Why is it that Jupiter and Saturn can be seen in the night sky every year, while seeing specific comets such as Halley and Hyakutake is a once-in-a- lifetime event?

Short Answer

Expert verified
Jupiter and Saturn can be seen from Earth every year due to their relatively close and circular orbits within our solar system. In contrast, comets like Halley and Hyakutake have highly elliptical orbits that take them far out of our solar system, taking many years to make a full rotation around the sun. It's only when these comets come close to Earth during their orbits that we can see them, which due to the length of these orbits, often results in a once-in-a-lifetime viewing opportunity.

Step by step solution

01

Understanding the Orbits

To start, we must recognize that planets like Jupiter and Saturn have relatively circular orbits that are fairly close to the sun and are within our solar system. This allows for a consistent annual view from Earth, as their position and distance in the sky are predictable.
02

Comet Rotation Time

On the other hand, comets like Halley and Hyakutake have highly elliptical orbits, meaning they travel very far out of our solar system. This results in it taking a much longer time for these comets to orbit the sun. For example, Halley’s comet comes close enough to Earth for us to see it just once every 76 years, while Hyakutake’s comet has an orbit of approximately 70,000 years. During these long periods of time, the comets are too far away from Earth to be seen.
03

Why Once in a Lifetime

Because the visibility of a comet is dictated by its proximity to Earth during its highly elliptical orbit, and because these orbits can take many human lifetimes to complete, the appearance of a visible comet (like Halley’s or Hyakutake’s) can quite literally be a once-in-a-lifetime event.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Jupiter Visibility
Observing Jupiter in the night sky is quite dependable and delightful for amateur astronomers and enthusiasts alike. Its visibility is due to its relatively shorter orbital period around the Sun of about 12 Earth years. As one of the five planets visible to the naked eye from Earth, Jupiter follows what is known as a near-circular orbit, residing within a band of space called the 'ecliptic plane' where most of our solar system's planets orbit.

Jupiter’s large size also contributes to its brightness as seen from Earth. The fact that Jupiter is one of the brightest objects in the night sky makes it easier to spot, often not requiring telescopes. Additionally, due to its rapid rotation, lasting about 10 Earth hours, many features of its atmosphere can be studied over several nights of observation.
Saturn Visibility
Similar to Jupiter, Saturn is also a consistent fixture in our night sky due to its orbit within the solar system’s ecliptic plane. Saturn takes approximately 29.5 Earth years to complete one orbit around the Sun, which means it's visible from Earth for extended periods annually.

While not as bright as Jupiter, Saturn is still visible to the naked eye and can be identified by its unique golden hue. The planet's stunning ring system, although not visible without a telescope, adds to the excitement of tracking its location in the sky. Furthermore, the tilt of Saturn's rings in relation to Earth varies over time, offering different views of the planet to astronomers.
Comet Orbits
In stark contrast to the planets, comets like Halley and Hyakutake follow highly elliptical orbits. These elongated paths take them on long journeys to the far reaches of the solar system and beyond, into the Oort Cloud or the Kuiper Belt, depending on their origins. The time it takes a comet to complete its orbit around the Sun, known as its 'orbital period', can range from a few years to several millennia.

Comet orbits are often influenced by gravitational interactions with other celestial bodies, which can alter their paths and visibility from Earth. The highly unpredictable nature of these orbits is what makes predicting comet appearances so challenging and why some comets may only be seen once in a lifetime, or not at all, over the span of human history.
Halley's Comet
Halley's Comet is the most famous of the short-period comets, boasting an orbital period that allows it to grace our skies approximately every 76 years—a blink of an eye in cosmic terms, yet long enough that most people will witness it only once in their lives. Named after Edmond Halley, who correctly predicted its return in 1759, the comet's visits are highly anticipated events.

The last time Halley’s Comet was visible from Earth was in 1986, and it is projected to return in 2061. Each appearance can vary in brightness and visibility due to factors such as its position relative to Earth and the Sun, as well as the amount of material it sheds to create its tail when it comes close to the Sun, a process known as outgassing.

Notable Observations

Throughout history, Halley's appearances have been recorded by different cultures around the world, linking it to significant historical events and making it a symbol of continuity and wonder across human civilization.

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Most popular questions from this chapter

A very crude model of a typical comet nucleus is a cube of ice (density \(1000 \mathrm{~kg} / \mathrm{m}^{3}\) ) \(10 \mathrm{~km}\) on a side. (a) What is the mass of this nucleus? (b) Suppose \(1 \%\) of the mass of the nucleus evaporates away to form the comet's tail. Suppose further that the tail is 100 million \(\left(10^{8}\right) \mathrm{km}\) long and 1 million \(\left(10^{6}\right) \mathrm{km}\) wide. Estimate the average density of the tail (in \(\mathrm{kg} / \mathrm{m}^{3}\) ). For comparison, the density of the air you breathe is about \(1.2 \mathrm{~kg} / \mathrm{m}^{3}\). (c) In 1910 the Earth actually passed through the tail of Comet Halley. At the time there was some concern among the general public that this could have deleterious effects on human health. Was this concern justified? Why or why not?

What are the differences between asteroids and transNeptunian objects?

Scientists can tell that certain meteorites came from the interior of an asteroid rather than from its outer layers. Explain how this is done.

Use the Starry Night Enthusiast ?M program to study the motion of a comet. First set up the field of view so that you are observing the inner solar system from a distance (select Solar System > Inner Solar system in the Favourites menu). In the toolbar, click on the Stop button to halt the animation, and then set the date to January 1,1995 , and the time step to 1 day. Select View \(>\) Solar System \(>\) Asteroids in the menu to remove the asteroids from the view. Open the Find pane and center on Comet Hyakutake by typing "Hyakutake" in the Search All Databases box and then pressing the Enter key. Use the Zoom controls to decrease the field of view to about \(25^{\circ} \times\) \(17^{\circ}\). Then click on the Run Time Forward button. (a) Watch the motion of Comet Hyakutake for at least two years of simulated time. Describe what you see. Is the comet's orbit in about the same plane as the orbits of the inner planets, or is it steeply inclined to that plane? (You can tilt the plane of the solar system by holding down the Shift key while clicking on and moving the mouse to investigate this off-ecliptic motion.) How does the comet's speed vary as it moves along its orbit? During which part of the orbit is the tail visible? In what direction does the tail point? (b) Click on the Stop button to halt the animation, and set up the field of view so that you are observing from the center of a transparent Earth by selecting Guides \(>\) Atlas in the Favourites menu. Set the date to January 1, 1995, and the Time Flow Rate to 1 day, and again center on Comet Hyakutake. Use the controls at the righthand end of the toolbar to zoom out as far as possible. Then click on the Run Time Forward button and watch the comet's motion for at least two years of simulated time. Describe the motion, and explain why it is more complicated than the motion you observed in part (a). (c) Stop the animation, set the date to today's date, set the Time Flow Rate to 1 month ("lunar m."), and restart the animation. Comet Hyakutake is currently moving almost directly away from the Sun and so, as seen from the Sun, its position on the celestial sphere should not change. Is this what you see in Stamy Night Enthusiast \(\mathrm{\text {??? }}\) Explain any differences. (Hint: You are observing from the Earth, not the Sun.)

Suppose you found a rock you suspect might be a meteorite. Describe some of the things you could do to determine whether it was a meteorite or a "meteorwrong."

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