RA Dial

[Philosophaie]

RA or Right Ascension is measured in hours (also may be converted into degrees by multiplying by 15). Ra is the angle around the Equator. It starts at the Vernal Equinox on March 21 at 0 then counts around the Earth.

My question is what does the RA dial do? I know the telescope moves when you twist the RA adjustment rod and over time it makes an arcing motion. How does it follow the motion of the planets, stars, nebulas, etc?

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Sky-W

Sky-Watcher 130mm EQ2 Reflector Telescope

-130mm EQ2 Reflector Telescope130mm (5.1 inch) diameter primary mirror made from grade-A glass and multi-coated for optimal reflection

-900mm focal length, f/6.9

-20.4 sq. in. light grasp

-307x maximum theoretical magnification and 1.08 arc-sec resolving power

-High-quality super Plossl fully-coated 25mm and 12mm 1.25” eyepieces provide clear, sharp images at magnification of 36x and 75x with a 52° apparent field-of-view and great eye relief

-1.25” 2x Barlow lens doubles magnification of the included eyepieces to 72x and 150x for up-close planetary and lunar viewing

-Red-dot finderscope with variable brightness makes locating night-sky objects easy

-Stable 1.25" rack-and-pinion focuser

-EQ-2 equatorial mount provides proper stability with dual slow-motion controls, 360° azimuth adjustment

-130mm (5.1 inch) diameter primary mirror made from grade-A glass and multi-coated for optimal reflection

-900mm focal length, f/6.9

-20.4 sq. in. light grasp

-307x maximum theoretical magnification and 1.08 arc-sec resolving power

-High-quality super Plossl fully-coated 25mm and 12mm 1.25” eyepieces provide clear, sharp images at magnification of 36x and 75x with a 52° apparent field-of-view and great eye relief

-1.25” 2x Barlow lens doubles magnification of the included eyepieces to 72x and 150x for up-close planetary and lunar viewing

-Red-dot finderscope with variable brightness makes locating night-sky objects easy

-Stable 1.25" rack-and-pinion focuser

-EQ-2 equatorial mount provides proper stability with dual slow-motion controls, 360° azimuth adjustment

[Cornelius Varley]

The RA dial together with the Dec axis dial help you find objects in the sky. Stars, galaxies etc have fixed coordinates measured as right ascension and declination. To find on oject in the sky using the setting circles, first align the telescope on an object of known RA and DEC and adjust the RA dial to suit. The mount can now be slewed to the new coordinates noting the rotation of the RA and DEC dials. How to use setting circles video

Peter

[Capricorn]

RA is time.

It is the time at which the object will be on 0 deg latitude.

What you do is set the dial to your Local Siderial Time, LST, this is then your offset.

I suspect that the RA dial has to be rotated to match the local time as well.

With the 2, (3?) you can point your scope at an object.

If you have set your LST then you rotate the scope to the RA value of the object.

Then you must do the same with the Dec.

It is a number system that uses hours, minutes and seconds instead of degrees, minutes and seconds.

As everything is in hours/mins/sec no need to try and convert. Stop thinking in degrees.

By the way, never used it and this is what I think it does, If utterly wrong then sorry.

[Philosophaie]

The LST is dependent on:

Date and Time

UTC time difference from Greenwich

local Latitude and local Longitude.

I can calculate LST, RA and Dec due to these parameters.

I just need to know how to how to dial them into the RA and Dec dials so I can view the stars more effectively.

[gareththegeek]

I usually point my scope at a bright star that I know the coordinates of then set the RA and Dec wheels to match these coordinates. Then you can use them to find other objects with known coordinates.

The RA dial usually has more than one line to read the RA off against. These are usually spaced out every ten minutes or some such. If you calibrate the RA at midnight, for example, and are trying to find something using RA dial at ten past you use the ten minute line instead of the zero line.

[Philosophaie]

If I calibrate to North Pole Declination do you need to set the RA as well as DEC?

I will make sure DEC dial set at 89.3deg and the RA dial at 2.7hr. Is this correct for 8-7-10?

Then I will loosen the DEC bolt on the bottom and find Polaris tightening it when in center view keeping the dial settings the same.

I will then have my telescope calibrated unless I move it to a different Latitude?

[gareththegeek]

I find that my mount's setting circles do not hold calibration well and must be calibrated each session, sometimes more than once so I do not worry about my particular longitude/latitude when setting RA. As I said I just point at a bright object with known coordinates and set RA to whatever it read in Stellarium. Since I will recalibrate next session it doesn't matter what the absolute value of RA is, just its relative values when going from one object to another.