Posts Tagged ‘Jovian Moons’

04/12/2016 – Ephemeris – Can you tell the Jovian moons apart without a program?

April 12, 2016 Comments off

Ephemeris for Yuri’s Night, Tuesday, April 12th.  The Sun will rise at 7:02.  It’ll be up for 13 hours and 21 minutes, setting at 8:24.   The Moon, 1 day before first quarter, will set at 2:22 tomorrow morning.

It’s the 55th anniversary of Yuri Gagarin’s flight as first human to orbit the Earth.  Speaking of orbits, we can see Jupiter’s 4 largest moons orbit that planet in small telescopes.  Their orbits are nearly edge on to us, so they seem to move back and forth from one side to the other of the planet in pretty much a straight line.  So how can you tell them apart without a reference?  The four moons from Jupiter in order are Io, Europa, Ganymede, and Callisto.  They are not normally arranged like that.  Ganymede is the brightest and Callisto the dimmest, and is usually the farthest away.  Io is usually the closest appearing and has a slight reddish hue due to its sulfurous volcanic surface, and Europa is the dimmer moon close in to Jupiter.  Io also can be seen to noticeably move in an hour.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Jupiter's moons

One of my old pictures of Jupiter. Callisto is obvious from its far left position and dimmer brightness. On the right, the farthest is Ganymede due to its brightness and position. Inside of it is Europa, again, dimmer than Ganymede and inside position is probably Europa. That leaves Io, which may be trying to duck behind Jupiter, as a bump in the left edge of the planet.

Jupiter and moons tonight

Jupiter and its moons as simulated by Cartes du Ciel for tonight, 10 p.m. April 12, 2016. The bodies, from let to right are Ganymede, Callisto. a background star, Jupiter, Io, and Europa.

04/06/2016 – Ephemeris – Mercury makes its spring appearance in the west – Plus Jovian moon hijinx

April 6, 2016 Comments off

Ephemeris for Wednesday, April 6th.  The Sun will rise at 7:13.  It’ll be up for 13 hours and 3 minutes, setting at 8:17.   The Moon, 1 day before new, will rise at 7:30 tomorrow morning.

Let’s check out the whereabouts of the bright naked eye planets.  Mercury is in the west-northwest, very low to the horizon, setting at 9:35 p.m.  Jupiter is in the southeast in the evening, and will pass due south, astronomers call it a transit, at 11:45 p.m., and will set at 6:16 a.m.  It’s below the stars of Leo this year.  Binoculars can make out some of Jupiter’s moons, but a telescope is required to see all four bright moons and Jupiter’s cloud formations.  Mars will rise next at 12:31 a.m. in the east-southeast.  It’s above Scorpius but moved into western Ophiuchus now.  Saturn will rise at 1:06 a.m. in the east-southeast.  It’s just left of Mars.  Its rings are a telescopic treat.  Venus will rise at 6:47 a.m. due east.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Evening sky


Mercury appears low in the sky in the west at 8:40 p.m. April 6, 2016. Created using Stellarium.

Jupiter in the evening

An animation of Jupiter in the night sky with and without lines and captions at 10 p.m., April 6, 2016. Created using Stellarium and GIMP.

If you are using Firefox right-click on the image and select View image to enlarge.

Telescopic Jupiter

Jupiter and its moons at 10 p.m. April 6, 2016. It’s going to be busy night with the three closest moons playing tag with Jupiter. See the table of events below. Jupiter appears 43.2″ in diameter.  Created with Cartes du Ciel (Sky Charts).

Jovian satellite events overnight

Io and Ganymede will pass in front (transit) the face of Jupiter, while Europa pass behind and be occulted by Jupiter.

Event Date/Time EDT Date/Time UT
Io Transit Starts 6 9:52 p.m. 7 01:52
Io Shadow Crossing Starts 6 10:30 p.m. 7 02:32
Europa Occultation Starts 6 10:48 p.m. 7 02:48
Io Transit Ends 7 12:06 a.m. 7 04:06
Io Shadow Crossing Ends 7 12:47 a.m. 7 04:47
Ganymede Transit Starts 7 1:00 a.m. 7 05:00
Europa Eclipse Ends* 7 2:53 a.m. 7 06:53
Ganymede Shadow Crossing Starts 7 3:44 a.m. 7 07:44
Ganymede Transit Ends 7 4:15 a.m. 7 08:15
Ganymede Shadow Crossing Ends 7 Not up 7 11:00
* When Europa’s occultation ends it will still be in Jupiter’s shadow and will enter sunlight a bit away from the planet.

Timings are from Project Pluto.

Morning sky

Morning planets

Looking south at 6 a.m. at Mars and Saturn in an animation with and without annotations. 6 a.m. April 7, 2017. Created using Stellarium and GIMP.


Mars as seen in a large telescope with high power at 6 a.m., April 7, 2016. Mars apparent diameter 12.7″. Created using Cartes du Ciel (Sky Charts).


Saturn with some of its satellites. Normally only Titan is visible. The disk of Saturn has the apparent diameter of 17.6″ while the rings span 40.9″. Created using Cartes du Ciel (Sky Charts).

The planets at sunrise and sunset

Planets at Sunrise and Sunset

This is a chart showing the sunrise and sunset skies for April 6, 2016 showing the location of the planets and the Moon at that time. Created using my LookingUp program.




01/29/2015 – Ephemeris – The first thing noticed about Jupiter in a telescope

January 29, 2015 Comments off

Ephemeris for Thursday, January 29th.  The sun will rise at 8:05.  It’ll be up for 9 hours and 41 minutes, setting at 5:46.   The moon, 3 days past first quarter, will set at 4:33 tomorrow morning.

If it’s clear tonight dress up warmly and take the telescope out to look Jupiter.  Jupiter is the brightest star-like object out tonight.  It outshines Sirius the brightest night-time star lower in the sky and to its right.  Jupiter, being the largest planet most of the time is the biggest planet in the telescope,  It’s only challenger is Venus for a couple of months when its closest to us.  The first thing one notices about Jupiter in a telescope is that it has companions, up to 4, strung out on either side of the planet.  Those are the four moons or satellites discovered by Galileo in 1610.  They will shift position from night to night and even as you watch.  They can hide behind Jupiter or in its shadow or in front of the planet.

Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.


Jupiter's path

Jupiter’s retrograde path against the stars between Cancer and Leo October 2014 to July 2015. Created using Cartes du Ceil (Sky Charts).  Click to enlarge.

Jupiter and moons

Jupiter and its four Galilean moons. The planet has to be over exposed to pick up the moons. But the eye can handle the brightness difference with no problem. This is one of my old pictures back in the days of film.

Jupiter eclipse

Jupiter with a solar eclipse in progress as Ganymede, lower left, casts its shadow on Jupiter on November 14, 2011. Credit: Scott Anttila.

Check out the Great Red Spot (GRS) above Ganymede’s shadow.  It’s not really red.  When I first aimed my telescope toward Jupiter back in the late 1950’s the GRS was indeed very red.  Nowadays the GRS is very hard to find.

01/23/2015 – Jupiter will experience three simultaneous total solar eclipses tonight!

January 23, 2015 1 comment

Total solar eclipses on Jupiter are nearly a daily occurrence on Jupiter.  However what we’ll see is the shadows of the moons crossing the face of the planet.  Shadows of the Jovian moons on the fave of Jupiter are difficult to see with small telescopes.  The look like tiny inky black dots.

Another way to watch the event is via Griffith Observatory in Los Angeles.  The link is here.  Their event starts at 11:30 p.m. EST because Jupiter rises later there.  The email I received from them says the next triple shadow event on Jupiter won’t occur until 2032,

Here’s the schedule:  Moons:  I = Io, II = Europa, IV = Callisto; SHA = Shadow,  Tra = Transit (a moon crossing disk of Jupiter)

Moon Event      UT Date    hh:mm  EST Date    Time
 IV: Sha start: 24 Jan 2015 3:11  23 Jan 2015  10:11 p.m.
  I: Sha start: 24 Jan 2015 4:36  23 Jan 2015  11:36 p.m.
  I: Tra start: 24 Jan 2015 4:56  23 Jan 2015  11:56 p.m. 
 IV: Tra start: 24 Jan 2015 6:20  24 Jan 2015   1:20 a.m.
 II: Sha start: 24 Jan 2015 6:28  24 Jan 2015   1:28 a.m.
 I:  Sha end  : 24 Jan 2015 6:53  24 Jan 2015   1:53 a.m.
 II: Tra start: 24 Jan 2015 7:08  24 Jan 2015   2:08 a.m.
 I:  Tra end  : 24 Jan 2015 7:13  24 Jan 2015   2:13 a.m.
 IV: Sha end  : 24 Jan 2015 8:02  24 Jan 2015   3:02 a.m.
 II: Sha end  : 24 Jan 2015 9:23  24 Jan 2015   4:23 a.m.

Note: All three shadows will be on Jupiter at the same time from 1:28 to 1:53 a.m. EST.
Times provided by the Jevent.exe DOS program downloaded from

Here’s an animation of what the event might look like at half hour intervals look like starting at 9:45 p.m.

Jovial Shadow Play

Animation of Jupiter’s satellite shadows starting at 9:45 p.m. and ending at 4:45 a.m. Created using Cartes du Ceil Sky Charts) and GIMP.  The circle in the center of Jupiter is an artifact of the program.  Click for a larger view.