APOD 2.1- "Merging NGC 2623"

NASA's astronomy picture of the day from October 19 is an elegant sort of shape, and mixes the orange sorbet color scheme of a conch shell.

The image displays what is known as NGC 2623, which is actually two galaxies becoming one some 300 million light-years away towards the zodiacal constellation Cancer. Such a uniting is likely similar to the one that happened with the Milky Way Galaxy with its combining nucleus. Star formation ensued around the newly-forming nucleus, for many, many miles, part of tidal tails, with luminous stellar dust and gas.

APOD 1.8 - The Hubble Extreme Deep Field

I remember the day this photo came out; my family was genuinely excited about it, as it is the farthest-shot image from space ever taken. Something so beautiful and helter-skelter is ineffable to me, though deep space seems to bear a remarkable resemblance to the final unexplored frontier of Earth, which is the deep sea. Pitch blackness with unusual sources of wild color.

Anyhow, the image reveals some of the most ancient galaxies ever seen by man- by ancient, we are talking billions and billions of years. All that time is difficult to comprehend.

The infrared channel of a Hubble camera took the shot. It is considered an eXtreme Deep Field (XDF) shot. The XDF will continue to be heavily studied and utilized by astronomers.

Astronomy Observation Log 4 (Astronomy Cast - The Hubble Space Telescope)

Managing to get a telescope above the atmosphere is a tremendous feat for mankind, benefiting our knowledge of space in an incredible amount of ways and also illuminating the beauty of distant celestial objects. 

As the podcast makes an important point of, the atmosphere has been "astronomers' worst enemy."

The concept for the Hubble Telescope, an extraterrestrial tool, arose in the 1940s. The materialization of the actual instrument came about by the 60s. Many great astronomical affairs take part through committees- the funding for the Hubble Telescope was no exception, although even Congress lent money to the affair. The Hubble Space Telescope was carried into orbit in 1990. 

Originally, there were major issues with the curvature of the telescope's mirror- the outside was not sufficiently polished, and the first pictures taken by it were hideous. Once the astronomers in charge figured out this error with the outer edges of the mirror, they could fix the failing facets and install new detectors. Astronauts, interestingly, are excellent construction workers for these instruments in space...

Corrective optics were incorporated directly into the instrument. Improvements are consistently being made upon the Hubble.

I learned from the podcast that infrared is one of the most important parts of the spectrum for astronomers, because it allows them to see the most distant parts of the galaxy. The Hubble Space Telescope was the first to allow us to pick up on those incredibly long wavelengths.

The Hubble Space Telescope has been serviced many times. 

Ch. 5 Sections 1-3

5.1- Optical Telescopes

• Telescope = A "light bucket" whose primary function is to capture as many photons as possible from a given region of the sky and concentrate them into a focused beam for analysis.
• Optical telescopes are designed to collect wavelengths visible to the human eye.
• History since Galileo in 17th centuries.
• Refracting telescopes use lenses to gather and concentrate a beam of light. 
• Lens thought of as series of prisms combined in a way so that all light rays arriving parallel to its axis (imaginary line through center of lens) are refracted to pass through a single point called the focus. Distance between primary mirror and focus is focal length. 
• Reflecting telescopes use curved mirrors instead of lenses to focus the incoming light.
• The mirror that collects the incoming light is called the primary mirror, as telescopes often have more than one mirror. Focus of the primary mirror is called prime focus.
• Prime-focus images are often magnified with a lens called eyepiece before being observed by eye, or recorded as a photograph/digital image. 
• Reflecting telescopes tend to be favored over refracting ones:
• The fact that light must pass through the lens is a disadvantage of refracting telescopes. Tends to focus red and blue light differently.
• When light passes through lens, glass absorbs some of it. This is a problem for infrared and ultraviolet observations because glass blocks most of the radiation in those regions.
• Large lenses are heavy, so they deform under own weight. Meanwhile, a mirror doesn't have this problem because it is supported over it's entire back surface.
• A lens has two surfaces that must be accurately machined and polished, while a mirror only has one. 
• Types of reflecting telescopes:
• In Newtonian telescope, the light is intercepted before it reaches the prime focus and then is deflected by 90 degrees, usually to an eyepiece at the side of the instrument. Uncommon in larger instruments but popular for smaller more common ones.
• In Cassegrain telescope, incoming light hits the primary mirror and then is reflected upward toward the prime focus, where a secondary mirror reflects the light back down through a small hole in the main mirror into a detector or eyepiece. Has rear platform. 
• In Nasmyth/coudé focus, starlight is reflected by several mirrors- by primary mirror toward prime focus, down the tube by a secondary mirror, and then a third, smaller mirror reflects light out of the telescope where the beam may be analyzed by a detector mounted alongside, at the Nasmyth focus, or via a series of further mirrors into an environmentally controlled laboratory "coudé" room. This lab room is separate from the telescope itself, allowing astronomers to use heavy and finely tuned equipment that cannot be placed at any other foci.

5.2- Telescope Size

• Development of astronomical instruments has led to an increase in size for 2 reasons: The amount of light a telescope can collect- light-gathering power.Amount of detail to be seen- resolving power.
• Light-gathering power
• Larger telescopes have greater collecting area- total area capable of gathering radiation.
• Observed brightness of an astronomical object is directly proportional to the area of our telescope's mirror and therefore to the square  of the mirror diameter. (eg. a 5-m telescope will produce an image 25 times as bright as a 1-m instrument.) Relationship also in terms of time required for a telescope to collect enough energy to create a recognizable image on a photographic plate.
• Resolving power
• Larger telescopes have finer angular resolution- Ability of a telescope to distinguish between adjacent objects in the sky.
• Diffraction and light bending around corners limits resolution. When rays spread out and are not focused to a sharp point, fuzziness ensues. 
• The amount of diffraction is proportional to the wavelength of the radiation and inversely proportional to the diameter of the telescope mirror. 
• For a circular mirror and "perfect" optics we can write: angular resolution (arcsec) = 0.25(wavelength(in micrometers)/diameter(m)) when one micron is 10(^-6) m
• Diffraction-limited resolution- Theoretical resolution that a telescope can have to to diffraction of light at the telescope's aperture. Depends on the wavelength of radiation and the diameter of the telescope's mirror.
• Larger telescopes produce less diffraction than small ones.

5.3- Images and Detectors

• Many different detectors and devices to study radiation are placed at various points along light path outside the telescope.
• Computers play a vital role in observational astronomy.
• Electronic detectors called charge-coupled devices (CCDs) send output directly to a computer. Composed of many tiny pixels, each of which records a buildup of charge to measure the amount of light striking it.
• The amount of charge is directly proportional to the number of photos striking each pixel, or the intensity of the light at that point. Buildup of charge is monitored electronically.
• Advantages of CCDs include: 
• they are more efficient than photographic plates, recording as many as 90 percent of the photons striking them, compared with less than 5 percent for photographic methods. thus shows objects 10 to 20 times fainter. does this in less than a tenth of the time of photographic techniques.
• CCDs produce a faithful representation of an image in digital format that can be placed directly on magnetic tape or disk or across a computer network to an observer's home institution.
• Computers used to reduce background noise of astronomical images. Noise corrupts integrity of messages
• Large reflectors are good at forming images of narrow fields of view, wherein all the light that strikes the mirror surface moves almost parallel to the axis of the instrument. 
• As angle at which light enters increases, accuracy of the focus decreases. Effect is called coma, which worsens as we move farther from the center of the field of view. 
• Photometry- Measurement of brightness of star. Astronomers often combine photometric measurements using colored filters to limit the wavelengths they measure.
• When highly accurate and rapid measurements of light intensity are required, a specialized device known as a photometer is used, to measure the total amount of light received in all or part of the field of view.
• When astronomers want to study the spectrum of incoming light, large spectrometers work in tandem with optical telescopes. 

Astronomy Observation (Log 3) 10.14.12

As I have not yet attempted to use my telescope yet, I again analyzed the sky with the help of the Star Walk application. Clouds were covering some areas of the sky, but especially along the ecliptic, I was able to make out clear distinctions between constellations. From my front yard, I saw the individual stars that made up both my zodiac sign Pisces, and also Aries. I could see Ursa Minor, with the north star Polaris standing out very clearly. There was a new moon, and I saw what I thought might have been Jupiter, but it was near the constellation Perseus. I also saw the set of constellations that include Vulpecula and Delphinus.

APOD 1.7- Color Illusion

When you see the image from the NASA APOD website without rolling your mouse over the image, the line connecting A and B is not there, which makes the illusion much trickier. With the two squares connected, it is easier to see that the colors of A and B are actually the same! This does not seem like something that is directly connected to astronomy, but it is meant to be a testament to the fact that human observations, especially those based on celestial objects, are certainly are not always reliable- as the majority of people are likely to be quick to think that the squares are different colors. Even with using measuring devices, people cannot always escape the illusions perceived by the brains and eyes of humans.

Grimaldi Biography

Letts 1

Olivia Letts

Mr. Percival

Astronomy, Per. 3

12 Oct. 2012

Francesco Grimaldi – A Life

            Francesco Maria Grimaldi had the opportunity to become highly educated, being born into a well-respected and well-to-do family in 1618 in Bologna, Italy.  The seventeenth century, generally considered to be the final century of the Italian Renaissance, was a time marked by both great religiosity and fervent intellectuality.  Grimaldi’s life reflected this – by 1632, he and his brother Vincenzo had joined the Society of Jesus (for Jesuits).  He studied philosophy in Parma, Ferrara, and Bologna.  One of his teachers, Giovanni Riccioli, would later assist and be assisted by Grimaldi during some important experiments.  From 1638 to 1642 he taught rhetoric and humanities at the College of  Santa Lucia at Bologna, where he also studied theology after 1642.  By 1647, he was qualified to teach philosophy, but this was a time-consuming course to teach and thus, suffering from tuberculosis, he had to teach something that he found “less strenuous.” He began to teach mathematics and physics, being skilled in all branches. Full vows for priesthood were taken by Grimaldi in 1651. 

From the 1640s until his death in 1663, he focused heavily on his chief interests, astronomy and optics.  He was the first to observe and record the optical diffraction phenomenon; he was also the one to name it (diffractio).  This was discovered after during a specific experiment in which he introduced sunlight into a darkened room through a tiny hole, projecting it only a white surface.  Between 10 and 20 feet from the slit, Grimaldi put a thin, opaque rod into the cone of light so as to cast a shadow on this white surface.  He was surprised to note that the shadow of this cone was far wider than how it was geometrically predicted, and

Letts 2

also, there were external diffraction bands of different colors bordering the shadow.  The brightness of these colors was more intense near the shadow, in fact.  In 1665 he published these findings.  Grimaldi had conducted other experiments for diffraction, where he discovered internal paired tracks of light and “fringing.”  His findings further proved the fluid nature of light as opposed to rectilinear passage. Grimaldi’s Physico-mathesis de lumine, published in 1666, the geometrical foundations for the wave theory of light were laid.  Later, Isaac Newton would create a set of careful measurements that made it clear that the phenomenon was of a periodic nature.  Yet this great figure himself did not accurately reflect upon Grimaldi’s experiment, as he treated the concept of diffraction like a mode of refraction, and he could not explain the fringes of color that occurred around the shadow.  Grimaldi as well was never able to properly explain why diffraction occurred – his death was sudden and interrupted further experiments with light - this was not accomplished by anyone until Joseph von Fraunhofer could in the 1800s.

            With former teacher Riccioli, Grimaldi carried out another important experiment, in which the two Jesuits dropped weights from a tower and timed the occurrences with a pendulum. They discovered the time of the fall squared was proportional to the distance of free fall source to rest.  Grimaldi was considered vital to Riccioli’s completion of his Almagestum novum, a major work which actually made Riccioli an incredibly important contributor to astronomy and falling bodies.  Riccioli noted Grimaldi’s great skill in devising and building telescopes and other observational instruments, through which the two frequently observed celestial bodies.  Grimaldi is well-known for his lunar measurements, and his famous selenograph of the moon.  There is a copy of this lunar map in the entrance to the National Space Museum in Washington, D.C.  He began a trend of describing lunar regions by naming them after famous astronomers and physicists.  Grimaldi often did not receive proper credit for his findings, and during his lifetime, his works were not published by his name.  

APOD 1.6- Goat Aurora

The picture of the "Goat Aurora" over Greenland is one that looks surrealistic, and indeed, incredibly goat-like. This aurora was very vivid, and fast-changing, so that even veteran sky-watchers were genuinely shocked by its appearance. This head of a goat apparently morphed into other forms as well, including an elephant and "fingers on a celestial hand." The Milky Way Galaxy also shone bright during that late august night spectacle, with a variety of constellations and nebulas visible to the naked eye. The farm in the picture is in Tasiusaq, Kujalleq, Greenland.

Seeing this picture reminds me how difficult it actually is to connect stars that form constellations... There are so many stars dotted around them in this rich sky that often I cannot possibly link together the groups of stars.