Speed of light This ability to look back in time is based on the fact that even light has a speed limit. It bowls along at 186,000 miles per second. So if you look at a star that is 30 light years away, that is what it looked like 30 years ago. The same applies to stars that are millions of light years away.

The reason distant galaxies = young galaxies is the finite speed of light. Then, you can compare those galaxies to the ones you find 10 billion light years away, because those will appear as they were 10 billion years ago.

The most distant galaxies are caught up in the expansion of the Universe, causing distant galaxies to redshift past the point where our optical and near-infrared telescopes (like Hubble) could detect them. Finite sizes and observing times meant that only the galaxies above a certain brightness threshold could be seen.

Because light takes time to travel from one place to another, we see objects not as they are now but as they were at the time when they released the light that has traveled across the universe to us. Astronomers can therefore look farther back through time by studying progressively more-distant objects.

The most distant thing we can see with our bare eyeballs is Andromeda at 2.6 million light years, which in dark skies looks like a fuzzy blob. If we cheat and get a little help, say with binoculars – you can see magnitude 10 – fainter stars and galaxies at more than 10 million light-years away.

Energy can change from one form to another. For example, when you switch on a lightbulb, electrical energy changes to thermal energy and light energy. A car changes energy stored in the chemical bonds of gasoline to several different forms. A chemical reaction in the engine changes chemical energy to light …

Heat can be transferred in three ways: by conduction, by convection, and by radiation.

• Conduction is the transfer of energy from one molecule to another by direct contact.
• Convection is the movement of heat by a fluid such as water or air.
• Radiation is the transfer of heat by electromagnetic waves.

There are different forms of energy stores, including:

• kinetic energy.
• internal energy.
• elastic potential energy.
• gravitational potential energy.
• electrical energy.
• magnetic energy.

Energy transfer takes place when energy moves from one place to another. Energy can move from one object to another, like when the energy from your moving foot is transferred to a soccer ball, or energy can change from one form to another. Three more ways energy can be transferred are through light, sound, and heat.