Posts

Scaling Laws in Nature: The laws that explain the absence of a magnetic field on Mars and why squirrels can jump so high

Image
We know that the interior of Mars is cooler than the interior of the Earth, but why is that the case? Both planets would have been very hot and fully molten during their formation 4.5 billion years ago, but Mars has cooled down faster than the Earth. One of the main reasons for this is that Mars has a smaller volume to surface area ratio than the Earth. What determines an object’s heat energy and cooling rate? The total heat energy in an object is determined by its temperature and mass. If we assume that the Earth and Mars started off with approximately the same temperature and density, then the energy contained within the planets only depends on their volumes. The rate at which an object loses heat (cooling power) is proportional to its surface area. The volume and surface area of a sphere with radius r is given by: If we divide the volume (total energy) by the surface area (cooling power), the resulting ratio tells us how long it takes for the object to lose its heat. Let’s confirm t...
Post a Comment
Read more

Executing a telescope observation session

As the Observation Secretary at the Cambridge University Astronomical Society, I had to plan and execute numerous observation sessions – both as a public advertised event, and as a small group with my friends. There are several aspects to consider when stargazing – from the weather conditions to photographing the objects that you’re observing. Here are some of the main points to think about for a night of stargazing. Weather conditions This is usually the most frustrating aspect of planning an observation night. Cloudy skies or precipitation are astronomers’ largest enemies. Weather conditions can change quite rapidly depending on your location, and the weather forecast may not be accurate beyond a day or two into the future. We usually plan our observations only a few days in advance and frequently check the forecast to see if there are major changes to the weather. Certain bright objects such as the Moon and planets can be observed even with the presence of some thin high-altitude cl...
Post a Comment
Read more

Douple Solar Eclipses on Jupiter

Image
Solar eclipses happen on Earth when our Moon blocks sunlight from reaching the Earth’s surface. This casts a shadow on our planet, and people in the shadow can see that the Sun has been covered by the Moon. Here is a view of a solar eclipse from space (picture taken by astronauts on the International Space Station): The large black blob on the surface is the Moon's shadow. People within the shadow region would see a solar eclipse when they look up at the Sun. What happens on planets which have multiple moons? Jupiter, the largest planet in our solar system, has 95 moons! 4 of these moons are large and can cast noticeable shadows on Jupiter. During one of my stargazing sessions at the Northumberland Telescope in Cambridge, I was lucky enough to see this happen. I saw, not one, but two shadows on Jupiter simultaneously! These were caused by the moons Europa and Ganymede passing between Jupiter and the Sun. I managed to take a (blurry) picture of this by placing my phone camera on t...
Post a Comment
Read more

What determines the time of sunrise and sunset?

During a recent trip to the Andaman Islands, I noticed that the sunrise and sunset times in the city of Port Blair were almost exactly an hour earlier than those in my hometown of Bengaluru in mainland India. My father believed that sunrise and sunsets are determined by the latitude, while my mother said that it was caused by the longitude. Both cities follow the same time zone (UTC+5.5hrs), which prompted me to study the factors that determine the sunrise and sunset times for a particular place. Longitude The Earth has 360 degrees longitude which runs from 180 degrees in the West to 180 degrees in the East. The longitude of a particular place denotes its location with respect to the Prime Meridian. As the Earth rotates from West to East, places further east will experience sunsets and sunrises earlier. Since 360 degrees of longitude corresponds to one whole day, we can calculate that 1 degree corresponds to a 4-minute time difference for the sun’s movement (assuming both places are ...
Post a Comment
Read more

Why don't eclipses happen every month?

  You probably know how eclipses happen – a solar eclipse happens when the Moon blocks the Sun by coming between the Earth and the Sun, and a lunar eclipse happens when the Earth is between the Moon and the Sun and sunlight is blocked from the Moon. This raises the question of why solar and lunar eclipses don’t happen every month. After all, the length of the lunar cycle is about one month, and the Moon is between the Earth and the Sun every time there is a New Moon. Similarly, the Earth is between the Moon and the Sun every time there is a Full Moon. Doesn’t this mean that we should experience solar and lunar eclipses every month when there is a New or a Full Moon? The reason why this doesn’t happen is because the Moon’s orbit around the Earth is tilted by about 5 degrees with respect to the ecliptic . The ecliptic is the straight line connecting the Earth and the Sun. The tilt of the Moon’s orbit causes the Moon to usually cross slightly above or below the Sun during a New Moon...
Post a Comment
Read more

Can life travel between planets?

There are several ways in which living organisms can travel millions of kilometres through space and spread between planets. The most common way in which this happens is through meteorites. Meteorites are rocks from space which crash on a planet’s surface. Most of the meteorites which crash on Earth are small asteroids. However, several of these meteorites are believed to be rocks which were once on the surface of Mars, our neighbouring planet. How is this possible? When a big asteroid collided with Mars (like the one which killed the dinosaurs) sometime in the past, a large number of rocks from the surface of Mars would have been thrown into space. Many of these rocks fall back down to Mars due to the planet’s gravity. However, some of these rocks will be travelling fast enough to escape Mars and start orbiting the Sun. The orbits of some of these rocks would be elliptical and cross the Earth’s orbit. When the rocks get close enough to Earth, they are pulled by Earth’s gravity and cra...
Post a Comment
Read more

How can life exist on the Earth?

Earth is the only planet that we know of where life exists. The conditions on a planet must be suitable for life to begin, and there are several factors which helped life to exist and evolve on Earth.   Habitable zone/Goldilocks zone Our planet is just the right distance from the Sun. The scientific term for this is “Circumstellar Habitable Zone”, but it is commonly known as the “Goldilocks Zone”. This is because the Sun’s distance is such that it is neither too hot nor too cold on the Earth.   Type of star Our Sun is a G-type main-sequence star, which means that it is relatively small and cool. Larger stars have a shorter lifespan, which would give insufficient time for life to evolve. Small stars are unstable and frequently emit high levels of dangerous radiation that can be harmful for life. Therefore, the size of our Sun makes it a suitable host star as it is stable and long-living.   Magnetic field The Earth has a liquid outer core which contains me...
Post a Comment
Read more