{"id":52995,"date":"2024-01-04T11:39:35","date_gmt":"2024-01-04T11:39:35","guid":{"rendered":"http:\/\/25b581ae-3524-423b-b523-a4ba35275a92"},"modified":"2024-01-04T12:32:36","modified_gmt":"2024-01-04T12:32:36","slug":"see-jupiter-and-galilean-moons-in-january-2024","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/see-jupiter-and-galilean-moons-in-january-2024\/","title":{"rendered":"See Jupiter and Galilean moons in January 2024"},"content":{"rendered":"

Observe Jupiter’s Galilean moons this month. <\/p>

By Pete Lawrence\n <\/p>

Published: Thursday, 04 January 2024 at 11:39 AM<\/p>

\n\n

Observing Jupiter’s Galilean Moons is a great activity to undertake when the planet is approaching opposition.<\/p>

Jupiter reached opposition on 3 November 2023, a time when it is opposite the Sun in the sky.<\/p>

Opposition<\/a> is when a planet appears largest and brightest to us viewing from Earth.<\/p>

For more advice, read our guide on how to observe Jupiter through a telescope<\/a><\/em><\/strong><\/p>

There are a good number of Jupiter moon events to observe on 6\/7 January 2024. Credit: Pete Lawrence<\/figcaption><\/figure>

Jupiter Galilean Moon transit events<\/strong><\/h2>

With Jupiter well placed for observation in January 2024, there\u2019s great opportunity to catch some of the planet\u2019s interactions with its moons.<\/p>

A good challenge is to observe or image as many different types as you can. A freeware application such as WinJUPOS<\/a> can be used to determine when these events will occur.<\/p>

Jupiter has many moons, but only four are large and bright enough to be seen easily through a telescope.<\/p>

As they orbit Jupiter, Earth gets to view various interactions between them and the planet\u2019s globe. A common event is a transit, which is when a moon appears to cross Jupiter\u2019s disc.<\/p>

\"The
The freeware program WinJUPOS can be used to predict upcoming Jupiter moon events.<\/figcaption><\/figure>

The point of first contact at the start of the event is called transit ingress, abbreviated as TrI.<\/p>

The point of last contact is known as transit egress (TrE).<\/p>

A moon transit will be accompanied by a shadow transit.<\/p>

This too has an ingress (ShI) and egress (ShE). A moon trails its shadow before opposition and precedes it after. \u00a0<\/p>

At opposition both transit in sync, a phenomenon which only lasts for a day or so.\u00a0<\/p>

All four Galilean moons can show the transits described, but outermost Callisto\u2019s orbit, combined with the shallow 3.1\u00b0 axial tilt of Jupiter, means for most of the time Callisto misses Jupiter\u2019s disc, passing north or south of it.<\/p>

Only near a Jovian equinox do Callisto and its shadow transit Jupiter\u2019s disc.<\/p>

\"Io
Io and Europa Double Transit by Avani Soares, Parsec Observatory, Canoas, Brazil.<\/figcaption><\/figure>

Jupiter Galilean Moon eclipses and occultations<\/strong><\/h2>

In addition to transit events, there are eclipses and occultations, events caused by Jupiter itself.<\/p>

An occultation occurs when a moon passes behind Jupiter\u2019s globe.<\/p>

The two parts of this event are the occultation disappearance (OcD) and occultation reappearance (OcR).\u00a0<\/p>

Eclipses occur when one of the moons passes into Jupiter\u2019s shadow.<\/p>

\"A
A double shadow transit of Jupiter’s moons. Credit: Pete Lawrence<\/figcaption><\/figure>

When the moon disappears, this is referred to as eclipse disappearance (EcD) and when the moon reappears it\u2019s an eclipse reappearance (EcR).\u00a0<\/p>

How occultations and eclipses occur depends on the angle between the Sun, Jupiter and Earth.<\/p>

Before opposition, Jupiter\u2019s shadow hangs west of the planet and a moon undergoes an eclipse disappearance but may remain within the shadow as it passes behind Jupiter, re-emerging as an occultation reappearance.<\/p>

\"Jupiter
Jupiter with triple moon transit by Sona Shahani Shukla, New Delhi, India, 15 August 2021<\/figcaption><\/figure>

After opposition the reverse is true: a moon undergoes occultation disappearance then re-emerges from Jupiter\u2019s shadow as an eclipse reappearance.\u00a0<\/p>

This slightly more complex scenario has a twist for the three outer Galileans, Europa, Ganymede and Callisto.<\/p>

At certain times before opposition, these may enter Jupiter\u2019s shadow (EcD), reappear from it (EcR) and then disappear behind Jupiter (OcD), finally re-emerging from the opposite side (OcR).<\/p>

After opposition the sequence would be OcD, OcR, EcD and finally EcR.<\/p>

This isn\u2019t always the case, and the extra reappearance\u2013disappearance stage in the middle doesn\u2019t happen if Jupiter is close to opposition.<\/p>

\"Jupiter,
Jupiter, Ganymede and Io by Paul Cotton, Lincolnshire, UK.<\/figcaption><\/figure>

Observing Jupiter’s Galilean moons: tips and tricks<\/strong><\/h2>

Not only is Jupiter the largest of the planets \u2013 it would take 1,321 Earths to fill the volume of Jupiter<\/a> \u2013 it\u2019s also more than likely that it keeps the largest entourage of moons.<\/p>

It\u2019s the massive gravitational effect of Jupiter that does the trick, attracting more than 100 moons into orbit around the planet at the latest estimate.<\/p>

Many of these satellites are fairly small and can\u2019t be observed from Earth, but the biggest four are easy to spot with just a small pair of binoculars.<\/p>

Binoculars<\/strong><\/h3>
\"\"<\/figure>

A minimum size pair of binoculars for spotting the four Galilean moons of Jupiter would be 7x50s, which magnify what your eyes see seven times and have front lenses that are 50mm in diameter.<\/p>

You can certainly catch glimpses of these Galilean moons<\/a> (named after Galileo<\/a>, who first observed them) with hand-held binoculars.<\/p>

However, your view will be much improved by resting the binoculars on a wall or fence, or even attaching them to a binocular tripod or mount<\/a> with an inexpensive bracket.<\/p>

With binoculars though, Jupiter itself will not appear as anything more than a large, slightly oval-shaped disc.<\/p>

Telescope<\/strong><\/h3>
\"\"<\/figure>

The next step in viewing Jupiter Moons is to use a small telescope \u2013 one with a front lens 3 to 6 inches in diameter.As this gathers more light, it can magnify the view more, so the Moons will appear brighter and fill more of the field of view.<\/p>

Don\u2019t necessarily expect to see all four, however: as the moons travel around the planet they may be behind or in front of Jupiter when you\u2019re looking.<\/p>

It\u2019s by using a larger scope with a front lens over 6 inches in diameter that you really start to see detail on Jupiter itself: not only the darker belts and lighter zones, but features within the gaseous atmosphere as well.<\/p>

At this level of detail, observers can also see the occasional dark spot caused by the moons casting their shadows onto Jupiter\u2019s atmosphere.<\/p>

The joy of Jupiter is that whatever your level of equipment, there\u2019s always something to see.<\/p>

Galilean Moons at opposition<\/strong><\/h2>
\"\"
Jupiter\u2019s four bright Galilean moons appear in a line, shining like stars near to the planet. Credit: Pete Lawrence<\/figcaption><\/figure>

At opposition an interesting thing happens to the Galilean Moons<\/a> when they transit the planet.<\/p>

At this time their shadows appear to fall directly in line with the moons.<\/p>

The alignment would be perfect if the declination of the Sun from Jupiter were 0\u00b0 and the Sun\u2013Earth\u2013Jupiter alignment a perfect straight line.\u00a0<\/p>

In practice the declination won\u2019t be 0\u00b0, but a little off at 3.1\u00b0.<\/p>

Catching a moon passing at the exact point of opposition is down to luck and an offset of just a few hours either side is enough to show a misalignment.<\/p>

However, it is interesting to see how a moon\u2019s shadow precedes the moon that\u2019s casting it before opposition and follows it after opposition.<\/p>

\"Jupiter's
Jupiter’s moon Callisto casting its shadow on the gas giant. Credit: Pete Lawrence<\/figcaption><\/figure>

Owners of smaller scopes will even be able to enjoy some amazing interactions between the planet and its 4 largest moons: Io<\/a>, Europa, Ganymede and Callisto.<\/p>

These moons are bright and easily visible through smaller instruments as points of light.<\/p>

For those with larger-aperture scopes, it may be possible to perceive the moons as tiny discs, the apparent diameters being:<\/p>