Light Pollution vs. Technology

Go-To to the Rescue

Before the advent of "go-to" technology, locating particular deep space objects required mastering an often difficult proccess called "star hopping." Novices sometimes wonder why it would be difficult to find such highly magnified objects. That the objects require magnification to be seen at all should be a tip-off. Celestron and Meade hand controllers Nearly all deep space objects (DSOs) are invisible to the unaided eye. From a naked-eye stadpoint they occupy a space no larger than the period at the end of a sentence held at arms length. Move the telescope a fraction of an inch in the wrong direction and you miss the target entirely.

Up until recently the best way to locate astronomical objects involved the use of star charts and finder scopes. A finder is a small, low power refracting scope fixed to the body of the main telescope, pointing in the same direction. The low magnification allows a wider field of view. The user then "hops" from one bright star to the next, gradually closing in on the target.

Most people on the North American continent live around cities or large towns. In recent years light pollution has become so widespread that few inhabitants of most population centers are able to see more than a hundred stars on an average night. During the blackout following California's Northridge earthquake in 1994 police station switchboards were flooded with calls from worried citizens who reported unexplainable lights in the sky. The lights were the milky way-- a sight unfamiliar to most 21st century Americans. With few stars visible, the problem with the star hopping method is obvious. Though still possible in suburban areas, to star hop to a target is no easy task, to say the least. Fortunately there are alternatives.

Manual Setting Circles (right ascension and declination guides)

Whether or not a telescope system has an automated go-to function, nearly every telescope sold on an equatorial mount includes digital setting circles. These are graduated metal disks attached to the right ascension (Right Ascension - RA) and declination (Declination - Dec) axis of the telescope's mount. To better understand right ascension and declination coordinates, envision the earth's lines of longitude and lattitude projected onto a celestial sphere.The right ascension disk (east/west sky motion) is divided into hours, minutes and seconds. The declination disk (north/south sky motion) is divided into degrees, minutes and seconds. The right ascension disk is setting circles driven by a clock device running on sidereal time.

In theory setting circles enable the user to locate deep space objects by their assigned RA & Dec coordinates. But in practice, most setting circles that ship with telescope mounts are cheaply constructed, probably added to enhance the appearance or value of the mount. The numbers engraved or painted on the disks are usually too small to easily read, or they are inacurate. Some of the more expensive mounts, such as the Takahashi product pictured at left, do provide well made manual setting circles. Even so, they seem superfluous since the same mounts nearly always include full "go-to" capability.

Altazimuth Setting Circles ("Push-to" systems)

In recent years so-called "dobsonian" telescopes have become very popular. Actually, these are reflector telescopes. Dobsonian is simply an adjective used to describe a simple and inexpensive lazy-susan type mount with altitude and azimuth motion. John Dobson was the man who popularized these mounts and made them accesible, hence "dobsonian.".