Ask us About Space: Vol. 2

How close to the edge of a galaxy can planets exist?

We think about 20,000 lightyears from the edge.

With missions such as the Kepler Space Telescope finding thousands of planets outside our solar system, the number and location of these foreign worlds is grabbing people’s attention. One question that always follows discussions of exo-planets is whether or not life could exist on them and a way of figuring this out relates to the ‘habitable zone’. This region of space around a star represents the location that is ‘just right’ not too hot or too cold. It has been suggested that this idea may apply to planets in galaxies. This often contested idea was put forward by Guillermo Gonzalez. He suggested that a planet would need to be far enough away from the galactic centre to avoid harmful radiation but far enough away from the edge of the galaxy to ensure enough heavy elements to form the planet. This gives the Milky Way’s habitable zone as a 6,000 lightyear band 25,000 lightyears from the centre, This sits roughly halfway between the centre and the edge.

Currently not enough planets have been detected to put solid limits on where planets can form in the galaxy but more and more missions are collecting data and adding to our knowledge.

How many artificial satellites can you see with the naked eye?

A lot!

Surprisingly there are a large portion of artificial satellites that can be seen with the naked eye. Sightings can number up to a hundred in a single night if you have good viewing conditions. To identify a satellite you are looking for a star that looks like it is slowly moving across the night sky. On average they are visible for up to 10 minutes although some can be present for longer. The important thing to note is that unlike a plane, satellites do not ‘blink’ or flash. They remain a steady brightness and follow  consistent speed and direction across the sky. Occasionally they can disappear if they move into the Earth’s shadow. So next time you find yourself away from a city in a dark rural area, study the sky for these slow moving objects and see how many you can spot.

Can a telescope be used for Solar observing?

Only special types of solar telescopes should be used to look at the Sun.

With the correct filters and safety checks almost any telescope can be used to look at the Sun, however the proper precautions must be taken if you intend to embark on a solar observing session.
It should go without saying that the Sun is bright and that looking directly at the Sun can cause permanent eye damage or even blindness. This danger becomes even more apparent when you are focusing the light from the Sun using lenses.
If you do not want to splash out on a dedicated solar telescope, or filters for your telescope then you can project the image from your telescope onto a piece of white paper. Alternatively, you can purchase special hydrogen alpha solar filters which filter out most of the wavelengths of light, allowing you to concentrate on those wavelengths associated with hydrogen, and therefore most interesting to solar observers.

Would we have been able to live on early Mars?

It is possible that we might have been able to live on Early Mars, although we still do not know enough about the early atmospheric conditions to be sure.

Mars now is a dry, cold planet with a very thin carbon dioxide atmosphere, certainly not habitable now.  However, observations of river channels and ocean beds on Mars show that the atmosphere was once much thicker so liquid water could exist.  Turn back the clock to a time when Mars still had a magnetic field able to deflect high energy charged particles that would otherwise strip the atmosphere, we would find a Mars with a much thicker atmosphere.

And recent research by scientists at Oxford University studying the difference between Mars surface rocks and Martian meteorites suggests that about 3700 million years ago, Mars may have had an oxygen rich atmosphere.  So, for a short time at least, Mars may have been habitable for humans.