You can usually predict cloud cover several hours in advance using NOAA Satellite Images and NOAA Radar Maps (NOAA is the National Oceanic and Atmospheric Administration). Weather forecasts for our area are available from The National Weather Service.

Sky and Telescope magazine provides a free Java-based sky chart that is very useful in planning your observations.

Of the deep sky objects on this chart, the following Messier Objects are your best bets when viewing in suburban areas in the northern hemisphere: M7, M8, M22, M24, M31, M41, M42, M44, M45 (The Pleiades) and M47. Also good bets are The Hyades and NGC 7000. Southern hemisphere suburban best bets are the Large and Small Magellanic Clouds, NGC 104, NGC 2070, NGC 2516, NGC 3532, NGC 5139 and The Coal Sack. has current information on interesting viewing opportunities.

The best viewing is always in areas far from city lights. You can find dark sky areas using the National Atlas Map Maker. Choose "People", "Population" and click on the "Nighttime Lights" checkbox. Then push the "Redraw Map" button.

Research Links

Images (and a lot of good information!) are available at

In addition, the home page for the Solar Data Analysis Center at NASA Goddard Space Flight Center includes current solar images in a variety of wavelengths.

NASA maintains a great deal of useful information about the Solar System. Information on minor bodies is available from the International Astronomical Union Minor Planet Center.

NASA also provides a wealth of information in

NOAA has a nice glossary of solar-terrestrial terms.

SIMBAD is an extremely useful portal for finding current scientific data on outer space objects. However, you must use accepted nomenclature for it to understand what you want.

Astronomy Answers: Positions in the Sky explains the math used to write programs such as the Sky and Telescope Sky Chart and the Solar System Viewer.

The University of Alaska Fairbanks Geophysical Institute has a good Aurora FAQ.

Universidad Complutense de Madrid maintains a very large list of Libraries of Stellar Spectra.

Lambda, the "Legacy Archive for Microwave Background Data Analysis", is "One Stop Shopping for CMB Researchers".

Our standard choice of parameters is based on the data set labeled "WMAP7+BAO+SNSALT" for the "ΛCDM" model.
Here is a list of elementary particles from the Particle Data Group, who also publishes a review of astrophysical constants.

Here is a Periodic Table from Los Alamos National Laboratory. You can get information about isotopes from NIST, and from The Berkeley Laboratory Isotopes Project's Exploring the Table of Isotopes.

Useful Equations and Constants

All units are assumed to be m, kg, s and K unless otherwise noted.

Astronomical Unit (A.U.)average radius of Earth's orbit1.496 * 1011 m
speed of light (c)299,792,458 meters per second in a vacuum
electron volt (eV)energy scale for electrons1.602 * 10-19 J
Newton's Constant (G)measure of strength of gravitational attraction6.674 * 10-11 N m2/kg2
Hubble Parameter (H0)measure of rate of expansion of the universe69.9 km/s / Mpc
Planck's Constant (h)6.626 * 10-34 kg m2 / s
Boltzmann Constant (k)1.381 * 10-23 J / K
solar luminosity (LS)3.843 * 1026 W
solar mass (MS)1.988 * 1030 kg
parsec (pc)distance to a star whose parallax angle is one arcsecond3.086 * 1016 m = 3.262 ly
solar radius (RS)6.955 * 108 m
Stefan-Boltzmann Constant (σ)measure of strength of blackbody radiation 5.67 * 10-8 W / m2 K4


absolute magnitude (M)the apparent magnitude a star would have at a distance of 10 parsecs
acceleration (a)rate of change of velocitym / s2
Angstrommeasure of very small distances10-10 m
angular momentum (L)measure of how hard it is to change the rotation rate
angular resolutionangle subtending smallest resolvable details
apheliondistance of farthest planetary orbital approach
apogeedistance of farthest lunar orbital approach
apparent magnitude (m)same as apparent brightness; see visual magnitude Δm = 1 ~ Δ brightness = 1001/5
arcsecond1/3600th of a degree
blackbodyan perfect absorber and radiator of thermal radiation
celestial equatorplane of Earth's equator extended into space
centripetal accelerationacceleration responsible for maintaining circular orbits
declination (dec)celestial latitude relative to celestial equatordegrees, minutes, seconds
Doppler Effectdifference between emitted and absorbed frequencies due to relative motion
electromagnetic radiationelectromagnetic waves emitted or absorbed by vibrating charges
electromagnetic waveswaves transporting energy through changing electric and magnetic fields
energy level (n)a positive integer identifying an atomic electron's energy
frequency (ν)number of wave cycles emitted per secondmeasured in Hz
Hertz (Hz)1 Hertz = 1 cycle per second
intensitypower per unit area
Joule (J)measure of energykg m2 / s2
Kelvin (K)measure of temperatureCelsius + 273.15
kilogram (kg)measure of mass2.2 pounds
light-year (ly) the distance light travels in a vacuum in one year 9.461 * 1015 m
luminosity (L)total power output of a star
luminosity classgrouping of stars by absolute magnitude
meteorbright streak that meteoroids make as they burn up in the atmosphere
meteoritea meteoroid that survives the atmosphere to hit the surface
meteoroida small (< 100 m) piece of interplanetary debris; often found along the orbits of comets
meter (m)measure of distance39.37 inches
milliarcseconds (mas)1/1000th of an arcsecond
Newton (N)measure of forcekg m / s2
parallaxapparent change in position over 1/2 of a year
perigeedistance of closest lunar orbital approach
periheliondistance of closest planetary orbital approach
powerenergy per unit timemeasured in Watts (W) = J / s
radianangular measure180 degrees = π radians
red shift (z)measure of cosmological distance
right ascension (RA)celestial longitude relative to sun at vernal equinoxhours, minutes, seconds
spectral classgrouping of stars by coloroften includes luminosity class
Tully-Fisher Lawgalactic rotational velocity = 220000 * luminositysolar0.22, for 22000 Angstrom band
velocity (v)rate of change of distancem / s
visual magnitude (v)logarithmic function of intensity observed in the visual part of the spectrumless for brighter stars
wavelength (λ)distance between successive wave crests

©2012, Kenneth R. Koehler. All Rights Reserved. This document may be freely reproduced provided that this copyright notice is included.

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