My Science School

Sometimes, you may have watched the moon near the horizon and wondered "Why is the moon unusually bigger tonight?" Does the moon grow bigger near the horizon and shrink when it moves high up in the sky? This perception is called Moon illusion: Your brain is playing a trick on you.

Sky watchers have observed this phenomenon for thousands of years. The precise reason for the moon appearing to be expanding and contracting continues to puzzle scientists even today. But in general, our brain is tuned to think that objects near the horizon are (usually) more distant and larger than those overhead. But one thing is for sure - the moon isn't changing size.

Here is an activity to test this: Take a sheet of paper and roll it up into a narrow tube. Point it at the rising moon, look through it and adjust the tube's size until it's slightly larger than the moon. Fix the tube using a tape so its size stays the same and look at the moon again a few hours later when it's higher in the sky. You'll see it fills the same space.

 

Picture Credit : Google

A galaxy is a huge collection of stars, their solar systems, dust and gas. It is held together by gravity.

Earth is a part of the solar system, which is a small part of the Milky Way Galaxy. All those stars you see in the sky at night belong to the Milky Way.

When you are far away from city lights, some place really dark, you can even see the dusty bands of the Milky Way stretch across the sky.

How many are there?

There are countless galaxies out there. Once, when the Hubble-Space Telescope looked at a small patch of space for 12 days. It found nearly 10,000 galaxies of all sizes, shapes and colours.

Some scientists believe there could be as many as one billion galaxies in this universe!

How do they look?

Galaxies came in different shapes. But the two most common types, based on ones discovered so far, are Spiral Galaxy and Elliptical Galaxy.

The Milky Way is a spiral-shaped galaxy. This type of galaxy has curved arms that make it look like a pinwheel.

Elliptical galaxies, on the other hand, are smooth, and oval shaped.

Just like ours, other galaxies too get their light from stars that inhabit them.

On collision course

There are times when two or more galaxies can get too close and smash into each other. For example, the Milky Way galaxy will someday bump into the Andromeda galaxy, its closest neighbour.

However, this won’t happen for another five billion years at least, and even if it were to happen anytime soon, you wouldn’t notice and spread out at the ends that even if they do bump into each other, the planets and solar systems often don’t get close to colliding.

 

Picture Credit : Google

Moonlight takes approximately 1.28 seconds to reach Earth's surface. Light travels through space at almost 300,000 kms per second. The moon is 384,400 kms from Earth, so light from the Moon's surface has to travel more than one second to reach us.

The color of moonlight, particularly around full moon, appears bluish to the human eye compared to most artificial light sources due to the Purkinje effect. Moonlight is not actually tinted blue, and despite often being described as "silvery", it has no inherent silvery quality.

The Moon's albedo is 0.136, meaning only 13.6% of incident sunlight is reflected from the lunar surface.

 

Picture Credit : Google

When one object crosses in front of another in space, it is known as transit. For example, when the Moon passes between the Earth and the Sun, the Moon is ‘transiting‘ the Sun.

Why is it important?

Just like objects in our solar system that transit the Sun, there are objects outside our solar system too that transit stars there. These objects include planets known as explants, and their transit help scientists identify these planets.

If the orbit of a planet is lined up right, the planet is lined up right, the planet will transit the star it orbits. When this happens, the light from the star dims by a small amount of time between each transit. This is how scientists discovered seven exoplanets around a star called TRAPPIST-1. There of these planets were discovered in 2015, while four more were identified in 2017.

Bottomline, transits not only help scientists identify new planets but also understand the world beyond our solar system.

The transits we can see

From Earth, there are two main transits that can be seen by people. One is the transit of the Moon, as it passes the Sun. this is when we witness a solar eclipse. The other is the transit of the planet Venus when it passes between the Earth and the Sun during its orbit.

While solar eclipse can be observed often, the transit of Venus cannot be seen frequently because of how he orbits of Venus and Earth are lined up. The last transit of Venus was on June 6, 2012. The next one, however is not until 2117!

 

Picture Credit : Google