Night Sky Questions

Q. I saw a bright light streak across the sky last night. Was it a meteor?
A. Meteors are the bright trails left by fragments of natural space debris called meteoroids (usually chunks of rock or metal) falling through the EarthтАЩs atmosphere. A typical meteoroid hits our atmosphere at about 72 000 km/hr, traveling through the air at this speed warms it up until itтАЩs white hot, so it appears as a bright streak in the sky. Most meteoroids are tiny, smaller than a grain of rice and are quite common; if you watch the sky on a dark night youтАЩll probably see several in an hour. Some arrive in regular showers at particular times of the year. However, since it was so bright, the one you saw was probably a bit bigger than average, this is very rare and cannot be predicted.

Most burn up about 100 km above the ground, occasionally the core of a larger one will reach the EarthтАЩs surface. These are called meteorites.  You have been very lucky; youтАЩve seen a very rare and wonderful sight.m

Q. I saw a bright light hanging in the sky for hours last night. What was it?
You may have seen one of the EarthтАЩs neighbouring planets. Venus, Mars and Jupiter can all look very bright to the naked eye. As the Earth moves around the Sun over a year, planets will move in and out of view, so the sky changes.To confirm if it was one of the planets, go to www.heavens-above.com. You will have to register with this site but this is easy and they will not ask for personal details, you then can investigate which planets were visible from your location using the Whole Sky map at the Astronomy section of the www.heavens-above.com site.€а

Q. IтАЩve heard that the world is going to end soon! A planet called Nibiru or Planet X is going to pass close to Earth or an asteroid is going to hit Earth. Is this true?
A. Firstly, please let me reassure you. There is no reason to be concerned ; there are no astronomical or geological disasters predicted . The planet тАШNibiruтАЩ simply does not exist and was invented by a cranky author in the 1970s so it will not present any danger to us.

There is no question of governments covering up an impending disaster either. There are hundreds of thousands of astronomers worldwide in every country, most of them are not employed by governments and it would be impossible to silence every single one of them.

Scientists estimate that our planet will survive for another 7 billion years at the very least so we all have many, many years ahead of us to enjoy.

Q. I saw a bright light moving steadily across the sky last night. What was it?
A. You may have observed the International Space Station (ISS). It can appear very bright and moves across the sky over a few minutes. To confirm if it was the ISS, go to www.heavens-above.com. You will have to register with this site but this is easy and they will not ask for personal details, you then can investigate when the ISS and other bright satellites passed over your location.€а
The ISS is the biggest and most expensive space project ever undertaken. It has been under construction by NASA in the US, the Russian, Japanese and Canadian Space Agencies and the European Space Agency since 1998.
The ISS is intended to be a laboratory where scientists from many countries research into important fields. Most of the experiments depend on the micro-gravity environment of Earth orbit. Currently the ISS is over 100m across and weighs about 500 tonnes. It orbits 350 km over the EarthтАЩs surface and can accommodate a crew of six.

Q. IтАЩve received an e-mail saying that soon Mars is going to come really close to Earth. It will look as big as the full Moon.€а Is this true and should I be worried?

The information you have been sent about Mars coming spectacularly close to Earth is absolutely not correct but is based on misunderstandings and exaggerations. It has been circulated every summer since 2004 or so (see Astronotes Sept 2006 page 4, BBC News  and snopes.com). Luckily for us, Mars remains in its orbit millions of kilometres from our planet as it has for billions of years.

Q. I saw a strange ring of light around the full Moon last night. What was it?
A. Probably you have seen is a halo (also known as an icebow, a nimbus or a moondog). Halos are optical phenomena that appear near or around the Sun or Moon. There are many types of halos, but they are mostly caused by ice crystals in cold cirrus clouds located high (5 to10 km, or 3 to 6 miles) in the atmosphere. Light is reflected and refracted by the ice crystals and may split up into colours because of dispersion, just as in rainbows. An icebow has red on the inside and blue on the outside. Halos observed around the Sun are known as sundogs.
A moondog is a halo seen at night. Moondogs appear around the Moon and are approximately 22€ђ across. Moon dogs are somewhat rarer than sundogs, because in order to produce moondogs or other types of halos, the Moon must be bright and therefore full or near full. Here is a picture showing this phenomena: http://apod.nasa.gov/apod/ap000515.html.

How far into space can the Hubble Telescope see?

Distant objects are less bright than nearby objects. To capture images of very far away and therefore faint galaxies the Hubble Telescope looks at them for long periods (11.5 days is the record) and builds up the image during this exposure.€а By doing this, the Hubble Space Telescope has seen the most distant galaxy ever seen, about 13 billion light years away (the Universe is only about 13.8 billion years old). In practise, the HST will probably not ever see anything further away than this as the conditions in the early Universe did not permit starlight to shine freely. Basically, the HST sees as far into space as is theoretically possible.

If the Hubble Telescope can see objects in deep space, why doesnтАЩt NASA point it at the moon and get pictures of the flags and equipment left there by astronauts?

There is a mathematical relation called the Rayleigh Criterion which links the diameter (or aperture) of a telescope with its resolution. Using the values for the Hubble telescope shows that the smallest things it can see on the Moon are about 60 metres across. This is much bigger than any piece of Apollo equipment. Starting in 2009, the LRO spacecraft has made images of the landing sites of the Apollo missions.