A night in the shadow of the Earth
Planetary positions
Lunar eclipses can only happen when the Sun, Moon and Earth are exactly aligned. The Earth must be between the Sun and the Moon so that the Moon is full i.e. opposite the Sun in the sky. The Moon’s orbit is slightly angled with respect to the plane of the Earth’s orbit. For this reason the Moon also has to be in a special position (where it is aligned with the plane of the Earth’s orbit) otherwise we would get lunar eclipses at every Full Moon!
Wrap up warm
The golden rule of observational astronomy is make yourself comfortable. Lunar eclipses last hours and it can get pretty chilly under clear crisp dark skies. Make sure you wear lots of layers and have a warm drink and some food to hand. The worst thing, I find, is having to cut short a great observing session because you can’t feel your fingers!
Know your umbra from your penumbra
The Earth’s shadow is made of two parts. The outer lighter part is called the penumbra. As the Moon moves into the penumbra you begin to see the edge of the Moon dim and eventually get ‘eaten away’- this is called the partial phase. The centre of the Earth’s shadow is called the umbra and it is much darker. When the Moon starts to enter the umbra it rapidly begins to disappear until it is completely immersed, usually going a deep red colour – this is the ‘total’ phase.
Why does it go red?
The Moon goes red for the same reason the sky is blue. The Earth’s atmosphere scatters blue light. So as sunlight passes through our atmosphere most of the blue wavelengths are scattered away leaving predominantly red light to get through. This goes out into space and lights the Moon in a deep red glow.
But hang on if the Moon is in shadow why is it bathed in red light?
The simple answer is that the Earth’s atmosphere refracts (or bends) light around it so that even though the Moon is in the Earth’s shadow the bent red light is directed towards the darkened Moon.
Look out for the blue fringe
I only found out about this during the lunar eclipse on 3rd March last year. As light passes through Earth’s lower atmosphere it is reddened but as light passes through Earth’s upper atmosphere the ozone gas there absorbs light at red wavelengths. This can sometimes result in a noticeable blue fringe around the edge of the eclipsed Moon. I saw it during last years eclipse and you can see a slight hint of it in my image above.
How dark is the Moon?
How dark the Moon is during the total phase of the eclipse generally depends on how much dust and pollution there is in Earth’s atmosphere. You can estimate the darkness of the Moon using the Danjon scale. On the five-point Danjon scale 0 is a total phase where you can hardly see the Moon at all whilst 4 is a total phase where the Moon goes a bright coppery red.
Set your alarms!
February’s eclipse comes at a fairly unsociable time. Mid-eclipse when the Moon is in the darkest part of the Earth’s shadow is at about 3:30 in the morning. If you want to watch the whole eclipse you will have to start watching at about 00:40 on the 21st when the Moon begins to enter the Earth’s shadow. The Moon enters the umbra at about quarter to two and leaves it at about ten past five. Finally the Moon returns to normal as it completely leaves the Earth’s shadow at about quarter past six!
Grab a friend
Eclipses are definitely a social event so why not grab a few friends to share in the experience; even if it is just sitting in darkness waiting for completely cloudy UK skies to clear! ;-)
Equipment
The great thing about lunar eclipses is that you don’t need any special equipment to observe them. If you want to, it’s useful to use a pair of binoculars to get a closer look but these are by no means a prerequisite.
Good luck and clear skies!
Above: The total lunar eclipse of 3rd March 2007; copyright Will Gater.
Carnival of Space no. 41
The new Carnival of Space is in town over on the New Frontiers blog.
Galaxy eating monster reveals its secrets
A monster so huge it is capable of slowly devouring whole galaxies at a time. Sounds incredible doesn’t it? But that is what astronomers working on the Hubble Space Telescope think that the giant elliptical galaxy NGC 1132 is – a cosmic cannibal if you will. In this stunning new image from the NASA/ESA Hubble mission astronomers are seeing the vast hulk of a galaxy, 320 million light years distant, whose past is much darker than it might at first seem. That’s because whilst the stunning elliptical in Hubble’s new image looks serene and peaceful, it is in fact the aftermath of gravitational dance which saw the death of many smaller galaxies; and it all clinches on how astronomers think galaxies form.
One of the most popular current theories is that giant galaxies like NGC 1132 are made from the merger and assimilation of lots of smaller galaxies. Over time these vast elliptical giants like NGC 1132 emerge as enormous conglomerations of stars. Sounds all very vicious but in fact this galactic cannibalism is probably quite commonplace in the Universe if our theories of galaxy evolution are correct. Indeed Hubble scientists believe that our own Milky Way may have been partial to devouring the odd dwarf galaxy which strayed too close to it.
Yet the one question that we are bound to ask is how do we know? Well the answer comes from two main lines of evidence. The first is globular clusters. Galaxies like the Milky Way are home to globular clusters which reside above and below the disc of the galaxy. These are extremely ancient (and fairly compact) balls of stars and are useful tools for studying the evolution of stars. If you know where to look you can spot them through a small telescope on a clear night.
When Hubble scientists looked at NGC 1132 they noticed something interesting. A vast collection of globular clusters around the massive galaxy. They believe that what they are seeing are the globular clusters of NGC 1132′s victims – whole globular clusters that have been cast away as NGC 1132 merges with their parent galaxies. Since the stars in globulars are packed much more densely than the normal stars in the unfortunate galaxies their collective gravity holds the globular together. This means they can survive the huge gravitational disruptions involved in the merger and breakup of their parent galaxy.
The second piece of evidence comes from material we can’t see in this image – dark matter. Observations have shown that NGC 1132 is surrounded by a truly enormous cloud of dark matter. The dark matter cloud is thought to hold quantities of dark matter that are normally found residing in whole galaxy clusters of between ten and a few hundred galaxies – not one galaxy as seen with NGC 1132! NASA’s Chandra X-ray observatory was able to show that the galaxy is also surrounded by a glow from X-rays emitted from hot gas – about 120,000 light years in diameter – roughly the size of a galaxy cluster, giving yet more support to the idea that NGC 1132 is the result of the merging of one entire galaxy cluster.
If you want to find about more about this fascinating new result visit the Hubble website and whilst you’re there check out the latest Hubblecast.
Above: NGC 1132 from the HST
Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: M. West (ESO, Chile)
Book news (part I)
I achieved a milestone today in that I have finally got all the necessary image permissions for my book. The images are really cool and I can’t wait to submit my manuscript later in the year. Now I just have to finish the text…so it’s back to the word processor for me! In the mean time check out this incredible new image from Hubble and if you want to find out more about what’s going on in the image download the Hubblecast!
How did Mercury get so dense?
I’ve done several radio interviews in the past few weeks on the NASA Messenger mission to Mercury. One question that keeps popping up is – ‘How did Mercury get so dense?”. It’s a great question and one that is sometimes difficult to answer, fully, in a few seconds on air so I thought I would take some time to explore it in a post on the site.
Mercury is a tiny planet, some 4879km across, not much bigger than our own Moon. Its density of 5.3 grams for every cubic centimetre makes it the densest of all the terrestrial planets (those are Venus, Earth, Mercury and Mars) but also one of the most intriguing. The Mariner 10 probe which studied Mercury during the mid seventies mapped not quite half of the planet but it did give us an insight into a peculiar little world with some fascinating geology. Fascination that runs much deeper than the cratered, volcanic and battered surface that we see in the latest Messenger images. Measurements of Mercury’s density infer that much of the planet must be made of a iron-rich core that accounts for 60% of the planet’s mass and an incredible 75% of its radius! But why is it so dense? At the moment scientists just aren’t sure, which is just one reason why Messenger and other missions are going to be scrutinizing Mercury over the next few years. But we do have some ideas.
One theory argues that the bright, extremely hot young Sun played a role in vaporising away rocky material on the surface of Mercury as it was in the process of forming. This would mean that Mercury would be predominantly made of metallic material that had (by then) formed a substantial core; any elements and chemicals that could be easily vaporised and blown away would be notably absent or depleted in the Mercurial geology.
Another suggestion, according to NASA scientists, says that when the Sun and all the planets were forming in the solar nebula (the great cloud of dust and gas around the young Sun), tremendous amounts of gas could have had an important role in deciding what materials Mercury formed out of. To understand this let’s look at a simplified view. Rocky particles (silicates) in the solar nebula, when the planets were forming, were much lighter than their metallic counterparts. As such the gas around our star was able to whisk the lighter particles away and into the Sun, effectively sieving out the lighter silicates in the material from which Mercury went onto form. What was left was a metal rich cloud from which Mercury formed.
Lastly then and perhaps the most exciting idea is that Mercury was smashed into by a large body after its formation. This scenario requires Mercury to have already formed in much the same was as the normal terrestrial planets. The layers in Mercury’s internal structure would be fairly well defined by this stage rather than a mix of all sorts of material. It would have a metallic core with a rocky (silicate) crust and mantle (similar to the Earth’s structure). The theory says that a large body (like a rogue proto-planet) might have collided with the young Mercury blasting away its crust (and much of its mantle) leaving the mostly metallic material at its centre. (Think of it as smashing a boiled egg so that the shell and the white fly away leaving a little yellow core.)
So the answer to the question of ‘How did Mercury get so dense?’ is…we just don’t know yet. Nevertheless Messenger and the handful of other European and Japanese missions to Mercury will be more than equipped with their instruments to try and find out by studying Mercury’s magnetic field, its surface geology and composition.
To find more about the Messenger mission go to the NASA website.
Above: Mercury in colour imaged by Messenger
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“Hazy red sunset on extrasolar planet”
Here is the latest release from the ESA/Hubble office that I have been working on. Hubble astronomers have used the orbiting space observatory to study the atmosphere of the extrasolar planet HD189733b (a number I can’t seem to get out of my head having written it so many times over the past few weeks). This world had previously been observed by the Spitzer Infrared Space Telescope but now Hubble has shown that it actually has a layer of hazes in its upper atmosphere made up of tiny grains of (probably) silicates, iron and aluminum oxide. To read the full press release visit the ESA/Hubble website and of course there is the latest episode of the Hubblecast out where Dr J talks to the head of the ESA/Hubble group Dr Bob Fosbury about this amazing world.
Image credit: ESA, NASA and Frédéric Pont (Geneva University Observatory)
“A grand design in a galactic festoon”
The latest Hubblecast is now out! In this episode we present a new stunning Hubble image. M74 is a beautiful spiral galaxy located 32 million light years away. Hubble imaged the galaxy with its Advanced Camera for Surveys between 2003 and 2005.
“Messier 74, also called NGC 628, is a stunning example of a ‘grand-design’ spiral galaxy that is viewed by Earth observers nearly face-on. Its perfectly symmetrical spiral arms emanate from the central nucleus and are dotted with clusters of young blue stars. In the new Hubble image we can also see a smattering of bright pink regions decorating the spiral arms.
These are huge, relatively short-lived, clouds of hydrogen gas which glow due to the strong radiation from hot, young stars embedded within them; glowing pink regions of ionized hydrogen (hydrogen that has lost its electrons).”
You can watch the Hubblecast here.
Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration
“Hubble shows ‘baby’ galaxy is not so young after all”
The latest news release from the NASA/ESA Hubble Space Telescope is out now on the ESA Hubble website – www.spacetelescope.org. It’s the story of how a galaxy we thought (for quite a long time as it happens) was really young is in fact very old.
“The NASA/ESA Hubble Space Telescope has found out the true nature of a dwarf galaxy that astronomers had for a long time identified as one of the youngest galaxies in the Universe. Astronomers using the NASA/ESA Hubble Space Telescope have made observations of the galaxy I Zwicky 18 which seem to indicate that it is in fact much older and much farther away than previously thought.”
Image credit: NASA, ESA and A. Aloisi (ESA/STScI)
I Tune, You Tube, We Rule
One of the projects which the ESA/Hubble group here in Germany is involved with is the International Astronomical Union’s commission on Communicating Astronomy With The Public.
Part of this project involves the publication of a journal for science communicators (with a focus on astronomy communicators). The journal hopes to be a repository of ideas and information as well as tips on communicating astronomy with the public.
The first issue has now been released online to coincide with the 2007 Communicating Astronomy With The Public conference held in Athens. I have an article (co-authored with Raquel Yumi Shida) on the use of new media in communicating astronomy. Entitled ‘I Tune, You Tube, We Rule’ you can download it to read for free online here.
NGC3603 – An extreme star cluster bursting into life!
Finally it’s here! – News from the NASA/ESA Hubble Space Telescope “NGC3603 – An extreme star cluster bursting into life!”
This is the release & Hubblecast I have been working on for the last few weeks. It is now online and you can read the full amazing story here. Also why not view the latest Hubblecast (no.9) here.
Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration
Touchdown in Germany
A few days ago I arrived in Germany to begin three months working on a science communication internship for the ESO/ESA/ST-ECF Hubble Europe Information Centre (HEIC) in Garching near Munich. The centre is located about 2km from Garching and is about an hour and a half from the Bavarian Alps. HEIC is part of the ESO headquarters here (alongside the Max-Planck Institute for Astrophysics) and is the central production hub for all media/press information and science communication literature and media, from Europe, about Hubble.
Each month our group sends out news and photo releases, vodcasts and much more about Hubble’s latest discoveries. They also manage outreach and public affairs for a number of other astronomical organizations and projects such as the IYA 2009.
Yesterday was my first day working in the offices here and I enjoyed it hugely! My job here is as a science writer so my main responsibilities lie in writing news and photo releases for the press, editing other releases and scripting the Hubblecast, ESA’s vodcast about recent Hubble results. I am also editing part of the Hubble website www.spacetelescope.org, helping to update sections with the latest science results. The pace of the work makes for a really exciting day. I started work at 9am and by 10am was doing my first teleconference with a scientist in Spain whose research I was writing a photo release on. The image we are working on is incredible and I will show everyone on this site once it is released (and the embargo is lifted) sometime in the coming weeks.
Within our offices there are graphic designers, science writers, web developers and others working on cool projects that the HEIC teams are related to. The team also consists of many other people who work on Hubble outreach and science communication projects, these include the people who turn data into amazing images. One of the coolest things to see is how the image you see on the news or in astronomy magazines goes from the raw Hubble data to these stunning pictures we’ve come to know and love. I think I’ll devote another whole post to that process later. It is quite something to see a fresh image which only the scientists working on and the people in the HEIC office have seen!
For now though why not go and watch the latest version of the Hubblecast here?
Astronomy Now special report on infrared astronomy
The latest issue of Astronomy Now is now in the shops. Why not check out my Special Report on the latest incredible images from the AKARI Infrared spacecraft as well as my feature on 10 astronomy experiments for the younger audience.
New Astronomy Now article
I have a new feature article entitled “A day out at Europe’s ‘space city’” published in the June issue of Astronomy Now.
