Roger Samworth

Asteroid fly-by

Posted by Roger Samworth

According to “Spaceweather”:

“On Jan. 8th, asteroid 2019 AS5 flew past Earth only 8600 km above our planet’s surface. Nine hours after the flyby, it was discovered by the the Mt. Lemmon Survey telescope in Arizona. The asteroid was closer to our planet than many satellites.”

Note the word “after”! Useful that!

To be fair it goes on to say:

“If the 1 to 2 meter-wide space rock had hit Earth (and it almost did) it would have caused a brilliant fireball in the atmosphere with sonic booms and scattered meteorites on the ground–but no serious damage.”

Phew!

Image processing lore

Posted by Roger Samworth

There is an article in January’s “Sky at Night” magazine under “Skills” and “Image Processing” entitled “Improve your deep-sky images with luminosity layers”. While not entirely BS, it seems to me that it is a complicated way of doing something relatively simple. There is nothing new about the point that most of the resolution information in a colour image is in the luminance part of the image. After all, this is how colour TV signals have been transmitted for ever. With colour TV, the image is decomposed into a luminance, or black and white signal and a chrominance signal that contains the colour information. Luminance is then transmitted on a high-bandwidth channel, and the chrominance on a low-bandwidth sub-carrier. They are combined again inside your TV receiver.

The author of the article used Photoshop, but you can do essentially what he did (and to me, much more simply) with GIMP. How to do it is in an article from 3 years ago on our own web-site at http://www.thornett.net/Rosliston/Astrophotography/DSO.pdf.

AND, of course, as we keep reminding everyone, GIMP is FREE!

Venus and the Schroter effect

Posted by Roger Samworth

Dichotomy, or half-phase for Venus was predicted to be 6th January but due to the Schroter effect may appear late. This is a phenomenon in which the observed phase of Venus appears less than the predicted phase. As a result, dichotomy (half phase) occurs early at evening elongations, and late at morning elongations. The time difference between calculated and observed dichotomy is about a week. The effect was discovered by the German astronomer Johann Hieronymus Schröter (1745–1816). The cause may be that the region near the terminator is darker than the rest of the illuminated disk.

Here is a rather poor image of Venus from the window-sill this morning.

 

Here is the general view from this morning (9/1/2019). I didn’t manage this yesterday. Early risers can look forward to the Venus-Jupiter conjunction on 22nd January.