Active optics: A technique for taking into account slowly varying forces such as gravitational deflections and temperature that can distort a mirror and result in imperfect images.

Adaptive optics: A set of techniques used to adjust the telescope mirrors hundreds of times each second to correct for distortions in images due to turbulence in the earth’s atmosphere.

Alt-azimuth: A type of mounting system that uses both up and down and back and forth motion. It does not compensate for the motion of the sky.

Aperture: Diameter of the mirror.

Areal Density: Weight of the primary mirror measured in kilograms divided by the surface area of the primary mirror measured in squared meters.

Axis Factor: Dependent upon whether the system operates in an on-axis or off-axis fashion.

Collimation: The proper alignment of the optical elements in a telescope. It is critical for achieving optimal image quality.

Design Life: On-orbit lifetime measured in months. Design life for ground-based telescopes is limited only when the instruments can no longer meet the science requirements.

Diffraction Limited Telescope: A diffraction-limited telescope has a transmitted wavefront whose root mean square (rms) deviation from ideal is less than 1/14 of the wavelength of light. The shorter the diffraction limited wavelength, the smoother the optics. (Stahl, 2001)

Equatorial: A type of telescope mount that compensates for the motion of the sky.

F-ratio or F-number: Quantifies the brightness of the image produced by the mirror and the size of the image produced. A smaller f-ratio gives a brighter image.

F-ratio=(Focal length)/Diameter (using identical units)

F-ratio=(Radius of Curvature)/(2*Diameter).

Focal length: The distance between the mirror surface and the focus or focal point. Focal length = (Radius of Curvature)/2.

Focus or Focal Point: The point where light reflects off the mirror and converges when light source is effectively an infinite distance away.

Light Collecting Ability (Light Grasp): The theoretical ability to collect light compared to the fully dilated human eye. It is directly proportional to the square of the aperture.

Light Weighting Factor: The percent removed from the primary mirror during mirror fabrication.

Monolithic Mirror: A mirror that is constructed from one solid surface.

Number of Curved Optical Elements: Total number of curved mirrors in a telescope system.

OTA Weight: Weight of the optical telescope assembly measured in kilograms. Does not include mount, yolk, or azimuths.

Operating Temperature: Coldest-operating temperature measured in Kelvin.

Optical Facesheet Material: The material from which the mirror blank is fabricated.

Period of Development: Period of time in months required to fabricate the optical telescope assembly, measured from the date the contract is awarded to completion of fabrication. Does not include time required for testing.

Primary Mirror Diameter: Effective aperture measured in meters.

Radius of Curvature (ROC): Radius of the sphere that would fit inside the mirror. 1^st order approximation of ROC=(2)(f-number)(Diameter)=(2)(Focal length).

Resolving Power: The ability of a telescope to separate two closely spaced binary (double) stars into distinct images, measured in seconds of arc.

Resolving power (arc seconds)=(4.56) / (primary mirror diameter).

Resolving power (radians)=(1.22)(wavelength (cm))/(primary mirror diameter (cm)).

Seeing: Term used by astronomers to describe the atmospheric blurring of stellar images.

Segmented Mirror: A mirror that is made of many smaller pieces or segments.

Strehl Ratio: Measure of how close you are to having 84% of light in the diffraction spot.

Wavefront Error: Two times the surface error.

Wave Number: (2*p)/l; where l is the wavelength of light.

Surface Error: A measure of the surface roughness of the mirror.

Wavelength Diffraction Limited Performance (WDLP): As the wavefront number gets smaller, the optical quality is progressively better. When the size of the geometric optics image is smaller than the ideal Airy disk, the optical system is said to be diffraction limited.

WDLP (microns)= (wavefront error (microns))(14).

Year of Development: Year the telescope development is completed. For space-based telescopes, it is the time when fabrication is completed and testing begins. For ground-based telescopes, it is also known as first light.

Coefficient of Determination (R²): The proportion of variability in the Y variable accounted for by the predictors. (Minitab User's Guide, 2000, 2-11)

Cook's Distance: Combines leverages and studentized residuals into one overall measure of how unusual the predictor values and response are for each observation. Values greater then F (.5,p, n-p) are considered unusual. Note that F is a value for an F-distribution. (Minitab User's Guide, 2000, 2-9)

DFITS: The difference between the fitted values calculated with and without the i^th observation scaled by standard deviation. DFITS>2 are considered unusual. (Minitab User's Guide, 2000, 2-9)

Leverages: The diagonals of the "hat" matrix Indicate "outliers" in the X (predictors). Leverages greater than 2p/n (where p is the number of predictors including the constant) are considered unusual. (Minitab User's Guide, 2000, 2-9)

Residual: The difference in the actual and predicted value. Residual=actual-predicted.

Standardized Residual: Residual/standard deviation of the residual. Where the standard deviation of the residual is calculated by:

standard deviation (residual) =

A standardized residual greater than 2 is generally considered large. Used as a guide to identify observations that are not well fit by the model. (Minitab User's Guide, 2000, 2-5)

Studentized Residual: residual/standard deviation of the residual. The i^th studentized residual is calculated with the i^th observation removed. A large studentized residual may indicate that the observation had a large affect on the parameter estimated or that including the observation increases the error variance. (Minitab User's Guide, 2000, 2-6)

Sample Size (n): The number of data points used in the analysis, for this project it is the number of telescopes.

Power Model: A model of the format Y=a*X^b. This is called a power model since the relationship between X and Y is such that Y is a multiple of X raised to some power, b.

P-Value (p): The p-value is the observed significance of a test of hypothesis. The p-value measures the probability of getting a data set like the one obtained or one more extreme (in the direction of the alternative) given that the null hypothesis is true.

Sample Correlation Coefficient (r): The sample correlation coefficient also called Pearson's correlation coefficient tells the strength of the linear association between two variables.