference point of tropical year. The position of the sun is measured using a vertical stick also known as gnomon by measuring the shadow casts on the gnomon at noon. The variations day by day is then calculated.

Tropical year varies by minutes but the mean tropical year is 365.2422 SI days because of the gravitational effects of the different celestial bodies such as the moon and planets on earth. Scientists, therefore, have determined the different tropical years along the four ecliptic points, which include vernal equinox, autumn equinox, summer solstice and southern solstice. The values of each of the tropical years are then averaged to get the mean tropical year. The vernal equinox is of particular importance since this marks the start and end of one tropical year.

A Year on Earth

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One light-year is equivalent to approximately less than ten trillion kilometers. In technical definition, the International Astronomical Union (IAU) defined a light-year as the distance travelled by light in a vacuum using the Julian calendar as the reference for time. The Julian year is not similar to the Gregorian year we are used to and the IAU published the constants that accompany these. The unit of light-year is the official galactic scale, though some publications and astrometry still prefer the use of parsec.

The use of light-years can also be simplified by using the prefixes kilo-, mega- and giga- to signify very large distance values. This unit of measurement represents the distance between the observer and the celestial body or between one celestial bodies to another celestial body located in the same star system.

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When people talk about astronomy, especially when it comes to aging systems, stars or other concepts that relate with age, the term sidereal year is mentioned.

This term is defined in science as the measure of time for a planet, star constellation or celestial body to complete its orbit around the sun, in terms of angular measure (degrees) as the unit of measurement and in regards to its position from the sun.

To add on the definition, it is the concept that introduces orbits and rotations in the solar system. According to studies, the time for a certain constellation to complete a single revolution or to complete a 360 degree around space skies and then return to their original positions in Earth skies is then called the sidereal year.

In relation to the rotation and revolution of the earth, the term sidereal year comes in when here because of the planet’s rotational speed and direction. As the earth revolves around the sun with nearly a degree per earth day (23 hours and 6 minutes), the rotation of the planet on its axis makes the direction of the earth differ, thus making the different seasons as well.

Once the direction of the earth is towards the sun, then it becomes spring. The direction of the earth also defines the local noon and meridian in a certain area of the world.

Also, this term is different from that of solar year. A solar year has little more days than that of a sidereal year, for a single sidereal year is a quarter less compared to a solar year.

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According to the still referred to Euclidean space perceptions, the universe is composed of 3 dimensions space and a fourth dimension called time. By combining these 2 aspects, many and various physical theories have been proven and simplified. And explaining concepts many theories and principles are made in a uniform manner at both super-galactic and subatomic levels.

In mechanics, since the concept of time is considered as a universal and constant matter, the use of the Euclidean perceptions is usually applied. However, when relativity is talked about, time cannot be separated or used as an independent variable, mainly because a certain objects rate of velocity is relative to that of the time that the said object passes through light. In relation to gravity, it can intensify and affect the speed as to which a certain object passes after a period of time. It greatly decreases the speed of the said object as well.

Understanding SpaceTime

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The mega parsec was said to have been first used by the international scientific and astronomical community in the year 1920. In reality, astronomers cannot use the normal units of measurements such as meters and square meters as the measurements would be too big a number. For convenience, astrologists looked for a way to emphasize a great distinction in measurements, especially if you’re talking about measuring galaxies or clusters in space.

Using earth-land measurements for distances in space is simply mind-boggling, to say the least. Let’s say that a parsec is about 30 trillion kilometers. Roughly converted to miles would give us an approximate value of 19 million trillion (is there such a thing?) miles. Though unimaginable, it gives us the idea that the earth may be big, but the distance in space is definitely immense.

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Tides are the periodic fluctuations of large bodies of water. They are caused by the gravitational interaction between the Earth and the Moon in what is generally called tidal forces. Although tidal changes may occur as a result of other factors like the Moon's altitude and distance, the positions of the sun and the Earth and the depth of ocean floors and coastal topography.

The Moon exerts more than twice the sun's gravitation force on earth, making it the most important factor. Its gravitational pull causes the oceans to bulge out to its direction. Another bulge appears on the opposite side due to the Earth's gravity too and the spherical shape is retained although the pull o the opposite side is weaker. Most places experience two high tides and two low tides every day, most because of the interplay of Earth's rotation, the moon's gravity and the sun's gravitational force.

There are generally four stages in the rise and fall in the bodies of water. First, the sea level rises over a period of several hours, ultimately covering the inter-tidal zone in what is called the flood tide. Then, water rises to the maximum level in what is called high tide. After that, water levels fall over the same period and revealing the inter-tidal zone in what is called as ebb tide and finally, the water stops falling and reaches low tide phase.

Tides can be especially weak or strong, with differences in water levels reaching 20%. Spring tides, which have nothing to do with the season, occur when the moon, sun and the Earth are in a row and there is a combined gravitational force of the Moon and the Sun. They usually occur during new and full moons.

Proxigean Tides are unusually high tides generally occurring during the new moon where the moon is between Earth and the Sun and when it is especially close to the Earth. Neap tides are weaker tides, occurring when the moon and sun are perpendicular to each other.

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Photo by: Lars Lindberg Christensen Creative Commons

size of a grain of sand that before they touch earth’s surface they have crumbled. A forceful and bizarre meteor shower is termed as either a meteor storm or meter outburst. During these extraordinary events, more than a thousand meteors appear hourly.

The Zenith Hourly Rate is the number of meteors you will see in an hour. If the shower’s peak has a magnitude of 6.5, it can be discerned by the naked eye. The best way to observe and appreciate a meteor shower is when there is no moon, light pollution and cloud. A meteor shower occurs when a planet makes contact with dust or debris from a comet. This debris moves in the trail of the comet and the moment a planet moves through it, a meteor shower happens.

The Perseids is a meteor shower that has been observed in the past years with its peak clearly seen on August 12. Of all the meteor showers, it is the Leonids that stuns and impresses observers and it usually occurs sometime on the 2nd or 3rd week of November. It is noted that every 33 years, Leonids produce meteor storms with a Zenith Hourly Rate of a thousand meteors falling.

Perseid Meteor Shower

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