1950 DA, The (not so) Friendly Neighborhood Asteroid

1950 DA is an asteroid that was discovered in 1950 (hence the name) by Carl A. Wirtanen. After it was first discovered, it was lost after 17 days of observation because the period was too short to determine the asteroid’s future location. It was rediscovered in December 2000 and recognized as 1950 DA in January 2001. It is classified as both a near-Earth object (NEO) and a potentially hazardous object (PHO). Based on the definition of a NEO, 1950 DA’s perihelion is less than 1.3 AU. The definition of a PHO tells us that 1950 DA makes exceptionally close approaches to Earth (mimimum orbital intersection distance of less than 0.05 AU) and is large enough to cause significant damage in the case of an impact. This asteroid is also classified as an Apollo object, which details that it has a semi-major axis greater than that of the Earth but perihelion distances less than Earth’s aphelion distance. Apollo objects currently make up the largest group of NEOs.

                There are two main things that I think make this asteroid very interesting. The first thing is the fact that it is a PHO. After observations were made and analyzed, it was determined at one point to have the highest probability of impacting Earth. In 2002, it had the highest Palermo rating for a possible collision in 2880. The Palermo rating scale is used to rate the potential hazard of impact of a NEO. In addition to this, I also think its composition is interesting. In 2014, physicists from the University of Tennessee found that it is not a single continuous object, but actually a mile-long collection of rocks held together somehow. They determined that the body was held together by weak electrical attractions between the molecules of the rocks, showing that Van der Waals forces are the reason the form is held.

I promise this is not an ultrasound photo, but actually the asteroid 1950 DA

Hypervelocity Stars

In 2005, the first hypervelocity star (HVS) was discovered by Smithsonian astronomers. These objects are defined as stars with very high velocities compared to normal star velocities in a galaxy. Some of them have velocities that exceed the escape velocity of the galaxy. They are thought to originate from encounters of binary stars with the supermassive black hole at the center of the Milky Way Galaxy. One of the partners of the binary star is “captured” by the black hole, entering orbit around it, while the other partner escapes with a high velocity to become an HVS. In addition to the black hole origin of HVSs, it is also thought that HVSs can be induced by supernovas. In this case, a HVS is ejected from a binary system when the other partner undergoes a supernova explosion.

Diagram Showing Star Ejection from a Galaxy

As of 2014, there are 20 known HVSs. These HVSs all have masses a few times that of the Sun, though dwarf HVS candidates have also been discovered. There are so few confirmed HVSs because they are pretty difficult to track down. It’s not easy to search through a billion stars and find a couple that are moving abnormally. In order to locate them successfully, astronomers have used a specific type of telescope to focus on a large group of stars on the edges of the Milky Way’s black hole that had traveled a notable distance. They then were able to narrow down this large group to stars that were travelling at speeds consistent with ejection from the center of the Milky Way. Once we learn more about HVSs, we can use information about them to learn about stars that form in the centers of galaxies and the sizes of black holes at the centers of galaxies.

This link from Harvard contains a complete collection of links to general information, podcasts, scientific publications, and other links about hypervelocity stars. This article serves as a good introduction to the topic.

Exploration and Geology of Mercury

Because it is so technically difficult to reach Mercury with spacecraft’s from Earth, the geology of Mercury is understood the least of all the terrestrial worlds. The main reason it is so hard to reach is due to how close Mercury is to the Sun.  When a spacecraft moves down Sun’s gravitational potential well to get closer to Mercury, its potential energy is converted to kinetic energy. In order to not pass by Mercury quickly, the spacecraft must rely completely on rocket motors to enter a stable orbit or land. This is very fuel intensive; in fact, a trip to Mercury from Earth requires more fuel than the amount required to escape the Solar System. I thought this was a very interesting piece of information to illustrate the concept of a potential well and just how much Sun’s gravity can affect space travel as objects travel closer to the Sun.

Since Earth-based observation of Mercury is made difficult because of its proximity to the sun, most of the information we have about Mercury’s geology is space-observed. All of the space-observed information we have about the geology of Mercury comes from two NASA space probes, the Mariner 10 (Nov 1973 – Mar 1975) and the MESSENGER (Aug 2004 – Apr 2015).  Less than 45% of the surface was mapped after the Mariner 10 completed 3 separate flybys, but more than 99% of the surface was mapped after the MESSENGER successfully entered Mercury’s orbit in 2011.               

Map of Mercury’s Northern Hemisphere

The surface of Mercury is mainly made up of plains and impact craters, and is overall very similar to the moon in appearance. These were created as a result of flood volcanism, which occurred fairly early in Mercury’s geological history. There are also vents located on Mercury’s surface, and they are thought to be the source of magma-carved valleys. Fault scarps showing thrust faulting are found inside craters at the poles of Mercury.  Based on what we know about Mercury’s density, it is implied that it has a solid iron-rich core that takes up about 75% of its radius. Its magnetic equator is shifted to the north nearly 20% of the radius, and this is thought to be caused by one or more iron-rich molten layers around the core or uneven weathering and deposition by solar wind. There has been an observed possibility of ice on Mercury’s poles, but this claim is not confirmed. If the ice observations are correct, astronomers believe that it must have originated from external sources like impacting comets.

Thom & Stone Circles

Alexander Thom was a Scottish engineer who, later in his life, became curious about megalithic monuments, specifically the stone circles of the British Isles and France. He was interested in the prehistoric peoples that built them, and any astronomical meaning behind their construction.  His first interpretation of the sites suggested that megalithic yards were used as a standardized prehistoric measurement. He visited over five hundred megalithic sites throughout his researching years and developed ways to classify sites of varying shapes and sizes. Thom’s studies eventually lead to theories about the sites being used to predict eclipses and model solar and stellar alignments. This research actually provided a foundation for Archaeoastronomy.  He published several works detailing specific observations and results from his years of research. One important conclusion he made was that the prehistoric man’s calendar derived declinations fairly close to information known at the time of research.  Although his research was met with resistance and conflict, Thom ended up forming the standards for fieldwork in Archaeoastronomy, and his practices are still used in the field today.

Long Meg and Her Daughters, an example of a megalithic site

Historical Astronomers in Context

Historical Figures of Astronomy

Astronomer Birth Date Death Date
Nicholas Copernicus 19 February 1473 24 May 1543
Galileo Galilei 15 February 1564 8 January 1642
Johannes Kepler December 27, 1571 November 15, 1630
Isaac Newton 4 January 1643 31 March 1727
Tycho Brahe 14 December 1546 24 October 1601

Note: Galileo Galilei and Johannes Kepler lived at the same time for 59 years (1571-1630). Besides this, no other two figures lived at the same time.

Johannes Kepler

Johannes Kepler was born in December of 1571 and dies in November of 1630. Kepler was a very important figure in the scientific revolution in the 17th century. He made key contributions to the study of astronomy, specifically concerning planetary motion. Throughout his studies and published works, he developed his 3 laws of planetary motion. These were rejected at first by other astronomers, but they ended up being the foundation for the universal gravitation theory developed by Newton. The most influential works that impacted this theory are Astronomia nova, Harmonices Mundi, and Epitome Astronomiae Copernicanae.

Key Historical Events (1571-1630)

                During Kepler’s time, many key world events occurred. Below are a couple that are commonly known and provide perspective about the times.

                In 1595, Shakespeare was busy developing his works. He created most of his works between 1589 and 1613. Many of his pieces, specifically his tragedies, became very famous around the world. They’ve consistently been an essential part of education since their creation, and they were an important part of the development of the arts at the time.

In 1620, the Puritans landed in Massachusetts. This colony is the reason for Thanksgiving in America, and they played many roles in political ventures with the Native American tribes in the area. It did not exist for very long because it ended up merging with another colony and becoming a part of the colonization of the states.

Key Historical Figure

                Oliver Cromwell was born in 1599 and died in 1658, and the first 40 years of his life are actually quite unknown. Later in his life, though, Cromwell became an English political and military leader. He is known as a very controversial figure in history, as some believed him to be a dictator and others believed him to be a hero. He was a very large influence on Britain, Scotland, and Ireland, though it depends on who you ask if it was positive or negative.

Reflection

                Looking at the historical events that occurred during Kepler’s time, it made it easier to conceptualize when the development of astronomical theories took place. For example, it was very interesting to realize that Kepler had developed his theories on planetary motion around the same time that colonization of America was occurring. This contrast of scientific development in one place and societal development in another place is really cool to think about. It’s also thought provoking to compare the development of the arts with the development of science, as Shakespeare was creating his works at this time. It seems as though this era in general contained a lot of revolutionary events around the world.


References

En.wikipedia.org. (2019). Galileo Galilei. [online] Available at: https://en.wikipedia.org/wiki/Galileo_Galilei [Accessed 29 Jan. 2019].

En.wikipedia.org. (2019). Nicolaus Copernicus. [online] Available at: https://en.wikipedia.org/wiki/Nicolaus_Copernicus [Accessed 29 Jan. 2019].

En.wikipedia.org. (2019). Oliver Cromwell. [online] Available at: https://en.wikipedia.org/wiki/Oliver_Cromwell [Accessed 29 Jan. 2019].

En.wikipedia.org. (2019). Plymouth Colony. [online] Available at: https://en.wikipedia.org/wiki/Plymouth_Colony [Accessed 29 Jan. 2019].

En.wikipedia.org. (2019). Tycho Brahe. [online] Available at: https://en.wikipedia.org/wiki/Tycho_Brahe [Accessed 29 Jan. 2019].

En.wikipedia.org. (2019). William Shakespeare. [online] Available at: https://en.wikipedia.org/wiki/William_Shakespeare [Accessed 29 Jan. 2019].

NASA Solar System Exploration Website

NASA Our Solar System

While searching for a website that is useful for observing the solar system, I found the NASA Solar System Exploration website. The landing page rotates through all of the planets in our solar system and provides quick facts about each planet. Currently, listed below this display are facts telling the time until a total lunar eclipse, number of planets in our solar system, and number of planets beyond our solar system. Another number listed describes the one-way light time to Voyager 1. The Voyager 1 space probe was launched by NASA in 1977, and it is the human-made object that is furthest from Earth. The webpage contains dropdown bars for the Solar System, Planets, Moons, and Asteroids, Comets, & Meteors. These options make it easy to quickly explore essential elements of space and learn about them in depth. For example, from reading into some planets and asteroids, I found that each individual page contains the same key sections; Overview, In Depth, Exploration, and Galleries. When comparing it to other websites that provide similar information, I believe that the NASA Solar System Exploration website is the best site to reference. It is easy to navigate and provides an abundance of information in a format that isn’t too overwhelming. I would recommend it to anybody trying to build a foundation of knowledge about space!