• When: December 21, 2011 at 4:05pm (so come at 3:30pm)
• Actual sunset is supposed to be at 4:20, but at the summer solstice we noticed that the Sun set about 10 minutes earlier than the USNO says it does, so I’ve moved the time of our sunset watch up so we don’t miss it. I added another 5 minutes for the tall trees of Lincoln Park blocking our view. In Autumn the timing seemed to line up correctly – what will it do this time?
• Where: Solstice Park – all the way up the hill from the tennis courts (or, if you’re not in Seattle, wherever you have a view of the western horizon!)
• Who: Everyone welcome, as usual.

Sunset on September 23, 2011 Image credit: Jason Gift Enevoldsen

Come watch the winter solstice sunset at Solstice Park in West Seattle on Wednesday the 21st. We’ll see if the sunset lines up with the placed marker (it did for summer, but will it for winter?). I’ll be there even if it is cloudy because sometimes the Sun peeks through just as it begins to set, but if it is driving rain or sleet I’m staying home with some hot tea!

If you’re interested – here’s the timing of various celestial events on Saturday from Seattle, courtesy of the U.S. Naval Observatory Astronomical Applications Department:

Sun and Moon Data for One Day

The following information is provided for Seattle, King County, Washington (longitude W122.3, latitude N47.6):

Wednesday 21 December 2011 Pacific Standard Time

SUN
Begin civil twilight 7:19 a.m.
Sunrise 7:55 a.m.
Sun transit 12:07 p.m.
Sunset 4:20 p.m.
End civil twilight 4:56 p.m.

MOON
Moonset 1:07 p.m. on preceding day
Moonrise 4:30 a.m.
Moon transit 9:11 a.m.
Moonset 1:47 p.m.
Moonrise 5:45 a.m. on following day

Phase of the Moon on 21 December: waning crescent with 11% of the Moon’s visible disk illuminated.

This event is my part of the NASA’s Solar System Ambassador program, and thanks to West Seattle Blog for publicizing the last few!

Everyone is welcome, see you there!

~ A l i c e !

Dawn

Vesta

NASA Caption

Date acquired: November 8, 2011
Release Date: November 22, 2011

This Dawn image shows a young, fresh crater, which is about 7 km in diameter, in the lower right part of the image. This crater has both dark and bright rays fanning out from it. The bright rays extend much farther from the crater than the dark rays, which are located close to the crater rim. Rays around a crater are formed when relatively small sized pieces of material are ejected by the impact that formed the crater. When larger pieces of material are ejected they can form secondary craters. Clusters and chains of sub-kilometer diameter secondary craters occur roughly 15 km to 20 km away from the rim of the 7 km crater. They are called secondary craters because the blocks that formed them were ejected from a crater formed by a primary impact. Sometimes blocks fall back into the initial crater. Many of these blocks can be seen on the floor and walls of the 7 km diameter crater. These blocks are several tens of meters in size.
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Alice Says:

Pretty good description of crater rays and why this is cool by NASA. Why is it cool? Because it has dark AND light rays. Looks pretty neat to me.
Vocabulary from above: “sub-kilometer diameter” – craters that are less than a kilometer across.
Interpretation notes: “Why do you think there are two colors of rays?” “Were the rays made by the same impact or two events?” “Why do you think that” Which craters in this picture happened before or after the main crater on the right?”

MESSENGER

Mercury

NASA Caption

Released November 22, 2011

Date acquired: October 28, 2011

Of Interest: This image, taken with the Narrow Angle Camera (NAC), shows a pair of secondary crater chains. These features are formed when ejecta from a primary impact is thrown outward from the growing crater cavity. As chunks of ejecta fall back to the surface, they can form chains of secondary craters that often overlap.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Alice Says:

Just like in the Dawn image above, we’re talking about “secondary craters” – craters formed by stuff tossed up by an impact. This is, believe it or not a crater chain, but the impacts are so close together it makes what looks like a single gouge.
Interpretation notes: “What do you think this is?” “How do you think this shape could have been made?” “What do you think did this?” “What about this picture is interesting to you?”

Want More?

Worlds of Stone at Pacific Science Center

MESSENGER

Dawn

~ A l i c e !

Dawn

Vesta

NASA Caption

Released November 7, 2011

PASADENA, Calif. — These Dawn FC (framing camera) images show part of Vesta’s equatorial region, which contains a prominent, deep impact crater (lower center of image) and large troughs (linear depressions). The various colors correspond to the height of the area that they color. For example, the white areas in the bottom corners of the image are the highest areas and the blue areas along the top of the image are the lowest. The prominent impact crater is set into a topographically high area defined by the red and white color-coding. Above this area there are a number of deep troughs represented by green and blue color-coding. A conspicuous trough on the left, which looks like it could be quite deep in the albedo image, is shown by the color-coding in the topography image to be only a little shallower than the area surrounding it.
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Alice Says:

This is a standard terrain image with rainbow colors corresponding to elevation. Pink and white are high elevations, blue and green are low. There’s a weirdness in this one though – the colors go in this order: blue, green, yellow, orange, pink, brown, white. Orange and brown look almost the same.
My favorite feature here is the line running up to the left from the big crater in the middle. Due to the weirdness with the scale, I can’t tell if this is a ridge or a valley. What do you think? I have an e-mail out to JPL.

MESSENGER

Mercury, or a puddle?

NASA Caption

Released November 8, 2011

Date acquired: October 31, 2011

Of Interest: This eastward-looking image shows a wider view of the beautiful unnamed crater highlighted in yesterday’s featured image (center). The complicated folds and fractures that deform the once smooth floor of the Caloris basin can also be seen.
This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury’s surface at resolutions much higher than the base maps. It is not possible to cover all of Mercury’s surface at this high resolution during MESSENGER’s one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Alice Says:

If this image doesn’t take your breath away I can’t help you. Those craters look like raindrops in a puddle to me. This picture is so beautiful. Mercury looks like a PLANET here, not just a desolate collection of black-and-white photos. Of note: the bright areas are not highlights, they are crater rays – new dirt (“regolith”) kicked up by recent impacts.

Want More?

Worlds of Stone at Pacific Science Center

MESSENGER

Dawn

~ A l i c e !

Dawn

Vesta in enhanced color

NASA Caption

Released October 25, 2011

Date acquired: August 11th 2011
Instrument: Dawn FC (framing camera)

PASADENA, Calif. — This Dawn FC (framing camera) composite images show the spectacular spectral diversity of Vesta’s surface. This image shows a Red-Green-Blue color composite image of Vesta. The images from these 3 filters were combined into this one RGB composite image, which enhances Vesta’s coloration..

Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Alice Says:

In short, this is a false-color image. I’ve chosen one of the two that was originally part of this release. I chose this one because it is what I would call “less false” color. Instead of an image with crazy colors depicting specific minerals, I thought it would be interesting to look at a picture that gives us a bit of a sense of what color Vesta might be rather that the greyscale images we’ve been seeing so far.

MESSENGER

What made that funny crater shape on Mercury?

NASA Caption

Released October 23, 2011

Date acquired: October 10, 2011
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)

Of Interest: The large crater here was formed by a very low angle, or oblique, impact. Although impacts at most angles produce circular craters, impacts with incidence angles <15º (from the horizontal) will create elliptical craters. This crater is superposed on an older, circular crater.

Alice Says:

NASA’s explanation is good. I picked this image because it’s a great way to engage with the geology of Mercury.

Here’s a teachable moment: ask guests why the crater might have such a strange shape.

And what about that ridge in the middle? Often when you have a peak in the middle of a crater it’s a “splashback” – like those in slow-motion images of milkdrops.

Want More?

Worlds of Stone at Pacific Science Center

MESSENGER

Dawn

~ A l i c e !

~ A l i c e !

Dawn

NASA Caption

Released October 11, 2011

PASADENA, Calif. — A new image from NASA’s Dawn spacecraft shows a mountain three times as high as Mt. Everest, amidst the topography in the south polar region of the giant asteroid Vesta.

The peak of Vesta’s south pole mountain, seen in the center of the image, rises about 13 miles (22 kilometers) above the average height of the surrounding terrain

Another impressive structure is a large scarp, a cliff with a steep slope, on the right side of this image. The scarp bounds part of the south polar depression, and the Dawn team’s scientists believe features around its base are probably the result of landslides.

This image was created from a shape model of Vesta, and shows an oblique perspective view of the topography of the south polar region. The image resolution is about 300 meters per pixel, and the vertical scale is 1.5 times that of the horizontal scale.

Alice Says

NASA’s caption is pretty clear, most important is to note that THIS IS A CGI IMAGE, and it is vertically exaggerated 1.5 times. This mountain is measured from the average height of the ground around it.

MESSENGER

Lava Flow on Mercury Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

NASA Caption

Date acquired: April 20-22, 2011

Release Date: October 17, 2011
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)

Of Interest: This mosaic shows the geological contact between a lava flow front, which advanced from the west (left) and the pre-existing terrain that it covered. The lava flowed into and almost completely filled a medium-sized crater in the center of the scene. Other amazing lava flow features were shown in recent Gallery releases.

Alice Says

NASA’s caption says you can see an ancient, solidified lava flow here, and you can see how it covers the land behind it. The front is just like the crest of a water wave – only this was a wave in rock and it froze in place as the lava solidified.

It is a little hard to tell which is the lava flow front here – the line that runs vertically through the image, or the one that runs horizontally. They cross exactly in the middle of the image. NASA’s caption is talking about the vertical line. You can see the crater they’re talking about – you can only see the top right-hand quarter of the rim of the crater, just above where the two lines cross.

Want More?

Worlds of Stone at Pacific Science Center

MESSENGER

Dawn

~ A l i c e !

As part of that show we’re updating the images we show from MESSENGER and Dawn on a weekly basis. I’ll try to show them to you the week after we use the in the planetarium.

Dawn

Boulders on Vesta Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

NASA Caption

Released October 12, 2011

PASADENA, Calif. — This detail of a Dawn FC (framing camera) image shows a fresh scarp rimmed crater with many boulders on the crater floor. These boulders have diameters of 100-200m, which is roughly the size of many asteroids! Also evident in this image are linear mass movement features, which originate from the rim of the crater (bottom of image) and are due to material slumping towards the center of the crater. There are also many smaller, and presumably younger, impact craters on the walls of this crater.

NASA’s Dawn spacecraft obtained this image with its framing camera on September 20th 2011.

Alice Says

Let me unpack what NASA said for you:

• “Fresh scarp rimmed crater “ – This crater is new, and it has a sharp edge, like a cliff (a scarp).
• “Boulders on the crater floor. These boulders have diameters of 100-200m,” – That’s those tiny black dots in the middle there.
• “Linear mass movement features” – Dirt moved. It moved in a straight line. The lines you see that go from the edge of the crater in towards the middle are these “linear features.” And technically I shouldn’t call it dirt. Regolith is better, but dirt gives you the right idea.
• “Due to material slumping towards the center of the crater.” – slumping is like sliding. Imagine yourself sitting against a wall. You sit straight at first and then get tired so you scootch down a little, and maybe lean over on your elbow. Slumping is dirt doing the same thing, it’s just … slumped. It’s different that sliding because when you slide you end up all in a completely different place. Slumping you just compact in place, maybe spreading out a little at the bottom.
• “Presumably younger” – when one crater is on top of another you can assume the crater on top is younger.

The boulders (dots) are my favorite part of this image.

MESSENGER

Mercury in Limb-O Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

NASA Caption

Date acquired: September 19, 2011
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Of Interest: This image provides us with a beautiful view of a portion of Mercury’s southern hemisphere. The bright rayed crater near the limb is Debussy.. Also visible, near the center of the image, is Matabei, a small crater distinguishable by its unique dark rays.
These limb images provide information about Mercury’s shape.

Alice Says

I love bright craters – they’re bright because they’re new, not because their composition is different. So rocks are made of minerals, and minerals are usually crystals: they have a lattice of atoms very perfectly aligned. If you just leave a crystal out on a planet it gets scratched up, banged around and the surface gets marred or weathered. If you crack that crystal open, it cracks (cleaves) along those perfect lattice boundaries, between atoms, exposing a new surface. This surface is perfectly flat –flat at the molecular level!! – and therefore reflective like a mirror. This is a cleavage plane. When you smack a meteorite into a planet, you kick up a bunch of rocks and minerals, cracking them all open along those cleavage planes. These fall back down to the planet, reflective, pretty, and unmarred – which looks from space like a bright white crater and rays.

Want More?

Worlds of Stone at Pacific Science Center

MESSENGER

Dawn

~ A l i c e !

Let me repeat that because it is awesome.

MY STAR EXPLODED LAST WEEK!!!!!!!!!!!

¹My star: back in the summer of 2000 I had the fortune to be working as an undergraduate peon researcher in an astrophysics lab at MIT. In my seemingly endless hours sifting through data I found a previously-unidentified star (technically “source”) which we creatively named XTEJ1837+037. I have ever since referred to this as “my star” assuming it was such a pointless little dot that no one would care if I claimed the credit or not. It’s pretty close to Vega, and might be a binary system – a star orbiting a black hole or neutron star. It is perhaps more accurate to say “there was an explosion at my star.”

²Exploded: I’m being very loose with the definition of “exploded” here. NASA’s SWIFT Telescope detected an outburst near the coordinates of “my star.” This does not mean my star exploded, but something did something at that location. If it is a binary system then this outburst could easily be material from the regular star falling onto the black hole/neutron star companion.

³Sometime in the week preceding last Monday: SWIFT detected the burst between September 25, 2011 and October 15, 2011. Well, that means the light got to Earth two weeks ago – but as to when the burst actually happened? To know that we’d have to know how far away “my star” is.

Basic Stats

Source: an unidentified x-ray source, probably a binary system of a star and a neutron star and a black hole.

Name: XTEJ1837+037 or SWIFTJ1836.6+0341

Satellite used: first XTE, the X-Ray Timing Explorer, now SWIFT from NASA

What happened: a burst in the same area was detected using the burst-detecting instrument onboard SWIFT.

When: the detection occurred between September 25 and October 15, 2011.

Where in the sky: near Vega.

Where in the galaxy/universe: we don’t know. It could be in the galaxy, or it could be farther. It is probably in our galaxy, likely at least one kiloparsec away (far).

More Details and More Story

My Unidentified X-Ray Source

Source just means there’s a point in the sky that photons are coming from. The Sun is an identified and named source of visible light, radio waves, x-rays … etc. I was working under Ron Remillard at MIT at the time we found this source, and I was searching through data from the X-Ray Timing Explorer (XTE) to see if I could find gamma ray bursts for his research. I call it a star above because it was not an outburst like we were looking for, this object was steady – not something that shone brightly and then disappeared. The quickest and easiest name for that is “star.”  It is important to note that we were using an x-ray telescope to do this research. This star was not visible – it shone only in x-rays, and it was very dim which is why it had not been found before.

I still asked Ron what constellation it was in. To me, even though the star wasn’t visible, being able to look towards it or point towards it was important. I don’t think Ron understood why. I know it isn’t visible. I also know it is there. It’s by Vega, at right ascension 18 degrees 37 minutes and declination +37 degrees.

We even got to name it. Ron explained how this would work. We named it XTEJ 1837+037, there was no discussion or debate, the name is formulaic. XTE is the name of the satellite used. J is there to let you know what years the coordinates are good for. In this case the coordinates are good during epoch J (12:00 Universal Time on January 1, 2000). 1837+037 are the coordinates: right ascension and declination (which can be positive or negative).

It is still an “unidentified source” because we didn’t take the time to figure out what it was. It wasn’t what we were looking for. Dr. Hans Krimm who recently rediscovered it with SWIFT speculates that it is probably a binary system – a regular star orbiting a black hole or neutron star. That would explain the recent outburst.

An Outburst

As I said, we actually have no idea what happened yet, and I am no longer involved in this research. NASA’s SWIFT telescope detected an outburst in that same area. In Hans’s words – SWIFT detected an outburst only 1.3 arc minutes from “my star.”  That means it is very likely it is the same source.

With a binary system including a regular star and a black hole or neutron star, material can fall off the star and into the black hole or onto the neutron star. This is a catastrophic event, although not destructive to the binary system, and can easily create a large outburst. In fact, it is one of the types of supernovae. (Oops, I was confused. Type 1a supernovae are caused by mass falling from a star in a binary system onto a white dwarf not a neutron star or black hole. It can still create an outburst though.)

Stay tuned, I’ll be keeping up to date on this research. I hope you’re excited too!

Want More?

This is where it gets intense. The only links I have to point out to you are very, very technical. It took me three tries to read the first sentence of the first one … which could have something to do with how excited I was. Have fun deciphering!

The Astronomers Telegram and the second one.

XTEJ1837+037

Here are some more tractable links about the spacecraft in question:

XTE

SWIFT

~ A l i c e !

Is This New?

We’ve seen this before. Neutrinos do not interact with anything (pretty much) – they sail through solid rock like it is empty space. Photons do interact, that’s why you can see. Imagine a race between two particle-people “N” and “P.” First, let’s have them both in empty space. They race from the Sun to the Earth (zoom!) and P wins by a bit. So we know P is faster. Now, let’s give P a handicap. P is going to race by swimming through molasses, while N still gets to run the race in empty space. Now who wins? Well, in this case N does, because he’s not hampered by the molasses. It is just like that with photons, they’re slowed down as they interact with matter – the Sun, the Earth, the solar wind, whatever is out there. The neutrinos just zip right through. So neutrinos from the middle of the Sun get to the Earth long before photons from the middle of the Sun – the photons have to get through all that Sun-material first. Neutrinos and photons from the surface of the Sun would arrive at Earth at about the same time though, because it’s mostly just space in between.

Three Ideas

Three ideas about these FTL (faster than light) neutrinos:

1) They’re not faster than light, they’re just not interacting and the light is. This idea is simplistic and too easy for the scientists not to have ruled it out already.

2) Measurement error. As per the Bad Astronomer, these scientists need to measure the distance to within 3 meters exactly. Is that possible? Maybe. If they’re off by more than 3 meters, those 60 nanoseconds are probably just error.

3) The speed of neutrinos is pretty darn close to the speed of light, maybe our measurements before weren’t sensitive enough to pick up that the speed limit of the universe is the speed of neutrinos, not the speed of light. Now we have to go rewrite all of science fiction in addition to all of physics. What a pain.

Pretty much everyone is unconvinced, but no one has come up with a problem in the scientific evidence yet.

Want More?

Bad Astronomer’s Post

The Actual Paper (you are unlikely to want to read this)

~ A l i c e !

More Interesting

What I found most fascinating is why they were unable to predict the exact decay of this orbit: solar radiation. Solar radiation (think heat from the Sun, though it would be more precise to say photons from the Sun) heats up the Earth’s atmosphere, specifically the upper atmosphere where satellites in Low-Earth Orbit can be as their orbits decay. This heating makes that part of the Earth’s atmosphere both larger and less dense. NASA likens this to a marshmallow being toasted over a campfire. So now your satellite is travelling through a different density of atmosphere, where it will experience more or less drag depending on what exactly is happening between the Sun and the Earth’s upper atmosphere. Complicated, especially if you can’t see that density changing.

Want More?

NASA’s UARS site with the most recent official updates

More about solar radiation and satellite orbit decay

Twitter and Spaceflight Now have more information, but not official information

~ A l i c e !