Henrietta Swan Leavitt

The parallax method used to measure the distances to nearby stars, pioneered by Bessel and others could only be used on stars closer than 100 light years away.  But most stars and other galaxies are far beyond that distance. The key for finding the distance to stars much further away was discovered by Henrietta Swan Leavitt who worked at Harvard College Observatory as a “computer,” one of several women paid 25 to 30 cents per hour to extract data from thousands of photographic plates.

Unfortunately stars are not the same intrinsic brightness (or luminosity), so it is impossible to tell if a star appears dim because it’s far away, or because it doesn’t put out much light. The key for finding the distance to stars was discovered by Henrietta Swan Leavitt who worked at Harvard College Observatory as a “computer,” one of several women paid 25 to 30 cents per hour to take data from thousands of photographic plates.

Leavitt’s assignment was to identify variable stars, which are stars that change in brightness over a few hours, days, or weeks. To do this she would compare two photos of a star field taken a few days or weeks apart. She used an instrument called a blink comparator that flips back and forth quickly between the two images so that a variable star shows up as a flashing spot. With this method she found more than 2,400 variable stars.

Leavitt became curious about whether there might be a relationship between the brightness of a variable star and the length of its period (how long it takes for the star to get brighter, dimmer, then brighter again). That was difficult because she did not know the intrinsic brightness of any given variable. She solved the problem by restricting her search to a particular kind of variable star known as Cepheid variables that reside in the Small Magellanic Cloud—a distant star cluster. She reasoned that all stars in the cluster must be approximately the same distance from Earth.

Her hunch paid off. Leavitt discovered 25 Cepheid variables in the cluster and created a graph showing the maximum brightness of each star and the length of its period. As she suspected, there was a clear relationship. Brighter stars had longer periods. All that was needed to find actual distances was to find the distance to just one nearby Cepheid variable. A few years later a team of astronomers did just that, making it possible to measure the distance to any Cepheid.

Image Credit: Dana Berry/NASA

On August 24th at 12:17 UT, NASA’s Solar Dynamics Observatory recorded this M5.6-category explosion near the eastern limb of the sun.

The source of the blast was sunspot AR2151. As the movie shows, an instability in the suspot’s magnetic canopy hurled a dense plume of plasma into space. If that plasma cloud were to hit Earth, the likely result would be strong geomagnetic storms. However, because of the sunspot’s location near the edge of the solar disk, Earth was not in the line of fire.

Even so, the flare did produce some Earth effects. A pulse of extreme UV radiation from the explosion partially ionized our planet’s upper atmosphere, resulting in a Sudden Ionospheric Disturbance (SID). Waves of ionization altered the normal propagation of VLF (very low frequency) radio transmissions over the the dayside of Earth, an effect recorded at the Polarlightcenter in Lofoten, Norway: data.

Credit: NASA/SDO

Planets of Our Solar System

Our solar system officially has eight planets and one star: the Sun. The discovery of an object larger than Pluto in 2005 rekindled the debate over whether such objects, belonging to the Kuiper Belt – a collection of icy bodies located beyond Neptune – should be called planets. Pluto and other large members of the Kuiper Belt are now considered “dwarf planets.”

Planet facts: space-facts.com

Our Sun constantly emits plasma which moves out in all directions at very high speeds and fills the entire solar system. The complex interaction between the Sun’s plasma atmosphere and its magnetic field gives rise to a wide range of fascinating and spectacular phenomena. The fluctuation of the sun’s magnetic fields can cause a large portion of the outer atmosphere to expand rapidly, spewing a tremendous amount of particles into space. These large eruptions of magnetized plasma are called coronal mass ejections. CMEs are the most spectacular and potentially harmful manifestations of solar activity. Some of these eruptive events accelerate particles to very high energies, high enough to penetrate a space suit or the hull of a spacecraft and can cause severe disturbances in the geospace environment when they encounter Earth’s magnetic field. However, only about 1% of the CMEs produce strong SEP (solar energetic particles) events. 

Credit: NASA/SDO/Duberstein

Propylene on Titan

With a thick atmosphere, clouds, a rain cycle and giant lakes, Saturn’s large moon Titan is a surprisingly Earthlike place. But unlike on Earth, Titan’s surface is far too cold for liquid water - instead, Titan’s clouds, rain, and lakes consist of liquid hydrocarbons like methane and ethane (which exist as gases here on Earth). When these hydrocarbons evaporate and encounter ultraviolet radiation in Titan’s upper atmosphere, some of the molecules are broken apart and reassembled into longer hydrocarbons like ethylene and propane.

NASA’s Voyager 1 spacecraft first revealed the presence of several species of atmospheric hydrocarbons when it flew by Titan in 1980, but one molecule was curiously missing - propylene, the main ingredient in plastic number 5. Now, thanks to NASA’s Cassini spacecraft, scientists have detected propylene on Titan for the first time, solving a long-standing mystery about the solar system’s most Earthlike moon.

NASA PlanetaryScientist Conor Nixon explains his discovery of propylene on Titan, Saturn’s largest moon. Scientists have known about the presence of atmospheric hydrocarbons on Titan since Voyager 1 flew by in 1980, but one molecule, propylene, was curiously missing. Now, thanks to new data from NASA’s Cassini spacecraft, propylene has been detected for the first time on Titan.

Credit: NASA’s Goddard Space Flight Center

Millisecond Pulsars

As the name suggestions, millisecond pulsars have pulse periods that are in the range from one to ten milliseconds. Most such millisecond pulsars are found in binary systems, typically with white-dwarf companions. These pulsars are highly magnetized, old neutron stars in binary systems which have been spun up to high rotational frequencies by accumulating mass and angular momentum from a companion star. Neutron stars form when a massive star explodes at the end of its life and leaves behind a super-dense, spinning ball of neutrons. A pulsar is the same thing as a neutron star, but with one added feature. Pulsars emit lighthouse-like beams of x-ray and radio waves that rapidly sweep through space as the object spins on its axis. Most pulsars rotate just a few times per second, but some spin hundreds of times faster. These millisecond pulsars are the fastest-rotating stars we know of.

  • To hear the sound of a pulsar, click here

Credit: NASA

Soft X-ray Emissions from Charge Exchange in the Heliosphere

The solar wind originates in the sun’s corona, the hottest part of its atmosphere, so its atoms have been ionized, stripped of many of their electrons. When these particles collide with a neutral atom, one of its electrons often jumps to the solar wind ion. Once captured, the electron briefly remains in an excited state, then emits a soft X-ray and settles down at a lower energy. X-rays with photon energies above 5–10 keV (below 0.2–0.1 nm wavelength) are called hard X-rays, while those with lower energy are called soft X-rays.

Credit: NASA’s Goddard Space Flight Center

Helioseismology: seismology of the Sun

The Sun oscillates and vibrates at many frequencies, like an ocean surface or …like a bell. Certain frequencies are amplified by constructive interference(wave propagation) and the turbulence “rings” the sun like a bell. Unfortunately, sound does not carry through the vacuum between the Sun and the earth, so we have to “listen" to the oscillations by looking at the motions of material on the surface of the Sun. With the right instruments, scientists can "hear" this ringing or pulsations from the Sun. To do this, they use an instrument called a Michelson Doppler Imager (MDI), mounted on the SOHO spacecraft and the Helioseismic and Magnetic Imager (HMI), one of the three instruments that make up the Solar Dynamics Observatory (SDO).

Although direct study of its interior is impossible —mostly because the Sun is nearly opaque to electromagnetic energy, insights into the conditions within the Sun may be gained by observing oscillating waves, rhythmic inward and outward motions of its visible surface. These oscillations on the surface are due to sound waves generated and trapped inside the sun. Sound waves are produced by pressure fluctuations in the turbulent convective motions of the sun’s interior. These trapped sound waves set the sun vibrating in millions of different patterns or modes. Using this acoustic energy, we can “see into the Sun”, just as geologists use seismic waves to study the structure of the Earth, the discipline of helioseismology makes use of acoustic pressure waves (infrasound) traversing the Sun’s interior. These oscillations are seen as volumes of gas called granules near the Sun’s surface that rise and fall with a particular frequency. It is like seeing the rolling motions of convection cells on the surface of  boiling water. This happens very close to the surface where the flow of energy that started in the nuclear reactions in the core reaches the surface and suddenly escapes. The sound from the convection is then trapped and filtered inside the sun to produce the solar music

Helioseismologists can use the properties of these waves to determine the temperature, density, composition, and motion of the interior of the sun. The spectral lines emitted from gas moving upwards will be slightly Doppler-shifted to the blue; spectral lines from gas moving downwards will be slightly Doppler-shifted to the red. In this way the rolling motions of convection near the Sun’s surface can be mapped out. There are three types of oscillations. Pressure modes (p-modes) are sound waves trapped in the temperature gradient (like an echo bouncing around inside a cavern). Fundamental modes (f-modes) or surface gravity waves are caused by gravitational interactions with the sun’s surface and resemble ocean waves. Gravity modes (g-modes) are not completely understood, but they are believed to be the result of buoyancy effects. All the known pressure and fundamental modes (some 10 million) have oscillation periods of less than 18 minutes, and most are around 5 minutes. The gravity modes are not known conclusively to exist, but they are predicted to have periods of 40 minutes or longer (160-min).

Further readings:

As Seen by STEREO-A: The Carrington-Class CME of 2012

STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission, it consists of two space-based observatories - one ahead of Earth in its orbit (STEREO-A), the other trailing behind (STEREO-B). The two nearly identical spacecraft were launched in 2006 into orbits around the Sun that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.

STEREO-A, at a position along Earth’s orbit where it has an unobstructed view of the far side of the Sun, could clearly observe possibly the most powerful coronal mass ejection (CME) of solar cyle 24 on July 23, 2012. The flare erupted in the lower right quadrant of the solar disk from a large active region. The material launched into space in a direction towards STEREO-A. This created the ring-like ‘halo’ CME visible in the STEREO-A coronagraph, COR-2 (blue circular image). As the CME expanded beyond the field of view of the COR-2 imager, the high energy particles reached STEREO-A, and caused the snow-like noise in the image. Researchers have been analyzing the data ever since, and they have concluded that the storm was one of the strongest in recorded history. It might have been stronger than the Carrington Event itself.

The solar storm of 1859, also known as the Carrington Event, was a powerful geomagnetic solar storm in 1859 during solar cycle 10. A solar flare or coronal mass ejection hit Earth’s magnetosphere and induced the largest known solar storm, which was observed and recorded by Richard C. Carrington. The intense geomagnetic storm caused global telegraph lines to spark, setting fire to some telegraph offices and disabling the ‘Victorian Internet.” A similar storm today could have a catastrophic effect on modern power grids and telecommunication networks.

Credit: NASA’s Scientific Visualization Studio

Jupiter’s Irregular Satellites

The planet Jupiter has 67 confirmed moons. This gives it the largest retinue of moons with “reasonably secure” orbits of any planet in the Solar System. In fact, Jupiter and its moons are like a miniature solar system with the inner moons orbiting faster than the others. Eight of Jupiter’s moons are regular satellites, with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter’s equatorial plane. The remainder of Jupiter’s moons are irregular satellites, whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were probably captured by Jupiter from solar orbits. There are 17 recently discovered irregular satellites that have not yet been named.

Image Credit: NASA/ESA/Lowell Observatory/J. Spencer/JHU-APL

Jupiter’s Irregular Satellites

The planet Jupiter has 67 confirmed moons. This gives it the largest retinue of moons with “reasonably secure” orbits of any planet in the Solar System. In fact, Jupiter and its moons are like a miniature solar system with the inner moons orbiting faster than the others. Eight of Jupiter’s moons are regular satellites, with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter’s equatorial plane. The remainder of Jupiter’s moons are irregular satellites, whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were probably captured by Jupiter from solar orbits. There are 17 recently discovered irregular satellites that have not yet been named.

Image Credit: NASA/ESA/Lowell Observatory/J. Spencer/JHU-APL

Quick Rosetta update:

This is the shape model of comet 67P/Churyumov-Gerasimenko. From the images taken on 14 July, the OSIRIS team has begun modelling the comet’s three-dimensional shape. The animated gif presented here covers one full rotation of the nucleus around its spin axis, to emphasise the lobate structure of the comet. This model will be refined as more data becomes available – it is still a preliminary shape model and some features may be artefacts.

More information: here
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Quick Rosetta update:

This is the shape model of comet 67P/Churyumov-Gerasimenko. From the images taken on 14 July, the OSIRIS team has begun modelling the comet’s three-dimensional shape. The animated gif presented here covers one full rotation of the nucleus around its spin axis, to emphasise the lobate structure of the comet. This model will be refined as more data becomes available – it is still a preliminary shape model and some features may be artefacts.

  • More information: here

Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Animations of Saturn’s aurorae

Earth isn’t the only planet in the solar system with spectacular light shows. Both Jupiter and Saturn have magnetic fields much stronger than Earth’s. Auroras also have been observed on the surfaces of Venus, Mars and even on moons (e.g. Io, Europa, and Ganymede). The auroras on Saturn are created when solar wind particles are channeled into the planet’s magnetic field toward its poles, where they interact with electrically charged gas (plasma) in the upper atmosphere and emit light. Aurora features on Saturn can also be caused by electromagnetic waves generated when its moons move through the plasma that fills the planet’s magnetosphere.  The main source is the small moon Enceladus, which ejects water vapor from the geysers on its south pole, a portion of which is ionized. The interaction between Saturn’s magnetosphere and the solar wind generates bright oval aurorae around the planet’s poles observed in visible, infrared and ultraviolet light. The aurorae of Saturn are highly variable. Their location and brightness strongly depends on the Solar wind pressure: the aurorae become brighter and move closer to the poles when the Solar wind pressure increases.

Credit: ESA/Hubble (M. Kornmesser & L. Calçada)

July 20, 1969: One Giant Leap For Mankind

Astronaut Buzz Aldrin descending the ladder and stepping onto the Moon.  Neil Armstrong's “one small step” onto the lunar surface was actually a 3-foot jump down off the lunar module’s ladder to the ground.

Credit: NASA

July 20, 1969: One Giant Leap For Mankind

Astronaut Buzz Aldrin descending the ladder and stepping onto the Moon.  Neil Armstrong's “one small step” onto the lunar surface was actually a 3-foot jump down off the lunar module’s ladder to the ground.

Credit: NASA

Fundamental Studies in Droplet Combustion and FLame EXtinguishment in Microgravity (FLEX-2)

The Flame Extinguishment - 2 (FLEX-2) experiment is the second experiment to fly on the ISS which uses small droplets of fuel to study the special spherical characteristics of burning fuel droplets in space. The FLEX-2 experiment studies how quickly fuel burns, the conditions required for soot to form, and how mixtures of fuels evaporate before burning. Understanding how fuels burn in microgravity could improve the efficiency of fuel mixtures used for interplanetary missions by reducing cost and weight. It could also lead to improved safety measures for manned spacecraft.

  • More information: here

Credit: Reid Wiseman/NASA

(Source: youtube.com)

Titan’s Atmosphere

Titan is the largest moon of Saturn. It is the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found

Titan is primarily composed of water ice and rocky material. Much as with Venus prior to the Space Age, the dense, opaque atmosphere prevented understanding of Titan’s surface until new information accumulated with the arrival of the Cassini–Huygens mission in 2004, including the discovery of liquid hydrocarbon lakes in Titan’s polar regions.

The atmosphere is largely nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog. Titan’s lower gravity means that its atmosphere is far more extended than Earth’s and about 1.19 times as massive. It supports opaque haze layers that block most visible light from the Sun and other sources and renders Titan’s surface features obscure. Atmospheric methane creates a greenhouse effect on Titan’s surface, without which Titan would be far colder. Conversely, haze in Titan’s atmosphere contributes to an anti-greenhouse effect by reflecting sunlight back into space, cancelling a portion of the greenhouse effect warming and making its surface significantly colder than its upper atmosphere.

Titan’s clouds, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze.The findings of the Huygens probe indicate that Titan’s atmosphere periodically rains liquid methane and other organic compounds onto its surface. Clouds typically cover 1% of Titan’s disk, though outburst events have been observed in which the cloud cover rapidly expands to as much as 8%. One hypothesis asserts that the southern clouds are formed when heightened levels of sunlight during the southern summer generate uplift in the atmosphere, resulting in convection. This explanation is complicated by the fact that cloud formation has been observed not only after the southern summer solstice but also during mid-spring.

Image Credit: NASA/JPL/Space Science Institute