Venus

Actually, the planet Mercury has the same behavior of being visible at dawn and at dusk. However, it can only be observed during a few weeks in a year. Since Venus is much larger and closer to earth, it has earned the title.

Because of its proximity to the sun, Venus is always found on the same side of the sky. If the sun is just setting to the west, the “star” can only be found at the west too. Its sulfuric acid clouds are highly reflective, causing it to glow brightly.

Venus is usually called the earth’s twin in terms of size, composition and gravitational pull. However, the atmosphere of the Evening Star is too hostile for life to exist. The atmospheric pressure on its surface is about 90 times greater than the earth’s. The air is also mostly carbon dioxide.

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To understand it better, a comparison with a similar phenomenon in sound waves called Doppler Effect is used. Imagine that you are riding in the car moving towards the north when suddenly an ambulance passes by going in the opposite direction. You will notice that as you and the ambulance move closer to each other you will hear a higher frequency of the siren while as you move farther away from each other, you will hear a lower frequency of sound. Light behaves in a similar way because it has wave-like properties.

With regards to astronomy, the universe has been known to be continuously expanding and along with it galaxies tend to move away from us. Accordingly, the light emanating from these galaxies is redshifted or change into longer wavelengths. This shift isn’t observed by the naked eye and is usually measured by comparing the spectrum produced by this light to that of a reference laboratory spectrum. By comparing the spectrum to known wavelengths, astronomers are able to determine the redshift occurring from these distant sources.

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The Poynting-Robertson effect is named for the two men who first described the effect in 1903—John Henry Poynting and Howard Percy Robertson. It can best be likened to raindrops striking a speeding car. You may not feel it much, but the rain does slow the car down slightly. The same is true with the Sun’s radiation pressure falling on particles in space. It slows the particles down by working tangentially from the direction of the particles’ orbital motion, thus lowering their angular momentum. But while these particles are pulled gradually into the Sun, their orbital speeds do not falter and are instead continuously increasing.

These dust particles would then join the large disk-shaped cloud already orbiting the Sun between the orbits of Venus all the way to the asteroid belt between Mars and Jupiter. The Poynting-Robertson effect is also believed to give evidence that our solar system is quite young. For if it were old, we wouldn’t have as much interplanetary dust as we do now since the Poynting-Robertson effect would by then have caused most of these particles to spiral completely into the sun.

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Occultation is similar in concept to that of eclipses wherein the sun’s light is being blocked either by the planet earth or the moon when these three align at some point during a revolution. This term pertains to different celestial bodies that meet up and can block each other.

In this phenomenon, the nearer body or object blocks the farther or more distant celestial body. It can be between planets, stars or asteroids alike. One example already is the solar and lunar eclipses between the planet, the moon and the sun. Though the earth or moon blocks each other from the sunlight, it follows the shadow of the other planet or satellite, thus the process of eclipse happens.

In transits however, is the opposite of an eclipse. In here, the nearer celestial body seems to look smaller than the farther object. One example of this phenomenon is the transit between the planet Venus and the Sun. Venus, which is nearer to earth, seemed to look as if the planet shrunk due to size of the sun, not to mention, the distance between the two celestial bodies as well.

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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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There are also several mid-sized lightweight planets, just a few times larger than our beloved planet Earth. Most extrasolar planets rotate around stars, but there are also planets that orbit around brown dwarfs and planets that do not orbit on any body at all, floating freely to space.

Because of the discovery of many extrasolar planets, the interest in the possibility of extraterrestrial life has intensified in the field of science and astronomy. Various missions and projects have been made to determine if there is extraterrestrial life on these planets.

Astronomers have found two possible candidates that may hold extraterrestrial life: red dwarf planets Gliese 581 and Gliese 581 D. These planets have many Earth like qualities so possibility of life here is high. Because of this, scientists have sent a message to Gliese 581. Being 20.3 light years away from earth, the message is estimated to arrive by year 2029 and response, if ever there will be, will not come until year 2049.

ExtraSolar Planets

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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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The vast number of stars in the universe, there are binary or multiple systems. These are essential for astronomers to be able to measure the mass of stars. There are several types of binaries which include Visual, Eclipsing, Spectroscopic and Multiple star systems. An Optical double, which is sometimes called a binary star, is really not binary in nature.

Optical doubles are not real binary stars because they do not orbit each other. These are just pair of stars that appear exceptionally close together in the sky even though they have different distances on earth. They are also an illusion made by a possible alignment of stars. They are considered rarer than true binaries.

Giovanni Battista Riccioli, an Italian astronomer, observed the first double in 1650. In fact, the constellation Ursa Major’s two stars, the Mizar and Alcor form an optical double. Other astronomers followed, like Galileo and Robert Hooke, who discovered one of the first double-star systems.

Other recognized optical doubles are Alpha¹ Capricorni, Alpha² Capricorni, Xi1, 2 Sagittarii and Winnecke 4.

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H= v/d

Where H is the Hubble’s constant, v refers to galaxy’s radial outward velocity or speed and d is the distance from the Earth. Based on this relationship, the farther the galaxy, the faster it is moving away from Earth. It is not easy to determine the exact value of Hubble constant. This is because the two quantities required are difficult to measure especially the exact distance of a galaxy from the Earth. The current value of this constant as calculated by Edwin Hubble as 500 km/s/Mpc or 500 kilometer per second per megaparsec.

Hubble’s Law is very important in astronomy and cosmology. It was the first concrete support for Einstein’s theory of Relativity being applied to the universe. The determined value of Hubble’s constant can be used to estimate an age of the universe. It also helps validate theories of Dark matter and Dark energy. A recent discovery in 1998 revealed that the expansion of the universe is accelerating.

Hubbles Law

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Libration

Libration started by a to and fro movement of the Moon as perceived from the Earth. This has caused the observers from the Earth to be able to see the many parts of the surface of the Moon at various times of the day. There consist three main types of lunar libration.

1. Longitude libration- This happens because of the eccentricity of the Moon’s orbiting around the earth.
2. Latitude libration- This happens fro a slight inclining of the Moon’s axis.
3. Diurnal libration- This refers to the oscillation because of the rotating earth.

So therefore, Libration causes the Moon to be seen at different angles due to its orbit with respect to the Earth.

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