DSST Astronomy

# Astronomical while this distance is approximate it

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accepted value of the AU is nearly 93 million miles. : Astronomical. While this distance is approximate, it gives a guideline by which other distances can be compared. The ______________ period is the period of revolution of one body about another with respect to the stars. Explanation: Sidereal. By determining the period of revolution (how long it takes to complete one orbit) of the planets around the sun with respect to the stars, the relative distances from the sun could be determined. The apparent period of revolution about the sky with respect to the sun of a planet is called the _____________ period. : Synodic. The synodic period is also the time required for the planet to return to the same configuration again (i.e. the time it requires for the moon to go from full moon to full moon). The determination of both the sidereal and synodic period of a planet is used in calculating the distance of the planet from the sun. The difference between the synodic period and the sidereal period is that the sidereal period is the true time it takes for a planet to complete an orbit, while the synodic period is the time it takes for the planet to complete one orbit from the perspective of an observer on Earth. The sidereal period measures the orbital time from a fixed point in space, while the synodic period measures the orbital time from the perspective of Earth, which is not fixed--the Earth itself is also moving around the sun. By measuring the gravitational influences on other objects or on the stars within them, the _________ of galaxies can be determined. Explanation: Masses. Assuming that Newton's law of gravity is valid over galaxian and extragalactic distances, internal motions in galaxies provide the most reliable methods of measuring their mass. However, this process can only be used in comparatively nearby galaxies. The rotation of the galaxy is observed and then the mass can be computed with the help of Kepler's third law. The _______________ of the stars depend upon the gravitational attraction for them within their galaxy and upon the mass of the star. : Velocity. The velocity of a star consists of both the magnitude and direction of a star's movement and denotes both the speed and direction a body is moving. According to Newton's law of gravity, given a certain amount of gravitational attraction, a massive star will move more slowly than a star with less mass (obviously, a star with less mass will take less force to move).

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Galaxy Types, the Big Bang, the Sun and Moon's effects on the Earth The vast majority of observed ____________ fall into two general classes: spirals and elliptical. Explanation: Galaxies. In addition, a small minority of galaxies are classed as irregular. Our own galaxy (the Milky Way) and M31 (the Andromeda Galaxy) are both typical ______________ galaxies. Explanation: Spiral. A spiral consists of a nucleus, a disk, a corona, and spiral arms. Interstellar material is usually observed in the arms of spiral galaxies and bright emission nebulae are present. Other famous spiral galaxies include M81 - Bodes Galaxy (left image below) and M33 - Traingulum Galaxy (right image):
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