Spot the mistake! answer

Hey all! I'm so glad that exams are all over =D Now, back to our usual activities...

A few weeks ago I posted this.

Anyone managed to spot the mistake? If you couldn't, no matter, read on!

Everyone must be familiar with the terms "Big Dipper" and "Pole star", etc. both of which are supposedly useful in helping you locate the North direction and navigate your way when you're lost, as depicted in popular culture.

Now popular culture, more often than not, uses the terms interchangeably, while there is a marked distinction between the two.

A quick glance back to a diagram of the celestial sphere shows you this:

Image taken from http://www.astro.columbia.edu/~archung/labs/fall2001/images/celestial-sphere.jpg

As seen, the North Celestial Pole (NCP) is the point where the entire celestial sphere, or "sky", appears to rotate about. The NCP also happens to be marked by a star of apparent magnitude 1.97, thus it appears stationary as the sky rotates about the NCP. Polaris therefore is a good pointer to the North.

Polaris aka Pole Star belongs to the asterism Little Dipper, whose picture is shown below:

Image taken from http://my.execpc.com/60/B3/culp/astronomy/fig/LittleDipper.gif

Another good North pointer is the Big Dipper.

Image taken from http://my.execpc.com/60/B3/culp/astronomy/fig/BigDipper.gif

Big Dipper and Little Dipper share a little bit of resemblance, thus explain the names.

The bigger asterism, due to its close angular distance from the NCP (as seen at 2 o'clock on 1st picture), is also a good North pointer. It however does not stay motionless on the sky, and thus rotates about the NCP just like the rest. Its stars are brighter and the asterism is more recognisable than Polaris, thus Big Dipper can be used to find Polaris, then North.

As such, referring back to the image we had last time...

The image shown was that of Big Dipper, NOT Little Dipper, therefore our Pole Star appears to have been misplaced, removed from Little Dipper and placed at Big Dipper instead. Big Dipper thus is not stationary, or "always there", and as it goes, the boy deceived the poor little girl -_-

ALSO, Polaris, at an apparent magnitude of 1.97, is not "the brightest star". Our brightest star excluding the Sun would have to be Sirius of Canis Major, at apparent magnitude -1.46. For more information, just wiki.

Hope this clears up some's misconceptions!

Clear skies (:

Large Hadron Rap

At 1:30AM Wednesday, September 10th, scientists working at CERN's Large Hadron Collider will make their first attempt to circulate a beam of particles through the entire LHC. Initial tests through a part of this humongous particle accelerator were carried out on 8th-11th August, and the first high energy collisions are scheduled to take place after 21st October 2008.

As physics fanatics around the world rejoice (or wail about the world's end, for that matter), countless articles and clips and songs are created, this being one.
Enjoy!



Clear skies,
Anne (:

Sentosa Get-together star party photo

Some of us went, and so here's the photo.

A technique to star-hopping for beginners! =P

At this point of time, we're living in the world of high-technological devices. With just a slight push on the button, we could be pleased see from the nearest object in the dark sky to the farthest possible range of DSO!
However, enjoying astronomy is not always equal to satisfy with newly invented tools and machines, but also filled with some interest dating back to the most basic: manual star-hopping! =D
...
So what would you need? Simply a beginner's star charts and a decent binoculars or small telescope! For better joy, a telescope is recommended.

Once you have the atlas, the next step is to determine the visual field of the eyepiece you are using. In order to determine the power given by the eyepiece, you should divide the focal length of the instrument by that of the eyepiece. If for example we have an eyepiece with an apparent field of 50 degrees, which assembled to the telescope gives a power of 30x, then the visual field of the eyepiece will be equal to the apparent field divided by the magnifying power of the eyepiece, that is 50/30, which is about 1.7 degrees.

If you don't know the apparent field of the eyepiece the matter becomes a little more complicated... In order to find out the visual field of the eyepiece in this particular case, you should direct the instrument to a star as close as possible to the celestial equator, set the star at the edge of the visual field and measure the time it takes for the star to cross the eyepiece, without moving the instrument. Knowing that a star near the celestial equator will move one degree every four minutes, you can calculate the visual field of the eyepiece.

In order to find a celestial object with the star hopping method, the visual field of your eyepiece should be as large as possible, so don't use great magnification. This way you will be able to see several stars in the field, and will have reference points. Only when you have found the desired object should you use eyepieces with great magnifying power.

Next then to the checking on telescope.

Check the alignment of your finderscope: Find a bright star or planet, center it on the crosshairs, and make sure it is in the dead center of the 25mm eyepiece. It will be impossible to star-hop succesfully without a well-aligned finderscope. Locate the finding chart for the object you're looking for.

Center the finder on the bright, naked-eye star near the object. Knowing the field of view of your finder scope, match the stars on the finding chart with the stars you see in the finder scope. While looking through the finder scope, move the telescope so that the finder field of view moves in the direction of the object you want, but keeping some stars in the field of view so that you always know where you are. You will probably want to move only one axis at a time. You will need to move far enough that the fine-adjustment knobs won't be good enough; you'll have to unclamp the telescope and carefully move it by hand

Repeat the previous step until you get the finder scope centered on the object you are looking for. Particularly with nebulae and galaxies, you may not be able to see the object you're looking for in the finder scope! If this is the case, then you must center the crosshairs of the finderscope on the right spot so that the pattern of stars you see around the crosshairs in the finder scope match the pattern of stars you see on the finding chart.

Look in the telescope for the object. Start with the 25mm eyepiece. Focus the telescope as best you can. If you're looking for something fuzzy, you will have better luck by focusing on other stars in the field of view. If it's a double star you're looking for, you should be able to see it. If the star doesn't look double, star at it for a little bit; it may be that it's a very close double that you're having a hard time splitting! Or, you ended up on the wrong object....

If you're looking for a faint fuzzy object, like a galaxy or nebula, if you can't see it at first spend a couple of minutes looking through the telescope. Move your eye around; you may not be perfectly centered on it!You often get a better view of dim objects by using averted vision. The receptors that are most sensitive to dim light (the rods) are concentrated more away from the center of your field of vision. By looking a little off to the side of a dim object, the light from that dim object then falls on those dimmer receptors. Try this, to see if you can get a better view of a nebula, cluster, or galaxy.

Taken from:

http://www.nightskyinfo.com/star-hopping/

http://brahms.phy.vanderbilt.edu/a103/labs/tl_starhop.shtml

Spot the mistake

So. As the title says, can you spot the mistake in this manga script? No prize for the winner though, but it's good exercise once in a while (:

Will post the answer when I feel like it lols.

By the way, this is from an average shoujo manga named Orange Planet. You really shouldn't make the same mistake as I and waste your time with this XD

Clear skies,
Anne (:

Hanny's Voorwerp... new discovery by a primary teacher!

"A little bit news here and there" now showing... The New Cosmic Ghost, Hanny's Voorwerp !
...

"Hanny's Voorwerp" is simply "Hanny's object" ("Voorwerp" means "object" in Dutch!)
...
Hanny is just an ordinary primary teacher like any one would think of. As a member of the web GalaxyZoo.org, she was just doing her usual work that was to classify the pictures uploaded there. While poring through the photos, something has captured her eyes: an unusual object with peculiar green colour and also a big halo in the middle of itself.
Lying near the spiral galaxy classified IC2497, this object stands out because of its shape, together with the g magnitude so bright as to suggest a single very strong emission line. This object is different from any classified galaxies; this could suggest that a new category of galaxy might be created!!!

After many research and checking of a lot of observatories and astrophysicistss, The only hypothesis is that this so-called "Voorwerp" is a small galaxy but act like reflection nebula that reflected light from a quasar event in the centre of IC2497 around 100,000 years ago.

People from the Hubble Space Telescope have promised to take a look closer into this object in 2009. Maybe at this point of time, we'll have a clearer picture on what the Voorwerp really is? =P

Optical aberrations

To those who like optics, this is probably one of the simplest summary of optical aberrations that I came across in a thread from Cloudy Nights forum (: Something good to refer to (:

WHAT DO ABERRATIONS LOOK LIKE

ON_AXIS
Generally, not all aberrations are seen on-axis. The on-axis image created by aberrations is as follows:

curvature not seen on-axis.

coma not seen on-axis.

If the stars seem never to focus to a fine point, but at best remain slightly bloated and are still circular, and it cannot be focused out it is probably spherical aberration.

If the star seems to not come into sharp focus it may be astigmatism. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint. Passing in and out of focus will show the out-of-focus image to flip orientation by 90°.

Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point. Sometimes seen as a small circular band of color arounnd a finely focused star point.

OFF_AXIS
As for how you notice stars in the outer fov, the image created by aberrations is as follows:

If the star seems slightly bloated, but it can be refocused down to a finer point, then it is curvature.

If the stars seem flared as wedges with the point towards the middle and the flared wedge toward the outer edge, then it is coma. It cannot be focused out.

If the stars seem slightly bloated but are still circular, and it cannot be focused out it is spherical aberration.

If the star seems slightly bloated and slightly elongated than it is astigmatism. Astigmatism will show elongated images off axis. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint.

If you have both astigmatism and coma, the off axis images will look like comets with an oblong axis, or like seagulls.

Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point.

Lateral CA will produce color fringes around all bright objects when viewed slightly off axis, but you should see a different color towards the lens center than you see towards the lens edge.

Clear skies,
Anne (: