Black Holes, monsters of the cosmos

Dear Diary...

A black hole is an area of space-time dimensions where gravity has won over mass. Black holes are the evolutionary end point of a relatively big star (by ‘big’ I mean a star whose mass 10 to 15 times the mass of the Sun). When a star that massive dies, or in other words, runs out of fuel and undergoes a supernova explosion, it leaves behind burnt-out stellar remnant. These relics would later collapse on themselves due to gravitational forces, creating what’s mathematically known as a singularity, that’s briefly, a point of zero volume and infinite density. To give you a better idea, if Earth were a black hole, the blue planet would be the size of a marble. For a really cool animation to introduce black holes, check this link from an award winning astronomy website.

Black Holes are where God divided by zero.

          Keep in mind, that these black holes are not, contrary to popular belief, cosmic vacuum cleaners. For example, if the Sun were to be replaced by a black hole of equal mass, the Earth’s orbit would remain unchangeable.

            The gravity of a black hole is so strong that its escape velocity exceeds the speed of light (quick definition of escape velocity: the lowest velocity that a body must have in order to escape the gravitational attraction of a particular object), since we don't know of anything that moves faster than the speed of light, then nothing can escape it, ergo the appellation "black hole". 

               For a quick classification of black holes:

The anatomy of a black hole consists of: (for a cool animation click here)

Top 10 Mysteries of the Solar System

     Dear Diary...

     We know a lot of things about our Solar System, let's talk about what we don't know. There are plenty of unresolved mysteries around us that are driving scientists mad, and sponsoring haircuts as awkward as Einstein's. Here are, briefly, my top 10, the first being the most intriguing.

       10. Why is Uranus unusually tilted?

The seventh planet was discovered by British astronomer Sir Herschel in the 1781, it has an axial tilt of 97.7°. This means that it rotates on its axis horizontally, and its poles always point in the same direction, so that only one is exposed to the Sun at all times. Note its rotation sense in the following scheme depicting its motion around our star. (fun fact: seasons last 21 years on Uranus; each pole has 42 years of sunlight followed by 42 years of darkness)

Uranus has a weird rotation pattern

Now, why did this happen? We don't know, some astronomers have a hypothesis that goes like this: Uranus hit an object, probably a Mars-sized asteroid, some unknown time ago, in way that the planet was forced to rotate in this unusual way. An other hypothesis blames super-planet Jupiter's resonance, that might have affected the motions of its three neighboring gaseous planets (Saturn, Uranus, and Neptune). Either way, no scientific proof exists to back either one, they're not really testable. 

       9. The Sun doesn't know where to be hot!

Our precious star, the Sun, is really hot. Its core has a temperature of 15,7 million degrees Kelvins, its surface has a much lower temperature of 5,800°K. Further out is the Sun's Corona, its temperature is, surprisingly, some 5,6 million°K and decreases the further out you go. What's the process behind this odd segregation of temperatures? 

Odd Solar Temperature

       8. Enceladus has geysers spewing out water. Wait what?

NASA's Cassini spacecraft launched in 1997, on its way to Saturn,  assed by few of its satellites, including Enceladus, it sent back pictures of tiger-like stripes on its south pole and geysers spewing out water and organic compounds. (quick definition of geyser: spring in which water intermittently boils, sending a tall column of water and steam into the air). Does this mean there's water underneath its surface? Maybe it could hold some signs of ET life? Additional information from the orbiter assures that there are potassium and sodium salts dissolved in the water vapors, could this be proof of an ocean an maybe some algae? Scientists just know there are some underground activities similar to Earth's geophysics, like some sort of tidal heating. Everything else is a hypothesis since we're so short on data.

Artist's rendition of Cassini's flyby of Saturn's moon Enceladus

The Moon, An Old Friend

     Dear Diary...

     Let's talk about the Moon. For astronomers, it's the Blue Planet's only natural satellite. For poets and musicians, it's an inspiration. For pirates, it's a nocturnal shepherd. For Germanics, Babylonians and Islam, it's a calendar. For ancient cultures, it was a celestial deity. For ocean tides, it's a force.

     The Moon is the fifth largest natural satellite in our Solar System, trailing behind Jupiter's Ganymede, Saturn's Titan (without taking its atmosphere into consideration), and again Jupiter's Callisto and Io. The Moon is also the second densest moon right after Io. To better visualize how big the moon is, this picture is pretty accurate:

     Let's start with the lunar phases. There are four main phases, each needs almost one week to take place, making the lunar cycle (or what's called a moonth) nearly 29.5 days old.

1. New Moon
2. First Quarter
3. Full Moon
4. Last Quarter

     When the moon appears to be growing, we say that it's waxing, when it appears to be shrinking, we say that it's waning. Enough with the vocabulary, this diagram says it all:

Phases of the moon

     What we see when we look up to the moon is basically a light show caused by the Sun's total or partial illumination of the moon, whenever the moon is in the Earth's shadow, a lunar eclipse occurs (that's almost once every six months). Only one half of the moon is illuminated by the sun, because it's tidally locked to the Earth meaning that the same side always faces the earth. This following simulation simplifies everything I wrote:

     It's the geometry of the Moon, the Sun and the Earth that entertains us with phases and eclipses. Now, the Moon crosses the Earth’s equator twice on every orbit once going up and once coming back down.
     One every six months or twice a year, the Moon finds itself in Earth's shadow thus causing a lunar eclipse, and often the Moon places itself between the Earth and the Sun, blocking it and thus causing a solar eclipse.
     This is the precise lining of what we call the Nodes, where the Moon’s orbit crosses the Earth’s equator. Of course the fellas at NASA who love drawing tables have lots of cool calculations on their eclipse website, check them out here. The next lunar eclipse will occur on the 4th of June of 2012, just one day before the transit of Venus, more on the transit of Venus can be found in one of my previous entries here. To further clarify, it’s not the crossing of the Equator that necessarily causes the Eclipse, although that can happen if you precisely have one at a Solstice (quick definition: the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days). It’s actually the crossing of the Ecliptic which is the line that the Sun follows in the Sky that causes the Eclipses.

The Transit of Venus

     Dear Diary...

     Venus is the second planet from the Sun in our Solar system, more information regarding the planet can be found in one of my previous entries here.

     A transit is the passage of an inferior planet across the face of the sun (or of a moon or its shadow across the face of a planet). So, a transit is similar to a solar eclipse by the moon, and the Venusian transit lasts for a couple of hours; 50 minutes or up to 6 hours depending on your location of course. These transits are also called the black drop effect because of their appearance when passing in front of the Sun.

     Transits of Venus only occur a few times every century because of the Earth-Venus geometry. These transits have been used by ancient astronomers to get a sense of scale in the Solar System. It's important to mention that these transits don't occur once every year, like you'd imagine, simply because the orbit of Venus is shifted 3.4 degrees relatively to the Earth's.

the inclination between the two orbital planes is 3.4°

     Venusian transits are among the rarest of predictable astronomical phenomena. They occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The first transit of the twenty-first century pair took place in 2004, the second one will occur on june 5 or 6 2012, depending on your timezone. For a timeline of all the transits of Venus, click here (and then scroll down). The next one will take place in december of 2117, unless you plan to live for an extra 105 years, this is one more reason for you not to miss this!

This event will be visible from various locations around the Blue Planet, some better than others.

     To get a better sense of when to look observe the sun, NASA's Goddard Space Flight Center made a list of 121 international cities with corresponding transit contacts, make sure you see it here, you can find any city easily. If you're unlucky enough to be in Portugal, Spain, Brazil, Argentina, or Uruguay during this time, or if you don't want to wake up before sunrise, the Mauna Kea Observatory from the The University of Hawaii Institute for Astronomy will broadcasting a live webcast of the transit, in collaboration with NASA scientists. Since it's summer, I advise you to use an astronomical excuse for a vacation. Sky At Night Magazine recently wrote an entertaining article listing holiday options in well-calculated locations for perfect black-drop observation from places like Hawaii, Sydney and even a Tahitian cruise ship, read it here!

     There are four named "contacts" during a transit, moments when the circumference of Venus touches the circumference of the Sun at a single point:

• First contact (external ingress): Venus is entirely outside the disk of the Sun, moving inward
• Second contact (internal ingress): Venus is entirely inside the disk of the Sun, moving further inward
• Third contact (internal egress): Venus is entirely inside the disk of the Sun, moving outward
• Fourth contact (external egress): Venus is entirely outside the disk of the Sun, moving outward

A fifth named point is that of greatest transit, when Venus is at the middle of its path across the solar disk and which marks the halfway point in the timing of the transit.

     This video gives you an idea of what you're going to see, it's merely an animated sequence of pictures taken by a terrestrial telescope.

     For tips on how to better observe the transit, consult an eye-safety article here. Looking directly at the sun can be harmful, and may cause permanent damage. Beware, wearing sunglasses is in no way sufficient. Some helpful tips for safe viewing are:

• Solar viewing devices such as solar filters for you telescope
• Build a Sun Funnel for your telescope, here's an illustrated guide
• Eclipse Shades or Solar Shades that appear similar to sunglasses, but they have a special filter that permits safe viewing if the filter is in new condition
• Pinhole projectors that are usually used to observe solar eclipses
• You can project a magnified view of the sun, details on how can be found here
• Watch a live online webcast here.

     For all you Apple and Android phone users, download the free app! (yes, there is an app for everything). Don't forget to set reminders! And don't forget to share good photos of Venus' visit.

This is an example of the transit's main events when viewed from Beirut, generate one of these by typing in you location using this website!

Transit Of Venus From Beirut

References and credits:

www.astrodeneb.org

http://www.skyatnightmagazine.com/

http://www.transitofvenus.org/

www.nasa.gov/goddard/