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

(6478) Gault slimming down using the new YORP diet.

 Asteroid, Solar System  No Responses »
Mar 292019
 

Although (6478) Gault is a main belt asteroid, it has recently been acting very un-asteroidly. The tail visible here is material coming off the asteroid. The current theory is the YORP effect is causing the material to escape the asteroid’s gravitational field.

The surface of solar system objects absorb energy from the sunlight that hits them. If the object rotates, it re-radiates that energy in the form of infra-red radiation in directions determined by the rotation. This energy output can act like a small reaction jet. Depending on the objects rotation, the energy can over time, change the spin rate. If the spin rate increases enough, the material making up the object may drift off of the surface. This effect is named for four contributors (Yarkovsky–O’Keefe–Radzievskii–Paddack) whose concepts contributed to understanding the process.

(6478) Gault [C:15x300s]

The ATLAS (Asteroid Terrestrial-Impact Last Alert System) telescope in Hawai’i first noticed the tail in early January and a search of archived imagery showed additional evidence of the tail was recorded in December of 2018. Right now there are two distinct debris tails but only one is obvious here. Right now the asteroid is just outside of Mars’ orbit and slightly below the plane of the solar system.

I am still working on recovering from a camera power supply failure but the asteroid was very well placed last night (the 28th) so I went ahead and took the series of images that were used to construct the picture. The images were stacked using the asteroid as the reference point which is why the stars are trailed.

 Posted by at 15:45
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