Today is Christmas in the Christian world. The full moon also happens to fall on this day. A full moon occurring this time of year is called a cold moon as it is the beginning of winter in the northern hemisphere (though, right now, much of the eastern US is actually warm rather than cold).
The strange thing is that the full moon has not been on Christmas Day since 1977 and will not occur again until 2034.
Nothing else is unusual about the full moon today, but just the date it happens to fall on.
25 December 2015
21 December 2015
Twinkling Stars and Static Planets
Twinkle, Twinkle Little Star
How I wonder what you are.
Everyone remembers this nursery rhyme. The question is why do stars twinkle? And how come planets do not?
The short answer is that it has to do with the apparent diameter of the star and the planet. Stars are generally so far away that they have no apparent diameter, so that when light from the star enters our atmosphere, the light is easily diffracted due to different pockets of air. Since the width of the light is so small, these diffractions make it seem as if the star's light is constantly blinking in and out as the light is diffracted away from our eye as the light travels through the atmosphere.
For planets, however, they do have an apparent diameter, albeit much tinier than that of the Sun or the Moon. But this size is enough that when light from the planet travels through different pockets of air in the atmosphere, only a small portion of the light is diffracted away from our light of sight, so the brightness of the planet does not waver, and therefore does not twinkle.
How I wonder what you are.
Everyone remembers this nursery rhyme. The question is why do stars twinkle? And how come planets do not?
The short answer is that it has to do with the apparent diameter of the star and the planet. Stars are generally so far away that they have no apparent diameter, so that when light from the star enters our atmosphere, the light is easily diffracted due to different pockets of air. Since the width of the light is so small, these diffractions make it seem as if the star's light is constantly blinking in and out as the light is diffracted away from our eye as the light travels through the atmosphere.
For planets, however, they do have an apparent diameter, albeit much tinier than that of the Sun or the Moon. But this size is enough that when light from the planet travels through different pockets of air in the atmosphere, only a small portion of the light is diffracted away from our light of sight, so the brightness of the planet does not waver, and therefore does not twinkle.
02 October 2015
Supermoon Lunar Eclipse
On September 27th, we experienced an event that does not happen very often, a supermoon lunar eclipse. We have had a supermoon before, and I've talked about it (see Supermoon). A supermoon is just the moon at perigee. However, this time, we had a supermoon occur when we had a lunar eclipse.
Lunar eclipses aren't all that rare (they happen once every six months), but to have one occur when the moon is at perigee is a sight to behold. The moon appears the largest and the lunar eclipse at this time is actually the shortest total lunar eclipse to occur. It is the shortest because the moon is at its closest, so it is actually moving at its fastest. Many lunar eclipses can last a few hours, but totality for this eclipse was only an hour and a half.
If you want to know more about lunar eclipses, see here.
Lunar eclipses aren't all that rare (they happen once every six months), but to have one occur when the moon is at perigee is a sight to behold. The moon appears the largest and the lunar eclipse at this time is actually the shortest total lunar eclipse to occur. It is the shortest because the moon is at its closest, so it is actually moving at its fastest. Many lunar eclipses can last a few hours, but totality for this eclipse was only an hour and a half.
If you want to know more about lunar eclipses, see here.
Autumnal Equinox
This past September 23rd, the northern hemisphere experienced the beginning of our fall season.
In terms of astronomy, what does this mean?
In the sky, if we could see the ecliptic, the path the Sun travels on as it appears to cross the sky, the point of the autumnal equinox occurs when the Sun crosses the celestial equator as it travels south on the ecliptic. This marks the beginning of autumn for all of us in the northern hemisphere, and the beginning of the spring for those in the southern hemisphere.
Another way to look at it, is that the Sun is directly overhead at the equator, which means that the Earth itself is tilted in the plane perpendicular to the Sun. Neither the northern hemisphere or the southern hemisphere is tilted towards the Sun. But at this point, the southern hemisphere will begin to receive more sunlight as the southern hemisphere is beginning to be tilted more towards the Sun.
In terms of astronomy, what does this mean?
In the sky, if we could see the ecliptic, the path the Sun travels on as it appears to cross the sky, the point of the autumnal equinox occurs when the Sun crosses the celestial equator as it travels south on the ecliptic. This marks the beginning of autumn for all of us in the northern hemisphere, and the beginning of the spring for those in the southern hemisphere.
Another way to look at it, is that the Sun is directly overhead at the equator, which means that the Earth itself is tilted in the plane perpendicular to the Sun. Neither the northern hemisphere or the southern hemisphere is tilted towards the Sun. But at this point, the southern hemisphere will begin to receive more sunlight as the southern hemisphere is beginning to be tilted more towards the Sun.
04 August 2015
Ions
An ion is a particle that is similar to an atom but has more or less electrons than protons in the nucleus. In most cases, ions are present in compounds that have a metal and a non-metal (like NaCl, common table salt), but can also be present in hot gases or plasmas, like the Sun.
If an ion has more electrons than protons, i.e. it is negatively charged, we call that an anion. In the above example (NaCl), the chlorine ion has one more electron than proton (18 electrons vs. 17 protons) and therefore, has a charge of -1 e (-1.602e-19 coulombs). If the ion has less electrons than protons, it is a cation. The sodium ion in NaCl has one less electron than proton, so has a charge of +1 e.
Why are ions are important? They are found in the spectra of stars, in nebulae, and as stated above many compounds that we use everyday. In the Sun or any star, the gas is so heated, that it can strip electrons from the atoms, ionizing the gas, converting it into a plasma.
There are some elements that do not ionize easily. We call these elements inert and they are found on the far right of a periodic table. These are the noble gases: Helium, Neon, Argon, Krypton, Xenon, and Radon. This does not mean that they cannot be ionized. Under normal temperatures and pressures, the outer electrons are not readily removed from their orbits. However, under extreme temperatures and pressures, electrons can be stripped from the outer shells. In fact, the alpha particle is the bare nucleus of a helium atom with a charge of +2 e. We find helium ions in the core of the Sun, as it is the final product of the proton-proton chain. Electrons do not easily combine with the bare nucleus to form a stable helium atom.
Next time, we will learn about ion engines and how they may be a future propulsion system for solar system travel.
If an ion has more electrons than protons, i.e. it is negatively charged, we call that an anion. In the above example (NaCl), the chlorine ion has one more electron than proton (18 electrons vs. 17 protons) and therefore, has a charge of -1 e (-1.602e-19 coulombs). If the ion has less electrons than protons, it is a cation. The sodium ion in NaCl has one less electron than proton, so has a charge of +1 e.
Why are ions are important? They are found in the spectra of stars, in nebulae, and as stated above many compounds that we use everyday. In the Sun or any star, the gas is so heated, that it can strip electrons from the atoms, ionizing the gas, converting it into a plasma.
There are some elements that do not ionize easily. We call these elements inert and they are found on the far right of a periodic table. These are the noble gases: Helium, Neon, Argon, Krypton, Xenon, and Radon. This does not mean that they cannot be ionized. Under normal temperatures and pressures, the outer electrons are not readily removed from their orbits. However, under extreme temperatures and pressures, electrons can be stripped from the outer shells. In fact, the alpha particle is the bare nucleus of a helium atom with a charge of +2 e. We find helium ions in the core of the Sun, as it is the final product of the proton-proton chain. Electrons do not easily combine with the bare nucleus to form a stable helium atom.
Next time, we will learn about ion engines and how they may be a future propulsion system for solar system travel.
03 August 2015
Bright Spots on Ceres
I have previously posted about asteroid/dwarf planet Ceres before. The Dawn Spacecraft recently arrived at Ceres and began a comprehensive study of the dwarf planet that has never been done before. One of the strange things that Dawn found on Ceres were bright spots that confounded scientists at first. What were they?
Via NASA/Dawn
The bright spots were discovered in a crater now known as Occator, an 80-km diameter crater at 19.5° latitude on Ceres. They are called faculae which means “bright spots”. Faculae are more commonly known as the bright regions on the Sun surrounding a sunspot. Where do the faculae on Ceres come from?
One theory is that they are ice spots in the crater that are reflecting sunlight or salt deposits left over after salty water on the surface evaporated away. These spots might have come from Ceres actually having a dusty surface, and minor impacts on the surface exposed the underlying ice or salt.
Another theory, which is more widely accepted, is that the spots are actually ice geysers or cryovolcanoes (volcanoes that spew ice rather than lava). This is believed to be the true cause as Dawn has seen haze above the spots.
We will probably learn more as Dawn continues its reconnaissance around Ceres. And if these are ice features, Ceres could be a great place to build a future way station in the Solar System.
31 July 2015
Blue Moon
Tonight, July 31st, a rare occurrence will happen. You can say that it is something that happens once in a blue moon, because it is a blue moon.
What do we mean by a blue moon? There are actually two definitions of what a blue moon is.
If you miss the blue moon tonight, don't worry. There will be another blue moon on May 21, 2016. This will be the third blue moon in the northern spring (southern fall) of 2016.
What do we mean by a blue moon? There are actually two definitions of what a blue moon is.
- A blue moon is the third full moon in a season where four full moons occur. Most times, there are only three full moons in one season, but on the rare occasion when a full moon is at the beginning of the season, the season may have four.
- A blue moon may also mean the second full moon in a calendar month. The full moon of tonight is this type of blue moon.
If you miss the blue moon tonight, don't worry. There will be another blue moon on May 21, 2016. This will be the third blue moon in the northern spring (southern fall) of 2016.
30 July 2015
Travelling to the Planets
Recently, after over 9 years of travel through the Solar System, New Horizons arrived at Pluto and flew through the system. I've talked about the probe before and you can click the link above to see my previous post. New Horizons has already taken some amazing images of the system, and we will be getting more images as time goes on.
However, the amazing feat is not that we are taking images of Pluto and its moons, but that New Horizons actually made it to Pluto. Many things could have gone wrong: it could have been hit by an unknown asteroid or comet, it could have inexplicitly lost power, or a biggie: the trajectory could have been miscalculated.
When we go to any body in the solar system, we cannot aim directly for it. Much like a quarterback leads his receiver in American football, the probe must be aimed ahead of the planet or body and must arrive at the same place and time as the planet or body.
In the image down below, if we were to aim a spacecraft at Mars where it is now located, by the time we reached it, Mars would be farther ahead in its orbit. To reach Mars, we must aim to where Mars will be in about six months (the minimum time it takes to reach Mars from Earth). For longer travel times, we must aim farther ahead in the Martian orbit.
To reach Pluto took a little more doing. We had to know how long it would
take to reach Pluto, and aim New Horizons to where it will be then. Knowing
that New Horizons will reach the Pluto system in nine years and how fast Pluto
is moving on its orbit, engineers and scientists were able to determine where
New Horizons should be aimed towards in nine years. They also had to worry
about avoiding the other planets and moons, and had to hope that New Horizons
wouldn't encounter any stray asteroids or comets that we did not know about.
The Earth is in relatively the same
location on its orbit as it was nine years ago.
21 July 2015
Syzygy
In astronomy, objects can always cross in front of another object, if the alignments are right. They are usually referred to one of three terms: an eclipse, a transit, or an occultation. These three terms are part of a broader definition called a syzygy*.
*Syzygy in astronomy is when three bodies are in a line.
Let's define the three of them.
Previously, I posted about eclipses of the Moon. These occur when the Moon, Sun, and the Earth are lined up in such a way that the Moon eclipses the Sun (a total solar eclipse), or the Moon goes through the Earth's shadow (a lunar eclipse). An eclipse can also happen in multiple star systems when one companion star passes in front of the other. What occurs is that the obscured body is either completed blocked out temporarily as it passes through the shadow of the eclipsing body (lunar eclipse) or the eclipsing body passes between the observer and the eclipsed object (total solar eclipse).
A transit is when a smaller body passes in front of a larger body, mostly a planet crossing in front of a star, but can also occur when a moon crosses in front of a planet, partially blocking out the Sun. Transits of extra-solar planets can be used to help astronomers find the planet and determine its size based on the light-curve of the star. Exoplanet transits are discussed more here. Transits occur in the inner solar system when Mercury and Venus cross in front of the Sun as seen from Earth. On my post about opposition and conjunction, what configuration(s) are Mercury and Venus in when they transit the Sun? Comment below if you know the answer. Also, the moons of Jupiter and Saturn can also transit across the face of their parent planets.
Released with Image The Galilean
satellite Io floats above the cloudtops of Jupiter in this image captured on
the dawn of the new millennium, January 1, 2001 10:00 UTC (spacecraft time),
two days after Cassini's closest approach. The image is deceiving: there are
350,000 kilometers -- roughly 2.5 Jupiters -- between Io and Jupiter's clouds.
Io is the size of our Moon, and Jupiter is very big.
The last example of syzygy in astronomy is called occultation. In this case, the body that crosses between the observer and the more distant object appears much larger. These occur when the Moon, the Sun, or a planet pass in front of distant star, when the Moon passes in front of a planet, or when the satellite of a planet passes in front of an apparently smaller satellite.
Dione occulting Rhea (two moons of
Saturn)
In picture form, this is what the three types of syzygy look like:
14 July 2015
New Horizons
Today, July 14th, 2015 will go down
as a major milestone in humanity exploration of the cosmos. After 85 years of
pondering what Pluto actually looks like, we know and will learn more in the
upcoming days and months.
New Horizons made its closest
approach to Pluto at 11:50 UTC, allowing us to see it for the first time with
clarity. By now, many of you have probably seen the images of Pluto with its
heart-shaped surface feature, which was actually hinted at by Hubble images
taken between 2002 and 2003.
If you look at the 180° face, a hint
of the heart-shaped feature seen below may now be apparent.
This image
of Pluto from New Horizons’ Long Range Reconnaissance Imager (LORRI) was
received on July 8, and has been combined with lower-resolution color
information from the Ralph instrument.
And from images taken on July 11, a
composite of Pluto with its companion Charon.
A portrait
from the final approach. Pluto and Charon display striking color and brightness
contrast in this composite image from July 11, showing high-resolution
black-and-white LORRI images.
For more information, follow New Horizons on Twitter and here, Alan Stern, Principle Investigator for
New Horizons.
Also, visit the New
Horizons page for updated images as they are posted.
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