Questions & Answers

Karl's question

From: kpospisek [SMTP:kpospisek@telstra.com]
Sent:        Tuesday, 05 March, 2002 3:27 AM
To:        STEWART, Chris
Cc:        kpospisek

Subject: Dangers with the big light in the sky.

Hi Chris,

I saw a program on TV last night about the sun. The Sun is a powerful light emitter. Online one can control telescopes to look into different parts of the sky. Is there anything that stops these telescopes from being pointed at the sun and burning out the CCDs ?

I can see simple rules for ground based telescopes (eg only allowed to operate from Sunset to Sundown ).

But what space-based telescopes that have no day/night. What if I want to focus on a planet "close" to the Sun (eg mercury) - how would I prevent the telescope from passing across the sun's surface whilst it's moving to my object of interest ?

Karl

Chris Stewart's Reply

From: STEWART, Chris
Sent:         Tuesday, 05 March, 2002 9:24 AM
To:         'kpospisek'

Subject: RE: Dangers with the big light in the sky.

Hi Karl,

Of the telescopes that have a computer control system (many these days, my own Meade LX200 being one of them) most have built-in restrictions against pointing the telescope at or within a few degrees of the sun. However, the lesser control systems (again, like mine) only look at the destination co-ordinates when they start to slew, and apply that restriction. They do not DURING the slew check whether they are nearing the sun. So, with my scope as an example, it is possible for it to slew right across the Sun en route to some other co-ordinate, but it is not possible to tell it to go to the sun's co-ordinates. (It is also clever enough to know whether the target object is above or below the horison at the time, and doesn't bother going to targets below the horison.) More modern control systems, and particularly those for space-based telescopes, have elaborate protection schemes built in deliberately. Many of the instruments are so sensitive, that there are many more things other than the sun which would destroy the instrumentation, that have to be taken into account. In the case of Hubble, the earth itself is one such target, and that is nearby - so large in the field of view. In fact, Hubble even has to shut down for a while as it enters or leaves the Earth's shadow, since thermal effects cause vibration.

Cheers,
Chris