Eunike casts a long shadow

 Asteroid, Occultation, Solar System  No Responses »
May 132020
 

At 0447 Monday morning (the 11th) the 98 mile wide asteroid (185) Eunike passed in front of a distant star and cast a shadow that crossed the Earth and coincidentally the PTO. The event is called an occultation and can be used to determine a physical measurement of the asteroid by timing the duration of the shadow.

The chart below shows the predicted shadow path. The green line is the center of the shadow with the right and left limits shown in blue. The red lines are 1-sigma statistical limits. The two black lines are the locations in the path of observers. The other observer was near Chattanooga just south of the Alabama/Tennessee border. There is no option to change the observer’s icons so I’m stuck with the SCT. If there are enough observers spread out across the predicted path, a very accurate shape of the asteroid can be determined. This is the same mechanism that was used to predict the shape of (486958) Arrokoth – AKA 2014 MU69 prior to the close pass by the New Horizons spacecraft.

Predicted shadow path.

The occulted star (UCAC4 473-096350) and the asteroid are only one magnitude apart in brightness with the asteroid being the brighter of the two. This made it easy to watch the rock approach the star and once they appeared close enough, their light merged. It is during that time the analysis starts. The predicted maximum duration was 24.7 seconds. The PTO was near the eastern edge of the predicted shadow path so I only saw a 24.3 second drop.

(195) Eunike / UCAC4 473-096350 (Circled)


I was not able to see any change in brightness during the event since the two were so close in magnitude. The dimming was only apparent after analysis. During other occultations, where the asteroid is much dimmer, you can see the drop in brightness or if the asteroid is not visible at all, you can watch the target star disappear completely. The brightness of the pair is right at the limit of my occultation equipment. As you can see the brightness measurements are quite noisy, but the analysis software reports a 0.0% chance the drop was due to noise.
 

The information collected by the PTO during this event was reported to the IOTA (International Occultation Timing Association).
 Posted by at 13:01

Minerva, Goddess of Wisdom, gets in the way.

 Asteroid, Minor Planet, Occultation, Solar System  No Responses »
Nov 302019
 

Asteroid (93) Minerva, named after the Roman goddess of wisdom and strategic warfare, cast a shadow across the Earth very early on the morning of the 30th of November. As the shadow crossed the US it passed directly over the PTO. The source of the light blocked by Minerva was star UCAC4 0627:033066. The ‘telescope’ icons on the map of the shadow’s path show two other sites attempting to monitor the occultation.
 

These are two frames from the series of videos taken throughout the predicted time. The frames are 26 minutes before and 26 minutes after the event.

(93) Minerva 26 minutes before the occultation.


(93) Minerva 26 minutes after the occultation.


Once the asteroid and star are close enough, their light combines into one point. If the asteroid and the observer are exactly where they are supposed to be, the asteroid will totally block the stars light. If the asteroid is bright enough, the asteroid’s light is all that will be visible. That is what happened on the 30th. If the asteroid is not very bright the star will simply disappear. By measuring the brightness of the combined objects continuously throughout the event the diameter of the asteroid can be determined. Previous occultations of Minerva have established an estimated mean diameter of 150 kilometers (93 miles). This chart shows the brightness measured during the event. The drop in brightness, when only the asteroid’s light is visible, is obvious.
 
 Posted by at 22:05