Typical observations at the 60' Solar Tower are obtained in a continuous manner by which 2 images are taken every minute for up to 12 hours/day. One group of 12 images is taken in the early morning hours before the continuous observations are started. From this set of 12 images, a magnetogram, dopplergram, intensitygram, and velocity map are computed and added to this database on a daily basis (when the weather cooperates). In some cases it may not be possible to compute this series due to inclimate weather in the early morning hours, but the continuous data may still be obtainable for the rest (or portion) of the day. The opposite may also be true, whereby, the 12 image set is obtained but the weather has worsened for continuous observations of the sun.

Presently, all images are taken in the chromospheric Sodium D-line region of the solar atmosphere with the Magneto-Optical-Filter. The orientation of the images is north at the top and west to the right.

The 12 image set consists of 3 sets of 4 image groups. The 4 image group is taken over a course of 15 seconds, each image 5 seconds apart, starting at the top of the minute. The 4 images can be indentified as red+, red-, blue+, and blue-. The 2nd and 3rd sets are taken at 90 second intervals from the start of the 1st image set. By the time the 12th image is taken, 3 minutes 15 seconds have elapsed.

Below is an explanation of how the four image types are computed.

A filtergram is simply the addition of two images (a red and blue shifted component of a specific wavelength)

A dopplergram is a difference of a blue shifted image of the sun from a red shifted image, divided by the sum of the red and blue components. The dopplergram shows regions of the sun that are rising or sinking, and rotation of the sun has not been subtracted out (as can be seen by the large light to dark gradient across the disk of the sun). Since the sun rotates to the west and the darkest portion is on the right hand side, dark regions are those which are moving away from the earth and light regions are those moving toward earth. Two dopplergrams are computed (but only one is displayed), one in the first image group and one in the 3rd image group.

A velocity map is the difference between two dopplergrams separated by 3 minutes (this is roughly 1/2 of the 5-minute oscillation cycle). This procedure subtracts out the rotation of the sun and emphasizes the numerous up and down motions of the sun scattered across the disk. Color has been added to represent regions moving toward earth (blue) and those regions moving away from earth (red). The time labeled for the velocity map is the start time for the first dopplergram. The second dopplergram from which the velocity map is computed will always be 3 minutes later.

NOTE: As of September 27, 1999 the velocity map images will be discontinued. On a day-to-day basis, these images show no change, and take up precious disk space. The older velocity images will remain on disk for access through the image-database, but no future images will be provided. Eventually, the existing velocity images may be unavailable through this URL to save on disk space. Velocity images will continue to be processed but only available through request.

A magnetogram is computed from the entire set of 12 images (3 sets of 4) taken in the Sodium-D line spectrum of the sun. Each set of 4 images is used to compute 1 magnetogram. These 3 magnetograms are then integrated together to obtain an averaged image of the sun over a course of 3 minutes, 15 seconds. The time identified and labeled for the magnetogram is the start time for the entire set.

Fits format images are provided as courtesy to the scientific community. The fits header keywords are provided below as an example. Additional keywords may be added as they become useful or needed. If you see a reason to have another keyword added, please contact Perry Rose.

SIMPLE = T / Converted by mw2fits
BITPIX = 16 / 16 bit/pixel
NAXIS = 2 /
NAXIS1 = 1024 /
NAXIS2 = 1024 /
DATE = '25/05/99' / Observation date
TIME = '06:06:00' / Observation time, PST
KTIME = 1249236005 / Observation time, 100th sec since...
STATUS = 0 / Observation status
ORIGIN = Mt. Wilson / Telescope location
TELESCOP= MWO_60 Ft / Telescope name
OBS_MODE= HR_Na-Magnetogram / Image type
ORIENT = SESW / Image orientation
END

For more information on this project, or how to obtain additional images and/or data, contact Dr. Edward Rhodes of USC.