Reflections of The Soul – IC 1848 by Ken Crawford

IC 1848 by Ken Crawford

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If we want to be technical, Lynds Bright Nebula 667 is the designation and it’s also known as Sharpless 2-199. Captured here is Collinder open clusters 34, 632 and 634 and small emission nebula 670 and 669 along with the entire cluster designation known as IC 1848. However, let’s forsake science for just a few moments and take a look at what it’s more commonly known as…. The “Soul Nebula”.

Situated along the Perseus arm of the Milky Way galaxy, the “Soul Nebula” reflects true inner beauty as well as a generous portion of hard science. Just this year, this giant cloud of molecular gas was the target study for triggered star formation. According to the work of Thompson (et al); “We have carried out an in-depth study of three bright-rimmed clouds SFO 11, SFO 11NE and SFO 11E associated with the HII region IC 1848, using observations carried out at the James Clerk Maxwell Telescope (JCMT) and the Nordic Optical Telescope (NOT), plus archival data from IRAS, 2MASS and the NVSS. We show that the overall morphology of the clouds is reasonably consistent with that of radiative-driven implosion (RDI) models developed to predict the evolution of cometary globules. There is evidence for a photoevaporated flow from the surface of each cloud and, based upon the morphology and pressure balance of the clouds, it is possible that D-critical ionisation fronts are propagating into the molecular gas. The primary O star responsible for ionising the surfaces of the clouds is the 06V star HD 17505. Each cloud is associated with either recent or ongoing star formation: we have detected 8 sub-mm cores which possess the hallmarks of protostellar cores and identify YSO candidates from 2MASS data. We infer the past and future evolution of the clouds and demonstrate via a simple pressure-based argument that the UV illumination may have induced the collapse of the dense molecular cores found at the head of SFO 11 and SFO 11E.”

With an estimated age of 1 Myr, IC 1848 is home to seventy-four sources of young stellar objects and all of them increase from outside of the rim to the center of the molecular cloud. The bright rim is an ionization front – the barrier between between the hot ionized gas of the HII region and the cold dense material of the molecular cloud where high mass stars are forming. Why is reflecting on the “Soul” so important? Probably because recent studies of meteorites have shown Fe isotopes present in the early solar nebula – suggesting our Sun was given birth in a region on high-mass star formation that experienced a supernova event. Bright-rimmed clouds like IC1848 replicate those conditions.

According to the work of J. Lett: “A bright IR source has been detected within a bright-rimmed dust cloud at the edge of the IC 1848 H II region. The source appears to be an early-type star with a circumstellar dust shell typical of protostars. This star is associated with the position of greatest CO excitation in a dense molecular cloud. The contours of CO emission correspond to those of the bright-rimmed dust cloud, showing that the star formed within the bright rim. Formaldehyde observations at 6 cm, 2 cm, and 2 mm are used to determine the density of the layer between the star and the ionized gas of the bright H..cap alpha.. rim. The location of this star, with respect to the dense molecular cloud which is subject to the external pressure of HII region, indicates the possible role of the expansion of IC 1848 in triggering star formation in dense regions at the perimeter of the H II region. The observed CO emission is used to determine the required luminosity of the embedded star. An early-type star of this luminosity should be detectable as a compact continuum source.”

Indeed, NGC 1848 is in the earliest stages of massive star birth, but it’s hidden behind its dust. According to Murry (et al): “We have completed a multiband (ultraviolet, optical, and near-infrared) study of the interstellar extinction properties of nine massive stars in IC 1805 and IC 1848, which are both part of Cas OB6 in the Perseus spiral arm. Our analysis includes determination of absolute extinction over the wavelength range from 3 ?m to 1250 Å. We have attempted to distinguish between foreground dust and dust local to Cas OB6. This is done by quantitatively comparing extinction laws of the least reddened sightlines (sampling mostly foreground dust) versus the most reddened sightlines (sampling a larger fraction of the dust in the Cas OB6 region). We have combined previous investigations to better understand the evolution of the interstellar medium in this active star forming region. We found no variation of extinction curve behavior between moderately reddened and heavily reddened Cas OB6 stars”.

Shrouded in mystery yet home to Globulettes – the seeds of brown dwarfs and free-floating planetary-mass objects. From the work of G. F. Gahm (et al): “Some H II regions surrounding young stellar clusters contain tiny dusty clouds, which on photos look like dark spots or teardrops against a background of nebular emission which we call “globulettes,” since they are much smaller than normal globules and form a distinct class of objects. Many globulettes are quite isolated and located far from the molecular shells and elephant trunks associated with the regions. Others are attached to the trunks (or shells), suggesting that globulettes may form as a consequence of erosion of these larger structures. Since the globulettes are not screened from stellar light by dust clouds farther in, one would expect photoevaporation to dissolve the objects. However, surprisingly few objects show bright rims or teardrop forms. We calculate the expected lifetimes against photoevaporation. These lifetimes scatter around 4 × 106 yr, much longer than estimated in previous studies and also much longer than the free-fall time. We conclude that a large number of our globulettes have time to form central low-mass objects long before the ionization front, driven by the impinging Lyman photons, has penetrated far into the globulette. Hence, the globulettes may be one source in the formation of brown dwarfs and free-floating planetary-mass objects in the galaxy.”

Apparently there’s a lot to contemplate when you look into the “Soul”….

Many thanks to AORAIA member Ken Crawford for this hugely inspiring image!

Diameter of Uranus

Uranus, captured by Voyager 2. Image credit: NASA/JPL

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The diameter of Uranus is 51,118 km. Just for comparison, this about 4 times bigger than the diameter of the Earth, at 12,742 km across.

Things get a little more complicated, however. Here’s the thing. As you probably know, Uranus is spinning on its axis, completing a day in just over 17 hours. The rapidly spin of Uranus causes it to flatten out slightly. In other words, the diameter from pole to pole is slightly less than the diameter across the equator. The diameter of Uranus from pole to pole is 49,946. If you subtract the two, you’ll find that the polar diameter is 1,172 km less than the equatorial diameter.

Want more diameters? Here’s the diameter of Earth, the diameter of the Sun, and the diameter of Jupiter, the largest planet in the Solar System.

And do you want more information on Uranus? Nine Planets has a great write up about Uranus, and here’s one from Solar Views.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

Density of Uranus

Uranus, the blue gas planet that rotates on its side. credit: NASA/Hubble Team

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The density of Uranus is 1.27 grams/cubic centimeter.

Need a point of comparison? Well, Uranus actually is the second least dense planet in the Solar System after Saturn. The density of Saturn is 0.687 g/cm3. Earth is the densest planet in the Solar System, measuring 5.51 g/cm3.

Want to calculate the density of Uranus all by yourself? No problem. Go grab a calculator and then divide the mass of Uranus (8.68 x 1025 kg) by the volume (6.83 x 1013 km3. If you did the math right, you should come out with the same value for the density of Uranus: 1.27 g/cm3.

If you’re looking for more information on the density of planets. Here’s an article about the density of Saturn, and here’s the density of Jupiter.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

How Long is a Day on Uranus?

Uranus. Image credit: Hubble

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A day on Uranus is 17 hours, 14 minutes and 24 seconds. In other words, a day on Uranus is shorter than a day on Earth.

One of the most bizarre things about Uranus; however, is the fact that its axis is tilted to almost 90-degrees. Unlike the other planets, which spin like tops on a table, Uranus looks like it’s rolling around. For part of the year on Uranus, the Sun appears to be move thought the sky, just like we have on Earth. But then, as the year goes on, one hemisphere is in light, and the other is in darkness for an entire season.

What this means is that a day on Uranus is the same as an entire season on Uranus. Even though the planet is rotating on its axis, the Sun will just spiral around in the sky until the planet has gone far enough around the Sun for it to be obscured. Day on Uranus is as long as Summer on Uranus, and night on Uranus is as long as winter on Uranus. Wrap your mind around that…

We have written many articles about Uranus on Universe Today. Here’s an article about the discovery of new moons and rings around Uranus, and an article about Hubble’s view of Uranus.

Windows on the Universe has got a great description of this and a handy graphic to help you imagine it. And you can get more information from the Hayden Planetarium.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

What is Uranus Made Of?

Uranus. Image credit: Hubble

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While Jupiter and Saturn are mostly composed of hydrogen and helium, the ice giant Uranus is much different. Instead, it is mostly composed of various ices, like water, ammonia and methane. The mass of Uranus is roughly 14.5 times the mass of the Earth. Astronomers think that between 9.3 and 13.5 Earth masses of this is made up of these ices. Hydrogen and helium only account for about 0.5 to 1.5 Earth masses. The rest of the material in Uranus is probably rocky material.

Uranus probably has three layers inside it: a rocky core at the center, an icy mantle surrounding that, and an outer gas envelope of hydrogen and helium. The core of Uranus is very small, with only half the mass of the Earth. The largest portion of Uranus is the icy mantle. This mantle isn’t exactly ice as we understand it, but it’s actually a hot dense fluid consisting of water, ammonia and other substances. Astronomers sometimes refer to the mantle as a water-ammonia ocean.

We have done many articles about Uranus. Here’s an article about a dark spot in Uranus’ clouds, and here’s a view of Uranus with its rings seen edge on.

Want more information on Uranus? Here’s NASA’s Solar System Exploration page, and here’s NASA’s Uranus fact sheet.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

What Color is Uranus?

True-color and false-color image of Uranus. Credit: NASA/JPL

In all of those beautiful images of Uranus captured by Hubble and the Voyager, it’s got a blue-green color. How did Uranus get this color?

The color of Uranus comes from its atmosphere. Just like Jupiter and Saturn, Uranus is composed mostly of hydrogen and helium, with trace amounts of other elements and molecules. The third most common molecule in the atmosphere of Uranus is methane (CH4). This substance causes the blue-green color of Uranus.

Here’s how it works. Although it looks white, the light from the Sun actually contains all the colors in the spectrum, from red and yellow to blue and green. Sunlight hits Uranus and is absorbed by its atmosphere. Some of the light is reflected by the clouds and bounces back into space. The methane in the clouds of Uranus is more likely to absorb colors at the red end of spectrum, and more likely to reflect back light at the blue-green end of the spectrum. And that’s why Uranus has its blue color.

We have written many stories about Uranus on Universe Today. Here’s an article about recent Hubble images of Uranus and Neptune.

This photograph from NASA has one of the best true-color images of Uranus. And here’s more information on Uranus from Hubblesite.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

Atmosphere of Uranus

Uranus. Image credit: Hubble

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Seen from space, Uranus looks bland, enshrouded in blue clouds. This blue-green color of the planet comes from the fact that the atmosphere of Uranus absorbs the red wavelengths of the visible spectrum, and prevents it from bouncing back out into space. All we can see are the blue-green photons reflected into space.

The atmosphere of Uranus is composted mainly of molecular hydrogen and helium. The third most abundant molecule after hydrogen and helium is methane (CH4). It’s the methane in Uranus’ atmosphere that absorbs the red spectrum visible light and gives it the blue-green color.

Uranus (and Neptune) have different atmospheres from the larger Jupiter and Saturn. Although their atmospheres are mostly hydrogen and helium, they have a higher proportion of ices, like water, ammonia and methane. This is why astronomers call Uranus and Neptune “ice giants”.

Astronomers believe that the atmosphere of Uranus can be broken up into three layers: the troposphere (-500 km and 50 km); the stratosphere (50 and 4000 km) and the thermosphere/corona extending from 4,000 km to as high as 50,000 km from the surface.

We have written many stories about Uranus on Universe Today. Here’s an article about how Uranus can be stormy, and another about a dark spot on Uranus.

Want more information? Here’s an article from Windows on the Universe about the atmosphere of Uranus. And here’s a Hubble photograph of Uranus’ atmosphere.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

Farthest Planet from the Sun

Neptune, captured by Voyager. Image credit: NASA/JPL

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Like many planets, Neptune’s orbit isn’t exactly circular. Instead, Neptune orbits the Sun in an elliptical orbit. At its closest point, Neptune gets within 4.45 billion km, and then orbits out to a distance of 4.55 billion km. It takes almost 165 years to complete one orbit around the Sun.

It’s a shame Pluto isn’t a planet any more, because it’s really far. Pluto gets as close as 4.44 billion km. But its orbit is so elliptical that it gets out to a distance of 7.38 billion km. In fact, there are times in Pluto’s orbit when Neptune passes it. Then Neptune really is the farthest planet from the Sun, whether or not you think Pluto is a planet.

What’s farthest object from the Sun? Astronomers think that the long period comets come from a region of the Solar System known as the Oort cloud. It’s possible that this region extends out from the Sun to a distance of 50,000 astronomical units (1 AU is the distance from the Earth to the Sun).

Here’s an article that lists the distances to all the planets.

And here’s an article from Solar Views that talks about the Oort Cloud.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

Fusion in the Sun

Proton-proton chain reaction. Image credit: NASA

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The Sun is hot. Really really hot. But all of the heat and light coming from the Sun comes from the fusion process happening deep inside the core of the Sun. The core of the Sun extends from the very center of the out to about 0.2 solar radii. Inside this zone, pressures are million of times more than the surface of the Earth, and the temperature reaches more than 15 million Kelvin. This is where fusion in the Sun happens.

Every second, 600 million tons of hydrogen are being converted into helium. This reaction releases a tremendous amount of heat and energy.

The process of fusion in the Sun is known as the proton-proton chain. The Sun starts with protons, and though a series of steps, turns them into helium. Since the total energy of helium is less than the energy of the protons that went into it, this fusion releases energy.

Here are the steps.

1. Two pairs of protons fuse, forming two deuterons
2. Each deuteron fuses with an additional proton to form helium-3
3. Two helium-3 nuclei fuse to create beryllium-6, but this is unstable and disintegrates into two protons and a helium-4
4. The reaction also releases two neutrinos, two positrons and gamma rays.

As we said, a helium-4 atom has less energy than the 4 protons came together. All of the heat and light streaming from the Sun came from this fusion reaction.

Here’s an article about how the conditions inside supernovae have been recreated in the lab, and another about a white dwarf star that just shut down its fusion reactions.

Here’s an article from NASA that helps explain how the fusion process works. And here’s a project that lets your students understand the process by making their own fusion reactions.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.

Name of the Sun

Solar prominences on the Sun. Image credit: NASA

Many of the brightest, most familiar stars in the sky have names. For example, have you ever heard of Sirius – the brightest star in the sky? Or Polaris, also known as the North Star. If all these stars have names, does the Sun have a name?

Actually, the Sun doesn’t have its own name, apart from “the Sun”. But “sun” is also a generic name that you can use for any star. Sometimes people say that a star has the mass of 20 suns, or planets orbit other suns. You might have heard the term “sol”, but that’s just another name for Sun, based on the Roman God of the Sun.

We now know that the Sun is just a star. And so, it can be classified into categories like the other stars in the Universe. Just in case you were wondering, the Sun is a G2V star. The G2 part refers to the spectral class, and the V part is the luminosity. Stars with the “V” designation are in the main-sequence, or hydrogen burning, phase of their lives.

So it’s kind of strange to say, but Sun has no scientific name or designation, apart from, “the Sun”. Every other star in the sky does have a scientific designation.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All.