[UPDATE: The hangout's over. Thanks to all who watched! I'll have the YouTube video up as soon as I can!]

I know this is last minute, but I decided to do a live Hangout on Google+ to talk about the solar eclipse. I’ve embedded the video below if you want to watch. If you want to ask questions, go to the link above or send me something on Twitter. If you leave a comment here I won’t see it!

Today’s the eclipse! I’m excited, though our weather here in Boulder has been fairly touch-and-go the past few weeks. I’m hoping for clear skies so I can see it; I got my eclipse glasses in the mail yesterday, so I’m all set. Locally, CU Boulder is holding a viewing in the football stadium! That’s a pretty nifty idea. As a reminder, the eclipse begins at 20:56 UTC (13:56 Pacific US time) on May 20, and ends at 02:49 UTC May 21 (19:49 on May 20 Pacific time).

I have links in an earlier post on where and when to watch (and yesterday I posted about why the "Supermoon" two weeks ago guarantees today’s eclipse being annular).

Observing the Sun during an eclipse can be tricky, since it’s very bright and can damage your eyes. Wikipedia has an excellent article about this. Something I want to make special note of: during the deepest eclipse, when the Sun is blocked the most, is ironically the most dangerous time to look at it with your unaided eye. Your pupil dilates (opens wide), letting in more light, but the parts of the Sun not blocked by the Moon are still just as intense. That makes it easier to damage your eye, so be very careful.

Of course, you shouldn’t look at the Sun with binoculars or through a telescope! That’ll destroy your eyes — literally — so seriously, it’s not recommended. The only exception is if you have the proper equipment designed specifically to view the Sun. Sky and Telescope’s site has a great rundown of how to observe the eclipse safely, including what equipment you can use.

For more on safe observations, check out Mr. Eclipse’s page, where he has a thorough list of how-tos. The websites io9 and for Astronomy Magazine have some good info, too.

Want an optometrist’s opinion? Here you go. Or you can try some of the tricks listed at The Exploratorium.

If you want to photograph the eclipse, again Mr. Eclipse has great stuff, and this You Tube video demonstrates making a Sun filter for your camera out of a Pop Tart bag! That’s not for your eyes; it’s just for taking pictures (and while some websites say it’s OK for cameras, your mileage may vary — and DO NOT USE THIS for binoculars or telescopes because it does not block enough light to be effective).

The picture here is of the Sun from just this morning, taken by NASA’s Solar Dynamics Observatory. It’s just to give you a reference of what the unblocked Sun looks like. There are some good-sized sunspots today, so they’ll provide a pretty contract and a nice background to the eclipse. To get a current picture, go to the SDO site and you’ll see it there (click the drop-down menu under the picture and select "HMI Intensitygram" to get the visible light view).

You can watch the eclipse online, too. Sky and Telescope has some info on that, and as I understand it NASA will have some live feeds on their Sun-Earth Connection site. The Japanese space mission Hinode will be watching the eclipse, too.

Finally, if you want a number of people to be able to see this event at the same time, the best way is to project the image of the Sun onto a wall or screen. Here’s a video with a very simple and clever method that I may try myself tomorrow. All you need is foil and a makeup (or other flat) mirror:

Cool! It’s essentially a pinhole camera with a bigger hole but a longer focal length, so you achieve the same results.

I hope everyone has clear skies and good, safe viewing of this wonderful event!

Image credit: NASA/SDO

As a change of pace, I was the guest rogue on this week’s episode of The Skeptics’ Guide to the Universe. We covered a lot of ground, from Futurama heads to asteroid mining to Mayans… and I have an abysmal record at the Science or Fiction segment when I’m on the show, so you can hold your breath in anticipation to see if I finally get one right, or once again go down in flames. I’ll note, obviously, that I always get it right when I listen to the show at home.

And nothing says love like Rebecca promising she’d freeze my head. Such a romantic.

The launch of the SpaceX Falcon 9 this morning was aborted at literally the last second — the sensors detected too high a pressure in a combustion chamber in one of the engines. Apparently this didn’t put the rocket in any danger, but it was outside the limits for an allowable launch so the computer shut things down.

[UPDATE: SpaceX is reporting a faulty valve caused the issue, and it's being replaced. They should be ready for the Tuesday launch window.]

Here’s video of the last few seconds of the countdown.

Ouch. My thoughts on this are pretty clear: it’s a bummer, but then again that’s all it is. Not a disaster, not a failure, just a setback. These are complicated, complex machines, and delays are inevitable.

The good news is there’s a backup launch date of Tuesday, May 22, at 07:44 UTC (03:44 Eastern US time), and another the next day, May 23, at 07:22 UTC. Hopefully, this glitch can be fixed and the rocket launched on one of those dates.

I wrote earlier about the annular eclipse happening this coming Sunday. It’s a solar eclipse, with the Moon blocking the Sun, but because the Moon is at apogee — the point in its orbit farthest from Earth — the Moon appears smaller in the sky, so it doesn’t completely block the Sun. We’re left with a ring of solar surface surrounding the Moon, the so-called Ring of Fire.

I got a couple of people asking me why this eclipse is happening at lunar apogee when we just had a "Supermoon", when the Moon was full at perigee (when it’s closest to Earth in its orbit). This is a good question! It’s not a coincidence. In fact, it must happen this way! Here’s why.

First, here’s a drawing of the Moon’s orbit, courtesy NASA:

The Moon orbits the Earth in an ellipse, so sometimes it’s closer to us, and sometimes farther. The ellipticity is exaggerated in the drawing; it’s actually about a 10% difference in distance between apogee and perigee. The Moon orbits the Earth once every 27.3 days, so it takes about 13.7 days for it to go from apogee to perigee — a little less than two weeks.

This is different than the phase of the Moon, which is how much of the Moon we see lit by the Sun. When the moon is between us and the Sun, it’s new: we only see the unlit side. When it’s opposite the Sun in the sky — when the Earth is between the two — the side of the Moon we see is lit, so we say it’s full. There are approximately 8 billion web pages describing how this works; here’s one I wrote. The time it takes to go from full Moon to full Moon is 29.5 days. That means to go from full Moon to the next new Moon takes half that time, or about 14.7 days — a little more than two weeks.

We can only get a solar eclipse when the Moon is between us and the Sun. This happens when the Moon is new (I’ll note in passing that it doesn’t happen every time the Moon is new, because the orbit of the Moon doesn’t align exactly with the Earth’s orbit around the Sun).

The phases of the Moon don’t line up perfectly with its position in the orbit because of the two different periods: 27.3 days to go around the Earth, but 29.5 days to go from full to full again (this video might help you). So sometimes full Moon happens at perigee, sometimes at apogee, and most of the time sometime in between.

Now let’s put this all together! The Supermoon is when the Moon is full and at perigee, right? That’s what happened on May 5th. On Sunday, a bit more than two weeks will have elapsed since then. That means the Moon will have moved halfway around its orbit — it actually reaches apogee on Saturday May 19th. But the phase has been changing, so it’s new on May 20, and it so happens that things have aligned for it to eclipse the Sun.

Since this happens the day after apogee, the Moon is farther away than usual, and from Earth it looks smaller. BOOM. Annular eclipse.

I think the confusion stems from folks not knowing the Moon orbits the Earth once per month on an ellipse, so it goes from perigee to apogee in two weeks. Once you get that, hopefully the rest of this makes more sense.

And because why not, I’ll leave you with this video showing the phase of the Moon as well as its apparent size in the sky as they change over the course of the year. If you want a detailed explanation of what you’re seeing, here ya go.

Enjoy the eclipse! And make sure if you watch it, you do so safely.

Image credits: NASA; Sancho Panza on Flickr.

Space X is looking good to launch its Falcon 9 + Dragon capsule on Saturday morning at 08:55 UTC (04:55 Eastern US time). NASA tweeted about it, saying there’s a 70% chance of good weather at that time. It’s Florida, so that can change in an instant. Check with NASA and Space X for updates.

Space X put together a press kit with details on the launch and mission activities. Via Universe Today I saw this nice video with a great CGI animation of what will happen:

It’s actually a couple of years old, but still fun to watch. NASA TV will be carrying the launch live, as will Space X, and Elon Musk — CEO of Space X– will be live-tweeting it.

Well, what can I say about this devastating and jaw-dropping picture of our nearest spiral neighbor, the Andromeda Galaxy?

[Click to massive chainedmaidenate. Do it!]

Well, I could start with HOLY HALEAKALA!

This image is a collection of 11 separate observations of Andromeda taken by NASA’s GALEX satellite. Launched in 2003, GALEX (which stands for Galaxy Evolution Explorer) scans the sky in ultraviolet light, specifically targeting galaxies. Hot stars produce UV light, and so does the gas it illuminates, so by looking in the ultraviolet astronomers can learn about how galaxies are constructed. In the decade since its launch, GALEX has been phenomenally successful, cataloging hundreds of millions of galaxies, some as far as ten billion light years away!

This image of Andromeda is simply stunning. It’s comprised of two colors: what you see here as blue is higher-energy ultraviolet light, and red is lower energy (closer to the kind of light we see). Right away you can see that objects emitting the higher-energy UV are confined to the spiral arms, and lower-energy emitters are spread out across the galaxy. That’s exactly what I would expect: massive stars, the kind that really blast out UV, don’t live very long. They’re born, live out their short lives, and die (as supernovae) pretty much near the spot where they formed, which is in spiral arms. Lower mass stars live long enough to gradually move away from their nurseries, populating the rest of the galaxy.

Also, star formation at the very center of the galaxy probably occurred long ago and shut down, so we don’t see many or any massive stars there.

One thing I didn’t know is that the arms of Andromeda are more like rings! The galaxy is at such a narrow angle that it’s hard to tell, but if you trace the blue emission, the pattern does look more like a ring than a spiral. This jibes with earlier images in infrared taken by Spitzer Space Telescope (which I’ve inset here) and a huge and incredibly beautiful newer one taken with ESA’s Herschel far-infrared telescope (and OMFSM you want to click that link).

From what I’ve read, it’s not clear why the spiral arms appear to be more ring-like. Which I love. Why? Because Andromeda is the nearest big spiral galaxy in the sky, a mere 2.5 or so million light years away. It’s easily visible to the naked eye from a dark site, and I’ve seen it myself countless times using my own eyes, binoculars, and telescopes ranging from small ones up to Hubble. Yet there it is, in all its huge and obvious splendor and beauty, still able to surprise me. That rocks.

And a note about GALEX: NASA recently handed off its operations to Caltech, a very unusual move. The satellite was put into standby mode in February, and I was worried it would be shut down permanently. However, Caltech signed a three-year agreement with NASA — while NASA still owns the satellite, Caltech will now be in control of GALEX’s science mission, managing and operating it. At the end of the agreement it can be renegotiated if GALEX is still in good operating condition. This is an interesting idea, and I’m not sure how I feel about it. I love that GALEX gets to continue operations, but handing off science missions to private groups makes me a little uneasy. In this particular case I think it’s fine — Caltech is a research institute after all — but the precedent may have unforeseen consequences. We’ll see.

Still and all, it’s good to see new life breathed into an important and wonderful instrument like GALEX. I certainly hope it will continue to produce cutting-edge science for years to come… as well as amazingly beautiful images like this one.

Image credit: NASA/JPL-Caltech