Archive for the ‘Astrophotography’ Category


Aperture is the diameter of the main lens or mirror of a telescope in inches or cm.

The larger the aperture, the greater the light grasp and resolving power. Optical instruments with a larger aperture can therfore see fainter objects and separate more closely spaced objects.

The effective aperture of a reflecting telescope is reduced by the secondary mirror. Size for size therefore, a refracting telescope is better.


The angle measured from the south point of the horizon toward the west to a point at the foot of a star’s vertical circle. When used as an indication of the position of a star on the imaginary celestial sphere it is referred to as Right Ascension.

Bailey’s Beads

Brilliant points of light along the edge of the moon disc, just at the start or the end of totality of a total solar eclipse.When caught on camera they are spectacular and can give the diamond ring effect.

They are caused by the irregularities at the edge of the Moon’s disc when seen from Earth. These irregularities are in fact the hills and valleys of the Moon. It is the valleys that allow the light from the Sun to reach the observer when the Moon obscures the Sun.


How to observe eclipses

Barlow Lens

Put a Barlow lens between the main mirror or lens of your telescope and its eyepiece and increase the magnification. Effectively it increases the focal length of the main mirror or lens. The most usual magnification for a Barlow lens is X2. In practice, they are rarely used since they cause a large light loss in the telescope. It is a cheap way of getting a short focal length eyepiece. Better to spend more on an eyepiece, you get better quality.

Blue Shift

If an astronomical body is moving towards the observer, the light will seem to be shifted to the blue end of the spectrum. The faster the movement, the greater the blue shift. It occurs because the wavelength of light is slightly compressed by the Doppler effect as the body moves towards the observer. Blue shift is measured by looking at the key spectral lines. For an object moving towards the Solar System, they will appear closer to the blue end than normal. The faster the object is approaching, the greater the blue shift will be.


An extremely bright meteor, also called a fireball.

Celestial Latitude

The angle north or south of the ecliptic to an object. Used to help to describe the location of a star on the imaginary celestial sphere.

Celestial Longitude

The angle that is measured eastward along the ecliptic, from the vernal equinox, to the foot of a circle that is perpendicular to the ecliptic and passing through the object.

Celestial Sphere

This does not actually exist. Early humans believed that stars were fixed to a crystal sphere in the sky, at a great distance from Earth. This is because there is no sense of distance in the night sky and the stars always seemed to be fixed in position relative to each other. The idea is a handy one when dealing with positioning and angles between objects in the sky. See also celestial latitude, longitude, azimuth.

The Analemma

In everyday language, an analemma is the base of a sundial but in astronomical terms it means the angular offset of an astronomical body from its mean position.

When astronomers refer to the analemma, they are normally referring to that of the Sun.

If you take a picture of the Sun at the same time each week, from exactly the same position, on a single frame of film, the figure of eight shape that results is called the analemma. It takes patience and dedication to take a photograph of the analemma.

Wikipedia article

Switch to our mobile site