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# Calculator blog

## Astronomy for HP Calculators

Astronomy calculations in RPN/RPL

Recently my son was given a telescope as a gift. It was a beginners' refractor telescope, but at least it had an equatorial mount. I knew that the mod difficult would be to find objects to see. Maps of the sky cover the main constellations (which are static in the sky), but not the planets that are moving all the time. So I set to find some astronomical programs to see what could help us.

At the same time, my son started to look for apps on the IPad that could help as well. I must say that he was much more successful than I. Even with the restriction of free apps, he was able to find a couple of tools to set up a tellscope and find stars.

The first is a tool to set up the telescope. It is called Scope Help, and it assists you in leveling the tripod and orienting the axis to North. It also has a night "red" mode. It also allows you to set the angles to aim for the North pole, based on your actual location and height. I need to explore more in depth, since I am not an astronomy expert in any way. I am here just learning together with my son!

But the real eye-opener is the dynamic sky map. I have learned that there are several available - this is just one of them, and even not the most famous, but at our current knowledge level, it is much more than needed, and enough to keep us occupied for many nights. It is called goskywatchp , and it basically is a map of the sky of where you are currently aiming it. Let me explain it better.

Imagine a screen that uncovers things hidden where you aim it. You just hold your iPad, aim it to the sky area you want, and you see a map of the sky of that area. If you move it slightly, the map moves with you. If you aim the central cursor to a point in the map, the app shows what this object is, and in the case of planets, it shows a picture of it.

The screen shows as well the ecliptic line, which is (I have learned) the projection of the plane where the planets of the solar system lie. It looks as a line since the earth is as well a part of the plane (in a way, we are seeing the plane from within) You need to look to that line to find the planets. (I am very sorry if my inaccurate descriptions are driving mad the astronomy experts among you, but, as I repeat, I am learning)

One amazing thing is that the iPad application does not stop in the horizon line: you can continue down and "see" what you will need many hours to see appearing on the horizon: the planets in the other side of the earth, and even the stars that can only be seen in the Southern hemisphere.

Once seen this iPad application, what is the point of using RPN/RPL software for astronomical purposes? I really see here the advances that we have made over the last years. The amount of calculations required to 1st, calculate an accurate sky map for a given day and time and location, and 2nd, make it rotate according to the fast movements of a gyroscope in a consumer product like the iPad, is mind-boggling.

But anyway, I promised it and here is what I found:

Astronomy
Phases of the Moon
Gravitational n-body Problem
Transformation of Coordinates and Precession
Astronomical Ephemeris
Terrestrial Geodesic Distance
Local Solar Time
Satellites of Jupiter
Saturnian Satellites
Tides
More Accurate Tides
Rising-Transit-Setting
Binary Stars
Calculating a Fix
Nutation - Obliquity of the Ecliptic - Sidereal Time
Astronomical Refraction

Programs for HP 41c family

Programs for HP 48

Programs for HP49/50g

Programming Astronomical data

Astronomy on the HP39g

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