Sundials
Human beings have been dealing with the concept of time since ancient times. He used different methods to divide the time during the day into various parts. Sundial is one of these applications. At first, time measurement did not need to be done in detail, it was just waiting for the appropriate time to do certain tasks; such as when the weather will warm up, when it will cool down, and the best time to plant. Here we will try to give information about sundials. 
A sundial is a device used to measure time based on the position of the sun. In common horizontal sundial designs, the shadow of a vertically placed rod falls on the dial that shows the hours of the day on a horizontally placed surface. As the sun moves across the sky, the tip of the stick moves to coincide with different hour lines. In these designs, the rod must be aligned with the Earth’s axis of rotation. Therefore, for this type of sundial to show the correct time, the bar must point to geographic north, not magnetic north. In addition, the angle the rod makes with the horizontal plane must be equal to the geographical latitude where the clock is located. However, sundials can also be designed that do not have these two features but work within the framework of different principles. 
A sundial is a mechanism that finds the parts of the day by making use of the shadows cast by the sun’s rays on an object.
It was used for the first time in the form of a vertically arranged bar and the time of day was determined according to the shadow length.
Different sundials were used in ancient Greece. Apollonius of Perga (250 BC) created an even more precise clock by using a conical section. Ptolemy developed a clock that showed shadows in various inclined planes. B.C. in a tower in Athens. There are eight sundials dating back to 100 BC in Rome. The first sundial appeared in 290 BC.
Sundials became widespread with the Renaissance. However, since the 19th century, it has become no more than an ornament.
The working principle of the sundial is related to the movement of the sun in the sky. This apparent motion is related to the rotation of the earth around itself and the sun. However, there are three other effects that must be taken into account for the precision of the sundial: The first of these is that the earth moves by considering the sun as the focus; Secondly, the orbit is elliptical and thirdly, the Earth’s axis of rotation is tilted. 
ISS Live Now
The ISS Live Now app is an application that allows you to watch live video streaming of Earth from the International Space Station (ISS). The ISS orbits approximately 400 kilometers (250 miles) above our planet. The app offers an exciting experience with an impressive design and numerous customization options.
With ISS Live Now, you can watch live HD video streams from the ISS’s cameras. The app uses Android Google Map (ISS tracker), which allows you to track the ISS’s orbit. You can zoom, rotate, drag and tilt the map; you can choose between different map types (e.g. satellite or terrain); You can view data such as orbital speed, altitude, visibility, latitude and longitude, and which country the ISS is over at any given moment. All these options can be easily customized from the settings menu. 
You will have seven different live video streaming sources, including:
- Live HD camera: An amazing HD video stream of our planet.
- Live standard camera: Shows a live stream of the Earth and occasional details about the ISS (e.g. tests, maintenance, and communications with Earth).
- NASA TV: Television service of the United States government agency NASA (National Aeronautics and Space Administration). You can watch science and space documentaries, interviews with scientists, astronauts, engineers and people like Elon Musk.
- NASA TV Media.
- Spacewalk (recorded): HD footage of astronauts from cameras outside the ISS.
- Inside the International Space Station: Take a video tour of every module of the ISS, all explained by astronauts.
- Temporary channel: Temporary live cameras from NASA, European Space Agency (ESA), Russian Space Agency (Roscosmos) and SpaceX.
You can also watch these live broadcasts on your television via Google Cast. You even have an option to get notifications of when the next sunset or sunrise will occur, so you can watch it live from the International Space Station. You will be able to receive timely notifications about the arrival and departure of manned and unmanned spacecraft such as Soyuz, SpaceX Crew Dragon, Boeing CST-100 Starliner, Rocket Lab, Arianespace, Blue Origin, Northrop Grumman, spacewalks, launches (Falcon, SpaceX, Dragon, Progress, Cygnus). , ATV, JAXA HTV Kounotori), you will be able to watch live events such as connections, disconnections, rendezvous, captures, experiments, NASA/Roscosmos ground control and communication between astronauts.
If you are interested in space or astronomy, I am sure you will love the ISS Live Now app.
Link: ISS Live Now | Just an amazing way to see the Earth from space live
What is a Nebula?
A nebula is a nebula structure consisting of cosmic dust, hydrogen, helium and other ionized gases located in space and spread over large areas. Nebula means “fog” in old Turkish. Nebulae are located in the spaces between stars and become visible with the light energy emitted by the stars. Nebulae are fundamental components of galaxies.
The formation of nebulae is closely related to the life stages of stars. A nebula is a star before it forms. After this star grows, it either becomes a white dwarf, neutron star or a black hole. But all stars become red supergiants before becoming one of these. Since these stars are very large, they release gas into space under the influence of internal pressure and high temperature. These gas eruptions are quite large and fast. Later, these gases come closer and form a gas cloud. The temperature of this gas cloud is more than 15,000 °C. This temperature and various pressures combine with the gases (hydrogen) there and initiate a fusion reaction. This fusion reaction is the first foundations of a new star. 
Sometimes stars go supernova and explode. As a result, instead of releasing gas slowly into their environment, they release it suddenly. These gases are diverse and they react and increase diversity. This creates a multi-colored image. Supernova explosions are events worth watching. The last recorded eruption occurred in 1987 and was recorded as 1987A. In supernova explosions, red supergiants explode and form neutron stars. Sometimes a black hole forms. When a black hole forms, it attracts everything around it. When a neutron star forms, it does not attract its surroundings like a black hole. The matter density of a neutron star is very high. 
Types of nebulae are classified according to the differences in the gases, dust, radiation and shapes they contain. Some types of nebulae are:
- Reflection nebula: These nebulae consist of dust particles that reflect light from stars. Reflection nebulae take on the color of stars. For example, the nebula around the Pleiades star cluster is colored blue.
- Emission nebula: These nebulae are formed as a result of high-energy rays from stars ionizing gas atoms. Emission nebulae are usually red because hydrogen atoms emit red light.
- Dark nebula: These nebulae consist of dense dust and gas that absorb light. Dark nebulae reveal themselves by blocking the light of the stars behind them. For example, the Horsehead nebula is a dark nebula that covers part of the Milky Way galaxy.
- Planetary nebula: These nebulae are formed when aging stars eject their outer layers into space. Planetary nebulae are generally round or elliptical in shape. Their name comes from their resemblance to planets when viewed through a telescope. For example, the Cat’s Eye nebula is a planetary nebula.
- Supernova remnant: These nebulae consist of gas and dust created as a result of the supernova explosion. Supernova remnants often have complex and irregular shapes. For example, the Crab nebula is the remnant of a supernova that exploded in 1054.
Nebulae are spectacular celestial objects that help us understand the structure of the universe and the formation and death of stars. For more information about nebulae: spaceplace.nasa.gov
This Week in Our Art Corner
The Last Man on The Moon
If you think traveling in space is easy, we recommend you watch this documentary; because “The Last Man on the Moon”; It reveals how difficult and difficult the life of an astronaut is, mentally and physically, with archive footage, interviews and visual effects. The 2014 documentary allows you to connect with astronaut Eugene Cernan during his journey to the Moon in 1972.
