The magnitude system used by astronomers ranks
stars by brightness, with the brightest stars having the
lowest values of magnitude. A star's magnitude is generally
measured after the starlight has passed through a colored
filter, which gives a measure of a star's color. Literally
dozens of filter systems are used by astronomers. The
most common system for measuring color over the infrared,
visible, and ultraviolet wavelengths is the Johnson-Cousins
UBVRI system.
Stellar Types
In the nineteenth century, astronomers recognized
that stars could be classified by their spectra into a handful
of types. Over time, this system was refined to characterize
a star in terms of prototypical stars with similar spectra.
This is the meaning of the jargon that the Sun is a G2 V
star: the G2 refers to the pattern of lines in the Sun's
spectrum, which is directly dependent on temperature, and
the V refers to the widths of these lines, which are
dependent on luminosity. The advantage of this system
is that astronomers can determine what stars are like the
Sun in temperature and luminosity simply by looking at
the patterns of lines in the stars' spectra.
Brown Dwarfs
A class of object, long predicted by astrophysicists,
sits in the mass range between the giant gaseous planets
and the M dwarf stars. These objects are called brown
dwarfs. They are massive enough to burn deuterium, but they
are too light to burn hydrogen. The first brown dwarf was
observed orbiting an M dwarf star in 1988, and since that
time, hundreds of additional brown dwarfs have been found.
They are cool, so they are primarily emitters of infrared
radiation. In the early stages of their lives, they are
powered by deuterium fusion and gravitational potential
energy, but when they consume their deuterium, and when
the electron degeneracy pressure stops their shrinkage,
they grow cold and dark.
Mercury in Color
Messengers look at Mercury. Click for larger. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
As the Messenger spacecraft approached Mercury for its third and final flyby, it took this image of the planet. Taken through red, green and blue filters we can see Mercury in full color. I am a little surprised at how much color there is actually, I had expected a rather bland grey tone with the occasional bright crater.
Mercury is a pretty remarkable planet. It’s a pretty bright place too. Apparent brightness is inversely proportional to the square of the distance, so if Mercury is 3 times closer to the Sun, the Sun appears 32 or 9 times brighter than it does to us on Earth.
You would think that being so close to the Sun the orbit of Mercury would have a pretty circular orbit, it doesn’t, it has the most elliptical orbit of ANY of the planets!
Of course you know it’s hot, as hot or hotter than the oven in your kitchen, but you knew that. A long hot day on Mercury is really long too, 176 days long actually. As hot as it is, the nights are bone chilling to say the least, how about -279 oF! At one time there was speculation there may be ice in some of the craters in the perma-shade at the poles – sound familiar? I”m not sure what the current thinking is on that.
Mercury is very dense, 5.43 grams/cc, almost as dense as Earth at 5.52 grams/cc. How come? Mercury has a HUGE iron core, the iron core is about 75 percent of the radius of Mercury. Messenger has found that iron is also prevalent in the mantle. This was kind of an unexpected finding, the conventional thinking was the mantle was mostly basalts like the moon.
How the iron core came to be is for another time.
Head over to the Messenger site for much more on Mercury.
Hubble and M83
Hubble's image of a portion of M83. Click for larger. Image credit: NASA, ESA, R. O'Connell (University of Virginia), the WFC3 Science Oversight Committee, and ESO.
Hubble was trained on the spiral galaxy M83 and the new camera took this image. WOW! This is just a portion of the galaxy, click the Hubblesite link below to see the image in it’s full context.
M83 is the designation in the famous Messier catalog for the galaxy is also known as the Southern Spiral. Here’s the SEDS page.
I really enjoyed the description of the image from Hubblesite (click the link for more images) be sure to give it a read:
The spectacular new camera installed on NASA’s Hubble Space Telescope during Servicing Mission 4 in May has delivered the most detailed view of star birth in the graceful, curving arms of the nearby spiral galaxy M83.
Nicknamed the Southern Pinwheel, M83 is undergoing more rapid star formation than our own Milky Way galaxy, especially in its nucleus. The sharp “eye” of the Wide Field Camera 3 (WFC3) has captured hundreds of young star clusters, ancient swarms of globular star clusters, and hundreds of thousands of individual stars, mostly blue supergiants and red supergiants.
The image, taken in August 2009, provides a close-up view of the myriad stars near the galaxy’s core, the bright whitish region at far right.
WFC3’s broad wavelength range, from ultraviolet to near-infrared, reveals stars at different stages of evolution, allowing astronomers to dissect the galaxy’s star-formation history.
The image reveals in unprecedented detail the current rapid rate of star birth in this famous “grand design” spiral galaxy. The newest generations of stars are forming largely in clusters on the edges of the dark dust lanes, the backbone of the spiral arms. These fledgling stars, only a few million years old, are bursting out of their dusty cocoons and producing bubbles of reddish glowing hydrogen gas.
The excavated regions give a colorful “Swiss cheese” appearance to the spiral arm. Gradually, the young stars’ fierce winds (streams of charged particles) blow away the gas, revealing bright blue star clusters. These stars are about 1 million to 10 million years old. The older populations of stars are not as blue.
A bar of stars, gas, and dust slicing across the core of the galaxy may be instigating most of the star birth in the galaxy’s core. The bar funnels material to the galaxy’s center, where the most active star formation is taking place. The brightest star clusters reside along an arc near the core.
The remains of about 60 supernova blasts, the deaths of massive stars, can be seen in the image, five times more than known previously in this region. WFC3 identified the remnants of exploded stars. By studying these remnants, astronomers can better understand the nature of the progenitor stars, which are responsible for the creation and dispersal of most of the galaxy’s heavy elements.
M83, located in the Southern Hemisphere, is often compared to M51, dubbed the Whirlpool galaxy, in the Northern Hemisphere. Located 15 million light-years away in the constellation Hydra, M83 is two times closer to Earth than M51.
Cassini Flyby of Enceladus
Image: NASA/JPL/Space Science Institute – Cassini
Cassini has weathered its Nov 2, 2009 flyby of the Saturn’s moon, Enceladus, in good shape. The flyby placed the spacecraft at about 100 km (60 miles) above the surface of Enceladus at its closest point, and directly through the plume you see imaged here in the south polar region. Water vapor, sodium, complex hydrocarbons such as propane and ethane, and other organic molecules have been detected in the plume in previous flybys. This closer look at the material in the plume might help answer some of the questions science has for Enceladus.
Currently thought to have an ocean of liquid water under a mantle of ice, and known to be geologically active, Enceladus looks like a good place to search for extraterrestrial life. Material released from Enceladus is also thought to be the source of Saturn’s E ring. Modest in size (its diameter is only about 500 km), this moon certainly is an interesting study. As it’s surface is covered in water ice, Enceladus reflects almost 100% of light reaching it. In addition, it has a source of internal heat, and it even has a thin atmosphere composed of water vapour, nitrogen, carbon dioxide, and methane.
Here is a beautiful image of Enceladus with Saturn behind it, and the rings below it:
NASA/JPL ESA SSI Cassini Imaging Team
This natural color image was taken early in 2006. The marks on Saturn in the upper left of the image are ring shadows.
NASA scientists will be working to interpret the information Cassini collected as it passed through the icy plume Monday. I’m hoping we’ll gain more of an idea of what lies beneath the ice crust of Enceladus.
You can read more about Cassini by going to the Mission homepage.
Happy Halloween!
The Witch Head Nebula. Click for larger. Image Credit and copyright: APOD and Star Shadows Remote Observatory (Steve Mazlin, Jack Harvey, Rick Gilbert, Teri Smoot, Daniel Verschatse).
This is an Astronomy Picture of the Day selection from last year featuring the Witch Head Nebula.
The Witch Head Nebula is about 1,000 light-years away in the constellation of Orion. The nebula is known as a reflection nebula because it is illuminated by a nearby star or group of stars, in this case the star is the blue supergiant Rigel.
I was going to use a different version of this nebula for today, but this one is just too good not to use, the bright star Rigel just makes the image all the better.
You can see this image in it’s original context AND links to other scary sights (be very sure to look at the link for the veiled spectre) at APOD.
The original image: A “Witch by Starlight” Credit & Copyright: Star Shadows Remote Observatory (Steve Mazlin, Jack Harvey, Rick Gilbert, Teri Smoot, Daniel Verschatse). I tried to image the Witch Head a couple years ago and had very little success so in my book this image isn’t just good, it’s extraordinary.
If you are out and about tonight HAVE FUN AND BE SAFE!
Oh and when you go to the APOD site you can get a larger version so you can put it on your desktop.
Ares 1-X Launch
Click here to view the embedded video.
I had a meeting out of town and missed the launch, so I thought I’d put it up in case you did too. I like the imagery from the rocket.
Some were trying to do their best to make the launch a failure because of a partial parachute failure for the booster section as it returned. Partial = one of three parachutes and the one that failed actually deployed first.
The parachutes are being checked out this weekend and it could be a failure of he suspension system and not of the chute material.
It may be a moot point. The Obama administration may be heading towards ending human spaceflight anyways. Some will cheer this news I suppose, I don’t exactly cheer the “dumbing down” of America any more than we have. Even from an economic standpoint it’s not a great move either, unless putting thousands more out of work is good.
Course, the argument is well we can leave these things to someone else and just get what we need from them. Them being somebody else, anybody else. Yep that is true, and look how good that’s working for us in general. In the whole country we don’t even have a single manufacturer for the flu vaccine for crying out loud. We have allowed ourselves to be at the mercy of everybody else because we have lost the ability to do for us.
It’s a disgraceful situation. Oh and for the record, the handling of he H1N1 thing is an embarrassment, good thing it’s not a more serious flu we’d really be up the creek.
Here’s the video source.
Confessions of an Alien Hunter
Confessions of an Alien Hunter, by Dr. Seth Shostak of the SETI Institute, is a look at SETI from the inside. In addition, Dr. Shostak talks about who, and what, our first alien contacts may be (aside from microbes or pond scum). You know me; I would be excited out of my tiny little mind with a microbe.
The hope, the belief, that we are not alone in the universe has been with us since we could envision ourselves as “self”. We have always looked to the sky and wondered. Science now tells us that there must be other life; the universe is simply too big for there not to be. Life is ubiquitous on Earth, it’s found from the bottom of the Mariannas Trench to the summit of Mount Everest.
The SETI Institute was officially funded and created by NASA in 1971, although the first SETI experiment took place eleven years earlier at Green Bank, West Virginia. Now privately funded, SETI uses scientific methods for the systematic search for evidence of intelligent extraterrestrial life. They aren’t looking for pond scum.
Confessions of an Alien Hunter is published by the National Geographic Society, one of the world’s largest non-profit organizations. National Geographic is involved in natural science, education, geology, archaeology, exploration, and conservation… just to name a few.
Dr. Shostak gives televised lectures and interviews, in addition to writing books. Here is a link to just one of them. I’d recommend you take time to watch as Dr. Shostak is an incredibly interesting speaker.
This is the link to SETI@home, if you’re interested in linking your computer to assist SETI during the times you aren’t busy. It functions much like a screen saver. I’ve had my computer linked to SETI for over a year, and haven’t had any trouble, although some people say it makes their computer over-heat.
Dr. Shostak has already promised us an interview in the future, so if you have any questions for him, let me know and I’ll ask him.
LRO Spies Apollo 17 Site
Region of Taurus Littrow valley around the Apollo 17 landing site. Click for larger. Credit: NASA/GSFC/Arizona State University
The Lunar Reconnaissance Orbiter captured this look at the landing site for Apollo 17. If you click the image above you will get a larger version of the image. You can see an enlargement of the Challenger Descent Stage and the immediate area by clicking here.
Want to know what the more cryptic annotations mean? Here’s the LRO press release:
Apollo 17 Lunar Module Challenger descent stage comes into focus from the new lower 50 km mapping orbit, image width 102 meters. Credit: NASA/GSFC/Arizona State University.
LRO maneuvered into its 50-km mapping orbit on September 15. The next pass over the Apollo 17 landing site resulted in images with more than two times better resolution than previously acquired. At the time of this recent overflight the Sun was high in the sky (28° incidence angle) helping to bring out subtle differences in surface brightness. The descent stage of the lunar module Challenger is now clearly visible, at 50 cm per pixel (angular resolution) the descent stage deck is 8 pixels across (4 meters), also note that the legs are also now distinguishable. The descent stage served as the launch pad for the ascent stage as it blasted off for a rendezvous with the command module America on 14 December 1972.
Tracks are clearly visible and can be followed to the east, where astronauts Jack Schmitt and Gene Cernan set up the Surface Electrical Properties experiment (SEP). Cernan drove the Lunar Roving Vehicle (LRV) in an intersecting north-south and east-west course to mark positions for laying out the SEP 35-meter antennas (circle labeled “SEP” marks the area of the SEP transmitter). The dark area just below the SEP experiment is where the astronauts left the rover, in a prime spot for monitoring the liftoff.
The WHAT Cloud?
Okay. The solar system is, like, really big, you know? No, I mean really, really big. Like, super-massive “epic” big, you know?
Sorry about that. I couldn’t resist. Although the wording is annoying, the statement itself is correct. The solar system is a big place; a lot bigger than some people realize. Beyond the planets (and poor, demoted Pluto), beyond the Kuiper Belt and the scattered disc, we find the Oort Cloud (rhymes with “fort” and “short”).
NASA/JPL (Artist’s conception of Kuiper Belt and Oort Cloud)
It’s mind-boggling to think that the tiny little blue rectangle contains the sun, all the planets, and the Kuiper Belt.
Although no confirmed, direct observation of the Oort Cloud has been made, most astronomers believe it to be the source of all long-period comets (like Halley), and of many of the Centaur and Jupiter class comets. Loosely bound to the solar system, objects in the Oort Cloud are easily influenced by passing stars and the pull of the Milky Way itself. These shifting gravitational influences will occasionally dislodge an Oort Cloud object and send it shooting into the inner solar system, where we see the objects as comets.
Composed of an inner and outer region, the majority of Oort Cloud objects are believed to be made up of ices such as water, methane, ethane, carbon monoxide, and hydrogen cyanide. Object 1996 PW is a rocky asteroid believed to originate in the Oort Cloud.
Comet Hale-Bopp; an archetype of Oort Cloud objects:
Image: Mkfairdpm; English WikiPedia (some rights reserved) April 1997
Besides long-period comets, only four objects so far are believed to belong to the inner Oort Cloud: 90377 Sedna, 2000 CR105, 2006 SQ372, and 2008 KV42.
While the exact size of the Oort Cloud is unknown, it is believed to extend about 30 trillion km from the sun (18 trillion miles). That puts its outer boundaries at slightly over three light-years (a light year is exactly 9,460,730,472,580.8 km). To put some perspective to that distance, after 32 years Voyager I is only 16.596 billion km from the sun.
The Jewel Box
The Jewel Box, NGC 4755 from the ESO. Wallpaper links below. Credit the ESO.
The Jewel Box is another name for the open cluster NGC 4755. From the looks of this ESO image, it’s little wonder how English astronomer John Hershel came up with the name when he coined it in the 1830’s.
NGC 4755 is an open cluster, a collection of stars bound loosely by gravity evolved from the same “nursery”, or cloud of dust and gas, so they tend to be similar in age and composition. Because they are all of the same approximate age, but do vary in mass so they can be at differing life stages.
Higher mass stars will age faster than lower mass stars and sometimes you can see stars in the red giant phase (more mature and nearing the end of their lives) right along with other stars that might only be half way through their lives or even less.
Located about 6400 light-years away, in the constellation of Crux, near the Southern Cross, I know many readers can see it just fine, sadly it’s too far south for me. No matter, The Jewel Box is stunning and I decided it would make a very nice desktop. While I was at it I made up a few different sizes, most required some clipping of the image. Many thanks to the ESO for sharing this.
Here’s the wallpapers:
Log in and Join the Conference
You can watch us this week as the conference progresses in many ways. We are on Ustream, Twitter and YouTube.
Twitter is integrated into the site in the sidebar of the homepage, but if you want to Tweet a question to us then simply include the text ‘@dotastronomy’ in your message on Twitter.
YouTube videos are going up during the event, but may be delayed. Not all talks are available via YouTube due to technological constraints.
Ustream will be broadcasting our talks live, for the most part. Talks being given via video are not being broadcast but will appear on YouTube later on.
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Conference Ends
All good things must come to an end. The conference is now over, but in some ways this is the start of other things. The conference proceedings are now going to be written and compiled into a book. You’ll be hearing a lot more about this book in the coming weeks and months on this website. You will be able to purchase it here and to discuss it here.
Over the next few weeks the video from each of the talks will go up here as an archive of the conference. When the proceedings are written, they too will be placed here along with the videos, to enable fuller understanding and discussions. Finally when the book is available, you will be able to purchase it, either personally or on behalf of an institution.
As the organiser, thoroughly enjoyed .Astronomy and would like to thank all those of you that took part. The speakers, poster presenters, attendees and those who watched live via the web too.
For now I am off to struggle with UStream’s non-open source audio codec (grr) and to attempt to crash the market price of a telescope or two by disparaging its worth to other astronomers.
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Conference Archive Opens
Over the coming days and weeks, the .Astronomy Conference Archive will begin to fill up. There are a handful of talks available already and more will be added each day.
Each talk that was given as the conference, including the video talks, are available. You can download the presentation slides and watch the video of the talk. Eventually you will also be able to read the conference proceedings with illustrations.
In the spirit of transparency, it has been decided to open the doors to the archive before it is a completed product. As such if you spot any errors or issues then please get in touch and we will correct them. If you are a speaker and would like to make any corrections/amendments, drop me a line using the contact form or via email.
Have fun watching the talks and learning more about networked astronomy and the new media.
Link: .Astronomy Conference Archive
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Galaxy Zoo
Chris talks about Galaxy Zoo at the first .Astronomy Conference, in Cardiff 2008. Galaxy Zoo is an online astronomy project which invites members of the public to assist in classifying over a million galaxies. It is an example of Citizen science as it enlists the help of members of the public to help in scientific research. An improved version - Galaxy Zoo 2 - went live on the 17th February 2009.
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.Astronomy 2009 Dates
.Astronomy 2009 will be held in the Lorentz Center, part of Leiden University in the Netherlands between 30th November and 4th December 2009. We aim to explore further the themes outlined in our first conference (Cardiff, 2008) and to have hands-on, hack-day-style sessions where new ideas can be developed.
Registration is not yet open for the conference. When it begins we will announce it here and on our Twitter feed, along with more details. If you would like to be alerted when registration opens please email us on registration@dotastronomy.com.
For general enquiries, please send us mail on info@dotastronomy.com.
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- .Astronomy 2009: Programme and venue details Preparations for the 2009 .Astronomy workshop (30 November – 4...
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.Astronomy 2009: Programme and venue details
Preparations for the 2009 .Astronomy workshop (30 November – 4 December) are progressing quite nicely, and we’ve added some details on the venue and programme sections of these pages. Go take a look and let us know if you have any questions.
We’re in the process of putting together a list of people who are maybe interested in attending, so if you have great ideas or you have a pet project that has .Astronomy written all over it, now’s the time to get in touch with us on poc AT dotastronomy dot com, or via twitter (@dotastronomy).
Registration isn’t open yet but you can check out the “official” workshop information page at the Lorentz Center. Places will be very limited and we expect them to fill up fast, so get in touch to stay updated. Registration will be free of charge.
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.Astronomy Gets Some IYA Love
The .Astronomy conference is featured on the front page of the offical International Year of Astronomy webpage, as a “featured event”. As the 2nd edition of .Astronomy will take place during the IYA, from 30 November to 4 December, we expect that many of our discussions, particulaly on outreach and education, will have an IYA-tinge to them. Indeed, we thing it’s the perfect opportunity to review our experiences and ideas, and look at how the many activities can be continued beyond 2009.
Got ideas? Comment, tweet, or send us an email!
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2009 Posters and Imagery
The posters for the conference have now begun appearing in astronomy departments. If you’d like to promote the conference online or print your own paraphernalia then you can find a Flickr set containing the images in various forms. If there is a specific format that would suit you better drop me a line in the comments either here on on the photos themselves.
[Flickr set: http://www.flickr.com/photos/ttfnrob/sets/72157618407149142/]
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