All the planets, moons, and smaller things in the solar system are just dust, compared to the star that they orbit; the Sun contains 99.9% of the mass of the solar system. We think of it as our source of light, but it doesn't just emit photons. The solar wind blasts fast-moving electrons, protons, and highly ionized atoms in all directions, a constant stream punctuated by ferocious coronal mass ejections. The solar wind carries with it a magnetic field wound into a tight spiral by the Sun's rotation.
The solar wind pushes outward against the interstellar medium, penning the solar system inside a bubble called the "heliosphere" that's at least 200 AU across. The twin Voyager spacecraft are now probing the heliosphere's edges. Closer to home, a fleet of spacecraft monitors the space weather generated by the Sun, warning us of its effects on Earth, from the benevolent (aurorae) to the potentially disastrous (irradiation of astronauts and damage to communications satellites and power grids). Currently operating solar space observatories include ACE, GGS, WIND, Hinode, PICARD, RHESSI, SOHO, SDO, Solar Monitoring Observatory, and STEREO.
Latest Blog Entries about the Sun, Heliosphere, and Space Weather
A reader comment on Jay Pasachoff's post last week about Venus transits viewed from other planets had me asking whether transits of other planets were also interesting to astronomers. Jay provided some answers!
Posted by Emily Lakdawalla on 2011/12/14 09:37 CST
An animation of comet Lovejoy entering the field of view of one of SOHO's Sun-monitoring cameras.
Posted by Bruce Betts on 2014/10/06 01:09 CDT
October 2014 brings big sky fun: a total lunar and partial solar eclipse, both visible from North America. The lunar eclipse will also be visible from most areas around the Pacific Ocean. Here is info on how to observe these eclipses.
A rare astronomical event occurs June 5/6. Find out why you should care and how to observe it.
The Planetary Fund
Help us accelerate progress in our four core enterprises: Robotic Space Exploration, Human Space Exploration, Planetary Defense, and The Search for Life.