Happy Perihelion 2015!

Just a quick note to let you know that tonight marks the point where the Earth is closest to the Sun all year: perihelion.

The moment this happens is at 06:36 UTC Jan. 4, 2015. That translates to 01:36 Eastern US time, or 10:36 Pacific time on Jan. 3. So technically, this happens tomorrow for people on the east coast, but today for those of us in Mountain and Pacific time. Living on a round ball can be weird.

At that time, the center of the Earth will be 147,096,204 kilometers (91,401,343 miles) from the center of the Sun. On average, that distance is 149,597,871 km, so we’re roughly 2.5 million km closer tonight than on average.

Mind you, the Earth’s distance from the Sun is always changing because we orbit our star on an ellipse, not a circle. Yesterday we were a wee bit further away than today, and tomorrow we’ll be a wee bit further away again. One day after perihelion, for example—on Jan. 5 at the same time—the Earth’s center will be 147,096,683 km from the center of the Sun, a difference of less than 500 kilometers from today’s distance. You’d never have noticed.

The date of perihelion changes every year due to many factors, the biggest, oddly, being the Moon. The Earth and Moon orbit around a common center of gravity, like two kids facing each other, holding hands, and swinging each other around in a circle. It’s that center of mass (called the barycenter) that orbits the Sun. When the barycenter reaches perihelion, the Earth might actually be a bit farther away than usual because the Moon has swung it out. This changes the moment of perihelion for the Earth, sometimes by a day or more.

I’ve written about all this many times for perihelia past: Here are my articles for 2014, 2013, 2012, 2011, and 2010 just to get you started.

Happy perihelion day!

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At the Heart of Orion

Near the center of this sharp cosmic portrait, at the heart of the Orion Nebula, are four hot, massive stars known as the Trapezium. Tightly gathered within a region about 1.5 light-years in radius, they dominate the core of the dense Orion Nebula Star Cluster. Ultraviolet ionizing radiation from the Trapezium stars, mostly from the brightest star Theta-1 Orionis C powers the complex star forming region's entire visible glow. About three million years old, the Orion Nebula Cluster was even more compact in its younger years and a dynamical study indicates that runaway stellar collisions at an earlier age may have formed a black hole with more than 100 times the mass of the Sun. The presence of a black hole within the cluster could explain the observed high velocities of the Trapezium stars. The Orion Nebula's distance of some 1,500 light-years would make it the closest known black hole to planet Earth. via NASA http://ift.tt/13M4tfg

An Icy Volcano and the Cosmic Cycle of Life

Living on the edge of the Rocky Mountains in the winter means getting up every morning and seeing those snow-capped peaks poking out over the nearer foothills. It’s a magnificent view to occupy me as I wait for my coffee to steep.

Seeing the mountains from the side is endlessly fun, but I sometimes wish I could see them from above. After all, when Landsat 8 does it, the view is simply incredible:

[You really want to see this image in all its high-definition glory, too.]

Now, to be fair, those aren’t the Rockies; those are the eponymitic Islands of the Four Mountains, a collection of islands in the Aleutian archipelago curving west off of Alaska. There are actually seven islands in the group, but these four volcanoes stand tall: Herbert (lower left), Cleveland (center), Carlisle (upper left), and Tana (the rugged one to the right).

The Landsat image shows them on June 8, 2013. As you can see, even in summer there’s snow on them thar hills, kindof. What’s funny to me is that Cleveland is the tallest of the four volcanoes (1730 m at its peak, about 5700 feet) but it’s the only one without snow on it. Weather can be weird sometimes.

I love the cloud patterns here, too. North is up, so the wind is clearly blowing north, and the volcanoes punching up into the sky break that flow. The wind blows around the islands, creating that lovely ship-wave effect. Note how the lower flanks of the volcanoes are relatively clear, but then clouds form higher up; as the wind blows up the windward face of the mountains it cools, and clouds form as water condenses out.

Herbert has no records of eruptions in modern times, but Cleveland erupted in 2006 (and again in subsequent years). Get this: That first eruption was actually discovered by astronauts on the International Space Station who happened to be flying over it at the time! They apparently caught it right after the eruption started, too:

It’s a pretty stark (and frankly gorgeous) reminder that we live on a planet that’s not nearly done cooking yet. We live on the cool, solid skin of a vast ball of superheated rock and iron, still roiling inside with energy leftover from its formation (as well as from the decay of radioactive elements and other forces). It’s slightly terrifying to think that all that separates us from all that is a thin veneer of rock just a dozen or two kilometers thick, but we owe our existence to all that heat. It generates tectonic forces that in turn have created the land we live on, and continental drift has pressured life into changing over the eons—allopathic speciation—evolving into us.

As always in the Universe, life and death hang on the same thread; creation and destruction are two sides of the same coin.

That may not be the first thought you have, looking at a pretty picture of Alaskan islands from space. But it’s not a bad one. One of the things I love about science is how it gives us perspective.

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Vela Supernova Remnant

The plane of our Milky Way Galaxy runs through this complex and beautiful skyscape. At the northwestern edge of the constellation Vela (the Sails) the telescopic frame is over 10 degrees wide, centered on the brightest glowing filaments of the Vela Supernova Remnant, an expanding debris cloud from the death explosion of a massive star. Light from the supernova explosion that created the Vela remnant reached Earth about 11,000 years ago. In addition to the shocked filaments of glowing gas, the cosmic catastrophe also left behind an incredibly dense, rotating stellar core, the Vela Pulsar. Some 800 light-years distant, the Vela remnant is likely embedded in a larger and older supernova remnant, the Gum Nebula via NASA http://ift.tt/1zz3XdH

Ceres, Target of NASA's Dawn Mission

Discovered on Jan. 1, 1801 by Giuseppe Piazzi of Italy, Ceres is the largest object in the asteroid belt - the strip of solar system real estate between Mars and Jupiter. On March 6, 2015, NASA's Dawn spacecraft will arrive at Ceres, marking the first time that a spacecraft has ever orbited two solar system targets. Dawn previously explored the protoplanet Vesta for 14 months, from 2011 to 2012, capturing detailed images and data about that body. Dawn has entered its approach phase toward Ceres, and the next couple of months promise continually improving views prior to arrival. By the end of January, the spacecraft's images and other data will be the best ever taken of the dwarf planet. This image of Ceres was taken by the Advanced Camera for Surveys on NASA's Hubble Space Telescope between December 2003 and January 2004. Hubble images of Vesta and Ceres helped astronomers plan for the Dawn spacecraft’s tour. Astronomers enhanced the sharpness in the image to bring out features on Ceres' surface, including brighter and darker regions that could be asteroid impact features. The observations were made in visible and ultraviolet light. The colors represent the differences between relatively red and blue regions. These differences may simply be due to variation on the surface among different types of material. Ceres' round shape suggests that its interior is layered like those of terrestrial planets such as Earth. Ceres may have a rocky inner core, an icy mantle, and a thin, dusty outer crust inferred from its density and rotation rate of 9 hours. Ceres is approximately 590 miles (950 kilometers) across. Image Credit: NASA/ESA/J. Parker (SWRI), P. Thomas (Cornell U.), L. McFadden (U-Md., College Park), and M. Mutchler and Z. Levay (STScI) via NASA http://ift.tt/1EPxF6i

Video: SpaceX in 2014

2014 - SpaceX Year in Review [Watch] "Relive SpaceX's 2014 highlights: launching rockets, landing stages, and unveiling our next generation crewed spacecraft." Marc's Note: What are your thoughts in looking back at the year that was for SpaceX in 2014?...



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The Beauty of a Grain of a Sand on the Cosmic Beach

I know I just posted a really beautiful image of a spiral galaxy by Adam Block recently, but right after that he sent me another photo that got me thinking, and I figure that’s worth sharing. Also, who doesn't want to start a new year with a gorgeous galaxy photo? And yeah, click that picture to get the whole high-res shot, because this is only a piece of it shrunk to fit the blog.

That is NGC 1169, which is actually quite similar to the galaxy I posted last week. It’s a barred spiral with an inner ring, and majestic spiral arms, but it differs from the other galaxy because it doesn’t have that obvious outer ring and flocculent, fluffy spurs. Instead, the arms themselves are patchy.

Can you see how the inner part of the galaxy is quite red, while the outer part is bluer? Apparently no stars have been born in the inner regions for quite some time; massive stars are blue, and don’t live long. Once they explode, it leaves behind redder and redder stars over time, so older galaxies (or older neighborhoods in galaxies) look red.

The blue in the spiral arms means there’s been star birth there in the past few million years. It’s probably a slow, continuous process, like it is in our home galaxy, the Milky Way. You can also see patches of pink, where gas is excited by those stars. The arms are accented by dust as well, but it’s stretched out along with the arms.

For all its beauty, I couldn’t find much info about this galaxy in the professional astronomical literature. Just one paper from 1994, discussing the distribution of gas in NGC 1169. Oddly, they drew the conclusion not much star formation was going on, or at least the density of gas in the galaxy wasn’t thick enough to sustain star birth except on a local level. Looking at Adam’s picture, I’m not so sure that’s true.

NGC 1169 is about 85 million light years away, a fair distance. It’s small in the sky, which may be why it hasn’t been well studied. I was surprised to see in the paper I found that the mass of the galaxy is very similar to that of the Milky Way, making it pretty hefty as galaxies go. It’s also roughly the same size as our galaxy, 100,000 light years across or so.

That gave me pause. I had certainly never heard of this galaxy before Adam sent me the note, and it looks like it’s not interesting (read: unusual) enough on its own to warrant much attention by the astronomical community.

Yet it’s an entire galaxy. Hundreds of billions of stars, probably just as many planets, huge amounts of gas and dust distributed by the dance of gravity, angular momentum, and collisional dynamics—all that, and so much more… yet it’s literally undistinguished in our huge catalog of steller cities.

An entire galaxy like our Milky Way, essentially anonymous. I have difficulty wrapping my primitive monkey brain around the concept of a galaxy, physically understanding just how vast it is. Yet distances in the Universe are so great that this entire colossal structure can be reduced down to another grain of sand on the beach, one among hundreds of billions.

It’s an astonishingly humbling experience. But, as always, I am not crushed by it, because I know that humans are amazing as well—because we can know about this galaxy. From across a black sea a billion trillion kilometers across we can gaze upon it, appreciate its beauty, and understand that there are so many others like it, including ours.

The Universe is big, but then, we can be too.

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