Back Ground to Yohkoh

Instruments Onboard Yohkoh

The Yohkoh spacecraft has four instruments: a Bragg Crystal Spectrometer (BCS), a Hard X-ray Telescope (HXT), a Soft X-ray Telescope (SXT), and a Wide Band Spectormeter (WBS). This combination of hard and soft x-ray imaging from the telescopes and spectroscopy instruments operating simultaneously, in coordination, makes the Yohkoh satellite unique and powerful tool for studying the Sun. These four instruments cover a wide energy range of the high energy solar spectrum and are extremely useful for studying solar flares which is Yohkoh's primary objective.

Yohkoh Satellite with the positions of the apertures to the four instruments indicated. Note that the WBS has three apertures: soft x-ray, hard x-ray, and gamma ray.

BCS

The Bragg Crystal Spectrometer

This is a high-resolution spectrograph for X-rays. This instrument acts like a prism for X-rays which allows scientists to analze the X-ray part of the solar spectrum in detail.

HXT

The Hard X-ray Telescope

A hard x-ray imaging instrument can not use conventional optics such as a lens or mirrors to form hard x-ray images because the hard x-rays are absorbed by these objects. Instead, the telescope consists of a series of aligned grids which form several collimated x-ray light paths. Each sub-collimator has a non-position-sensitive detector. The signal from each detector is then used to construct an image by computation.

SXT

The Soft X-ray Telescope

A soft x-ray telescope can be made with either a special normal incident mirror or glancing incidence mirrors. This telescope uses glancing incidence mirrors to form soft x-ray images of the Sun on a CCD sensor.

WBS

The Wide Band Spectrometer

This spectrometer records the Sun in two wide bands: x-ray and gamma ray. It is like the BCS instrument, in that, it also looks at the energy distribution of x-rays from flares but it records this information at a much lower energy resolution. Unlike the BCS, it can also record at at much high energys, making measurements of the energy distribution of hard X-rays and gamma rays from flares.