Wednesday, September 25, 2013

Solar Eclipses on a Distant World

Imagine how amazing it is to see the shadow of our Moon on Earth with your own eyes as it happens!

These two awesome videos show how that might look like aboard the International Space Station:

Most of us will not have a chance to go to Space to see this. Even if you can afford to go to Space during a solar eclipse (which will most probably double the price of your ticket), ironically, you need something to show up so Moon's shadow can be clearly seen - clouds!

So what is the next best thing for those of us who will be stuck on Earth for the rest of our lifetime? How about observing solar eclipses on a distant world (Jupiter) from Space (on Earth) through telescopes!

Jupiter has more than 60 over moons! But only the largest four of them are visible at bright dots of light through amateur-size telescopes and binoculars - Io, Europa, Ganymede and Callisto. Since these moons revolve around gigantic Jupiter and Sun is illuminating both of them at times, there will be certain periods where these moons will cast their shadows on Jupiter. These periods are known astronomically as Galilean Satellite Shadow Transits.

Since Jupiter is a giant gas planet, these moon shadows are projected on a dense "smoke screen". Thus, they can be seen very distinctly through telescopes - pitch black circular spots on the disc of Jupiter.

On clear enough nights, you can enjoy this view even if you are located in a light-polluted city. And if you have nice view of the sky at home, you may even be able to observe this celestial wonder in the comfort of your bedroom and in your favourite space-themed pajamas! Who wants to risk their life getting lost in Space after an accident on the International Space Station anyway? Not so scary you say? Go watch Sandra Bullock in Gravity which is opening next month in Singapore!

But I digress ...

This is a nice animation of a shadow transit from Wikipedia:

Check out this video by YouTuber 925cpc. This is an actual shadow transit captured live by a webcam attached to a 9.25-inch diameter amateur telescope. (One of the major bands of Jupiter disappeared during that year!)

So how can we know in advance when these shadow transits is going to occur?

One user-friendly way is via this free web app by Sky & Telescope. A more powerful and graphical free desktop software is WinJUPOS. It has a more intimidating user-interface for newcomers to stargazing. Hope to find time to do a video tutorial on how to use it to plan for Jupiter-observing sessions.

Shadow transits happen relatively frequently on Jupiter - about once every few days. But a few factors can decrease the chances of a successful observation:

- Jupiter not be visible from your observing location - it may be below the horizon, too near the Sun or the sky might be cloudy.
- It may not be a convenient time to observe when it happens - e.g. middle of the night, family and work commitments.
- Access to a telescope.

Considering these factors, to be able to observe one such shadow transits should be consider rare. Try asking all of your friends on Facebook if they have even seen one. Their response will most probably be "Shadow what? You mean we can actually see planets through a telescope?".

Amateur astronomers (or most people for that matter) like to brag about seeing or photographing super rare stuff. (Btw, have you seen the once-in-a-lifetime Transit of Venus on 6th June 2012? :P) That's why to see one shadow transit moving across Jupiter is rare. Two, very rare! THREE? Oh-my-god-you-lucky-***** rare! Due to the astrophysics involved between Jupiter and these four moons, three shadow transits appearing on Jupiter at the same time is the maximum, not four. Which brings me to my main motivation for writing this blog - most of the western astronomical publications and forum discussions mainly focus on shadow transits that are visible in their countries. Imagine my excitement while playing with WinJUPOS a few weeks ago, I found out that in October 2013, there are THREE double shadow transits that can be seen in Singapore and many countries in the East! YAY!

A few pointers before we look at the data extracted from WinJUPOS:

(1) For the month of October in Singapore, Jupiter rises above the horizon at about 1:41 am on 1 October. It rises earlier and earlier everyday and by 31 October, rises at about 11:52pm.
(2) Under clear sky conditions, it is possible to observe Jupiter until at least 7am in Singapore in October. Of course, pre-dawn dark sky is more preferable compared to the brighter bluish twlight skies.
(3) If the shadow transits happens when Jupiter is high up in the dark sky, the view will be potentially clearer and less distorted assuming everything else remain the same.
(4) Shadows that are very near the edges of Jupiter may be difficult to spot due to curvature of spherical object like Jupiter.

Multiple Shadow Transits on Jupiter in October 2013 in Universal Time (UT)
(Credit: WinJUPOS 10.0.21)

2013/10/01 13:42 - 14:07
2013/10/05 02:39 - 03:24
2013/10/08 15:35 - 16:43
2013/10/12 03:25 - 06:01 (triple shadow transits!)
2013/10/15 17:28 - 19:20
2013/10/17 11:57 - 13:28
2013/10/19 06:25 - 08:38
2013/10/22 19:22 - 21:34
2013/10/24 14:30 - 16:03
2013/10/26 08:37 - 10:31
2013/10/29 21:56 - 23:28

Converting these timings to Singapore Standard Time (+8 UT) (Visible from Singapore =Yes/No):

Tue   -- 01 Oct -- 21:42 -- 22:07 -- [No]
Sat    -- 05 Oct -- 10:39 -- 11:24 -- [No]
Tue   -- 08 Oct -- 23:35 -- 24:43 -- [No]
Sat   -- 12 Oct -- 11:25 -- 14:01 --  [Triple!] [No!Oh-No]
Wed -- 16 Oct -- 01:28 -- 03:20  -- [Yes] - [Duration = 1hr 52min]
Thu   -- 17 Oct -- 19:57 -- 21:28 -- [No]
Sat   -- 19 Oct -- 14:25 -- 16:38 --  [No]
Wed --  23 Oct -- 03:22 -- 05:34 -- [Yes] - [Duration = 2hr 12min]
Thu   -- 24 Oct -- 22:30 -- 24:03 -- [No]
Sat    -- 26 Oct -- 16:37 -- 18:31 -- [No]
Wed --  30 Oct -- 05:56 -- 07:28 -- [Yes] - [Duration = 1hr 32min]

Some implications from these multiple shadow transit data for October 2013:

(1) Super rare Triple Shadow Transit on 12 October not visible from Singapore! So if you really keen to see this, plan to go overseas to the other side of Earth in advance!

(2) Three double shadow transits visible in Singapore - 16th , 23rd and 30th. Three chances to catch at least one of them.

(3) All three double shadow transits falls on a Wednesday early morning before sunrise. Easy to remember - last three Wednesdays of October.

(4) To be able to see Jupiter's Great "Red" Spot (GRS) during multiple shadow transits is a rare visual bonus. Unfortunately, GRS is not visible for these shadow transits visible in Singapore.

(5) 15 Oct is a public holiday (Hari Raya Haji). Get plenty of sleep on that day so you can stay awake for the shadow transits on early morning of 16th.

(6) Duration of multiple shadow transits can be very short - e.g. one egressing out of Jupiter a few minutes after the ingress of the other. For these shadow transits in October 2013, they are much longer on average - more than one hour! Plenty of time to observe with diferent telescopes and accessories, take photos/videos and socialise with other stargazers!

Here are some screen captures from WinJUPOS showing some interesting framing for visual or imaging purposes during these three shadow transit periods:

16 October 2013

23 October 2013

30 October 2013

I will provide more details in October closer to these shadow transit dates. In the meantime, you may use your favourite planetarium software or phone app to find more detailed information - e.g. each moon/shadow exact ingress and egress timings. Now that you have plenty of time to prepare yourself to witness these celestial wonders, go get a telescope soon or befriend an amateur astronomer! :)

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