Tuesday 9 November 2010

The Telescopes on the Roof

This blog is about the telescopes on the roof at Southampton Physics and Astronomy Department.

This is the script for the talk I normally give when showcasing our dome observatories. 

The department has 2 Meade telescopes that look just like this one.

The Tour of the Observatory
Notes by Sadie Jones- updated 6 June 2012

1.    Keys to be collected from Sadie or Malcolm.  Please read user guide in the hut up on roof!  Students are to be given torches if its dark and a risk assessment is to be produced and guidance followed.
2.   Show the students the Observatory room first, explain the maps on the walls and computers and that modern astronomy is not done with astronomers looking with their eye to the telescope, but instead the astronomers watch that the correct objects are observed from the Hut…(most of the analysis of data done at a later date)
3.   Explain the two huts and how they rotate to allow the telescopes to look out of the gap, explain the use of the domes to protect the telescopes. Tell them the cost of 2 domes such as these (????)
4.   Turn on the domes at the wall in the Observatory room and let the student open and rotate them themselves with your guidance.
5.   Explain that one of these telescopes is like that used in Tenerife. Ask the students if they can think of why Southampton is not the best place to observe from and why Tenerife is?

6.   Take the students out to the telescopes (crawl under the door). Say ‘We have 2, 10 inch Meade telescopes here’, now when I say 10 inch I am referring to the size of the mirror (point to it)…Explain how light comes in and bounces off the primary and secondary mirror and then into the eye or CCD camera which is attached.

7.   Does anyone know what other object can be used inside a telescope to focus light? Hopefully they will say lenses if they need a clue point to your glasses. Explain 2 types of telescopes refractor and reflector.
refractor =lenses, reflector = mirrors .

8.   Now ask them what they think they would do to observe a certain galaxy or certain star, what important information does the telescope need in order to point at this galaxy…?? Hopefully you can help them toward the fact that GPS is used so that the telescope knows its position on top of the roof at Physics. Then it just needs to know what angle it needs to point at. One of easiest ways to ‘align’ the telescope is to point it at something easy like the moon by using the view finder, and then to tell the telescope it is on the moon. It can then work out where your galaxy is in relation to moon. This is called calibration.
So we have found our galaxy and are happily observing it and after a few minutes it is no longer within the view finder, the telescope is at exactly  the same alignment? What has happened?...Help them to the fact that the earth is spinning on its axis so this means the stars and galaxies appear to move across the sky over the night. Can they think of a way to stop this? Help them to the fact that you can make the telescope move around at the same rate the galaxy moves across the sky, so it is always in eye piece. This type of mount is called an Equatorial mount – which means it turns with rotation of sky. Mount rotation axis is aligned on pole star (north star) so one axis is parallel to rotation axis of earth so only need to track on one axis (and so can point out which way north is very accurately)
When you have calibrated the telescope you can can rely on the computer (point to computer) to locate objects i.e. Saturn, NGC 4051 etc.

9.   Explain about the light collection of the mirror i.e. 10inch refers to the diameter of the mirror = bigger, more light collection, but you also want the light to …Need better explanation here? (Andy?)
Need to find a happy medium since the light could be bounced back and forth a lot more, but then you lose light?!  For any photographers, these are equivalent to a 2500mm f/10 lens.

10.     Schmidt-Cassegrain design, allows compact design with spherical mirrors that are easier to make.  Schmidt is the corrector and the Cassegrain is the hole in primary mirror. Focus is behind primary mirror.

11.      Tenerife trip for the 2nd years - only exceptional students go.

Might want to mention about how cold it is in Tenerife, Hawaii etc where the telescopes are because so high up!! These places chosen because of the lack of clouds, which is good for astronomy (but does not keep in the heat....but the astronomers can be in relative warmth in the Observatory ....Students observe by night and sunbathe by day.
Optical astronomy is very different to radio astronomy which can be done in the day. But that is a whole other story...(dark art)

12.      These telescopes can image something about 1/2 the size of moon. A 10” Meade should have a field of view of about 15’ (a quarter of a degree, or half the width of the moon) with a big imager on the back, and a theoretical resolution of about 0.6 arcsec (0.6/60/60 degrees). The resolution will depend really on the number of pixels across the CCD. If you have a 16Mpix CCD (4000x4000 pixels) to view a 0.25 degree field, that should be quite well matched in resolution, putting 2 or 3 pixels across the telescope point spread function. Of course, with seeing (ie atmospheric) conditions, we never get close to that here!

13.      The CCD attached to the computer has a resolution like digital Cameras. For example your friend with 12M pixels has a better resolution and their camera can distinguish features in your face (eg spots!), but your other friend with the 6M pixel camera takes a photo and you cant see the spots :) In astronomy we often want very good resolution so we can see the finer details in our galaxies or in the regions around a black hole.

            Could also mention the size of the sensor, because megapixels isn’t the whole story. The size of each pixel defines how much light you can collect, so a good astro CCD will be much more sensitive than the tiny sensor in an iPhone (for example). A proper CCD (or a full-frame DLSR) is probably 10-50x bigger than a webcam sensor.

9.        Undergrad projects that use the telescope: -

·      Star variability
·      Astrophotography
·      Craters of the Moon
·      Solar telescope? Sunspots?
·      Extra solar planets -using transits, look for the brightness of star decreasing when the planet passes between us and the star...students like this one especially because of the aliens angle.
·      Transits and Moons of Jupiter

Nice to take them back in Observatory room and show them some of the good posters from Tenerife, Ruths is a nice one showing Transiting planets which Christian has.

Christian also now has spectrograph, so we can take spectra – measuring the temperatures of stars, seeing what stars are made of, planetary atmospheres.

Keen students may use telescopes with permission to look for Meteor showers etc.

Things you need: -

The Key!  & a poster from Tenerife? of students’ projects on the pc in the hut… or some photographs taken with the telescopes (Sadie has some of Liz’ and Nicks’ photos up outside her office )

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