New Jupiter Impact

Earlier today Australian astronomer Anthony Wesley reported a new impact site on Jupiter just as the sun was rising at his location. His image can be seen on his webpage. The time stamp on the image is Universal Time (UT). Renowned amateur observer Christopher Go has also captured a short video of the event which can be viewed on his site. There has not yet been a confirmation that there are leftover signs of the impact but observers are gearing up to try. To do this we need to know when the impact site is visible, according to Christopher Go the event occured at longitude 343 (System II). With this information we can calculate future observation opportunities:

6/4 5:04 15:00
6/5 0:56 10:52 20:47
6/6 6:43 16:39
6/7 2:35 12:30

All of the times in the table are transit times (UT). Practically the impact site is visible for a couple of hours on either side of the listed times. Unfortunately this does not work out well for viewing from my location in California – the time here is UT-7 hours so this gives the following local times for the transit:

6/3 10:04pm
6/4 8:00am 5:56pm
6/5 3:52am 1:47pm 11:43pm
6/6 9:39am 7:35pm
6/7 5:30am

The first opportunity at 10:04pm tonight (6/3) will not work because although the event is facing us Jupiter does not rise until 2 am and so is below the horizon! The following morning (6/4) the impact site will be visible from ~6am onwards and Jupiter will be high in the sky but the sun will have risen and be too bright. The first real chance is not until the morning of 6/5 from ~2am onwards as Jupiter is rising. This may be too long after the event for anything to continue to be visible.

Jupiter Impact Update

The Old Town Sidewalk Astronomers had some excellent views of Jupiter Saturday night through my 8 in SCT and Jane’s 7 in refractor. The impact site was clearly distinguishable and we watched it rotate across the disk. We finished the evening with a quick look at the other blue planet, Neptune.

I’ve had a number of requests about future times for viewing the impact site. Here are the best transit times from tonight onwards for Pacific Summer Time – remember the site is visible for about 1 1/2 hours either side of these times.

7/28/2009 1:33 AM
7/30/2009 3:11 AM and 11:03 PM
8/1/2009 4:49 AM
8/2/2009 0:40 AM
8/4/2009 2:18 AM and 10:10 PM
8/6/2009 3:56 AM and 11:48 PM

All times calculated using the excellent Astromist application for PDAs available from

Viewing Jupiter’s Impact Site

So you want to see the impact site on Jupiter that was recently discovered by Australian amateur astronomer Anthony Wesley and are wondering how. You need a suitable telescope and to be looking at the correct time when the impact site is facing us.

Let’s start with the when can I see it question:

This weekend there will be a couple of good opportunities to see the Jupiter impact site from the West coast with amateur telescopes. Jupiter will both be up and the impact site will be facing towards us.

The impact site is at longitude 216 deg (CMII longitude system) and the iceinspace site has conveniently calculated transit times for the next few days. A transit time is when the impact site is directly facing Earth. AS Jupiter takes ~10 hours to complete one rotation there are several times per day:

2009 Jul 24 05:16 ( 216°) 15:12 ( 216°)
2009 Jul 25 01:08 ( 216°) 11:03 ( 216°) 20:59 ( 216°)
2009 Jul 26 06:54 ( 216°) 16:50 ( 216°)
2009 Jul 27 02:45 ( 216°) 12:41 ( 216°) 22:37 ( 216°)
2009 Jul 28 08:32 ( 216°) 18:28 ( 216°)
2009 Jul 29 04:23 ( 216°) 14:19 ( 216°)
2009 Jul 30 00:15 ( 216°) 10:10 ( 216°) 20:06 ( 216°)
2009 Jul 31 06:01 ( 216°) 15:57 ( 216°)

These are UTC so have to be converted to Pacific Time by subtracting 7 hours. The next few opportunities together with the altitude of Jupiter (how high it is in the sky) are:

Friday night: the best time is 4:03AM Sat morning (altitude 29 deg)

Saturday night: the best time is 11:54 PM (altitude 37 deg)

Saturday night is the best option as the altitude is higher. Jupiter has a ~10 hour day so viewing is good ~1.5 hours either side of these times, provided Jupiter is above the horizon.

So now we know when to look but what do we need to look with?

The impact site on Jupiter is ~1/100th the diameter of Jupiter or <1 arcsec across. This is about 1/6000th the size of the moon.

To see this you need a telescope with a resolution of 1 arcsec or better and suitable atmospheric viewing conditions – the strong color contrast between the dark mark and the planet will help however. A telescope of 5 1/2 in (138 mm) diameter or larger has enough resolving power. You will also need to have enough magnification.

The rule of thumb is that a magnification of 50X per inch of aperture is typically the maximum possible. This means that for a 6 in diameter telescope the maximum usable magnification for a well collimated telescope under good atmospheric seeing conditions is ~300X. The eyepiece needed to get this magnification is found by dividing the telescope focal length by the magnification. Thus for my telescopes I get these results:

Takahashi FC76 refractor
Diameter: 76 mm
Focal Length: 600 mm
Resolution comment: too small to resolve impact site
Max Magnification: ~150x
Eyepiece focal length for max.mag: 4 mm

Celestron C8 Schmidt Cassegrain
Diameter: 203 mm (8in)
Focal Length: 2032 mm
Resolution comment: Has sufficient resolution
Max Magnification: ~400X
Eyepiece focal length for max.mag: 5mm

Meade 12in Lightbridge
Diameter:304.8 mm (12 in)
Focal Length: 1524 mm
Resolution comment: Has sufficient resolution
Max Magnification: ~600x
Eyepiece focal length for max.mag: 2.5 mm

So I will be using my SCT to try to view (image actually) the impact site as the combination of aperture and focal length is best for this object.

Where to look for Jupiter?

If you need help finding Jupiter there are several resources:

Sky and Telescope interactive sky chart monthly star chart

and many others online.

Good luck and Clear Skies.

Moon, Venus and Jupiter

This was first published on December 2nd, 2008, republished January 12th 2019 after website move.

Moon, Venus and Jupiter setting

Tonight’s photo was taken a little later than last night’s photo so the sky background is darker and not so interesting. We can see how the moon and the Venus/Jupiter pair have swapped position. If you live in Europe then you had the opportunity to see the Moon eclipse Venus earlier today – unfortunately not visible from N. America. If you haven’t caught this grouping yet you will get another chance tomorrow night although the distance between the moon and Venus/Jupiter will be increasing. The next planetary occultation will be on Dec. 29th when the 3-day old moon will occult Jupiter however you will need to be in Central/Western Australia or Tasmania to see this. The next lunar occultation of a planet visible from N. America will be on Apr 22nd when the moon will again occult Venus.

Astronomy Saturday

This was first published on December 1st, 2008, republished January 12th 2019 after website move.

Moon, Venus and Jupiter setting. (click for larger image)

Went out to Cottonwood Springs campground in Joshua Tree National Park yesterday so that Catherine could try out her new telescope. We packed both Catherine’s and Elizabeth’s 8 in Dobs together with my 12 in into the minivan together with camping gear and food for 4 people. There were a few other astronomers out there that were holding star parties for groups and dueling green laser pointers were in evidence.

It was pretty windy prior to sunset but the winds died down shortly after sunset and we had some reasonable observing. Transparency was very good although seeing was at best average – luminosity of nebulous objects was very good. Right at sunset there was a thin crescent moon together with Jupiter and Venus. Catherine just enjoyed pointing her telescope at random objects while Elizabeth settled down to completing more of the Messier list from “A Starhopper’s Guide to MESSIER OBJECTS” by Lenore (ISBN 0-913399-57-4). This book by Lenore Freeman is a great starter’s guide to star hopping (thanks Jane). We dueled to see who could find things the fastest, after finding something she would come over to my scope to confirm the view was the same and we had a lot of fun. When there was a particularly long star hop we would use Sky and Telescope’s Pocket Sky Atlas to provide a little more context.

She viewed the following:Andromeda: M31, M32, M33, M110 (I also did M34 and M76)Cassiopeia: M52, M103Cetus: M77Cygnus: M29, M39Gemini: M35Lyra: M56, M57Orion: M78 (she had done M42 and M43 back in March but we looked at them again in all their glorious nebulousness)Pegasus: M15Pisces: M74which was a pretty good total for a few hours.

After the girls had gone to bed I browsed around Auriga but the wind started to pick up and so I packed up the scopes and was done by 11pm. The wind rattled the tent all night and packing up the scopes for the night before retiring proved to have been a wise decision. This morning we headed back home early in order to meet commitments here in Pasadena. This evening the moon, Venus and Jupiter were setting over the tree in the neighbors yard and I captured the image above using the D50 on a tripod (200ASA, 80mm, 1sec, f# 4.5).