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Penumbral eclipse of the moon, tonight

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Most people won't notice it, but we will have a lunar eclipse tonight, visible from anywhere in Australia (weather permitting, of course) — and also from New Zealand, most of the Pacific, Alaska, China, parts of India and most of Russia. The continental US sees only part of the eclipse, with the Moon setting before it ends.

A penumbral eclipse happens when the Moon goes through the penumbra of the Earth, the area of "partial shadow" around the main shadow of the planet. Viewed from the Moon, this appears as a partial solar eclipse (an umbral eclipse is seen from the Moon as a total solar eclipse).

In eastern Australia, the eclipse starts at 23:36 AEST AEDT (12:36 UTC), with the maximum eclipse at 01:38 tomorrow morning (14:38 UTC). Visually, you will see one "corner" of the full Moon clearly darker that the rest of the disk. More information and a visibility diagram can be seen at the HMNAO eclipse's website.

Australia Day Eclipse

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Next Monday (26 January) is Australia Day, and nature will help in the celebrations with a partial solar eclipse visible from the whole country (except Tasmania) — even if barely, from some places.

This is actually going to be an annular eclipse in some parts of the world, most of them covered by water. The path of the eclipse starts over the South Atlantic, southwest of South Africa, and follows east from there over the Indic Ocean ending over Indonesia, which is the most significant land mass from where the annular eclipse will be visible.

In Australia, the places with the best view will be (not surprisingly) those closest to Indonesia. Darwin will see the Moon covering a bit less than half of the Sun (41.3%, to be precise), with the maximum occultation happening just before sunset, at 7.03pm local time (the sun will set during the eclipse). From Melbourne, we'll see the Moon covering just about 0.4% of the Sun at 7.54pm local time — just a barely visible "nick" on the Sun's disk, but it should still be visible (the sun sets at 8.38pm on that day). Sydney sees 1% of the Sun being covered at 7.59pm, which is just about at sunset.

The weather forecast for next Monday in Melbourne is for a sunny, cool day, so going out to look at the sunset and to try to spot the eclipse might be a good program for the end of the holiday (just remember to be very careful when looking straight at the Sun).


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Everyone is posting photos of the spectacular conjunction of Venus, Jupiter and the Moon that happened this Monday (and that famously greeted Australians with a pretty smiley face in the western sky). So I thought I'd post a photo of a different conjunction...


I know, not quite an astronomical image. Fun nonetheless.

More exoplanet images?

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2008-11-22-bpictoris.jpgNow, this is not 100% confirmed, but it does look like we've got another image of an extrasolar planet: this one (if real) is orbiting the star β Pictoris, a very young star 70 light-years away from us.

The potential discovery comes from a new analysis of images taken in 2003 with ESO's Very Large Telescope. The images were processed to subtract from them the light coming directly from the star, allowing scientists to see objects that are around it; this showed a very distinct point of light very close to the star and in the same plane as the dust ring that surrounds it, but we can't still rule out the possibility that this is a background or foreground object instead of something actually in the neighbourhood of the star.

If this is a real planet, it is closer to its star than the other ones imaged previously, being approximately as far from it as Saturn is from the Sun; it would be a very large planet, though, about eight times as massive as Jupiter.

New observations might prove this object to be a planet (by showing its movement around the star, presumably), so we will definitely hear more about β Pictoris in the future. More details at the ESO press release.

Extrasolar planets imaged directly

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2008-11-14-fomalhaut.jpgThis has been the talk of the Internet today, so I might well write about it as well... for the first time, scientists were able to capture images (in visible light, no less) of not one, but four extrasolar planets orbiting around two separate "normal" stars (we had already seen images of a planet orbiting a brown dwarf star).

First, we have star HR8799, a young star that is a bit larger than our Sun (1.5 times as massive and 5 times as bright) and that lies 130 light years away in the constellation Pegasus. Images taken with the Keck and Gemini North telescopes in Hawaii show three large planets orbiting this star; one is about seven times and other two are 10 times as massive as Jupiter. They orbit the start at distances ranging from 24 to 67 AU (the planetary limits of our own solar system are around 30 AU).

Apart from the historical value of directly imaging these planets, this event is significant for other reasons: this star is very similar to our own, and these large planets are orbiting it at a large distance, leaving space closer to the star for small rocky worlds; in other words, this might be a solar system similar to our own, which is something of a rarity among the hundreds of other solar systems we've already found.

Secondly, we have Fomalhaut, a larger star (2.3 times as massive and 16 times as bright as the Sun) 25 light years away in the constellation Pisces Austrinus, the southern fish. It's been known for a while that this star is surrounded by a large dust disk; in fact, the very sharp inner edge of this disk was a clue that there was a planet there, cleaning out debris just inside the disk. And, indeed, Hubble images do show a bright planet located there, in a very wide orbit around the star. The planet seems to be about twice as massive as Jupiter, and its brightness may indicate it is surrounded by a very large ring system.

The planet orbits the star once every 872 years at a distance that is almost four times the distance from Neptune to our Sun, but since Fomalhaut is brighter than our Sun its appearance would be similar to how the Sun appears when seen from Neptune. Just as is the case with HR 7899, Fomalhaut is a very young star and its solar system is still being formed, which helps in the detection of the planets: they're still hot enough that they radiate brightly in the infrared.

Both stars are visible with the naked eye from a dark sky site, and Fomalhaut should be easily visible even from a urban setting. If you are in Melbourne (or any place at the same latitude), Fomalhaut will be almost directly overhead today soon after sunset — it's bright enough that you can't really miss it. HR 7899 will be a bit harder to find; Pegasus will be visible on the northern sky in the middle of the night, and the Lowell Observatory press release has a diagram that will help you find the right star (it's likely you will need a binocular or small telescope, though).

For more details and images, in addition to the links in the text above, see the (very enthusiastic) Bad Astronomy blog and Centauri Dreams.

Close to the Moon

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Moon close to JupiterIf you like seeing close appearances of bright objects in the sky, this week is being very good for you (assuming the weather in your location is being better than here). Last Saturday, the (very thin crescent) Moon was very close to Venus soon after sunset; I went out to try to look at it, but the only clouded area on the sky was the western horizon up to some 45 degrees... so, no luck there.

Tonight it is Jupiter's turn, with the Moon (now considerably less thin) very close to it and both setting around midnight. Jupiter is not as bright as Venus but it's no less spectacular (especially considering that the sky will be darker as it sets later). The sky is fully clouded here, I hope people have better luck in other locations...

(the times above are for Melbourne, and things will look different — that is, the Moon closer or farther away from Jupiter — depending on where you are)

Flare in EV Lacertae

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One of the most important events in Greg Egan's novel Diaspora happens when a pair of neutron stars in the constellation Lacerta collide, sending out a powerful gamma ray burst and causing the extinction of most life on Earth. I was reminded of that while reading, earlier today, about an unassuming, small red dwarf star in that constellation sending out a massive flare, thousands of times more strong than the ones our Sun sends out every now and then.

There's no risk to us, of course, and Phil Plait does a much better job than I would be able to of telling the whole story; go there, it's an excellent read.

Still, that's one more way the universe can kill us all... (and I guess I'll go reread Greg Egan's novels...)

Lunar eclipse, 21 February

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Most people must have heard by now that there will be a total lunar eclipse later this week, on Thursday (or Wednesday, depending on your time zone). Unfortunately Australians will miss this one; it will be visible, at least in part, basically everywhere else but here (that's not entirely true: Japan, most of China, southeast Asia, New Zealand and several Pacific nations will also miss it, but it's close enough to the truth...).

The eclipse starts at 00:34 GMT on Thursday (11:34 ADST for those intent on following it online; or, for American readers, 19:34 EST or 16:34 PST on Wednesday — observers in the west coast of the US will see the Moon rise with the eclipse already in progress) and totality will go from 03:00 to 03:51 GMT (Thu 14:00-14:51 ADST, Wed 22:00-22:51 EST, Wed 19:00-19:51 PST). Full details are here.

For the record, Australian observers will see part of a partial (but almost total) eclipse on 16 August — the Moon will set for all of the country before the eclipse is over.

Annular solar eclipse, 07 February

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This Thursday we'll have the first solar eclipse of 2008, but very few people will actually see more than a very small partial eclipse. It won't be a total eclipse, but an annular one: this happens when the Moon is not large enough in the sky to cover the whole disk of the Sun (when seen from what would normally be the path of totality, the Sun will form a ring around the disk of the Moon).

The path of "annularity" covers just part of Antarctica and some areas of the southern Pacific; the annular phase starts at 03:20 UTC and ends at 04:30 UTC. A partial eclipse will be visible from eastern Australia, New Zealand and neighbouring island countries. From Melbourne, the eclipse will start at 2:38pm (local time) and end at 4:14pm; the maximum eclipse will happen at 3:28pm, but just a bit more than 8% of the Sun will be obscured, so it will be barely noticeable (and the forecast says it will be raining, anyway); add about 15 minutes to these times if you are in Sydney (and you'll see just over 11% of the Sun being obscured). For more details and for information about other locations, see the excellent website of the Nautical Almanac Office of the UK.

NEVER LOOK DIRECTLY AT THE SUN, neither with your naked eyes nor with binoculars or telescopes unless they are correctly fitted with the proper filters; if in doubt, don't to it.

Venus, Jupiter and the Moon get together

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Venus, Jupiter, Moon conjunctionIf you happen to be up just before dawn tomorrow morning, look to the east for a beautiful show: Venus and Jupiter have been very close to each other for a few days already, but tonight the Moon joins them to make for a nice trio lighting up the sky before dawn.

The planets should be very easy to identify, even if you don't know which side is east. Venus is now by far the brightest object in the sky and it is rising a few hours before the Sun; Jupiter is somewhat fainter but still brighter than almost anything else.

The Moon will be a very thin crescent, which probably will add to the show (a full Moon would "wash out" the brightness of Venus and Jupiter). Venus will be almost a full disk, but on a telescope it should be easy to see that it is not quite full (and Jupiter, of course, will be full, as always).

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