Q11: From the Moon's perspective.. How long is a "Moon day"? Are there also different phases of the Earth?

Time is based on the regular motions of celestial objects as seen from a specific body. 'Day' is defined as the time for a body to complete a rotation, but definitions vary as on what is the reference point for the rotation.  A sidereal day is the rotation about the axis such that the distant stars appear in the same position in the sky. This takes 27.3 days. If referenced to the Sun, it takes 29.5 days. Since the Earth is also revolving around the Sun, it takes an extra 2.2 days for the Sun to appear in the same position in the sky.

The Earth also undergoes phases, as the Earth and Moon is always half illuminated by the Sun and their movements cause the phases. They are always in reverse, when it is Full Moon, it is New Earth, since they are opposites. With this, the synodic month on Earth would be in the same length of time with synodic "Moon month", which is at 29.5 days.

References:
Cain, F. (2008, October 21). How Long is a Day on the Moon? Retrieved April 16, 2014 from http://www.universetoday.com/20524/how-long-is-a-day-on-the-moon/#ixzz2z3AHNqKw
Changing Earth phases, seen from the Moon. (2008, June 21). Retrieved April 16, 2014 from http://earthsky.org/space/what-would-earth-look-like-from-the-moon
Timekeeping. (n.d.) Retrieved April 16, 2014 from http://csep10.phys.utk.edu/astr161/lect/time/timekeeping.htm

Prepared by Keanu Jershon Sarmiento

Q10: Why does the Moon seem to follow us even if we run away from it at night?

This is motion parallax (For a demonstration, go to http://psych.hanover.edu/krantz/motionparallax/motionparallax.html). Nearby objects would move a sizable distance and since you’ve passed them, they move backwards. Farther objects don’t seem to move at all. Instead, they move forward with the observer. According to Richard Gregory of University of Bristol, “movement is attributed to unchanging retinal images when the observer moves”¹. The Moon is so far away it doesn't seem to move. It has the same image as we move therefore creating a stationary retinal image (imagine the image is pinned in your vision). As we move, it stays in the same position in our vision but the other elements in our vision has moved opposite the direction of movement, giving a sensation that it displaced forward from a previous point in space, hence, following the observer.


 Reference:
[1] Gregory, R. L. (2007). Emmert’s Law and the moon illusion. Spatial Vision, Vol. 21, No. 3–5, pp. 407–420 (2008). Retrieved from www.allpsych.uni-giessen.de/julia/SS09/Reading/Gregory_spatVis08.pdf

Prepared by Keanu Sarmiento

Q9: Why are stars called "stars"?

The word star is from the Middle English word sterre, from the Old English word steorra, which is from the Proto-Germanic word sterron. This is traced to the Proto-Indo-European h₂stḗr which means to "glower, shiner”. It is compared to Old High German sterno, Latin stella, Greek astēr, astro, among others.

The bottom line is that the word star was a result of a series of transformations from an earlier designated word for those twinkling objects in the sky. How the word came to be was a consensus of the people involved in naming that object, and that word may be modified by the new users of that word. Of course, the name varies depending on the language, and they may trace the same roots or not. Still, they pertain the same object and the name is a matter of choice on what they think may best describe the object. So why is a star called a star? Because they named it star.

Sources:
Star. (n.d.). Merriam-Webster.com. Retrieved December 19, 2013, from http://www.merriam-webster.com/dictionary/star
Star. (n.d.). Online Etymology Dictionary. Retrieved December 19, 2013, fromhttp://www.etymonline.com/index.php?term=star&allowed_in_frame=0
Star. (n.d.). Wiktionary.org. Retrieved December 19, 2013, fromhttp://en.wiktionary.org/wiki/star
Appendix:Proto-Indo-European/h₂stḗr. (n.d.). Wiktionary.org. Retrieved from December 19, 2013, from http://en.wiktionary.org/wiki/Appendix:Proto-Indo-European/h%E2%82%82st%E1%B8%97r#Proto-Indo-European

Prepared by: Keanu Sarmiento

“Graveyard” for Comets Discovered

Astronomers from the University of Anitoquia, Medellin, Colombia, led by Anitoquia astronomer professor Ignacio Ferrin, discovered the graveyard of the comets. They elucidated the way some of these objects have returned to life after having been inactive for millions of years. These objects are thus referred to as 'Lazarus comets'.

The asteroid belt, between the orbits of Mars of Jupiter was examined in the study.12 active comets have been cited in the asteroid main belt region in the last decade. This actually surprised the team, leading to the investigation of the origin of these objects.

Professor Ferrín says that indeed, they found a graveyard of comets. The asteroids taking paths around the Sun for years which seemingly have no activity, could not be dead rocks at all. It was found that some of them are dormant comets that may be active again once the energy that they obtain from the Sun increases minutely.

The latter is most likely to happen, since the orbits of many objects in the asteroid belt are pushed by the gravitational force of Jupiter, subjecting their orbits to alteration, thus lessening the minimum distance of the object from the Sun (perihelion) and leading to an increase in average temperature.

An illustration depicting the models of the main asteroid belt found between the orbits of Mars and Jupiter. The topmost image shows the traditional model, the second image shows the proposed model, and the last image shows how the belt looked like millions of years ago. (Ferrin, 2013)

Having this claim, it could be inferred that millions of years ago, the main belt was populated by thousands of active comets. Those active comets became mature and ceased from being active. Today, we are seeing the remnants of the active past. The 12 comets are true ones, which were “brought to life” again after their minimum distance from the Sun decreased. “The little extra energy they received from the Sun was then sufficient to revive them from the graveyard.”


The term Lazarus comets was used to describe those objects, having returning to life after being dormant for thousands or even millions of years.




Source:

Royal Astronomical Society (RAS) (2013, August 2). Astronomers discovery a graveyard for comets. ScienceDaily. Retrieved August 6, 2013,


Prepared by: Ericka Jane Angeles

Q8: How EXACTLY do astronomers measure the distance of a particular star to Earth? (In light years)

One cloudless night sky in July, you decide to take a look at stars. Six months later, work and responsibilities are getting the better of you so you decide to take another quick break from the world. You return to the same spot you observed the sky from last July and take a deep look at the night sky. Chances are, some of the stars you observed 6 months ago, have slightly changed their position when compared to the rest of the night sky. This apparent change in position is due to the Earth’s revolution around the sun. Think of it as looking at the star from a different angle. 

The above image helps illustrate parallax. Assume that the red dot in the image is a star while the January view and July view are the respective images of the night sky you observed. Obviously, the red dot is not in the same place in both views.

The image also contains the formula which shows the mathematical relationship between distance and parallax. In other words, the formula tells us how to compute for the distance given the parallax.

Alternate image to further help illustrate parallax and because who doesn’t like looking at images.

Going back to the above mentioned formula; p is the measure of the arc in seconds while d, which is the distance between the star and the Sun, is measure in parsecs. The average distance between the Earth and the Sun has its own unit which is known as 1 AU (astronomical unit). One parsec, to illustrate just how far a star can be, is equal to 206265 AU. Additionally, for those more comfortable with the measurement of lightyear (ly) which is the distance covered by light in one year, 1ly = 6.324 * 10⁴ AU.

The further away a star is from the sun, the greater the required displacement in space to obtain a discernible parallax. As such, the number of stars whose parallax can be observed simply due to the Earth’s rotation are limited. Satellites can help in this regard. They can take pictures of stars at various points in their exploration in space which astronomers on Earth can use to calculate the distances of those stars.

References and Images:

Department of Physics and Astronomy, Georgia State University. (2012). Parallax. Retrieved from: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/para.html
European Space Agency. (2013). ESA Science and Technology: Stellar Distances. Retrieved from: http://sci.esa.int/education/35616-stellar-distances/
Institute of Astronomy, University of Cambridge. (n.d.). Stellar Distances – Parallax. Retrieved from: http://www.ast.cam.ac.uk/~mjp/calc_parallax.html

Prepared by: Manuel Christian Schuldes

Q7: What's the planet closest to earth's structure and atmosphere that scientists have discovered?

Structurally speaking, the closest planet would be Kepler-62 e.

In 2011, Schulze-Makuch and his team decided to come up with 2 scales which would allow scientists to determine if an exoplanet could sustain life. The first scale is known as the Earth Similarity Index (aka easy scale) which compares the exoplanet with the Earth in terms physical or structural characteristics. The properties that are compared in the ESI are: radius, density, escape velocity,  and surface temperature. The scale goes from 0, which indicates no similarity, to 1, which indicates that the exoplanet is exactly similar to Earth.

Illustrated above is the basic ESI expression wherein x_i represents a planetary property (i.e. surface temperature, radius, etc.) and x_io represents the corresponding planetary property of the Earth.

The second scale proposed in Schulze-Makuch’s paper is called the Planetary Habitability Index or PHI for short. The PHI is basically seeks to determine if the proper ingredients and chemistry are available for life to exist. The PHI is constructed in such a way as to be unbiased in the search for extraterrestrial life. In other words, it takes into account life that might exist under more exotic or extreme conditions. However, the PHI is currently not used due to the extensive amount of knowledge required of the planet. Basically, astronomers lack the planetary data to make use of the scale.

Out of the all the exoplanets that have been discovered so far, Kepler-62 e is the exoplanet that rates the highest on the ESI with a score of 0.82. Below is in image which compares Kepler-62e’s position to the Earth’s position, relative to the star they rotate about.

References:

University of Puerto Rico. (n.d.). Earth Similarity Index (ESI). Retrieved from: http://phl.upr.edu/projects/earth-similarity-index-esi

Schulze-Makuch, D., Méndez, A., Fairén, A. G., von Paris, P., Turse, C., Boyer, G., . . . Irwin, L. N. (2011). A Two-Tiered Approach to Assessing the Habitability of Exoplanets [Abstract]. Astrobiology, 11(10). Retrieved from: http://online.liebertpub.com/doi/abs/10.1089/ast.2010.0592

University of Puerto Rico. (2013). The Habitable Exoplanets Catalog. Retrieved from: http://phl.upr.edu/projects/habitable-exoplanets-catalog

Strenge, R. (2011, November 21). New system would assess odds of life on other worlds. Retrieved from: http://news.wsu.edu/pages/publications.asp?Action=Release&PublicationID=28889

Images from:

University of Puerto Rico. (n.d.). Earth Similarity Index (ESI). Retrieved from: http://phl.upr.edu/projects/earth-similarity-index-esi

University of Puerto Rico. (2013). The Habitable Exoplanets Catalog. Retrieved from: http://phl.upr.edu/projects/habitable-exoplanets-catalog

Prepared by: Manuel Christian Schuldes

An Aurora: A Magnificent Art in the Sky

There are many things to do with the night sky, people tend to look at the night sky for stargazing or planet hunting or when there is a scheduled meteor shower, solar or lunar eclipses. But there are also variant things that can be seen in the sky like stray comets and auroras. This phenomenon can occur in the sky seemingly unpredictable yet it is most astonishing to see and leave us in awe.

Auroras occur as an after earth-directed light from the sun, you can assure to see some of them if you took your time to view it. It may not be a hundredth percent but it takes no dime to take a moment to look up to the night sky.

Solar winds can reach Earth’s atmosphere in a variety of ways. Solar flare is the most cause of an endless flow of solar wind. A solar wind can collide with the high energy ions in the atmosphere causing a rapid movement and then emit lights afterwards. Because of the currents of the charged particles that travels along a magnetic field on both poles, an aurora is created: the Aurora Borealis (northern lights) and an Aurora Australis (southern lights).

The solar cycle, which run from a higher activity to a lower activity is in an approximate of 11 year span. An increase in Aurora formation has been taken in the years 1980, 1990, 2001 and 2012 due to a solar maximum. Months of March and April in the spring and September and October of Autumn tend to have more Auroras too than other times of the year based on a yearly basis of sighting but is not explained scientifically up to date.

The sighting of an aurora varies from your position to the Earth. Your chances are better near the auroral oval and less in the southern oval. But aurora visibility is very clear in the northern sky.  Summer is not a good time to go to the auroral oval to see the lights because of a long daylight that limit the after earth lighting from the sun. Fortunately, a large part of it can be seen occasionally in southern locations of Arizona and Italy. 

The greenish glow along the northern horizon was captured from Wisconsin on April 23, 2012. Credit: Kelly Whitt

Pictures of the northern lights is often drop dead gorgeous due to its hue density and variety of color, with an electric blue whorls and silk like stash of red, but most of the time you would see a faint greenish bluish glow on the upper horizon.  To maximize the spectacle of the phenomenon, go to a secluded place where there is less light pollution and buildings to see a clear dark sky.

Source:

http://www.astronomytoday.com/astronomy/aurora.html

Prepared by:

Darren Bautista