Solar analog (–0.21) for solar twin. 16 Cygni B is sometimes noted as twin, but is part of a triple star system and is very old for a solar twin at over 9 Gyr. Another way of defining solar twin is as a "habstar" — a star with qualities believed to be particularly hospitable to an Earth-like planet. Qualities considered include variability, mass, age, metallicity, and close companions. The requirement that the star remain on the main sequence for at least 3 Ga sets an upper limit of approximately 1.5 solar masses, corresponding to a hottest spectral type of F5 V. Such
Sustain Our Planet analysis and a list of recommendations on how a business might reduce its carbon footprint over time. Sustain Our Planet's Green Schools Program is an online teaching resource for children and educators interested in learning and practicing techniques that help protect the planet. This downloadable teaching resource contains green lesson plans, environmentally themed experiments, and green classroom activities on the carbon cycle, saving energy, recycling, and endangered animals. All content compliments the National Standards set by the US Department of Education for Science, English and Art. Sustain Our Planet Sustain Our Planet is a consulting firm that provides carbon calculation