Hestia: the forgotten goddess
The Titan Cronos and his sister Rhea sired the first generation of gods. Their children were Zeus, Hera, Demeter, Hades, Poseidon, and Hestia, the last of whom was the first born. However, Cronos swallowed all these children except Zeus out of fear that they would overthrow him. Soon after, Zeus and Rhea tricked Cronos into swallowing an emetic that caused him to vomit up his children. Of these, Hestia was the last to be regurgitated. For this reason she is often confusingly called both the "first" and "last" born. Unlike her illustrious siblings, Hestia is the least known child of Cronos and Rhea. Paradoxically, we can ascribe her obscurity to her ubiquity: she was the goddess presiding over home, hearth and family. In this capacity she served as a guardian of domestic life and strove to protect each family from menace. As the home was her sole domain, Hestia took no part in the wars and quests in which the other gods participated. While having been otherwise engaged prevented Hestia from making many enemies or sustaining a grievous injury, she never attained the wide acclaim the world bestowed on the other deities. She became the quiet shade of a goddess who dwelt in shadowy corners and enlivened hearth flame. As such home fires were both purifying and yet meager, Hestia was worshipped as a virginal goddess more inclined toward tenderness than rage. In this manner she is distinguished from the furious and ill-tempered Hephaestus, god of fire and furnaces. Both Poseidon and Apollo attempted seductions, but were gently thwarted in these efforts. Such was their respect for Hestia that they neither persisted in these pursuits nor did they avenge the rejections. Even Aphrodite, the love goddess notorious for smiting those who resisted love's allures, did nothing to punish Hestia for her obstinate determination to remain chaste. By being both gentle and unyielding did Hestia forever maintain her dominion over house and hearth. Yet, though she was initially included as one of the dozen deities dubbed "the Olympians." Hestia lost her coveted place to another lover of mortals, Dionysus. No grand combat between Dionysus and Hestia preceded this usurpation. Dionysus merely assumed her place and Hestia relinquished it without protest. She knew she was much more suited for humble abodes than boundless skies. Within the mythological universe one will find her there still: a quiet goddess content to maintain the sanctity of mortal homes and sustain the vital flames of the hearth. While most gods and goddesses reside at unattainable heights, Hestia is as close as the nearest threshold, It is little wonder, then, that she was taken for granted and then largely forgotten.
THE SOUTHWORTH PLANETARIUM
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THE DAILY ASTRONOMER
Wednesday, July 15, 2020
Remote Planetarium 65: Exo-Planets II - The Transit Method
Yesterday we started our discussion about exo-planet detection techniques with a class about the "wobble" or "radial velocity" method. This method enables astronomers to detect planets by observing the wobbles they induce in their parent stars. The limitation of this method is that it is useful only for finding planets sufficiently massive to produce measurable wobbles. Earth-sized worlds do not induce such wobbles. Finding such worlds is the aim of those seeking other life for it is assumed -perhaps wrongly- that only Earth-sized planets can harbor life.* Detecting these smaller planets requires other methods than those involving gravitational perturbations. Fortunately, astronomers have developed other, more sensitive exo-planet detection techniques. The most successful of these methods involves "transits,' the passage of a planet across its parent star.
The image above shows Venus during different stages of its June 2012 transit across the Sun. When in transit, the second planet appears to move directly in front of the Sun. During the transit, the Sun's brightness from our perspective diminished slightly. The transit method involves observing the alterations in a star's brightness that occur when a planet moves in front of it from our perspective.
As seen in the above graphic a star's brightness diminishes during a planetary transit. The light curve remains steady prior to the transit and then bends downwards as the planet first moves in front of the star. The light curve attains its minimum level during the planet's passage and then ascends as the planet moves away from the star.
The light curve, itself, can reveal much about the planet.
- The duration of the minimum reveals information about the length of time the planet required to transit the Sun. When compared with subsequent light curves, an astronomer can determine the respective altitudes of the passages. Also, the timing between successive transits reveals the planet's period. As Kepler's laws demonstrated, a planet's period is directly related to the mean distance. By knowing the period, the planet's mean distance and other aspects of the orbit can be determined.
- The depth of the curve relates to the planet's size. The deeper the bend, the larger the planet. The formula below relates the light curve depth to the ratio of the planet's radius and the star's radius.
As we can see in the graphic below, the light curve depth is affected by the star's size and that of the transiting planet. If the astronomer can ascertain the star's size through the employment of other methods, he/she can discern the planet's size by analysis of this curve.
In 2002, the Polish astronomer Maciej Konacki and his team discovered OGLE-TR-56b, the first exo-planet through use of the transit method. Located about 5000 light years away in the constellation Sagittarius, OGLE-TR-56b is slightly more massive than Jupiter and orbits its parent star in 1.29 days. This planet is an example of a "Hot Jupiter," a highly massive planet orbiting relatively closely to its parent star.**
Ever since that first discovery, astronomers have found more than 2,300 planets using the transit method. We ascribe most of these discoveries to the Kepler mission which will be the focus of tomorrow's class.
*How often have assumptions been proven to be wrong. Astronomers assume that life can only thrive on rocky planets with comparatively thin atmospheres such as Earth. They base this assumption on their knowledge of the one known life-bearing world. It is possible that life could thrive on other types of worlds, as well.
**In the previous footnote we mentioned how sometimes our assumptions can be off-base. The existence of "Hot Jupiters" serves as a perfect example. Prior to the discovery of exo-planets, many astronomers assumed that small rocky worlds would revolve close to their stars while the highly massive ones were farther away. That is the arrangement in our own solar system. The terrestrial planets Mercury, Venus, Earth and Mars are closer to the Sun while Jupiter, Saturn, Uranus and Neptune are farther away. As the conditions along the outer solar system are cooler, the volatile gases such as hydrogen and helium move more slowly and so were able to become incorporated into the outer planets. The temperatures in the inner solar system are higher and so in this region such gases move much more quickly and could not be captured. Many astronomers assumed that planets throughout the Universe would be so arranged. Of course, they aren't.
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SKYWATCHING TIP: Pegasus rising!
No, autumn has not yet arrived. However, early this evening one can see the constellation Pegasus rising in the eastern sky. Around 9:00 p.m. one will see the "great square" above the horizon. Pegasus is considered an autumn constellation because it is during the early fall one can see it easily high in the eastern evening sky. Mid July is the time when it rises around sunset.
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