Units of measurement

• Guide for the Use of the International System of Units
• Section B.8 of that publication lists all the conversion factors you would ever need between related SI units, and between SI units and other measurement systems, including British/American.

Observational Astronomy

See Astronomy Links @ wx.awcolley.com

Space Missions

In Development

• James Webb Space Telescope (Hubble follow-on) • Building 29 clean-room webcam

Ongoing

• ACE — Advanced Composition Explorer
• Cassini-Huygens — mission to Saturn and Titan
• Herschel Space Observatory (ESA) • NASA • CalTech
• Hubble Space Telescope — not physically traveling through the solar system, but looking toward the edge of the universe!
• Mars Reconnaissance Orbiter — detailed views of the nearby red planet
• Mars Rovers — Spirit and Opportunity continue to provide incredible views of the Martian landscape.
• Planck (ESA) • Spacecraft Ops • Science Team
• SOHO — Solar and Heliospheric Observatory
• Voyager — the granddaddy of space missions, Voyager 1 was launched on the morning of 05 September 1977 and has traveled farther than anyone, or anything, in history (about 12 billion miles by September 2013). In September 2012, Voyager 1 crossed over into interstellar space. Voyager I continues to move away at more than 38000 miles/hour (61290 km/hour), which is 17 miles every second!
• WMAP — Wilkinson Microwave Anisotropy Probe

Completed

• Deep Impact — the headline: Man Hits Comet
• Genesis "Search for Origins"
• Stardust — through the tail of a comet and home again, the rest of this spacecraft was sent on to return to Comet Tempel (Deep Impact) hoping to get a good view of the man-made crater in 2011 (but didn't make it)
• Ulysses — traveling where no man-made object has gone before, in an orbit perpendicular to the plane of the planetary orbits, over the north and south poles of the Sun

Earth Observations

• NASA Earth Observatory
  • Blue Marble Next Generation
  • The Black Marble: Earth at Night 2012 • Global Views • Out of the Blue and Into the Black
• MODIS Mission • IOTD • Rapidfire • Rapidfire Image Gallery • MODIS Today
• CloudSat — a satellite conceived and monitored by my alma mater, Colorado State University, to provide 3d radar views of clouds
• SeaWinds on QuickSCAT — measuring the winds on the 75% of this planet that man cannot live on
• Earth Observing System — all of NASA’s programs studying Earth
• Visible Earth — NASA’s photo gallery of Earth, including from manned space missions

Cool videos

• What if Earth had rings like Saturn
• The Known Universe — scaling out from the Himalayas to the fringes of the observable universe
• The Geostationary Highway

Reference Data

• NIST Reference on Constants, Units, and Uncertainties
• The Photographic Periodic Table – The Wooden Periodic Table
• Dynamic Periodic Table

DIY Experiments

• Cellphone Spectrometer

Geoid

• GOCE High Precision Geoid

Earthquakes and Tectonics

• USGS – Recent Earthquakes

General Reference

• Wolfram's MathWorld — the web's most extensive mathematical resource, from Wolfram Research, makers of Mathematica.
• Handbook of Mathematical Functions (also contains physical constants; sadly, actual function value tables are omitted)
• NIST's Digital Library of Mathematical Functions (an update to the original Handbook above)

Logics

• Introduction to Logic

Various Topics

• Back-of-the-Envelope — "pages about approximation", includes "a million dots on one page" ◊ Your Body Ruler ◊ Measuring Angle and Distance with Your Thumb
• Karl's Calculus Tutor — more than just calculus (e.g. how to measure the radius of the earth, the Gaussian Elimination Demo)

Open Source Software

• The R Project for Statistical Computing
• ROOT: A Data Processing Framework

Online Calculators, Evaluators, Solvers, and Generators

• Good Calculators Online
• Sage — Open Source Mathematics Software (some features also provided online)
• Quick Math — an online calculator that solves equations and does all sorts of algebra and calculus problems
• Online Prime Factorization (9 digits)
• Online Prime Factorization (9.5 digits)
• Gaussian Elimination Demo (up to 7 equations)

Constants, Symbols, and Notation

• Table of Mathematical Symbols
• Mathematical Constants, to 50 decimal places
• Pi to 1,000,000 places (the actual page within that site keeps moving)
• Notation for intervals