Occulations

An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks from view (occults) an object in the background. 

Occultations are regular, predictable events because planets, dwarf planets, moons, and asteroids orbit the Sun and pass in front of stars in the background.

The term occultation is most frequently used to describe lunar occultations. These are not uncommon occasions when the Moon passes in front of a star, planet, or other heavenly body during the course of its orbital motion around the Earth. Occultations of bright stars and planets typically occur a few times per year, often clustering with several occultations of the same object in successive months, since the Moon traces roughly the same path across the sky each month.

But occultations also occur when a moon passes another moon, or a planet passes another planet. Mutual occultations or transits of planets are extremely rare. The most recent event occurred on 3 January 1818, and the next will occur on 22 November 2065. Both involve the same two planets: Venus and Jupiter.

Saturn occultation CC BY-SA 2.0 at, Link

A grazing occultation of Rhea (a large moon of Saturn)
by another of its moons, Dione. Image: assini–Huygens

The Firsts of Johannes Kepler

The German astronomer Johannes Kepler was born to a father who was a poor mercenary in Württemberg, Germany in 1571. Kepler was nearly blind from a smallpox epidemic when he was three. That led to one of several "firsts" in his career. He developed the first eyeglass designs for nearsightedness and farsightedness. 

He was also the first to explain that the tides are caused by the moon.

He was the first to propose that the sun rotates on an axis.

He was the first to use planetary cycles to calculate the year of the birth of Jesus Christ.

Kepler also tracked the orbital path of Mars and published his three famous laws of planetary motion — which validated Copernicus’s theory of a sun-centered solar system — and later helped Isaac Newton discover the law of gravity. 

So, it is no surprise that if you hear his name today it is probably in the context of the Kepler Space Telescope and its search for exoplanets. It has found many more lanets than expected, including some of the smallest and ones that orbit more than one star.

The Moon, Jupiter and Spica

This Memorial Day Weekend, from May 25 to 28, we had some clear skies and some rainy ones. Tonight should be clear in my neighborhood and I will be able to see a very bright “star” near the moon. But it is not a star. It is Jupiter.

Venus sets in the west not too long after the sun had set, and the Moon and Jupiter were the two brightest objects in the sky.

I knew to look for a fainter true star. It is fainter but still one of the brightest stars, even in moon’s glare. This is Spica. It is the brightest star in the constellation Virgo the Maiden. I'm not very knowledgeable about the zodiac, but I know it is a key star in that study.

Spica is a first-magnitude star, but it appears much fainter than Jupiter. That is because Jupiter is relatively close (or at least nearer)to Earth. This is what draws me to gazing at the night sky is my semi-knowledgeable way: the idea that Spica is about 262 light-years away, and I am looking at its light.

The universe makes me think about the first meanings of words like WONDERful and AWEsome.

Spica is the easiest star to spot in Virgo. There is a saying to find Spica you can "follow the arc of the Big Dipper to Arcturus and speed on to Spica." But that probably doesn't make it any easier for the average Earthling to find because most people know very little about the night sky.

Besides Spica, other bright stars in Virgo include many I had never heard of: β Virginis (Zavijava), γ Virginis (Porrima), δ Virginis (Auva) and ε Virginis (Vindemiatrix). Other fainter stars that were also given names are ζ Virginis (Heze), η Virginis (Zaniah), ι Virginis (Syrma) and μ Virginis (Rijl al Awwa).

Again, the wonder and awe of all this is discovering that one of the stars, 70 Virginis, has one of the first known extrasolar planetary systems and it contains a confirmed planet 7.5 times the mass of Jupiter. I can't even really grasp the size of my own Earth. And the star Chi Virginis has one of the most massive planets ever detected, at a mass of 11.1 times that of Jupiter. And there are 35 verified exoplanets orbiting 29 stars in Virgo.

All this makes me feel like such a small part of the universe. But it makes me feel like part of he universe. I feel better knowing these things.