Blog

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

Space.com monthly star chart

and many others online.

Good luck and Clear Skies.

The Twitter Phenomena

I’ve been using Twitter for a while and several things have converged to cause me to put my thoughts on Twitter in a blog. The first was a request from a professional society of which I am a member for thoughts on using Twitter, the second was a request from my employer on using Twitter in the workplace and the third was a comment by a reader on NPR to Scott Simon that Twitter was the CB radio of the time. I think this analogy is wrong but will discuss that later.

What is Twitter?

Twitter is an electronic messaging service that limits you to a message, called a tweet of 140 characters or less. When you send a tweet, it goes to anyone who has chosen to follow you and when anyone you have chosen to follow sends a tweet you receive it. In this way it is like CB radio in that tweets are broadcast however unlike CB Radio you only hear the people you have chosen to follow. You can send tweets directly to individual members, effectively making them private and there is a way to see all messages that mention your Twitter name. Twitter has a sister site, Twitpic, that enables tweeters to upload pictures for others to see. The key reason for the Twitter explosion is that clients exist for most cell/mobile phones. Twitter can be thought of as a variation of Instant Messaging &/or an RSS agregator for cell phones.

How do I use it?

For Twitter I have a split personality. One personality is my professional personality and the other is my personal life.I work for JPL which requires that all public communication be approved before release. This means that I almost never tweet about my work except in the most general sense or when doing so in an official capacity as happened at our recent open house. However I use Twitter in place of an RSS agregator to get news from organizations of relevance to my professional activities. Such organizations include the House Science and Technology CommitteeThe National Academies Press, my employer’s official tweets (multiple tweeters) and professional societies such as the Optical Society of America.In my personal life I follow a number of friends and tend to tweet about items of interest to me ie mostly my girls, astronomy, archery, photography and nature. Most of the people I know socially are not on Twitter at this time.

Privacy issues

I’m not in the mass-media business, my friends and I use Twitter as a convenient mobile messaging service and so I have developed a few strategies to control who can read my tweets.The most important tool on Twitter is the ability to block people so that even if they want to follow you they can not see your tweets. I always look at the profile of a new follower. Unfortunately, given the recent hype about Twitter, some are clearly just trying to promote themselves or dodgy schemes or look to be collecting information – these I immediately block from following me. I never start following someone who starts following me unless I know them personally. I give people I don’t know who start following me a grace period to see if their tweets are of interest, if they are I will eventually follow them. This provides me with considerable control over who reads my tweets. It should be noted that anyone can read my public tweets by looking at my page on Twitter I therefore try to be careful as to how much personal information I divulge.Twitter has a feature called “Trending Topics” and this used to contain interesting items when I first joined but with the explosion of membership it only shows lowest common denominator topics which are almost never of interest to me. It seems that whenever you put the mass into media it results in the same types of tabloid topics independent of the medium amd this presumably is what the NPR listener was referring to when he made the CB radio comparison. However the ability to control which tweets you see and who can see your tweets puts a simple filtering screen on this noise and clutter so you only see what interests you. Incidentally whoever comes up with a good algorithm for capturing the definition of “interesting” on a personal level and then implements it successfully in a general search engine can count me in as a user of their services.

The Future?

The popularity of Twitter is based on its ready availability on cell phones so that it is effectively everywhere – as an example I can now tweet over a 3G connection from the middle of the Mojave desert several miles from the nearest paved road at one of my favorite dark sky astronomy spots. The 140 character limitation is a key to Twitters success in that by forcing short communications it encourages frequent communication – look at the prior posts in this blog to see how hard I find it to get free time to type my thoughts these days .

As cell phone data connections and applications get better I’m sure something better will come along but for now Twitter works for mobile, everywhere communication.

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).