Institute of Astronomy


Ask an Astronomer at the IoA

Ever had a question about astronomy you've want answered? Have a look through the previous questions which we've been asked and if you can't find find your answer, ask us!

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What is the bulgy centre of spiral galaxies like Andromeda?

Published on 09/05/2011 

What is the yoke like bulgy centre of galaxy that we see in pictures like Andromeda, what is it made up of?

All spiral galaxies like Andromeda have a round bulge at the centre of the flat disc that contains the spiral arms. This 'bulge' is just a large ball of stars all tightly packed together; they are yellowy-red in colour as they are a lot older than the blue stars being formed in the spiral arms.

Stars on the Moon

Published on 02/05/2011 

Is it possible to see stars from the surface of the moon? I thought it was but in an interview in 1970 ( Neil Armstrong said you can only see the Sun and Earth.

When US astronauts visited the moon as part of the apollo program, people often comment in images that you don't see the stars. This is the same phenomenon Neil Armstrong described in the interview on the BBC in 1970.

The stars are actually visible from the surface of the moon but they are particularly difficult to observe. If on Earth you compare a night where there is no moon with a night with a full moon, it is much easier to see stars on the dark night with no moon. The same phenomena happens on the moon with the Earth reflecting the Sun's light as well as the astronauts only working in sunlight. And as you know from experience, during the day time we don't see any stars (unless you know exactly where to look using a telescope!) even though they're still shining.

So although the stars are there, the light conditions when the astronauts were working meant that they were unable to see them.

Is Betelgeuse about to explode?

Published on 01/05/2011 

I have never seen Betelgeuse so red with naked eye - is it about to blow?

Betelgeuse is remarkably red - but maybe it's just looked so brilliant at the moment because of the lovely clear nights we've been having! You're right that as Betelgeuse is a 'red giant' star it's in the final stages of its life and is (as you so poetically put it...) about to blow, in the form of a dramatic supernova explosion. The catch here is that when astronomers mean 'about', it could be any time in the next few  thousands of years... no-one knows exactly when it might happen, and there aren't any observations suggesting it's particularly imminent... We'll certainly know when it does occur; at around 640 light-years distant Betelgeuse will become very much brighter in the sky, perhaps briefly becoming bright enough to be visible during the day.

What are the Northern lights?

Published on 01/05/2011 

What are the Northern lights?

The Northern lights (or 'aurora') are caused by energetic particles that perpetually rain down onto the upper part of Earth's atmosphere - most of these particles stream from the sun in the 'solar wind',  although some originate from deeper out in space. Many are guided along the Earth's magnetic field down deeper into our atmosphere, where they collide with atoms and molecules of air. In such a collision, the particle gives up some of its energy to the atom, which later gives off this energy in the form of light. So if the sun is active there's a strong solar wind, and many millions of these collisions occur high up in the atmosphere to produce the luminous glow that is the northern lights. The actual colour observed depends on what kind of atom or molecule is giving off the light, and how much energy has been given to it by the collision. The northern lights are emitted from a region from about 100-300km above the Earth's surface.

Amateur detection of Near Earth Objects

Published on 04/04/2011 

Is it possible for an amateur astronomer to assist with detecting near-Earth asteroids or comets? If so, what would be the minimum telescopic aperture and type of photographic equipment required to conduct this kind of research?

Amateur astronomers can and do play an important part in detecting near-Earth objects. Today more than 5% of all near-Earth objects are discovered by amateurs and this proportion is on the increase. The Minor Planets Centre ( based at Harvard University is the organisation responsible for cataloguing and archiving all discoveries of small bodies in the solar system and have a wealth of information to help potential amateur astronomers. The professional search programs typically use telescopes with a diameter of ~1m; LINEAR, one of the longest running and most successful programs currently has two 1m telescopes and a 0.5m telescope. When conducting searches smaller telescopes are to some extent preferred since they have a larger field of view and can image a larger area of the sky at once.

When you have your telescope, discovering asteroids is still not trivial! Because these objects are particularly faint (due to their size), the detectors being used (usually a CCD) need to be sensitive enough to be able to distinguish them from the background noise from the device. For CCDs, when they are cooled the background noise is reduced and because of this, most of the CCD detectors you can purchase for amateur astronomy today use fans to cool the CCD well below the ambient temperature.

Even with both of these, the main requirement to successfully discover asteroids and other small (and faint) objects is a dark site with good seeing (clear, still skies). Combining all of these things together means you could potentially discover some new asteroids!