Happy Saturnalia!

To celebrate Saturnalia, enjoy Saturn's hexagon.

Today's APOD is just too Saturn cool!

(via)

Today's APOD: the Πortara

To celebrate the vernal equinox, APOD has a picture of the Portara--the entrance of the ancient Temple of Apollo on the island of Naxos--take at sunset during last June's summer solstice. However, when I look at the picture, I see an image which would have been very appropriate only four days ago(Pi Day). That's right, I see the silhuette of a Capital letter pi against a setting circle. I'm such a geek!

Christmas Eve 1968

40 years ago today one of the greatest photographs in history was taken.



(via APOD)

Ganymede occultation by Jupiter

This video released by NASA is too freaking cool!!!

According to NASA:

This movie shows Ganymede, Jupiter's largest moon, as it ducks behind the giant planet. Astronomers combined a series of images taken with the Wide Field Planetary Camera 2 aboard NASA's Hubble Space Telescope to make the 18-second movie. The 540 movie frames were created from Hubble images taken over a two-hour period on April 9, 2007.

Check it out!



(via Phil)

Credit: NASA, ESA, E. Karkoschka (University of Arizona), and G. Bacon (STScI)

Moon transit shot from EPOXI spacecraft

EPOXI's Spacecraft Observes the Earth-Moon System

Videos of the Moon transiting the Earth, as imaged by NASA's EPOXI spacecraft, were made from the still images collected when EPOXI's spacecraft imaged the Earth-Moon system on 28-29 May 2008. When the images were acquired, the spacecraft was just outside the orbit of the Earth and ahead of Earth by 31 million miles, 1/3 AU, making it as far from Earth as Mercury is from the Sun.

(via APOD)

Star halfway across the Universe goes BOOM!

Have you ever seen a massive supernova in action. On March 19th, Pi-of-the-Sky did.

2008.03.19 "Pi of the Sky" telescope detected the brightest ever optical outburst from a distant universe. The explosion happened 7.5 billion light years from the Earth, halfway across the visible Universe. The telescope is only 71 mm in diameter.

Just in case you missed it, here's the movie.

Earth setting on the Moon.

(Via)

Trilogy of Terror!

Hungry Andromeda!

The latest Spitzer video from Dr. Robert Hurt.

Last night's eclipse

In the end the weather did not cooperate with me and I missed the entire eclipse. It was there somewhere obscured by clouds, but alas I did not witness it. Here's a taste of what I missed.

Eclipses!

Tonight as the sun goes down the East Coast will be treated to a total Lunar Eclipse. This is some very exciting stuff.

Total eclipse begins 5:44 p.m.
Total eclipse ends 6:58 p.m.
Partial eclipse ends 8:12 p.m.
Last shading visible? 8:50 p.m.

In just another four hours I will be in for one helluva sky show. Or will I? I went and checked my local weather and...



...AAAARRGGGHHHH!!!!
They've been wrong before, so I'll just have to keep my fingers crossed that I'll be able to see something. In the meantime, I'll have to make due with a different type of eclipse. This movie (Quicktime required) is a transit of the moon in front of the sun, shot in UV light, from the STEREO satellites. COOL!!! (via APOD & BA)

Welcome to Aquarius

We have just entered into the zodiac constellation Aquarius. There's actually a little more to it than vague, fabricated fortunes from the daily paper; the zodiac is a good way to keep track of the sidereal year. Cider what, you ask? Simply put, the sidereal year is one complete orbit around the sun. The name comes from the latin word for star. Since the stars remain relatively fixed (compared to closer objects such as the moon and planets), they serve as a good metric to measure the year and determine dates. The zodiac are 12 constellations evenly spaced along the ecliptic--the plane formed by the Earth's orbit around the Sun. They can be used to gague our planet's position during its orbit. This might just sound like a year, why the fancy adjective? Because it turns out that there's more than one type of year.

Allow me to sidetrack by bringing up that there is more than one type of day. Ask your typical person on the street to define a day and tell you how long one is, you'll probably get an answer like "A day is he time it takes for the Earth to rotate once about its axis, and it lasts 24 hours." One rotation around its axis is a sidereal day since we can use the stars to track the rotation. However, the 24 hour day is the time the spinning Earth takes to line up the Sun to the same longitude. In other words, it takes the Earth just under 24 hours to spin one complete (sidereal) rotation. But during that interval, it has moved along ts orbital pass and so the Sun isn't lined up where it was at the start of the day. It must continue spinning a little longer to reach this point. Phil the Bad Astronomer has a great post explaining all this much better than I ever could hope to do.

Back to the year, besides the sidereal year, we also have a tropical year. This would be, for example, the time between winter solstices. This is determined by the tilt in the Earth. During the winter solstice (from the latin for "sun stop" or "sun pause" because it is the date when the sun's maximum position in the sky stops progressing and changes direction), the Earth's southern hemisphere is tilted towards the Sun while the northern is tilted away. The summer solstice is the opposite. The equinoxes occur when the tilt is perpedicular to the line with the sun, hence both hemispheres are equidistant from the sun. If the tilt of the earth were constant, then the sidereal and tropical years would perfectly jibe. But alas, it's not.

Which brings us to the precession of the equinoxes. (cool picture) Precession is a wobble. Think of a spinning top. Besides the primary spin, the top has a wobble which causes the axis to draw out a circle on the ceiling (ignoring proper movement of the top). The Earth is basically doing the same thing. It's tilt is slowly wobbling so that as time passes, the equinoxes and solstices fall at different times during the sidereal year. Therefore a time travelling astronomer should be able to tell you what century he's in by looking at the stars.

This brings me to the interesting case of The Farnese Atlas.

The Farnese Atlas is a 2nd-century Roman marble copy of a Hellenistic sculpture of Atlas kneeling with a globe weighing heavily on his shoulders. It is the oldest extant statue of the Titan of Greek mythology, who is represented in earlier vase-painting, and more importantly the oldest known representation of the celestial sphere. The sculpture is at the National Archaeological Museum (Museo Archeologico Nazionale ) in Naples, Italy. It stands seven feet (2.1 meters) tall, and the globe is 65 cm in diameter.
...
In 2005, at a meeting of the American Astronomical Society in San Diego, California, Dr. Bradley E. Schaefer, a professor of physics at Louisiana State University, presented a widely reported analysis concluding that the text of Hipparchus' long lost star catalog may have been the inspiration for the representation of the constellations on the globe, thereby reviving an earlier proposal by Georg Thiele. The constellations are fairly detailed and scientifically accurate given the period of its creation, implying that the globe was modeled after a scholarly work. The position of these constellations is consistent with where they would have appeared in the time of Hipparchus - leading to the conclusion that the statue is based on the star catalog.

In other words, Dr. Schaefer used his knowledge of precession to figure out where the constellations would've been at the time the atlas was made, and determine that it was a star map.

As the Earth precesses through the zodiac, we go through different ages which are determined by which constellation we're in around the begining of the year. When I first found out that we we entering the age of aquarius, I got so excited because I thought that I had finally figured out what that song from Hair meant. Boy was I disappointed when I went to listen to the song again and heard nothing but astrological hippie nonsense. I certainly sympathize with Julia Sweeney and her revelation about Deepak Chopra.

Infrared Sombrero

My homepage on my laptop is (and has been for my last 3 computers) the Astronomy Picture Of the Day (APOD). Today's picture is just fantastic! It is an infrared picture of the Sombrero Galaxy taken by the Spitzer space telescope. Doesn't it just want to make you do a hat dance?

Jupiter Spins

Seeing Ghosts in Space

One of the best layman’s responses I’ve seen to Intelligent Design’s “problems with Evolution” argument is

Every time you hear them say the word “evolution,” substitute the word “gravity.”

This statement is concise and doesn’t get into the nitty-gritty biological details. It points out the absurdity of the ID argument by drawing a parallel to something we all can understand: gravity. We all can see an apple falling from a tree; we all can (sort of) see the Moon orbit the Earth; we can all feel gravity’s effects when we ride a roller-coaster (well, all the time really). The above statement basically says that we can in fact see evolution happening, just as clearly as we see the effects of gravity. No serious biologist doubts that evolution is real just as no serious physicist doubts that gravity is. The devil is in the details.

What I always found ironic about that statement is that biologists actually know more about the workings of evolution than physicists know about the nature of gravity. Ask ten different physicists to explain the nature of gravity and you might get less than ten different answers only if more than one admits that they don’t really know.

Among the fundamental forces in nature, gravity is the rogue oddball. It doesn’t want to play by the same rules as everyone else. For decades, physicists have been searching for a grand unification theory that will unite all the fundamental forces under one umbrella. Many consider it the last great frontier of science. Michael Faraday made the first move in this direction when he showed the relationship between the electric and magnetic forces. Over the years physicists have been able unite them all, except for one: gravity. They have been able to quantize them all, except for one: gravity. It just wants to be different—so different that astronomers have discovered a type of matter that seems to be impervious to all the fundamental forces, except for one.

Dark matter is a funny animal. We know it’s there because we can see it’s gravitational effect on regular matter. You see, galaxies don’t have enough regular matter in them to keep them from flying apart. So there must be some other type of matter out there (in huge quantities, it turns out) that’s supplying the extra gravitational force to keep things together. Yet, apart from gravity, this dark matter doesn’t seem to interact with regular matter. It doesn’t come together to form atoms, or molecules or stars. It’s just there.

That’s why many physicists feel that it might not exist at all. Perhaps there’s another explanation for this observed gravitational effect. One of the more popular alternative explanations is MOND (Modified Newtonian Dynamics). MOND says that the laws of gravity (i.e. Newton’s and Einstein’s formulae) are wrong and that at galactic distances, gravity is proportionately stronger than the reciprocal of the square of the distance. These hypotheses have recently been dealt a blow by a new discovery made by astronomers around the world.

This discovery relies on the hypothesis that dark matter only weakly interacts with regular matter. One way to think about this is that dark matter only interacts with regular matter gravitationally. This would be like a movie ghost that walks through walls but is gravitationally bound to the earth. (However, most movie ghosts that can walk through walls can also fly, so perhaps ghosts aren’t made of dark matter after all.) But there’s another school (we don’t know who’s right—another mystery of dark matter) that says that dark matter can interact with regular matter if there’s a direct collision between particles of dark and regular matter. These collisions, however, should be so rare as to be practically ignored. Imagine an atom as filling an area the size of a soccer stadium, with a soccer ball sized object at roughly mid-field, several marble sized objects racing around the stands, and all the empty space in between filled by a powerful force field holding it all together. Now imagine trying to hit this atom with a pistol shot. If the bullet is affected by the force field, then hitting the atom is like hitting a stadium-sized target. However if the bullet is made of some dark material which is completely unaffected by the force field, then the atom becomes a soccer ball sized target—almost impossible to hit.

Therefore if two large objects (such as galaxy clusters) should collide, then the regular matter from the objects should interact, slowing down each object’s momentum, while each object’s dark matter, which doesn’t interact, should initially overshoot the collision before being brought back into the fold by gravity, like a stretched spring. If this indeed happens, then the effect should be observable using a technique called gravitational lensing. This method works because light is affected by gravity. Therefore light passing near a massive object—say, the dark matter from a galaxy cluster—will be bent (according to General Relativity) and focused, just as if it were passing through a lens. We should be able to observe this effect from earth, and we did! Furthermore, this observation is incompatible with MOND.

Does this finally prove that dark matter exists? Not quite. Can there still be another explanation for what we’re seeing? Yes, but that is becoming increasingly remote. Are we any closer to actually knowing what dark matter is? No, but I think we’re headed in the right direction.

And if that doesn’t satisfy you, then you can always just chalk it up to the designer.