I am fascinated by junk floating around stars. And no, not paparazzi, har har. I mean circumstellar material, literally gas and dust orbiting other stars. We see it around stars that are dying, we see it around stars being born, and we see it even after stars are well into their youth.

One such young’un is the bright and shiny HR4796, a star 240 light years away, with about twice the mass of the Sun. It’s known to be less than 10 million years old — compare that to the Sun’s age of 4.56 billion years; we’re 450 times older! — and has also been known for some time to have material around it in the shape of a ring. New observations by Japan’s huge 8.2 meter Subaru telescope have provided some of the sharpest views of this ring ever taken, and revealed some surprises.

Isn’t that lovely? [Click to enannulusenate.]

This picture is in the infrared, well outside what the human eye can see. The star itself is so bright it’s saturated, overexposed. That part of the picture is blocked out to make it easier to see details around it, but the star’s position is marked with a dot. The tendril-like structures radiating outward are not real, but are artifacts of the image processing techniques. You can ignore them.

The important thing is the ring itself, which is easy to spot. It’s almost certainly a circle, but we’re seeing it at an angle (about 13° from edge-on) so it looks like an ellipse. It’s huge; 22 billion km (14 billion miles) across, more than twice as wide as our entire solar system.

Again, the ring has been known for some time; for example it was seen in Hubble observations back in 2009 [NOTE: as astronomer (and my friend) Glenn Scheider points out in the comments below, HR 4706's ring was seen long before 2009. I wasn't clear when I wrote the previous statement; I was only alluding to one particular earlier observation, but it wound up sounding like it was the earliest such observation. My apologies for any confusion.]. But there is some new stuff here. For one, if you look along the long axis of the ring, you can see it looks fuzzy. That’s real! The ring is made of dust grains of various sizes, probably the result of bigger clumps colliding with each other and grinding themselves up into ever-smaller pieces (the authors of this reasearch (PDF) call this a "collisional cascade", my new favorite phrase for 2012). These grains of dust orbit the star, and the smaller ones get blown away from the star due to the pressure of its fierce light. Bigger grains are less affected, so they tend to stay in place.

So the main ring is made of bigger grains, while the smaller ones are blown back, forming a larger, extended ring. That fuzzier outer ring is fainter and harder to see, but we see it more easily along the long axis because of geometric effects (similar to why soap bubbles and giant shells of cosmic gas look like circles in space). So even though we only see a part of this outer ring, the fact that we only see it in those two spots is what makes it clear we’re seeing a ring at all! Funny how that works.

(more…)

When Expedition 29 astronauts Mike Fossum, Sergei Volkov, and Satoshi Furukawa returned to Earth from the ISS on November 21, Dan Burbank stayed aboard the station and got this dramatic picture of them coming home:

[Click to deorbitenate.]

See it? The returning Soyuz capsule itself is the bright dot in the center of the picture, and you can see the trail of plasma behind it, pointing almost straight down. It’s almost lost against the city lights below it.

I couldn’t find this picture on NASA’s Gateway to Astronaut Photography, unfortunately, but a little sleuthing gleans some info anyway. (more…)

Reports are starting to come in that Comet Lovejoy is fading rapidly, which isn’t too surprising. As it gets farther from the Sun it gets colder, and the ice on its surface doesn’t turn into gas quite so vigorously. It’s the cloud of expanding gas that reflects sunlight and makes a comet bright, so there you go.

Still, astrophotographer Colin Legg managed to get enough shots to make this wonderful time lapse animation of Lovejoy as seen over Esperance, Australia on the evening of December 26/27:

Make sure you make it high resolution, and watch it full screen. The movement of the sky you see here is due to the rotation of the Earth, of course, but if you look carefully you can see the head of the comet moving a small amount relative to the stars.

So it looks like we northern hemispherians may never get a good look at Lovejoy… but you never know. Comets are difficult to predict, and Lovejoy has proven itself to be feisty. I wouldn’t bet on it, but I’ll keep my ear to the ground and my eyes to the sky just in case.

Tip o’ the Whipple Shield to Fraser Cain on Google+.

The Moon and Venus make a pretty pair, don’t they?

I took this shot myself an hour ago as I write this, about 17:00 local time here in Boulder. I used my cell phone camera, then in Photoshop cropped it to 610 pixels wide (the biggest my blog width will allow) and blurred it a tiny bit to reduce the background noise. You can just barely see the "dark" part of the Moon, lit by reflected Earth light.

The pair were closer together last night, and the Moon’s motion around the Earth are separating them more as you read this. But they’ll be back together again on January 26th (they’ll get about 6° apart, 12 times the width of the Moon), and even closer on February 25th, when they’ll be about 3° apart! That’s a really nice photo op, so be prepared for it. If I can get such a nice shot with just my crappy phone, imagine what real photographers with nice equipment can get. I hope to see lots of gorgeous pictures of the pair then.

The comet called Lovejoy is still putting on an amazing show for folks south of the Equator. Stéphane Guisard, an astrophotographer who takes stunning pictures of the sky (see Related Posts, below), was in Chile where Lovejoy is making a splashy scene just before sunrise. He created an amazing and lovely time lapse video of the comet, showing just how incredible this ephemeral visitor is:

[The video is hosted on Vimeo; if you have a hard time seeing it, there's also a copy on YouTube. Either way, make sure the resolution is set to its highest setting, and make it full screen.]

That’s phenomenal. The comet is seemingly pinned to the tail of the constellation Scorpius, deep in the path of the Milky Way. You can see some of the stars of Scorpius around the comet as well as a few deep-sky objects like clusters and nebulae.

The tail of the comet — made of dust particles and gas streaming from the solid, frozen (and quite tiny) nucleus of the comet as it’s heated by the Sun — is millions of kilometers long; the comet was over 100 million kilometers from Earth when these pictures were taken!

If you live in the southern hemisphere, the comet is visible just before sunrise; face east to see it. Binoculars should help. Finder charts are all over the web; Heaven’s Above is one I use quite often. You’ll want the darkest skies possible, and a clear horizon.

What a week for observing! All 8 planets are visible in the sky, from Mercury to Neptune (you’ll need binoculars at least for Uranus, and a telescope for Neptune; again check Heavens Above for a chart), as well as the Moon, and this spectacular and short-lived traveler. It’s almost enough to make me want to catch a flight to the Outback and set up camp, just for this chance at a long and once-in-a-lifetime night of viewing.

Credit: Stéphane Guisard, used by permission.

[I don't repost very often, but this one from last year still works. -- The BA]

I know some people have Christmas on their mind today, but this is a bit too literal: a brain scan taken at Newcastle University turned up a familiar face nose:

I always pictured him as somewhat bigger.

The part of the brain they were imaging? The hippocampus. Eh, close enough.

Happy holidays to all, and to all a clear night!

Tip o’ the stirring creature to BABloggee Michael Lonergan

One of my favorite astrophotographers, Alan Friedman, spied something odd on the Moon.

Flying reindeer I’ll buy. But an inertialess propulsion system? C’mon.

Happy holidays everyone!

Credit: Alan Friedman