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Comet Lulin is a naked-eye object! February 19, 2009

Posted by dorigo in astronomy, news, science.
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Comet Lulin (C/2007 N3) is approaching the minimum distance from our planet – the conjunction will occur on February 24th at a distance of 61 million kilometers- and is already a naked-eye object in the sky, glowing at a visual magnitude of +5.6 with what is described as a bright green colour. The coma has a diameter of 20 arcminutes (two-thirds of the Moon’s diameter). As you can see from Jack Newton’s picture below, the comet shows both a tail and an anti-tail, with a bright oval coma.

The conjunction is very convenient given the absence of any moonlight, and its position in the sky, almost perfectly in the opposite direction with respect to the Sun.  A pair of binoculars, even low-power ones, will reveal the comet easily from your back yard even in light polluted areas, while under dark skies you should be able to detect the comet even with the unaided eye; a telescope should be used with low magnification to show the comet in all its glory.  The object moves quickly in the sky, and its apparent motion is easy to detect if you have patience to observe the comet for a while.

You can find the comet in Libra today and tomorrow (check the map below -click to enlarge), while at conjunction on Feb 24th it will be in Leo, just a few degrees due South of Saturn. In a few days its brightness could increase by another magnitude (magnitudes in the chart are not necessarily correct).

For a beautiful gallery of images of this beautiful comet, I advise you to visit the Spaceweather site.

Guest post: Marco Vedovato, “Jupiter: a little analysis about the GRS-LRS encounter” February 15, 2009

Posted by dorigo in astronomy, news, physics, science.
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Marco Vedovato, in his daily life, is a structural engineer. As an amateur astronomer, when his children allow him to do this, his main interest is the atmosphere of Jupiter, the giant planet of the Solar System, and he partecipates, as a measurer, to the Jupos Project, an international investigation about Jupiter. He is also the vice-manager of the Jupiter Program for the Italian Amateur Astronomic Union. When I saw his extremely interesting analysis of the Jovian atmosphere I begged him to write about it for this site. You can find the resulting piece below.

Last year I amused myself to analyze one aspect of the encounter between two Jupiter spots. For this aim, I used WinJupos, a software for measuring the Jupiter images (see here). In the following picture, a map composed by using some very good images, the reader will be able to meet the protagonists of this tale (click on the picture to get the full image!):

The first one is the famous Great Red Spot (GRS), a long-lived anticyclonic circulation, centered around -22,5ø South latitude, existing at least since the second half of 18th century. The second one is a smaller reddish spot (LRS, Little Red Spot), probably born around the end of 2007 and the beginning of 2008, a residue of a previous “Tropical Disturbance”, observed during the 2007.

It is well-known that the GRS has a 90-days oscillation around its mean motion in the Jupiter outer atmosphere; having a look to the map above, GRS is moving very slowly in longitude (with the same latitude) from left to right, forward to the increasing longitudes (retrograde motion). This lazy motion is not constant but presents an oscillation around the main drift. In the following graph the red points are the GRS center, the ones on the left (blue) and right (green) side are the ends of GRS; it is easy to note a period close to 90 days.

Instead the LRS moved in the opposite direction (prograde motion) than the GRS (and with higher speed), so an encounter was inevitable. In the the picture below, a graph I obtained before the encounter, using few points but from very good images (i.e. those of C. Go, F. Carvalho, A. Wesley, G. Grassman and others). I noted, also in the LRS case, an oscillation around the interpolating line.

After the encounter the LRS was quickly destroyed. The following graph documents the collision.

I was interested to see if this LRS oscillation were similar to the GRS one, with the same period and if in phase or not. So I matched “in parallel” the relative motions (by using a modified reference system for the LRS, artificially changing its speed, to have more or less the same slope for both the drifts); a light correlation between the two oscillations seems noticeable. I do not know whether the effect is casual or if it is real. In this last case, are the two oscillations determined by a same cause, hidden in atmospheric currents embedded in deeper layers?

John Rogers, Jupiter director of the British Astronomical Association, wrote me this comment: “Very interesting. Perhaps the oscillation of the GRS has an effect on the nearby LRS? Or perhaps the synchrony is a coincidence — it is difficult to say!”

I’ll have to prepare further analysis when there will be similar opportunities.

(Marco Vedovato)

Asteroid 2008 TC3 Hits Sudan October 7, 2008

Posted by dorigo in astronomy, internet, news, science.
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An asteroid with a size of a few meters in diameter hit the Earth a few hours ago. The news is reported by the Central Bureau for Astronomical Telegrams, circular 8990. Below is the expected trajectory of the body.

The small asteroid was discovered yesterday at Mt. Lemmon by R.A.Kowalski, as an object with a visual magnitude of about 30.4. The object was then at about 450,000 kilometers from our planet. Those who were able to look up this night might have spotted it before it entered our atmosphere only with a telescope, since its expected magnitude was probably around 11. A bright fireball might have been observed over northern Africa, and a possible fall might have resulted, depending on the composition of the rock.

More information is available at the CBAT site.

UPDATE: the body was 5 meters in diameter. It was a carbonaceous chondrite, and its darkness explains why the diameter had been underestimated by luminosity measurements before the impact. It is quite likely that many small bodies will be found in northern Sudan, which is above the impact point of the asteroid.

Also worth noting is that dr. Peter Brown, from West Ontario University, detected a sound wave from the impact with detectors located in Kenya.

The fireball made by the body at 4.46AM yesterday has been spotted by a airplane pilot from Air France-KLM, according to Jacob Kuiper, a meteorologist from the Netherlands who had informed the pilots of the possibility before the impact. The fall has freed an energy of about two kilotons of TNT, about a tenth of the energy of the first atomic bomb over Hiroshima.

UPDATE: thanks to the Meteosat, we now have a picture of the event. It is a temperature scan, which shows the impact of the object with the atmosphere. It is the first time that the impact of a body with the Earth is predicted and then observed. Near-Earth object surveys are getting better and better…

On the upper right you can read off a temperature legend, in degrees Kelvin.