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Astronomy/Latitude and Longitude of Planets.

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QUESTION: Dear Paul

How to compute Latitude and Longitude of Planets viz Mars, Jupiter, Venus, Saturn etc?.

Thanks
Prashant

ANSWER: Hi Parshant

We can't use latitude and longitude to describe the planets, because as the Earth orbits the Sun, the sky changes a little bit each year in relationship to the coordinates on Earth---and completes that rotation every year.  So a star that could be described as directly overhead (at the zenith) at a specific latitude and longitude on one night will have moved just a bit the next night, and won't return to that location for a year.  All because the Earth itself moves in relationship to the stars as it orbits the Sun.

So astronomers have developed a separate system for describing the positions of the stars.  While it is similar to latitude and longitude, it moves with the stars.  

(Actually, the stars don't move, Earth does.  So in fact the system that astronomers have  developed DOESN'T move, while the Earth slowly spins around the Sun).

This system is called the Celestial Coordinates system, and is based roughly on the same concept at latitude and longitude. But the bases are different.  Instead of latitude based on the Earth's equator, Celestial Coordinates uses "declination" to describe a celestial object in relationship to the Celestial Equator.  And more importantly, instead of longitude, Celestial Coordinates uses  Right Acension to describe a star's position in relationship to the Vernal Equinox--the position of the sun when it crosses the Equator in late March.

Here's a good explanation from UC Berkeley:

http://cse.ssl.berkeley.edu/segwayed/lessons/findplanets/coordinates.html

Hope that helps!

Paul Wagner



---------- FOLLOW-UP ----------

QUESTION: Dear Paul

Thanks.

Can the shape of the other planets influence and contribute to the
Computation of Latitude and Longitude?.

Example -  Earth is Spherical.

Thanks
Prashant

Answer
Hi Prashant

The other planets all have a very small effect on the orbits of each other---Jupiter has the most, and then Saturn.  But these effects are so small that they were never noticed, until extremely careful calculations were made using high powered telescopes.

With your naked eye, you would not notice any difference at all, and neither did the greatest scientist in the world.

As for effects on Earth, a 747 jet flying overhead has more effect on the gravitation of the Earth than any of the planets do....and it's obviously not much!

Hope that helps

Paul Wagner

Astronomy

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Paul Wagner

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Astronomy and telescope making. Have made at least seven telescopes, both refractors and reflectors, and have spent 30 years looking at the nighttime sky.

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