Celestron 91510 instruction manual Polar Alignment

Page 10

The celestial meridians of longitude are called "coordinates of right ascension (R.A.)", and like the Earth's longitude meridians they extend from pole to pole. There are 24 major RA. coordinates, evenly spaced around the 360º equator, one every 15º. Like the Earth's longitudes, R.A. coordinates are a measure of time as well as angular distance. We speak of the Earth's major longitude meridians as being separated by one hour of time because the Earth rotates once every 24 hours (one hour = 15°). The same principle applies to celestial longitudes since the celestial sphere appears to rotate once every 24 hours. Right ascension hours are also divided into minutes of arc and seconds of arc, with each hour having 60 minutes of arc and each arc minute being divided into 60 arc seconds.

Figure 5

Astronomers prefer the time designation for R.A. coordinates even though the coordinates denote locations on the celestial sphere, because this makes it easier to tell how long it will be before a particular star will cross a particular north-south line in the sky. So, R.A. coordinates are marked off in units of time eastward from an arbitrary point on the celestial equator in the constellation Pisces. The prime R.A. coordinate which passes through this point is designated "O hours O minutes O seconds". We call this reference point the vernal equinox where it crosses the celestial equator. All other coordinates are names for the number of hours, minutes and seconds that they lag behind this coordinate after it passes overhead moving westward.

Given the celestial coordinate system, it now becomes possible to find celestial objects by translating their celestial coordinates using telescope pointing positions. For this you use setting circles for R.A. and Dec. to find celestial coordinates for stellar objects which are given in star charts and reference books.

Polar Alignment

Polar alignment is the process by which the telescope’s axis of rotation is aligned (made parallel) with the Earth’s axis of rotation (see figure 7). Once aligned, a telescope with a motor drive will track the stars as they move across the sky. The result is that objects being observed through the telescope appear stationary (i.e., they will not drift out of the field of view). If your telescope does not use a motor drive, all celestial objects in the sky (day or night) will slowly drift out of the field. This motion is caused by the Earth’s rotation. Even if you are not using a motor drive, polar alignment is still desirable since it will reduce the number of corrections needed to follow an object and limit all corrections to one axis (R.A.). There are several methods of polar alignment, all of which work on a similar principle, but are performed somewhat differently.

For each hemisphere, there is a point in the sky around which all the other stars appear to rotate. These points are called the celestial poles and are named for the hemisphere in which they reside. For example, in the northern hemisphere all stars appear to move around the north celestial pole (see figure 6). When the telescope’s polar axis is pointed at the celestial pole, it is parallel to the Earth’s rotational axis.

Many of the methods of polar alignment require that you know how to find the celestial pole by identifying stars in the area. For those in the northern hemisphere, finding the celestial pole is not difficult. Fortunately, we have a naked eye star less than a degree away. This star, Polaris, is the end star in the handle of the Little Dipper. Since the Little Dipper (technically called Ursa Minor) is not one of the brightest constellations in the sky, it may be difficult to locate, especially from urban areas. If this is the case, use the two end stars in the bowl of the Big Dipper. Draw an imaginary line through them toward the Little Dipper. They will point to Polaris. The position of the Big

10

Image 10
Contents Models #21077 / #21016 / #31027 / #31056 / #91510 Identifying Parts of Figure C80-HD & C102-HDC114-HD & C150-HD CG-4 EQ MountSetting Up the Tripod IntroductionInstalling the Counterweights Installing the Counterweight BarAttaching the Optical Tube Balancing the Telescope Scope is properly balanced in right ascensionAttaching the Finderscope for #21077, #21016 & #31056 Attaching the Finderscope for #31027Attaching the Accessories Aligning the FinderscopeCalculating Magnification Celestial Coordinate SystemPolar Alignment Page Aligning the R.A. Setting Circle Using the R.A. Vernier Scale Telescope Maintenance Collimation for the #31027 and #31056 only#21016 C80-HD #21077 C102-HDC150-HD #31056Page Celestron TWO Year Warranty

91510 specifications

The Celestron 91510 is a remarkable telescope that offers astronomy enthusiasts a blend of quality, portability, and advanced features, making it a popular choice for both beginners and seasoned stargazers alike. Known for its impressive optics, the Celestron 91510 utilizes a 70mm refractor design that provides bright and clear images, ideal for observing celestial objects such as planets, stars, and deep-sky phenomena.

One of the standout features of the Celestron 91510 is its fully coated optics, which enhance light transmission and improve image quality. This ensures that users can observe fine details in celestial bodies, such as the rings of Saturn or the craters on the Moon. The telescope comes with two eyepieces of different focal lengths, allowing for varying magnification. This versatility enables users to explore the night sky with ease, offering both wide-field views of star clusters and higher magnification for detailed observations.

Portability is another significant advantage of the Celestron 91510. Designed with travel in mind, this telescope is lightweight and compact, making it easy to set up and transport. It features a sturdy yet portable mount that provides stable support during observations. The pan-and-tilt head allows for smooth tracking of celestial objects, ensuring that users can focus on their targets without hassle.

Moreover, the telescope includes a red dot finder which aids in locating objects quickly in the night sky. This user-friendly feature is especially beneficial for beginners who may find it challenging to navigate the stars. The adjustable tripod provides a stable base and can be set to various heights, ensuring comfort during extended viewing sessions.

Celestron's commitment to quality and innovation is evident in the design of the 91510. It incorporates durable materials that withstand the rigors of outdoor use, ensuring longevity. Additionally, the telescope's overall aesthetic appeal, complete with a sleek design, adds to the enjoyment of using this astronomical instrument.

In summary, the Celestron 91510 is an excellent choice for anyone looking to delve into the wonders of astronomy. With its high-quality optics, user-friendly features, and portability, it offers an enjoyable stargazing experience. Whether you are a novice wanting to explore the cosmos or an experienced astronomer seeking a reliable companion, the Celestron 91510 stands out as an exceptional option.