Star hopping
Encyclopedia
Star hopping is a technique that is often used by amateur astronomers
to locate objects in the night sky. It can be used in place of or in conjunction with setting circles
.
of interest are too faint to be visible to the unaided eye. Telescopes
or binoculars
collect much more light, making faint object visible, but have a smaller field of view, thus complicating orientation on the sky.
The field of view of binoculars is rarely more than eight degrees, while that of typical amateur telescopes may be substantially less than one degree, depending on the magnification used. Many objects are best observed using higher magnifications, which inevitably go along with narrow fields of view.
s as a guide to finding fainter objects. A knowledge of the relative positions of bright stars and target objects is essential. After planning the star hop with the aid of a star chart
, the observer first locates one or more bright stars in a finderscope
, reflex sight, or, at a low magnification, with the instrument to be used for observation. The instrument is then moved by one or more increments, possibly using a reticle to identify specific angular distance
s, to follow identified patterns of stars in the sky, until the target object is reached.
Using a telescope equipped with a properly aligned equatorial mount
, the observer may also follow the equatorial coordinate system
on a star map to "hop" or "slide" along the lines of right ascension
or declination
from a well known object to find a target. This can be assisted using setting circles.
Once an instrument is centered on the target object, higher magnifications may be used for observation.
A simple example of star hopping would be finding Messier 13
, a globular cluster
in the constellation Hercules
, which is too faint to be seen by the unaided eye under most conditions. As shown on the star chart, M 13 lies on a line connecting the stars ζ Herculis and η Herculis. Using star hopping techniques an observer would first identify these two by the naked eye and then point an instrument (binocular or telescope) two thirds of the way up from ζ, one third down from η to site M 13. An observer using a telescope equipped with an equatorial mount would pan down from η in declination to site M 13.
Amateur astronomy
Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
to locate objects in the night sky. It can be used in place of or in conjunction with setting circles
Setting circles
Setting circles are used on telescopes equipped with an equatorial mount to find astronomical objects in the sky by their equatorial coordinates often used in star charts or ephemeris.-Description:...
.
The problem
Many celestial objectsAstronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...
of interest are too faint to be visible to the unaided eye. Telescopes
Optical telescope
An optical telescope is a telescope which is used to gather and focus light mainly from the visible part of the electromagnetic spectrum for directly viewing a magnified image for making a photograph, or collecting data through electronic image sensors....
or binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
collect much more light, making faint object visible, but have a smaller field of view, thus complicating orientation on the sky.
The field of view of binoculars is rarely more than eight degrees, while that of typical amateur telescopes may be substantially less than one degree, depending on the magnification used. Many objects are best observed using higher magnifications, which inevitably go along with narrow fields of view.
The technique
Star hopping uses bright starStar
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s as a guide to finding fainter objects. A knowledge of the relative positions of bright stars and target objects is essential. After planning the star hop with the aid of a star chart
Star chart
A star chart is a map of the night sky. Astronomers divide these into grids to use them more easily. They are used to identify and locate astronomical objects such as stars, constellations and galaxies. They have been used for human navigation since time immemorial...
, the observer first locates one or more bright stars in a finderscope
Finderscope
A Finderscope is a small auxiliary telescope mounted atop the main astronomical telescope and pointed in the same direction. The finderscope usually has a much smaller magnification than the main telescope can provide and therefore can see more of the sky. This helps in locating the desired...
, reflex sight, or, at a low magnification, with the instrument to be used for observation. The instrument is then moved by one or more increments, possibly using a reticle to identify specific angular distance
Angular distance
In mathematics and all natural sciences , the angular distance between two point objects, as observed from a location different from either of these objects, is the size of the angle between the two directions originating from...
s, to follow identified patterns of stars in the sky, until the target object is reached.
Using a telescope equipped with a properly aligned equatorial mount
Equatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...
, the observer may also follow the equatorial coordinate system
Equatorial coordinate system
The equatorial coordinate system is a widely-used method of mapping celestial objects. It functions by projecting the Earth's geographic poles and equator onto the celestial sphere. The projection of the Earth's equator onto the celestial sphere is called the celestial equator...
on a star map to "hop" or "slide" along the lines of right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
or declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
from a well known object to find a target. This can be assisted using setting circles.
Once an instrument is centered on the target object, higher magnifications may be used for observation.
Example
Messier 13
Messier 13 or M13 is a globular cluster of about 300,000 stars in the constellation of Hercules....
, a globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...
in the constellation Hercules
Hercules (constellation)
Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
, which is too faint to be seen by the unaided eye under most conditions. As shown on the star chart, M 13 lies on a line connecting the stars ζ Herculis and η Herculis. Using star hopping techniques an observer would first identify these two by the naked eye and then point an instrument (binocular or telescope) two thirds of the way up from ζ, one third down from η to site M 13. An observer using a telescope equipped with an equatorial mount would pan down from η in declination to site M 13.