what’s in the sky?

The clocks go back, giv­ing you an ex­tra hour of ob­serv­ing

All About Space - - Contents -

Jar­gon buster Con­junc­tion

a con­junc­tion is an align­ment of ob­jects at the same ce­les­tial lon­gi­tude. the con­junc­tion of the moon and the plan­ets is de­ter­mined with ref­er­ence to the sun. a planet is in con­junc­tion with the sun when it and Earth are aligned on op­po­site sides of the sun.

Right As­cen­sion (RA)

right as­cen­sion is to the sky what lon­gi­tude is to the sur­face of the Earth, cor­re­spond­ing to east and west direc­tions. it is mea­sured in hours, min­utes and sec­onds since, as the Earth ro­tates on its axis, we see dif­fer­ent parts of the sky through­out the night.

Dec­li­na­tion (Dec)

this tells you how high an ob­ject will rise in the sky. like Earth’s lat­i­tude, dec mea­sures north and south. it’s mea­sured in de­grees, ar­cmin­utes and arc­sec­onds. there are 60 arc­sec­onds in an ar­cminute and there are 60 ar­cmin­utes in a de­gree.


an ob­ject’s mag­ni­tude tells you how bright it ap­pears from Earth. in as­tron­omy, mag­ni­tudes are rep­re­sented on a num­bered scale. the lower the num­ber, the brighter the ob­ject. so, a mag­ni­tude of -1 is brighter than an ob­ject with a mag­ni­tude of +2.


When a ce­les­tial body is in line with the Earth and sun. dur­ing op­po­si­tion, an ob­ject is vis­i­ble for the whole night, ris­ing at sun­set and set­ting at sun­rise. at this point in its or­bit, the ce­les­tial ob­ject is clos­est to Earth, mak­ing it ap­pear big­ger and brighter.

Great­est elon­ga­tion

When the in­ner plan­ets, mer­cury and venus, are at their max­i­mum dis­tance from the sun. dur­ing great­est elon­ga­tion, the in­ner plan­ets can be ob­served as evening stars at great­est eastern elon­ga­tions and as morn­ing stars dur­ing west­ern elon­ga­tions.

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