Kicks of the White Dwarf

As Sun‑like stars near the end of their lives, they expand into red giants before evolving into white dwarfs. During the red giant phase, material from the star’s outer shell is expelled in random directions. Each ejection imparts a small recoil, or “kick,” to the star in the opposite direction.

Red Giant Star (Image Credit: Wikipedia)

(Image Credit: Jim Fuller/Caltech)

This phenomenon was proposed over forty years ago as a possible explanation for the unexpectedly low number of white dwarfs observed in open clusters. Michael Fellhauer at the University of California, Santa Cruz, showed that if enough of these small kicks occur, white dwarfs could be nudged out of their host clusters. Supporting evidence came in 2007, when astronomers using the Hubble Space Telescope discovered young white dwarfs at the edge of the globular cluster NGC 6397. This was surprising, since heavier, younger white dwarfs were expected to remain near the cluster’s center. Their presence at the outskirts strengthened the case that white dwarfs receive kicks during the red giant stage.

Credit: NASA, ESA, and H. Richer (University of British Columbia)

Jim Fuller, professor of theoretical astrophysics at Caltech, developed a model explaining how these kicks occur as matter is ejected. His work, presented at the 248th meeting of the American Astronomical Society in Pasadena, suggests that a star may experience up to 10,000 small kicks over hundreds of thousands of years, each randomly altering its position. The model also predicts that in binary systems, repeated kicks can shrink the orbital separation, potentially driving the stars into collision and triggering a catastrophic explosion. Future observations may provide direct physical evidence of this process.

Computer simulation of a red giant star near the end of its life. Color shading shows density, with white showing the high-density stellar core, and dim orange showing the stellar wind. The plume of material to the bottom right is a mass ejection event that imparts a kick to the star.

Credit: Bernd Freytag, Uppsala University.

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Venus–Jupiter Conjunction 2026: Understanding Right Ascension and Ecliptic Longitude Conjunctions

The Venus–Jupiter conjunction on 9 June 2026 will bring the brightest planet, Venus, and the largest planet in the Solar System, Jupiter, together in the evening twilight sky. Shortly after sunset, a glance toward the western horizon will reveal these two brilliant worlds shining side by side like diamonds. While most observers will simply enjoy the spectacle, astronomers define this conjunction in two different ways: a conjunction in Right Ascension and a conjunction in Ecliptic Longitude.

A simple example of a conjunction is the New Moon, which occurs every month and is nothing more than a conjunction of the Sun and Moon.

In astronomy, conjunctions are defined in two ways: Conjunction in Right Ascension and Conjunction in Ecliptic Longitude.

Conjunction in Right Ascension

First, let us look at a conjunction in Right Ascension (RA). For this type of conjunction, the celestial objects must have the same Right Ascension, meaning they are equally distant from the First Point of Aries when measured along the celestial equator.

For the Venus–Jupiter conjunction on 9 June, both planets have the same Right Ascension at 6:00 PM IST:

Venus: RA 07h 51m

Jupiter: RA 07h 51m

As shown in the chart, the planets align parallel to the Right Ascension lines. Another way of stating this is that they are aligned perpendicular to a declination line. This configuration is known as a conjunction in Right Ascension.

Conjunction in Ecliptic Longitude

Next, let us look at a conjunction in Ecliptic Longitude.

Ecliptic Longitude is the angle measured eastward along the ecliptic from the First Point of Aries. At first glance, this sounds similar to Right Ascension because both measurements begin at the First Point of Aries and increase eastward. However, the key difference lies in the reference plane used.

Right Ascension is measured along the celestial equator and is expressed in hours, minutes, and seconds, where 15 degrees equals 1 hour.

Ecliptic Longitude, on the other hand, is measured in degrees along the ecliptic, which is the apparent path of the Sun across the sky.

Since the ecliptic is tilted by approximately 23.44° with respect to the celestial equator, the two coordinate systems are not identical. As a result, a conjunction in Right Ascension and a conjunction in Ecliptic Longitude generally occur at different times.

In the chart below, the grid lines represent the Right Ascension and declination coordinate system, while the yellow line represents the ecliptic. Compare this with the ecliptic longitude chart, where the division lines are drawn perpendicular to the ecliptic.

Right Ascension and declination coordinate system

Ecliptic Longitude chart

By examining the orientation of these lines, we can clearly see why the conjunction in Right Ascension and the conjunction in Ecliptic Longitude occur at different times.

Let us examine both conjunctions in more detail using star charts with coordinate lines.

Conjunction in Right Ascension

Date: 9 June 2026

Time: 6:00 PM IST

Venus: RA 07h 51m

Jupiter: RA 07h 51m

The chart shows that, in the Equatorial Coordinate System, the planets are aligned parallel to the Right Ascension lines. This indicates that they are equidistant from the First Point of Aries when measured along the celestial equator.

If we now switch the same chart to the Ecliptic Coordinate System, it becomes visually obvious that the planets are not equidistant from the First Point of Aries when measured along the ecliptic.

Conjunction in Ecliptic Longitude

Date: 10 June 2026

Time: 1:30 AM IST

Venus Ecliptic Longitude      115°46'

Jupiter Ecliptic Longitude   115°46'

The chart below shows that the planets are now aligned parallel to the coordinate division lines that are perpendicular to the ecliptic. This indicates that the planets are equidistant from the First Point of Aries when measured along the ecliptic.

In other words, the planets had to move a little farther after the Right Ascension conjunction before achieving alignment in Ecliptic Longitude.

Conclusion

When you observe the Venus–Jupiter conjunction on the evening of 9 June, I hope you will remember that there is more than one way to define a conjunction. Whether it is a conjunction in Right Ascension or a conjunction in Ecliptic Longitude depends entirely on the coordinate system being used.

Understanding the difference between these two types of conjunctions provides a deeper appreciation of how astronomers measure positions in the sky and why the same celestial event can have slightly different timings depending on the coordinate system chosen.

SKY FOR THE WEEK

The concepts presented in this article were discussed during the Sky for the Week session held on 7 June 2026 at the Association of Bangalore Amateur Astronomers (ABAA). In these weekly Sunday sessions, members and visitors explore upcoming celestial events, learn how to observe them, and discuss the astronomical principles behind what we see in the sky.

From planetary conjunctions and lunar events to eclipses, meteor showers, and seasonal sky highlights, the sessions aim to connect celestial observations with the science that explains them. Understanding not only what happens in the sky, but also why it happens, helps observers develop a deeper appreciation of astronomy.

The Sky for the Week sessions are conducted every Sunday and are open to anyone interested in exploring the wonders of the night sky.

 

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