steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Lights On | Lights Out

This piece has some nice graphics and discussion of changes in nocturnal satellite images of Earth between 2012 and 2016. There's a slider where you can compare two maps directly, as well as processed images showing increased lighting in blue and decreased lighting in pink.
thewayne: (Default)
[personal profile] thewayne
I'm not a man of wealth and fame. My main interest in astronomy is the fact that I'm married to an astronomer: I do enjoy astronomy, I'm just not a scientist. My wife operates the 3.5 meter telescope at Apache Point Observatory, and also runs the APOLLO lunar laser ranging experiment (got some good results last night in marginal weather). And she is famous, at least in some circles: she was the final segment of the Mythbusters episode in 2008 debunking the 'man has never been to the moon' garbage, along with several other TV programs.

We're hoping to head up to Oregon to see the solar eclipse this year, we'll see what happens. I had hoped to buy a solar telescope to take some photos of it, but I've been unemployed for about 10 months now, so that's not too likely. Maybe I can kitbash something together.

If you like big telescope pictures, or are interested in a video that I made about the lunar laser ranging conducted at APO, I have a photography web site. I need to upload a couple of photos of the Clark telescope at Lowell Observatory that I shot in February, unfortunately the Pluto Discovery Telescope and dome are closed for a refurb. I'm hoping next year to be able to get some fresh photos of them.
thewayne: (Default)
[personal profile] thewayne
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Back in October I wrote about Alpha Centauri B's first known planet, and associated discoveries about Alpha Centauri B. I talked about all the work that went into filtering out noise (redshift and blueshift from other sources) to find the signal from the planet.

Well, that was a very complex process, and some work since then has followed up and suggests that it may have gone awry, and there may not be a planet after all. Here's an article with more info:
No Planet of Alpha Centauri B?

It doesn't conclude for sure that there is no planet, but it casts doubt on the idea that there is; ultimately, more data will be needed to resolve the issue, and we might have to wait a while for that data, since the orbits of Alpha Centauri A and B are bringing them closer together in the sky from our point of view, which will make it impossible to study just the light of Alpha Centauri B without some light from Alpha Centauri A getting mixed in.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Cassini spots mini Nile River on Saturn moon

Cassini's radar imaging of Titan has spotted evidence for a 400 km long river on Titan, with its mouth in a lake. Lakes and rivers on Titan are made of liquid methane/ethane, not water, which is frozen rock-like at Titan's temperatures. The riverbed-shaped structure is apparently full of liquid, not a dry empty riverbed, because it appears dark to the radar, indicating that it has a smooth surface.

I'm not sure why it's compared specifically to the Nile river.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
A piece of big astronomy news came out yesterday: An earth-sized planet has been discovered orbiting Alpha Centauri B, a relatively sun-like star (a bit smaller and fainter than the Sun) in the nearest star system to the Sun. The planet is not particularly earth-like, though, since it orbits the star in only about 3.2 days, and thus would be extremely hot.

I started to write a long entry talking about Alpha Centauri system the system and the discovery, but I think instead I'm going to link a few articles - there are many more that could easily be found - and talk a bit about some things I noticed in reading the original paper.

News stories )

Links to the original paper )

I gave the paper a quick reading, and while some of it was too technical for me to understand, I was able to follow the basics of it. And I was once again amazed by the amounts of information that astronomers are able to squeeze out of apparently tiny amounts of data - in this case, the spectrum of a star observed repeatedly over time.

Details )

Here's an article that talks about some of the noise sources in non-academic terms.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
I posted about a week ago about a double meteor sighting on September 21st where calculations seemed to show that they were in fact the same object which had once skimmed through Earth's atmosphere, then out again, then gone around the earth and re-entered the atmosphere.

Other/newer calculations are showing that that seems not to have happened after all. Instead, it seems like it really was just two independent fireballs.

I'm not sure the question is 100% resolved yet. Science takes time.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
I keep seeing articles about how Voyager 1 is leaving the solar system, or about to leave the solar system, or may just have left the solar system. An example is a science blog post titled More evidence that Voyager has exited the solar system.

These articles are talking about a real and interesting phenomenon, but I find the description of it as "leaving the solar system" misleading.

What they are primarily talking about is Voyager leaving the sun's heliosphere, the region of space affected by the charged particles of thesolar wind. Outside the heliosphere is the interstellar medium. Passing the heliopause between the heliosphere and the interstellar medium is crossing a significant boundary between a kind of space that is heavily influenced by the sun and one that isn't. So it is a significant event that Voyager 1 is passing this boundary, and in the process giving us evidence about the location of the boundary and what conditions are like at it and on either side of it.

Voyager 1 is currently about 122 astronomical units (au) from the sun, or 122 times earth's distance from the sun. That's a long ways away, but there are still many objects in the solar system whose orbits take them out that far; not only many comets, but also Sedna, which goes as far as 940 au from the sun at its most distant. And the Oort cloud, a hypothesized reservoir of comets that have never yet come close to the sun, is hypothesized to be between around 5000 and 50,000 au from the sun. All these orbits are still orbiting the sun, and thus still part of the solar system. It seems misleading to me to say that Voyager 1 is leaving the solar system when it's still well within the orbits of many things orbiting the sun.

But crossing the heliopause is still neat and noteworthy.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Amazing Meteor Boomerangs Around Earth

In the evening of September 21st, a bright fireball meteor was seen in western Europe and the British Isles.

A few hours later, a bright fireball was seen in eastern North America.

At first, this seemed like it had to be a coincidence - two independent bright fireballs that happened oddly to occur on the same day. It couldn't just be that the fireball had crossed the Atlantic - for one thing, that would have taken much less time than a few hours.

It turns out, though, that calculations of the meteor's path indicate that they were actually the same object; it had just gone all the way around the earth in between. It had skimmed shallowly through the edge of the atmosphere making a fireball as it passed over Europe and the British Isles, and then out again on the other side. Its passage through the atmosphere slowed it down enough to put it into an elliptical orbit around the earth. It went around the earth once-and-a-bit, and came back down to atmospheric height over North America, where it entered the atmosphere again as another fireball, never to exit again.

(One simplification I made in the above story is that the meteor actually fragmented during its first pass through the atmosphere; the fireball seen over North America would have been probably just the biggest fragment of it.)

EDIT: Newer calculations show that this story is probably not accurate after all.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
There's a recently-discovered comet that could put on a spectacular show in late 2013 - at its brightest (when it's hard to see because it's really close to the sun), it could be brighter than the full moon, and visible in daytime.

However, predicting comet brightness is notoriously difficult, and this one could end up being nothing spectacular; Comet Kohoutek (C/1973 E1) in 1973 is a famous case of something that was predicted to be brilliant but didn't live up to prediction.

Bill Gray, whom Emily Lakdawalla consulted on the matter, estimates that it has a 30% chance of being awesome, and a 60% chance of being a dud. (And what about that other 10%? He doesn't say.)
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
A fifth moon of Pluto has been discovered.

Here is a Hubble Space Telescope press release.

And here is an article from Sky and Telescope.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Cassini has found evidence that Titan has liquid water beneath its surface. Saturn causes tidal distortions in Titan; if Titan were solid all the way through, we'd expect to see relatively small tidal distortions, but Cassini has instead found much larger ones, which suggests that part of its interior is liquid and thus more easily distorted.

Here are two articles on the topic, one from NASA and one from ESA.

Salacia

Jun. 26th, 2012 01:46 pm
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
(Cross-posted from my own journal.)

According to recent research, the trans-Neptunian object Salacia seems to be about 900 km in diameter - that makes it about the same size as Ceres and Orcus and Quaoar. This is a bit of a surprise; it seems that Salacia is actually quite dark, reflecting only about 3 or 4 of the light that falls on it. Previous estimates of its size were based on assumptions that it reflected a higher percentage of light, which led to smaller estimated sizes.

Emily Lakdawalla explains in more detail here.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
There's a nice brief (3-minute) video by Emily Lakdawalla about how seasons on Mars are similar to and different from seasons on earth, and especially why winter in the southern hemisphere is difficult for Mars landers (it's long, cold, and cloudy).
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
One of the things that always amazes me about astronomy is the ingenious ways astronomers come up with to squeeze information out of seemingly tiny bits of data, and to find data in unexpected places.

This story about recent research on the star Eta Carinae is a good example of that. Eta Carinae currently appears to the naked eye as a fairly dim star, with an apparent magnitude of about 4.5, but its brightness has varied greatly during its observational history, from too dim to be seen with the naked eye at all, to being the second-brightest star in the night sky, after Sirius. Its bright episode lasted 20 years, and the peak brightness, with an apparent magnitude of -0.8, was observed in 1843. Unfortunately, astronomers at that time were not able to measure all the things about it that we would like to know about its unusual outburst. But some astronomers have come up with an ingenious way to observe the light from the outburst. The light from the outburst takes time to travel. Some of it took a while to reach some interstellar dust clouds, which then reflected it, sending some of its light back towards earth. That light is just reaching us now. So by observing the changes in the light reflected from those dust clouds, the astronomers can see changes in the light given off by Eta Carinae during its outburst.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
New Star Discoveries Found in Antique Telescope Plates

Over a hundred years' worth of photographic plates of astronomical photographs from the Harvard College Observatory are being digitized, and the digital images are being analyzed. This long timespan of data has allowed the discovery of several kinds of long-period variable stars, which vary in brightness on timespans of decades. The discovery is still fairly new, so the mechanisms behind many of the variables are still unexplained, but there are hypotheses about some of them. Only 4% of the glass plates have been digitized yet, so there are surely more discoveries still to be made.

I liked this quote from one of the researchers:
"Astronomy is driven by observation. If you have unique data, you will make unique discoveries, there's no doubt about that."
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
The smallest solar system yet discovered, including the smallest known extrasolar planets, has recently been announced.

Here is a news release from NASA.

And here is a longer one from Caltech.

The three planets are all smaller than earth in diameter; the smallest is about the size of Mars. They orbit a red dwarf star whose diameter not even twice as big as Jupiter's, although it'll be a lot more massive. (Neither of the articles gives an estimate of the mass of the red dwarf star that I can see.) And the distances of the planets from their star are similar to those of Jupiter's moons from Jupiter, making it seem almost more comparable to Jupiter + moons than to Sun + planets.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Hell on Earth: NASA’s Toxic Venus Test Chamber

Making a spacecraft to land on Venus (as opposed to orbit it) is really difficult, because the environment on Venus is so extreme. The surface temperature is extremely hot (hot enough to melt lead), the atmospheric pressure is 90 times that on earth, and the atmosphere contains corrosive gases. Because of this, none of the few spacecraft that have successfully landed on Venus so far have been active for more than a few hours.

So NASA is making a Venus environment simulation oven to do testing for possible future missions to Venus, so that they can determine what will or won't last without sending it to the planet and then finding it doesn't work very well.

The chamber could also be used for simulating some other non-Earth environments, such as Jupiter's outer atmosphere.

On an unrelated note, yesterday (at least from my time zone), January 9th, was the anniversary of the death in 1848 of astronomer Caroline Lucretia Herschel. She "found three nebulae and eight comets. In 1787, King George III gave Caroline a salary of 50 pounds per year as assistant to [her brother] William. She published the Index to Flamsteed's Observations of the Fixed Stars and a list of his mistakes in 1797." Caroline's brother William Herschel discovered Uranus.
steorra: Jupiter's moon Europa (europa)
[personal profile] steorra
Europa
A couple weeks ago, there was news about a new analysis of what's going on under Europa's surface.

We've been pretty sure for a while that somewhere under Europa's surface, there's an ocean. But a big question has been how far under the surface that ocean is. Some facts seemed to suggest that it was quite close to the surface - patches of 'chaos terrain' that looked like ice had broken up, jostled around, and refrozen back together. But other facts implied that the icy shell outside the ocean must be quite thick. It hasn't been at all clear how these apparently conflicting pieces of evidence should be resolved. The new work proposes a model where the icy shell is quite thick, but within the icy shell there are melt pockets - like underground lakes - that cause chaos terrain above them.

As usual, Emily Lakdawalla has a good write-up of it.

More links:
Sky and Telescope: Europa's Subsurface Lakes
University of Texas at Austin: Scientists Find Evidence for “Great Lake” on Europa and Potential New Habitat for Life
The original article in Nature, for those who have subscription access.
A NASA press briefing

Enceladus
On November 6th, 2011, Cassini did a flyby of Enceladus that was devoted to taking synthetic aperture radar (SAR) imaging. This is pretty unusual; normally, Cassini only uses the SAR imaging on Titan, in order to peer through Titan's haze. Since other moons don't have significant atmospheres, SAR isn't important to be able to see their surfaces.

The Cassini website has just released a news item about the flyby; it has a link to a video that shows the radar swathe overlaid upon an ordinary image of the surface, and then shows close-ups of two particular regions of the swathe.

Again, Emily Lakdawalla has a good post about the topic. She points out that the purpose of this is actually more to help us understand Titan than to help us understand Enceladus; SAR is often hard to interpret, and by using it on a surface where we can check what we're finding against visible-light (and ultraviolet/infrared) imaging, we can get a better idea of what SAR images of Titan mean.

EDIT Dec. 2, 2011: Apparently, Cassini has in fact taken SAR images of Enceladus before, as well as of Rhea and Iapetus; however, it seems that the previous images were much lower resolution. Discussion here on the Unmanned Spaceflight forum, with links to images.

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