We tend to take the Sun for granted, but it’s much more than just our source of light and energy. Once we figured out that the Earth was revolving around the Sun instead of the other way around, we’ve been striving to learn more about this amazing star.
After hundreds of years of observation via the naked eye and telescope, we were finally able to get a closer look when NASA launched the Pioneer space program in the late-Fifties. Pioneer probes 6 through 9 were all designed to orbit the Sun and take measurements about cosmic rays, the magnetic field, the bursts of charged particles known as solar wind, and solar storms. These first probes showed how these phenomena affected Earth’s communications and power.
The Helios probes were the next to visit the Sun. Helios I was launched in 1974 and Helios II just over a year later. Unlike the Pioneer program, which was designed overall to explore various regions of the solar system, the Helios program focused solely on the Sun. In this co-operative mission between NASA and the Federal Republic of Germany, both Helios probes expanded on the data provided by the Pioneer probes, and also performed experiments on magnetic fields and electrical fields.
NASA had initially planned an Apollo mission to observe the Sun, which would use elements from the Apollo Lunar program. The Apollo Telescope Mount (ATM) was a solar observatory that attached to NASA’s first space station, Skylab, when it launched in 1973. The ATM had windmill-like solar panels, which provided power for Skylab as well as its eight telescopes. During Skylab’s tenure in the sky, U V and x-ray telescopes provided the first hi-res photographs of the Sun.
The success of Skylab and the ATM spurred NASA to launch another mission in 1980. The Solar Maximum Mission, or SolarMax, specifically studied solar flares using seven different instruments. These instruments measured ultraviolet, gamma and x-ray radiation emitted by the flares. They also measured the electromagnetic radiation emitted by the Sun overall, known as the solar constant. SolarMax revealed that during the greatest concentration of sunspots, the rest of the Sun actually gets brighter.
Meanwhile, the ESA partnered with NASA to create a reusable research laboratory for use in space. Spacelab was used in more than two dozen missions. Spacelab 2, launched in July 1985, measured the magnetic fields in the photosphere (the visible surface of the Sun). Most importantly, Spacelab 2 took detailed images of the granulation on the Sun’s surface. These small cells on the surface form when the hot liquid inside rises, spreads, cools, and then sinks back into the Sun.
In 1990, NASA launched another probe, Ulysses, which focused on measuring the speed of solar wind and size of magnetic waves around the Sun’s polar regions. The Japanese Space Agency also got into Sun exploration in 1991 when it launched the Yohkoh satellite. Using a different type of x-ray telescope, Yohkoh sent back information about different types of solar flares and dynamic coronal activity. Hinode, the follow-up to Yokoh, launched in 2006 and is observing magnetic fields.
There are numerous on-going observations of the Sun via spacecraft, satellites and telescopes. In 1995, NASA and the ESA launched another spacecraft, the Solar and Heliospheric Observatory (SOHO). While SOHO was designed to further explore the outer layer of the Sun and solar wind, it also probes the Sun’s inner structure. From 1998 to 2010, NASA’s TRACE (Transition Region and Coronal Explorer) satellite provided detailed solar images.
In 2006, NASA launched STEREO (Solar Terrestrial Relations Observatory). Two probes will study how energy and matter flow between the Sun and the Earth and give 3D images of coronal mass ejections. In 2010, NASA launched the Solar Dynamics Observatory (SDO). This craft is studying how the Sun impacts the Earth, through an observation of the solar atmosphere, and how the Sun’s energy is created, stored, and released.
SDO – living with a star
The SDO (Solar Dynamics Observatory) is part of NASA’s Living With a Star program, which studies the relationship between the Sun and the Earth. Its mission is to provide information on the solar atmosphere. It comprises three instruments. The Helioseismic and Magnetic Imager (HMI) studies changes in magnetic solar activity and measures the magnetic field. The Extreme Ultraviolet Variability Experiment (EVE) measures the Sun’s extreme ultraviolet radiation, which heats the Earth’s atmosphere. The Atmospheric Imaging Assembly (AIA) provides the most highly detailed, highest-resolution images of the Sun of any other satellite.
SOHO’s Sun images
Images of the Sun from SOHO come from different instruments on the spacecraft. The EIT (Extreme ultraviolet Imaging Telescope) takes hi-res images of the Sun’s corona in the ultraviolet spectrum, on four different wavelengths. EIT ceased taking images for the most part in July 2010, as the AIA on SDO can take better images. LASCO (Large Angle and Spectrometric Coronagraph Experiment) takes images only of the Sun’s corona by blocking the solar disc, essentially creating an artificial solar eclipse. It features coronal streamers, beams of light extending from areas of high magnetic activity and elongated by solar wind The goal is to learn more about the evolution and activity of the Sun’s corona. MDI (Michelson Doppler Imager) creates images from acoustic data using the Doppler effect. It produces two different types of images: magnetograms are visual representations of changes in the Sun’s magnetic field, while continuums look more like how the Sun appears to us and focus mainly on sunspots.