The green streak of Comet Lulin will be bright and visible in the night sky for the next few days. After reaching the point in its orbit closest to the Sun (the perihelion) back in January, Lulin reached its closest to Earth on February 24th. This point is less than half an astronomical unit from us, meaning less than half the average distance from the Earth to the Sun.

Comet Lulin will be moving quickly across the night sky, so if you stand outside long enough you can see its movement. It will be easy to recognize because of its green color, which is caused by the reflection of the Sun’s rays off the carbon gases in the comet’s Jupiter-sized atmosphere.

Lulin was likely much greener when it was at its perihelion, but at that time it could not be seen with the naked eye. Now, at a position so close to Earth, the comet will likely be able to be seen without a telescope. But if you have trouble, a pair of binoculars or a camera with a good zoom should do the trick.

As seen in the Stony Brook Independent on Thurs. Feb. 26,  2009

Welcome to my blog about binoculars, telescopes, pocket microscopes and monoculars.

I thought the most important thing to post first is some common terminology used (compliments of Carson Binoculars)….so here goes:

Coated Optics
The coatings on  a lens surface which reduces light loss glare due to reflection, which results in a brighter, higher-contrast image and reduces eye strain.

Types of Coatings:
Coated:  single layer on at least one lens
Fully-coated:  A single layer of all air-to-glass surfaces
Multi-coated:  multiple layers on at least one lens and all surfaces at least once
Fully Multi-coated:  Multiple layers on all air-to-glass surfaces

Exit Pupil
Exit pupil refers to the size of the column of light that exits and eyepiece.  The larger the exit pupil, the brighter the image.  To determine the size, divide the objective lens diameter by the magnification.  E.g. a 12 x 36mm binocular has an exit pupil of 3mm.

Eye Relief
The distance an eyepiece can be held away from your eye and still provide a full field of vision.  Extended or long eye relief reduces eyestrain an is what you shold look for if you wear glasses.

Field of View
This is the side-to-side measurement of the circular viewing field.  It’s defined by the width in feet (or meters) of the visible area at 1,000 yards.  Following fast-moving action (such as sporting events) or wildlife, the wider the field of view, the better.  The higher the magnification = a narrower field of view.

Magnification or Power
Binoculars and scopes are referred to by two numbers, with an “x” in the middle, such as 12 x 36mm.  The “12″ is the magnification of the lens, which means the object will appear 12 times closer than you will see it without a binocular/scope.

Objective Lens Size
The second number in the 12 x 36mm (36mm)refers to the diameter of the front lens in millimeters.  The larger the front lens (aka objective lens), the brighter the image because more light is passing through.

Prism Glass
Most optical prisms are made from either borosilicate (BK-7) or barium crown (BAK-4) glass.  BAK-4 is a higher quality glass which yields brighter images and sharper edges.

Prism Systems
Without a prism system, you would see your images upside down when looking through your binoculars or scope.

The two prism systems are:

Roof Prism
The prisms overlap closely, allowing the objective lenses to line up with the eyepiece.  This results in a slim, streamlined shape in which the lenss and prisms that magnify are correct the image, are in a straight line

Porro Prism
The objective or front lens is offset from the eyepiece.  This provides greater depth perception and usually, a wider field of view.

Waterproofing/Fogproofing
Some binoculars/scopes are sealed with o-rings and nitrogen purged for proction, allowing them to withstand total immersion while remaining dry inside.