# Horizontal Parallax Correction

1. Aug 13, 2012

### Philosophaie

Parallax is a way of measuring the distance of one object to another.

By taking the distance of an already known object, say the Sun, and drawing a line to the object.

Then drawing another line between you and the object in question.

The angle you get is the Horizontal Parallax angle.

Using the Trigonometric Identities the distances will present themselves.

My question is where is the error coming from that why would need to correct it?

2. Aug 14, 2012

### Simon Bridge

Which error are you talking about?
Note - you need two angles if you only know one distance - you usually do this by moving the observer.

There are uncertainties in each measurement you make, and an uncertainty on the original measurement of the baseline (Earth-Sun, in your example). This what you mean?

3. Aug 14, 2012

### Philosophaie

There is an uncertainty in each measurement which can be calculated. I could give you the formulas if you would like. If you know the Geocentric Latitude, the Equatorial distance, the horizontal parallax, the Hour Angle and the Declination you can find the delta of the Right Ascension due to the Horizontal Parallax. Also using the previous quantities you can find the total Declination corrected for Horizontal Parallax. Can anyone help me to explain why there is such an error.