Meade 4504 instruction manual Terrestrial Viewing, Astronomical Observing, Polar Alignment

APPENDIX B: Terrestrial Viewing, Celestial Movement, and Polar Alignment

Terrestrial Viewing

The 4504 is an excellent, high-resolution terrestrial (land) telescope. Viewing terrestrial objects requires looking along the Earth's surface through heat waves. These heat waves often cause degradation of image quality. Low power eyepieces, like the H 25mm eyepiece, magnify these heat waves less than higher power eyepieces. Therefore, low power eyepieces provide a steadier, higher quality image. If the image is fuzzy or ill- defined, reduce to a low-power, where the heat waves do not have such an effect on image quality. Observing in early morning hours, before the ground has built up internal heat, produces better viewing conditions than during late-afternoon hours.

Astronomical Observing

Used as an astronomical instrument, your telescope has many optical and electro- mechanical capabilities. It is in astronomical applications where the high level of opti- cal performance is readily visible. The range of observable astronomical objects is, with minor qualification, limited only by the observer’s motivation.

Polar Alignment

Lunar or planetary photography requires that the telescope be Polar aligned. In Polar Alignment, the telescope is oriented so that the horizontal and vertical axes of the tele- scope are lined up with the celestial coordinate system.

In order to understand Polar Alignment, it is essential to have an understanding of how and where to locate celestial objects as they move across the sky. This section pro- vides a basic introduction to the terminology of Polar-aligned astronomy, and includes instructions for finding the celestial pole and for finding objects in the night sky using Declination and Right Ascension.

Understanding Celestial Movements and Coordinates

Understanding where to locate celestial objects and how those objects move across the sky is fundamental to enjoying the hobby of astronomy. Most amateur astronomers adopt the simple practice of “star-hopping” to locate celestial objects by using star charts or astronomical software which identify bright stars and star patterns (constel- lations) that serve as “road maps” and “landmarks” in the sky. These visual reference points guide amateur astronomers in their search for astronomical objects.

Understanding How Astronomical Objects Move

Due to the Earth’s rotation, celestial bodies appear to move from East to West in a curved path through the sky. The path they follow is known as their line of Right Ascension (R.A.). The angle of the path that they follow is known as their line of Declination (Dec). The system of R.A. and Dec is analogous to the Earth-based coor- dinate system of latitude and longitude. Like Earth, imaginary lines have been drawn on the celestial sphere to form a coordinate grid. Celestial object positions on the Earth's surface are specified by their latitude and longitude.

Understanding Celestial Coordinates

Celestial objects are mapped according to the R.A. and Dec coordinate system on the “celestial sphere” (Fig. 31), the imaginary sphere on which all stars appear to be placed. The Poles of the celestial coordinate system are defined as those two points where the Earth's rotational axis, if extended to infinity, North and South, intersect the celestial sphere. Thus, the North Celestial Pole is that point in the sky where an exten- sion of the Earth's axis through the North Pole intersects the celestial sphere. In fact, this point in the sky is located near the North Star, or Polaris.

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