Treebeard's Stumper 30 March 2001

Catch an ISS Pass

We've been reading science fiction in my science classes lately, but NASA has been making it science fact with the International Space Station (ISS). At just the right time and place, the big ISS is visible as one of the brightest and fastest objects in the sky. We have several opportunities to view it next week. (See below.) The challenge is to observe an ISS pass. Early fog and sunrise and city lights might be a problem. The stumper is why all the view times are in the early morning and evening. Wouldn't it be easier to catch an ISS pass late at night when the sky is darkest?

View of the International Space Station (ISS) from the approaching Space Shuttle Atlantis on February 28, 2001. Space shuttle astronauts on this mission conducted the 100th space walk by an American. That's the Rio Negro region of Argentina two hundred kilometers below.

Note: Here's a table of the next few visible International Space Station (ISS) passes over Dunn Middle School in Los Olivos, California (34.6680°N, 120.1140°W, Epoch 27 Mar 2001). Pass times from Santa Barbara to Santa Maria are just seconds different. This data is from the Heavens-Above. The predicted viewing times change slightly from day to day because of course adjustments and other variables, but you can check the site for updated info and detailed sky charts. You have to specify your location, but it's easy to select from their huge database. (Or just click here for Los Olivos, Santa Barbara, or Santa Maria.) I had to edit the data because we switch to Daylight Savings Time (PDT) early Sunday morning, April 1. I made the change here by "springing ahead" an hour. Because of our usual morning fog, the best time to catch an ISS pass here in central California looks like next Wednesday evening, April 4, starting at 9:48 PM (PDT). There are many other viewing opportunities this coming week.

Where the ISS is now, moving to the right. Reload this page a few times to see it move! (Image from Heavens-Above.)

All times are Pacific Daylight Time (PDT). Magnitude (Mag.) is brightness. The smaller the number the brighter the ISS appears, and negative numbers are brightest of all. Altitude (Alt.) is how high to look in the sky, measured in degrees with 90° straight up. Azimuth (Az.) is the compass direction around your horizon. Note that an entire pass only lasts a few minutes, so don't be late!

Date	Mag.	Starts			Max. Altitude			Ends
		Time	Alt.	Az.	Time	Alt.	Az.	Time	Alt.	Az.
Sunday, April 1, 2001	-0.5	05:38:59 PDT 5:39 AM	12	NW	05:41:51	74	NE	05:44:58	10	SE
Monday, April 2, 2001	1.6	04:42:23 PDT 4:42 AM	26	ENE	04:42:23	27	ENE	04:44:34	10	E
Monday, April 2, 2001	0.9	06:15:16 PDT 6:15 AM	10	W	06:17:38	20	SW	06:19:58	10	S
Tuesday, April 3, 2001	-0.2	05:18:36 PDT 5:18 AM	45	S	05:18:36	45	S	05:21:04	10	SSE
Tuesday, April 3, 2001	0.9	20:11:48 PDT  8:11 PM	10	S	20:14:01	18	SE	20:14:25	18	ESE
Wednesday, April 4, 2001	-0.7	20:46:29 PDT  8:46 PM	10	SW	20:49:36	81	NW	20:50:35	40	NE
Thursday, April 5, 2001	0.1	19:46:29 PDT  7:46 PM	10	SSW	19:49:19	33	SE	19:52:10	10	ENE
Thursday, April 5, 2001	2.0	21:22:57 PDT 9:23 PM	10	W	21:25:18	19	NNW	21:26:08	17	N
Friday, April 6, 2001	0.6	20:21:35 PDT 8:22 PM	10	WSW	20:24:33	42	NW	20:27:32	10	NE
Saturday, April 7, 2001	2.6	20:58:19 PDT 8:58 PM	10	WNW	20:59:54	13	NNW	21:01:30	10	N
Sunday, April 8, 2001	1.6	19:55:58 PDT 7:56 PM	10	W	19:58:37	25	NW	20:01:17	10	NNE

Here's two more ISS stumpers I've been thinking about:

• I've wanted to do this stumper ever since the solar panels were deployed last December, since they made the ISS much brighter. But whenever I checked, there were no good viewing opportunities here in California. This week there are many opportunities. Why is this so variable?

• It's interesting that some of these ISS passes go from north to south, but others go from south to north. What kind of orbit is this? Why does it change direction? How does it change day to day?

Answer

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